WO2022258981A1

WO2022258981A1 - Multichain chimeric antigen receptor

Info

Publication number: WO2022258981A1
Application number: PCT/GB2022/051456
Authority: WO
Inventors: Marc MARTINEZ-LLORDELLA; Simon BORNSCHEIN
Original assignee: Quell Therapeutics Limited
Priority date: 2021-06-11
Filing date: 2022-06-10
Publication date: 2022-12-15
Also published as: GB202108366D0

Abstract

The present invention relates to a multichain chimeric receptor comprising: (a) a first polypeptide comprising (i) an extracellular domain comprising an antigen binding domain, (ii) a first transmembrane domain derived from a myeloid receptor protein which is capable of associating with DAP10 or DAP12, wherein said antigen binding domain is heterologous to said first transmembrane domain and (iii) optionally an endodomain optionally comprising at least one co-stimulatory domain and/or at least one intracellular signalling domain; and (b) a second polypeptide comprising (i) a second transmembrane domain derived from DAP10 or DAP12 which is capable of associating with a TREM protein, and (ii) an endodomain comprising at least one co-stimulatory domain and/or at least one intracellular signalling domain, wherein said first polypeptide and/or said second polypeptide comprise at least one heterologous co-stimulatory domain and/or at least one heterologous intracellular signalling domain. The invention further relates to nucleic acid molecules, vectors, cells, cell populations, pharmaceutical compositions and medical uses of a multichain chimeric receptor.

Description

Multichain Chimeric Antigen Receptor Field of the invention The present invention relates to the field of chimeric antigen receptors and particularly to the development of a multichain or split chimeric antigen receptor system, where costimulatory and intracellular signalling components can be shared between two chains which associate with one another through their transmembrane domains. Particularly, the multichain system comprises a first polypeptide comprising an extracellular domain comprising an antigen binding domain and a transmembrane domain derived from a myeloid receptor, such as triggering receptor expressed on myeloid cells (TREM) and the second polypeptide comprises a transmembrane domain derived from DAP10 or DAP12, where costimulatory and intracellular signalling domains may be present on either or both of the first or second polypeptides. Cells comprising the multichain chimeric antigen receptor are provided, as are their encoding polynucleotides, and their use in the field of immunotherapy. Background of the invention Immunotherapy is emerging as a beneficial tool for the treatment of many conditions, ranging from cancer to autoimmune disease treatment and the prevention of solid organ transplant rejection. For cancer treatment, immunotherapy may be used to strengthen the immune response by regulating the immune environment to allow immune cells to attack and clear tumour cells. Non-specific adoptive cellular immunotherapy for the treatment of cancer may utilise several different cell types, for example, dendritic cells (DC), natural killer cells (NKC), cytokine induced killer cells, tumour-infiltrating lymphocytes (TILs), lymphocyte activated killer cells (LAKs), and macrophage activated killer cells (MAKs). A number of antigen specific immunotherapies have also been tested successfully in the clinic. Engineered T cells have been developed, for example, that target CD19 in chronic lymphoid leukaemia and that target NY-ESO-1 in synovial cell sarcoma and melanoma. Engineered antigen specific oncology treatments have the advantage of potentially reducing the possibility of non-target adverse effects and have shown particular efficacy in the treatment of blood cancers. Regulatory T cells (Tregs) are immune cells with suppressive function that control cytopathic immune responses and are essential for the maintenance of immunological tolerance. The suppressive properties of Tregs can be exploited therapeutically, for example to improve and/or prevent immune-mediated organ damage in inflammatory disorders, autoimmune diseases and in transplantation. Treg immunotherapies usually involve isolation, culture and expansion of Tregs followed by infusion into patients. As part of this process, Tregs may be incubated with cytokines, or drugs, in order to improve their viability and function. Whilst polyclonal (non-specific) T regs have been used in clinical trials to investigate, for example, therapies for GvHD, type I diabetes and active cutaneous lupus, it has been reported that antigen specific Tregs may be more potent than polyclonal Tregs (Zhang et al, 2018, Front Immunol., 9, 2359). Further, non-specific polyclonal Treg therapies may be associated with unwanted effects such as systemic immunosuppression, which can be avoided by using antigen specific Tregs. Thus, there is a clear need to develop and use antigen specific immunotherapies across a variety of disease conditions. A variety of different methods are known in the art for producing antigen specific immune cells such as CD8+ T effector cells or Tregs. Tregs for example may be incubated with a particular antigen or antigen expressing cell line to produce Tregs which have specificity to the antigen, through their naturally occurring T cell receptor (TCR). Methods of engineering immune cells are further well known in the art, including introducing a polynucleotide sequence to a cell encoding an antigen specific TCR or a chimeric antigen receptor (CAR). CARs are modular protein receptors that comprise an antigen binding domain conjugated to structural domains that typically include an extracellular hinge domain, a transmembrane domain and an endodomain comprising an intracellular signalling domain. Upon antigen or ligand binding to the antigen binding domain of the CAR, downstream signalling initiated from the CAR activates the effector function of the immune cells, which may consist of direct tumour killing (for a CD8+ T cell) or the suppression of the immune response, e.g. by the production of IL10, and granzyme B (for a Treg). Naturally occurring T cells generally require two signals to become fully active; a first signal which is antigen- specific through the TCR (by binding to MHC and peptide on an antigen presenting cell (APC)) and a second signal which comes from a costimulatory protein by its interaction with its binding partner on the surface of an APC in an antigen independent manner. This feature has been incorporated into many CARs, taking the first generation CAR which only comprised an intracellular signalling domain to a second generation CAR which also comprises one costimulatory domain. Third generation CARs have further been developed comprising more than one costimulatory domain. Traditionally, single chain CARs have been used to provide antigen specificity to immune cells. However, the provision of the costimulatory and intracellular signals in cis is artificial in nature, given the conformation of proteins involved in the activation of naturally occurring T cells. Some groups have investigated providing the signalling domains in trans by developing a dual chain CAR, where both chains are capable of associating with each other to provide a functioning system capable of signalling into the cell. However, given the need to develop highly effective antigen specific therapies for a wide range of disease conditions, there is a desire to develop further multichain CAR systems which can be used alone or in tandem with those already developed to provide optionality for the design of particular CAR T therapies. Summary of the invention The present inventors have developed a multichain CAR based on using a first polypeptide comprising a transmembrane domain from a myeloid receptor (e.g. from TREM (particularly from TREM1 or TREM2)) and a second polypeptide comprising DAP10 or DAP12. Typically, the first polypeptide will comprise an extracellular domain comprising an antigen binding domain, and either the first and/or the second polypeptide will comprise at least one heterologous costimulatory domain and/or at least one heterologous intracellular signalling domain. In this way, a multichain receptor is provided which may generate greater activation of immune cells (e.g. Tregs) than a typical CAR which provides antigen binding, intracellular signalling and costimulatory domains in cis. Myeloid receptors comprise a number of transmembrane proteins which have distinct functions. For example, the CD300 molecules, including CD300B and E, transmit an immune-activating signal to myeloid cells upon which they are expressed, where CD300B can regulate the phagocytosis of apoptotic cells and CD300E may prevent monocyte apoptosis. Receptors such as CLEC5A may function on myeloid cells to enhance the inflammatory response. TREMs are a family of cell-surface molecules that control inflammation, bone homeostasis, neurological development and blood coagulation. TREM1 and TREM2 are both TREM receptors that have been reported to play divergent roles in several infectious diseases. TREM1 was initially identified in differentiated monocytes and in circulating blood neutrophils but has also now been reported to be expressed in macrophages and more recently in endothelial cells. TREM1 is considered to be an amplifier of inflammation when expressed in cells of myeloid origin. TREM2 was first detected on human monocyte-derived dendritic cells and later its expression was detected in microglia cells as well as in alveolar, hepatic and intestinal macrophages. TREM2 expression has been linked to anti-inflammatory activities, at least within some environments. In spite of their differing functions, importantly, several myeloid receptors, including TREMs, share common structural properties including a transmembrane domain which possesses a positively charged lysine residue that interacts with negatively charged aspartic acid residue of the DNAX Activating Protein of 10kDa or of 12kDa (DAP10 or DAP12, respectively). DAP10 and DAP12 are transmembrane adaptors which contain an immunoreceptor tyrosine-based activation motif (ITAM), and DAP10 and DAP12 are therefore capable of transducing a signal into the cell in which they are expressed. Whilst other DAP10/12 based CARs have been developed by other groups, these are mainly based on using receptors from the C type lectin superfamily and particularly receptors from Natural Killer (NK) cells which are well characterised, or on using specifically introduced dimerization domains to allow association between the antigen binding domain containing chain and DAP10/12. WO2014127261, for example, discloses a two-chain system where both the first polypeptide and the second polypeptide comprise a dimerization domain, typically not within the transmembrane domain. One disadvantage of such system is the inability to take advantage of any endogenous expression of DAP10/12 to potentially boost the signalling of the system. Further, systems such as those disclosed in WO2006/036445, are limited to the provision of particular extracellular antigen binding domains and thus are not of general applicability. The multichain CAR developed by the inventors utilises the transmembrane domain of a myeloid receptor, such as a TREM receptor for the first time to our knowledge, together with a DAP10/12 based second polypeptide to provide a flexible system where costimulatory and intracellular domains can be mixed between polypeptide chains, allowing the optimisation of the system for use in particular immune cells and when combined with different antigen binding domains. In one aspect, the present invention provides a multichain chimeric receptor comprising: (a) a first polypeptide comprising (i) an extracellular domain comprising an antigen binding domain, (ii) a first transmembrane domain derived from a myeloid receptor protein which is capable of associating with DAP10 or DAP12, wherein said antigen binding domain is heterologous to said first transmembrane domain and (iii) optionally an endodomain optionally comprising at least one co-stimulatory domain and/or at least one intracellular signalling domain; and (b) a second polypeptide comprising (i) a second transmembrane domain derived from DAP10 or DAP12 which is capable of associating with a TREM protein, and (ii) an endodomain comprising at least one co-stimulatory domain and/or at least one intracellular signalling domain, wherein said first polypeptide and/or said second polypeptide comprise at least one heterologous co-stimulatory domain and/or at least one heterologous intracellular signalling domain. Thus, in this aspect, if the second polypeptide does not comprise at least one heterologous co-stimulatory domain and/or at least one heterologous intracellular signalling domain, the first polypeptide comprises an endodomain comprising at least one heterologous co-stimulatory domain and/or at least one heterologous intracellular signalling domain (i.e. the endodomain is no longer optional). Alternatively viewed, the present invention provides a multichain chimeric receptor comprising: (a) a first polypeptide comprising (i) an extracellular domain comprising an antigen binding domain, (ii) a first transmembrane domain derived from a myeloid receptor protein which is capable of associating with DAP10 or DAP12, wherein said antigen binding domain is heterologous to said first transmembrane domain and (iii) optionally an endodomain optionally comprising at least one co-stimulatory domain and/or at least one intracellular signalling domain; and (b) a second polypeptide comprising (i) a second transmembrane domain derived from DAP10 or DAP12 which is capable of associating with a TREM protein, and (ii) an endodomain comprising at least one co-stimulatory domain and/or at least one intracellular signalling domain, wherein when the second polypeptide consists of an amino acid sequence derived from DAP10 or DAP12, said first polypeptide comprises an endodomain comprising at least one costimulatory domain and/or at least one intracellular signalling domain. Particularly, the second polypeptide is an exogenous polypeptide. In another aspect, the invention provides a nucleic acid molecule comprising a polynucleotide sequence encoding the multichain chimeric receptor of the invention. In a further aspect, the invention provides a vector comprising the nucleic acid molecule of the invention. The present invention also provides a cell (e.g. an immune cell) which expresses the multichain chimeric receptor of the invention and/or a cell (e.g. an immune cell) which comprises a nucleic acid molecule or a vector encoding a multichain chimeric receptor of the invention. The cell may be provided in a cell population which forms a further aspect of the invention. In another aspect, the invention provides a pharmaceutical composition comprising a cell or cell population of the invention. The present invention further provides a method for producing a cell of the invention comprising introducing a nucleic acid or a vector of the invention into a cell. The present invention further provides a method for treating and/or preventing a disease or condition in a subject, which comprises the step of administering a cell, cell population or pharmaceutical composition of the invention to the subject. Alternatively viewed, the invention provides a cell, cell population, or pharmaceutical composition according to the invention for use in therapy (e.g. treating and/or preventing a disease or condition). Detailed Description The term “multichain chimeric receptor” refers to a receptor protein comprising at least two polypeptide chains which are associated or bound to each other, particularly through their transmembrane domains. Whilst other sites may be present within the polypeptide chains which allow binding or association (e.g. further sites of dimerization), typically, the at least two polypeptide chains will associate or bind through their respective transmembrane domains. Typically, each polypeptide chain within the multichain chimeric receptor will comprise of two or more linked domains, for example, the first polypeptide comprises an extracellular domain and a transmembrane domain, and the second polypeptide comprises a transmembrane domain and an endodomain. At least the antigen binding and transmembrane domains within the first polypeptide chain are typically heterologous to each other. Thus, the antigen binding domain and the first transmembrane domain are heterologous, i.e. are not derived from the same protein or polypeptide, (e.g. are not derived from the same wildtype or naturally occurring protein or polypeptide). The term “heterologous” as used herein therefore refers to domains which are not derived from the same protein or polypeptide (particularly naturally occurring or wildtype protein). In this regard, alternatively viewed, the antigen binding domain of the first polypeptide may not be derived from the same myeloid receptor protein as the transmembrane domain of the first polypeptide. Thus, when the transmembrane domain of the first polypeptide is derived from a TREM protein, e.g. TREM1 or TREM2, typically, the antigen binding domain of the first polypeptide protein will not be derived from TREM1 or TREM2, respectively. Particularly, the antigen binding domain may not be derived from TREM2. Thus, the antigen binding domain of the first polypeptide may not comprise an antigen binding domain having a sequence as set out in SEQ ID NO: 13 (the ligand binding domain of TREM1). Particularly, where the first transmembrane domain is derived from TREM1, the antigen binding domain of the first polypeptide may not be derived from TREM1. Further, where the first transmembrane domain is derived from TREM2, the antigen binding domain of the first polypeptide may not be derived from TREM2. Heterologous antigen binding domains and transmembrane domains from myeloid receptor proteins, such as TREM, would encompass any non-natural arrangement of any antigen binding domain and myeloid receptor transmembrane domain (e.g. a TREM transmembrane domain). For example, any scFv based or TREM1 antigen binding domain could be used with a TREM2 transmembrane domain. Further, any costimulatory and/or intracellular signalling domains present within the first polypeptide may be heterologous to the antigen binding domain and to the first transmembrane domain. With regard to the second polypeptide, the domains may not necessarily be heterologous. Thus, as described in detail further below, the second polypeptide comprises a transmembrane domain derived from DAP10 or DAP12 and also comprises at least one costimulatory domain and/or at least one intracellular signalling domain within an endodomain. When the second polypeptide comprises at least one costimulatory domain, typically, this costimulatory domain is heterologous to the DAP10/12 derived transmembrane domain. However, when the second polypeptide comprises at least one intracellular signalling domain, the at least one intracellular signalling domain may be heterologous (e.g. derived from CD3zeta) or maybe derived from DAP10/12 and thus may not be heterologous. Given the heterologous nature of at least the first polypeptide, the multichain receptor of the invention is chimeric. The chimeric receptor may be viewed as an “engineered receptor” and these terms are used interchangeably herein. In accordance with the invention, at least the first polypeptide and/or the second polypeptide should comprise at least one heterologous costimulatory domain and/or at least one heterologous intracellular signalling domain. Thus, if the second polypeptide does not comprise a heterologous costimulatory domain or a heterologous intracellular signalling domain, the first polypeptide should comprise at least one heterologous costimulatory domain and/or at least one heterologous intracellular signalling domain. Thus, in this embodiment, the endodomain of the first polypeptide will no longer be optional. Further, if the first polypeptide does not comprise an endodomain, the second polypeptide should comprise at least one heterologous costimulatory domain and/or at least one heterologous intracellular signalling domain. In one embodiment of the invention, both the first and second polypeptides may comprise at least one heterologous costimulatory and/or at least one heterologous intracellular signalling domain. A “chimeric antigen receptor", "CAR" or “CAR construct” refers to an engineered receptor which can confer an antigen specificity onto cells (e.g. immune cells, such as Tregs). In particular, a CAR enables a cell to bind specifically to a particular antigen, e.g. a target molecule such as a target protein, whereupon a signal is generated by the endodomain of the CAR, e.g. a signal resulting in activation of the cell. The signal generated in the multichain chimeric receptor of the invention may be generated by either or both of the first polypeptide and the second polypeptide chains, depending on the combination of costimulatory and intracellular signalling domains present within the endodomain of each receptor. CARs are also known as artificial T-cell receptors, chimeric T-cell receptors or chimeric immunoreceptors. Thus, as the chimeric receptor of the invention functions to confer cells expressing the receptor (e.g. Tregs) with the ability to bind specifically to an antigen or ligand, it may be viewed as a CAR. As described above, although in one embodiment, the multichain chimeric receptor of the invention comprises a first and a second polypeptide chain, it is possible for further polypeptide chains to be comprised as part of the receptor. Thus, for example, there may be more than one polypeptide chain present comprising an antigen binding domain. The invention therefore encompasses the presence of a further polypeptide chain (e.g. a third polypeptide chain), wherein the further or third polypeptide comprises an extracellular domain comprising an antigen binding domain, wherein the antigen binding domain is different to that of the first polypeptide chain. The further or third polypeptide may therefore comprise an antigen binding domain which binds to a different antigen than the antigen binding domain comprised within the first polypeptide chain, or which binds to a different epitope on the same antigen. Typically, the third or further polypeptide chain may comprise a transmembrane domain from a myeloid receptor protein such as TREM. In this embodiment, the transmembrane domains of the first and third or further polypeptide chains may be the same or different. For example, the first polypeptide may comprise a transmembrane domain derived from TREM1 and the third or further polypeptide may comprise a transmembrane domain derived from TREM2 or vice versa. Alternatively, both the first and the third polypeptide chains may comprise a transmembrane domain from TREM1 or from TREM2. A skilled person will appreciate that the further or third polypeptide chains may additionally comprise an endodomain comprising at least one costimulatory and/or at least one intracellular signalling domain, which may be the same as or different to any endodomain comprised within the first polypeptide chain. As the third or further polypeptide chain may typically comprise a transmembrane domain derived from a myeloid receptor such as TREM, the third or further polypeptide chain may be capable of binding or associating with DAP10 and/or DAP12 and thus of generating a signal upon ligand or antigen binding through DAP10/12 and/or through any intracellular signalling domains present within the third or further polypeptide chain. A “polypeptide” as referred to herein encompasses a single chain of amino acid residues. An “extracellular domain” as referred to herein comprises an antigen binding domain which provides the CAR with the ability to bind a predetermined antigen of interest. The antigen binding domain preferably targets an antigen of clinical interest. The antigen binding domain may be any protein or peptide that possesses the ability to specifically recognize and bind to a biological molecule (e.g., a cell surface receptor or a component thereof). The antigen binding domain includes any naturally occurring, synthetic, semi-synthetic, or recombinantly produced binding partner for a biological molecule of interest. Illustrative antigen binding domains include antibodies or antibody fragments or derivatives, extracellular domains of receptors, ligands for cell surface molecules/receptors, or receptor binding domains thereof, and tumor binding proteins. Although as discussed below, the antigen binding domain may particularly be an antibody or derived from an antibody, other antigen binding domains are encompassed, e.g. antigen binding domains formed from an antigenic peptide/MHC or HLA combination which is capable of binding to the TCRs of Tcon cells active at a site of transplantation, inflammation or disease. Such antigen-binding domains have been reported for example in Mekala et al, Blood, 2005, vol 105, pages 2090-2092. As discussed above, an antigen binding domain of the first polypeptide chain is heterologous to the first transmembrane domain derived from a myeloid receptor protein, such as TREM. In a particular embodiment, the antigen binding domain is, or is derived from, an antibody. An antibody binding domain can be a fragment of an antibody or a genetically engineered product of one or more fragments of the antibody, which fragment is involved in binding with the antigen. Examples include a variable region (Fv), a complementarity determining region (CDR), a Fab, a single chain antibody (scFv), a heavy chain variable region (VH), a light chain variable region (VL) a camelid antibody (VHH) and a single domain antibody (sAb). In a particular embodiment, the binding domain is a single chain antibody (scFv). The scFv may be murine, human or humanized scFv. "Complementarity determining region" or "CDR" with regard to an antibody or antigen-binding fragment thereof refers to a highly variable loop in the variable region of the heavy chain or the light chain of an antibody. CDRs can interact with the antigen conformation and largely determine binding to the antigen (although some framework regions are known to be involved in binding). The heavy chain variable region and the light chain variable region each contain 3 CDRs. "Heavy chain variable region" or "VH" refers to the fragment of the heavy chain of an antibody that contains three CDRs interposed between flanking stretches known as framework regions, which are more highly conserved than the CDRs and form a scaffold to support the CDRs. "Light chain variable region" or "VL" refers to the fragment of the light chain of an antibody that contains three CDRs interposed between framework regions. "Fv" refers to the smallest fragment of an antibody to bear the complete antigen binding site. An Fv fragment consists of the variable region of a single light chain bound to the variable region of a single heavy chain. "Single-chain Fv antibody" or "scFv" refers to an engineered antibody consisting of a light chain variable region and a heavy chain variable region connected to one another directly or via a peptide linker sequence. Antibodies that specifically bind a predetermined antigen can be prepared using methods well known in the art. Such methods include phage display, methods to generate human or humanized antibodies, or methods using a transgenic animal or plant engineered to produce human antibodies. Phage display libraries of partially or fully synthetic antibodies are available and can be screened for an antibody or fragment thereof that can bind to the target molecule. Phage display libraries of human antibodies are also available. Once identified, the amino acid sequence or polynucleotide sequence coding for the antibody can be isolated and/or determined. Antigens which may be targeted by the present multichain chimeric receptor include, but are not limited to, antigens expressed on cells associated with transplanted organs, autoimmune diseases, allergic diseases and inflammatory diseases. It will be understood by a skilled person that when the multichain chimeric receptor is expressed in Treg cells, the antigen may be simply present and/or expressed at the site of transplantation, inflammation or disease due to the bystander effect of Treg cells. Antigens associated with organ transplants and/or cells associated with transplanted organs include, but are not limited to, a HLA antigen present in the transplanted organ but not in the patient, or an antigen whose expression is up-regulated during transplant rejection such as CCL19, MMP9, SLC1A3, MMP7, HMMR, TOP2A, GPNMB, PLA2G7, CXCL9, FABP5, GBP2, CD74, CXCL10, UBD, CD27, CD48, CXCL11. By way of example, the multichain chimeric receptor may comprise an antigen binding domain which is capable of binding HLA-A2 (HLA-A2 may also be referred to herein as HLA-A*02, HLA-A02, and HLA-A*2). HLA-A*02 is one particular class I major histocompatibility complex (MHC) allele group at the HLA-A locus. The antigen binding domain may bind, suitably specifically bind, one or more region or epitope within HLA-A2. An epitope, also known as antigenic determinant, is the part of an antigen that is recognised by an antigen recognition domain (e.g. an antibody). In other words, the epitope is the specific piece of the antigen to which an antibody binds. Suitably, the antigen binding domain binds, suitably specifically binds, to one region or epitope within HLA-A2. The antigen binding domain may comprise at least one CDR (e.g. CDR3), which can be predicted from an antibody which binds to an antigen, preferably HLA-A2 (or a variant of such a predicted CDR (e.g. a variant with one, two or three amino acid substitutions)). It will be appreciated that molecules containing three or fewer CDR regions (e.g. a single CDR or even a part thereof) may be capable of retaining the antigen-binding activity of the antibody from which the CDR is derived. Molecules containing two CDR regions are described in the art as being capable of binding to a target antigen, e.g. in the form of a minibody (Vaughan and Sollazzo, 2001, Combinational Chemistry & High Throughput Screening, 4, 417-430). Molecules containing a single CDR have been described which can display strong binding activity to a target (Nicaise et al, 2004, Protein Science, 13: 1882-91). In this respect, the antigen binding domain may comprise one or more variable heavy chain CDRs, e.g. one, two or three variable heavy chain CDRs. Alternatively, or additionally, the antigen binding domain may comprise one or more variable light chain CDRs, e.g. one, two or three variable light chain CDRs. The antigen binding domain may comprise three heavy chain CDRs and/or three light chain CDRs (and more particularly a heavy chain variable region comprising three CDRs and/or a light chain variable region comprising three CDRs) wherein at least one CDR, preferably all CDRs, may be from an antibody which binds to an antigen, preferably HLA-A2, or may be selected from one of the CDR sequences provided below. The antigen binding domain may comprise any combination of variable heavy and light chain CDRs, e.g. one variable heavy chain CDR together with one variable light chain CDR, two variable heavy chain CDRs together with one variable light chain CDR, two variable heavy chain CDRs together with two variable light chain CDRs, three variable heavy chain CDRs together with one or two variable light chain CDRs, one variable heavy chain CDR together with two or three variable light chain CDRs, or three variable heavy chain CDRs together with three variable light chain CDRs. Preferably, the antigen recognition domain comprises three variable heavy chain CDRs (CDR1, CDR2 and CDR3) or three variable light chain CDRs (CDR1, CDR2 and CDR3). The one or more CDRs present within the antigen binding domain may not all be from the same antibody, as long as the domain has the binding activity described above. Thus, one CDR may be predicted from the heavy or light chains of an antibody which binds to an antigen, e.g. HLA-A2 whilst another CDR present may be predicted from a different antibody which binds to the same antigen (e.g. HLA-A2). In this instance, it may be preferred that CDR3 be predicted from an antibody that binds to an antigen, e.g. HLA-A2. Particularly however, if more than one CDR is present in the antigen binding domain, it is preferred that the CDRs are predicted from antibodies which bind to the same antigen, e.g. HLA-A2. A combination of CDRs may be used from different antibodies, particularly from antibodies that bind to the same desired region or epitope. In a particularly preferred embodiment, the antigen binding domain comprises three CDRs predicted from the variable heavy chain sequence of an antibody which binds to an antigen, e.g. HLA-A2 and/or three CDRs predicted from the variable light chain sequence of an antibody which binds to an antigen, e.g. HLA-A2 (preferably the same antibody). For example, the three variable heavy chain CDRs may comprise: CDR1 -DYGMH (SEQ ID NO:1) CDR2 – FIRNDGSDKYYADSVKG (SEQ ID NO: 2) CDR3 – NGESGPLDYWYFDL (SEQ ID NO: 3) and the three variable light chain CDRs may comprise: CDR1 – QASQDISNYLN (SEQ ID NO: 4) CDR2 – DASNLET (SEQ ID NO: 5) CDR3 – QQYDNLPPT (SEQ ID NO: 6) The first polypeptide (and any third or further polypeptide comprising an extracellular domain comprising an antigen binding domain), and more particularly the extracellular domain thereof, may also comprise a signal sequence (or targeting domain). Such a sequence will generally be provided at the N-terminal end of the first or further/third polypeptide (construct) and may function to, co-translationally or post-translationally, direct transfer of the molecule. In particular, the signal sequence may be a sequence that targets the chimeric receptor to the plasma membrane of the immune cell (e.g. Treg). In some embodiments, the signal sequence is a CD8α signal sequence (e.g. SEQ ID NO: 7). In some embodiments, the signal sequence is the TREM1 signal sequence (SEQ ID NO: 8). In some embodiments, the signal sequence is the TREM2 signal sequence (e.g. SEQ ID NO: 9). This may be linked directly or indirectly (e.g. via a linker sequence) to the antigen binding domain, generally upstream of the antigen binding domain, at the N-terminal end of the chimeric receptor molecule/construct. The linker sequence may be between 1-30, more preferably 1-25, 1-22 or 1-20, amino acids long. The linker may be a flexible linker. Suitable linkers can be readily selected and can be of any of a suitable length, such as from 1 amino acid (e.g., Gly) to 20 amino acids, from 2 amino acids to 15 amino acids, from 3 amino acids to 12 amino acids, including 4 amino acids to 10 amino acids, 5 amino acids to 9 amino acids, 6 amino acids to 8 amino acids, or 7 amino acids to 8 amino acids, and may be 1, 2, 3, 4, 5, 6, or 7 amino acids or longer. Exemplary flexible linkers include glycine polymers (G)n, glycine-serine polymers, where n is an integer of at least one, glycine-alanine polymers, alanine-serine polymers, and other flexible linkers known in the art. Glycine and glycine-serine polymers are relatively unstructured, and therefore may be able to serve as a neutral tether between domains of fusion proteins such as the chimeric receptors described herein. In one embodiment the signal sequence is linked directly to the N-terminal end of the antigen binding domain. The antigen binding domain of the chimeric receptor (particularly of the first or further polypeptides) is optionally followed by a hinge domain. The hinge region in a chimeric receptor is generally between the transmembrane domain and the antigen binding domain. In certain embodiments, a hinge region is an immunoglobulin hinge region (e.g. derived from IgG1, IgG2 or IgG4) and may be a wild-type immunoglobulin hinge region or an altered wild type immunoglobulin hinge region, for example a truncated hinge region. In some embodiments, the hinge region may be derived from the extracellular regions of type 1 membrane proteins such as CD8α, CD4, CD28 and CD7, which may be wild-type hinge regions from these molecules or may be altered. In some embodiments, the hinge region may be derived from or comprise a portion of the extracellular domain of a myeloid receptor protein (e.g. a TREM protein). Thus, in this embodiment, it is possible, and in some cases, desirable that the extracellular domain comprises a portion of the extracellular domain of a myeloid receptor protein (e.g. a TREM protein), and particularly of the myeloid receptor protein from which the first transmembrane domain is derived. As discussed previously, the antigen binding domain of the extracellular domain of the first or further polypeptide is heterologous to the myeloid receptor protein (e.g. TREM) derived transmembrane domain, and thus, in this embodiment, any portion of the extracellular domain of a myeloid receptor protein (e.g. a TREM protein) which is present within the extracellular domain may not comprise the ligand binding domain of the myeloid receptor protein (e.g. of a TREM protein) (e.g. of the ligand binding domain of TREM1 as set out in SEQ ID NO: 13). Particularly, a portion of the stalk region of a myeloid receptor protein (such as a TREM protein) may be comprised within the extracellular domain of the first or further protein, typically, providing a contiguous sequence from the myeloid receptor protein (e.g. TREM) transmembrane sequence which is present. Thus, the first polypeptide or third/further polypeptide may comprise a portion of a myeloid receptor (e.g. TREM) protein typically between the antigen binding domain and the transmembrane domain, or between any additional hinge and the transmembrane domain, where the portion can be from the same or a different myeloid receptor to that from which the transmembrane domain is derived. In a particular embodiment, any portion of the extracellular domain of a myeloid receptor protein (e.g. a TREM protein) that may be present within the extracellular domain of the first or third/further polypeptide should be resistant to cleavage by any enzyme, particularly any sheddase, meprin beta or metalloproteinase 9 (MMP9). Thus, in some embodiments, the hinge domain may be derived from the exodomain of the stalk domain of a myeloid receptor protein, e.g. a TREM protein. The amino acid sequence for the stalk region of TREM1 is as set out in SEQ ID NO: 14, and therefore the extracellular domain of the first polypeptide (or further polypeptide) may comprise any of this sequence, particularly between the antigen binding domain and the first transmembrane domain. Most particularly, any portion of the sequence as set out in SEQ ID NO: 15 may be present within the extracellular domain of the first polypeptide, particularly between the antigen binding domain and the first transmembrane domain. SEQ ID NO: 15 comprises a portion of the stalk domain of TREM1 but is lacking the putative MMP9 cleavage site at PPTTTK (SEQ ID NO: 21) Thus, in some embodiments, the hinge region is, or is derived from, the hinge region of human CD8α, CD4, CD28, CD7 or TREM (e.g. TREM1 or 2). The hinge region is alternatively (and interchangeably) referred to as a spacer or spacer region. An "altered wild type hinge region" or "altered hinge region" or “altered spacer” refers to (a) a wild type hinge region with up to 30% amino acid changes (e.g. up to 25%, 20%, 15%, 10%, or 5% amino acid changes e.g. substitutions or deletions), (b) a portion of a wild type hinge region that is at least 10 amino acids (e.g., at least 12, 13, 14 or 15 amino acids) in length with up to 30% amino acid changes (e.g., up to 25%, 20%, 15%, 10%, or 5% amino acid changes, e.g. substitutions or deletions), or (c) a portion of a wild type hinge region that comprises the core hinge region (which may be 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15, or at least 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 amino acids in length). When an altered wild type hinge region is interposed between and connecting the antigen binding domain and another region (e.g., a transmembrane domain) in the chimeric receptors described herein, it allows the chimeric receptor to maintain specific binding to its target antigen. In certain embodiments, one or more cysteine residues in a wild type immunoglobulin hinge region may be substituted by one or more other amino acid residues (e.g. one or more serine residues). An altered immunoglobulin hinge region may alternatively or additionally have a proline residue of a wild type immunoglobulin hinge region substituted by another amino acid residue (e.g., a serine residue). Hinge regions comprising the CH2 and CH3 constant region domains are described in the art for use in chimeric receptors (for example the CH2CH3 hinge, referred to as an “Fc hinge” or ”IgG hinge”). However, it is preferred that when the hinge domain is based on or derived from an immunoglobulin it does not comprise a CH3 domain, e.g. it may comprise or consist of the CH2 domain or a fragment or part thereof, without including CH3. In one preferred embodiment the hinge domain has or comprises the amino acid sequence of SEQ ID NO: 10 (which represents the hinge domain of CD28) or an amino acid sequence having at least 95% sequence identity thereto. The “transmembrane domain derived from a myeloid receptor protein” as referred to herein refers to the transmembrane domain of any myeloid receptor protein (i.e. the transmembrane domain of any protein receptor which is expressed in myeloid cells), or a portion or variant thereof, as long as the protein receptor, portion or variant thereof is capable of binding to DAP10 or DAP12. Thus, as discussed previously, the transmembrane domains of myeloid receptor proteins (such as TREM proteins) may comprise positively charged residues which are capable of binding to negatively charged residues within the transmembrane domain of DAP12 or DAP10. Any portion or variant of a myeloid receptor protein (e.g. of a TREM protein) transmembrane domain used within the first polypeptide (or third or further polypeptide) of a receptor of the invention must thus retain the necessary positively charged residues to ensure binding to DAP10 or DAP 12. Preferably, a transmembrane domain derived from a myeloid protein receptor (e.g. TREM) of the present invention should be capable of binding to DAP10 or DAP12 (e.g. to a sequence of SEQ ID NOs: 29 or 34, or to a sequence comprising the transmembrane domains of DAP10 or DAP12, e.g. to sequences comprising SEQ ID NOs: 30 or 35) with at least 50, 60, 70, 80, 90, 95 or 99% of the affinity of a wildtype TREM1 or TREM2 molecule, when present within the first or third/further polypeptide. In one aspect, it is possible that a transmembrane domain derived from a myeloid receptor protein (e.g. TREM) of the invention (when comprised within a first or third/further polypeptide) may have an increased ability to bind to DAP10 or DAP12 (e.g. to the transmembrane domains of DAP10 or DAP12), e.g. it may have a 2, 3, 4, 5 or 10 fold affinity for DAP10 or DAP12 (or to the transmembrane domains of DAP10 or DAP12) as compared to a wildtype TREM protein (e.g. TREM1 or TREM2). Binding and the strength of binding of a first polypeptide comprising a transmembrane domain derived from a myeloid receptor protein (e.g. a TREM protein) to DAP10 or DAP12 can be assessed using any well-known method of the art, for example by using ToxR, TOXCAT, GALLEX or FRET. “Binding” as used herein refers to a direct association between two molecules, due to for example, non-covalent, covalent, electrostatic, hydrophobic, and ionic and/or hydrogen bond interactions, including interactions such as salt bridges and water bridges. In the present invention, the “association” between a transmembrane domain from a myeloid receptor protein and a transmembrane domain from DAP10/12 is typically through the formation of stable, non-covalent complexes (between oppositely charged amino acids, as described herein). Particularly, in one embodiment, a stable non-covalent complex may form between the positively charged lysine within the transmembrane domain of a TREM protein and the negatively charged aspartic acid within the transmembrane domain of DAP10 or DAP12. “A myeloid receptor protein” refers to any receptor which is primarily expressed on a myeloid cell which is capable of binding to DAP10 or DAP12 as described above. A myeloid cell refers to a class of cells which arise from a common myeloid progenitor cell, and typically which arise from the myeloblast lineage, including granulocytes, monocytes, macrophages, neutrophils, mast cell and dendritic cells. Receptor proteins which are primarily expressed on myeloid cells include receptor proteins which are only expressed on myeloid cells, particularly on cells derived from a myeloblast and not on cells from any other lineage. Further, receptor proteins which are primarily expressed on myeloid cells include receptor proteins which are mainly expressed on myeloid cells. Therefore, although the receptor proteins may be expressed on cells from other lineages or on non-myeloid cells, such expression is typically low, e.g. at least 95, 90, 80, 70, 60 or 50% lower than the level of expression seen on at least one myeloid cell type. A myeloid receptor protein does not need to be expressed on every myeloid cell type considered to be a myeloid cell. However, a myeloid receptor protein may be expressed on at least one myeloid cell type, e.g. at least two, or at least three, e.g. on at least one of granulocytes, monocytes, macrophages, neutrophils, mast cell and dendritic cells. Myeloid receptor proteins as described herein include TREM (e.g. TREM1 and TREM2), CD300E, CD300B, Clec5A, Siglec14, Siglec15, Siglec16, SirpB1 and PiLRB. In a particular embodiment, the myeloid receptor protein from which the first transmembrane domain may be derived may be a member of the Immunoglobulin (Ig) superfamily. Such receptors are known to share structural features with immunoglobulins, and possess an immunoglobulin domain or fold. “A TREM protein” refers to any receptor from the TREM class which is capable of binding to DAP10 or DAP12. A TREM protein therefore typically refers to any one of TREM1, or TREM2. TREM1 (also known as CD354) has an amino acid sequence as set forth in SEQ ID NO: 11 and is encoded by a nucleotide sequence as set forth in SEQ ID NO: 18. The extracellular portion of TREM1 is set forth in SEQ ID NO: 12, and comprises a signal sequence (SEQ ID NO: 8), a ligand/antigen binding domain (SEQ ID NO: 13), and a stalk region (SEQ ID NO: 14). The stalk region is cleaved by MMP9 at PPTTTK (SEQ ID NO: 21). The transmembrane domain of TREM1 is shown in SEQ ID NO:16 and the cytoplasmic domain is shown in SEQ ID NO: 17. TREM2 has an amino acid sequence as set forth in SEQ ID NO: 22 and is encoded by a nucleotide sequence as set forth in SEQ ID NO: 28. The extracellular portion of TREM2 is set forth in SEQ ID NO: 23 and comprises a signal sequence (SEQ ID NO: 9), a ligand/antigen binding domain (SEQ ID NO: 24) and a stalk region (SEQ ID NO: 25). The stalk region is cleaved by a sheddase (ADAM10 and/or ADAM17) at amino acid residues 157-158 of SEQ ID NO: 22. The transmembrane domain of TREM2 is shown in SEQ ID NO: 26 and the cytoplasmic domain is shown in SEQ ID NO: 27. CD300E has an amino acid sequence as set forth in SEQ ID NO: 65, and the transmembrane domain of CD300E is shown in SEQ ID NO: 66. CD300B has an amino acid sequence as set forth in SEQ ID NO: 67 and the transmembrane domain of CD300B is shown in SEQ ID NO:.68. Clec5A has an amino acid sequence as set forth in SEQ ID NO: 69 and the transmembrane domain of Clec5A is shown in SEQ ID NO: 70. Siglec14 has an amino acid sequence as set forth in SEQ ID NO: 71 and the transmembrane domain of Siglec14 is shown in SEQ ID NO: 72. Siglec15 has an amino acid sequence as set forth in SEQ ID NO: 73 and the transmembrane domain of Siglec15 is shown in SEQ ID NO: 74. Siglec16 has an amino acid sequence as set forth in SEQ ID NO: 75 and the transmembrane domain of Siglec16 is shown in SEQ ID NO: 76. SirpB1 has an amino acid sequence as set forth in SEQ ID NO: 77 and the transmembrane domain of SirpB1 is shown in SEQ ID NO: 78. PiLRB has an amino acid sequence as set forth in SEQ ID NO: 79 and the transmembrane domain of PiLRB is shown in SEQ ID NO: 80. A transmembrane domain derived from a myeloid receptor protein (also referred to herein as a first transmembrane domain), may comprise or consist of SEQ ID NO: 16, SEQ ID NO: 26, SEQ ID NO: 66, SEQ ID NO:.68, SEQ ID NO: 70, SEQ ID NO: 72, SEQ ID NO: 74, SEQ ID NO: 76, SEQ ID NO: 78 or SEQ ID NO: 80. Particularly, the transmembrane from a myeloid receptor protein may comprise or consist of SEQ ID NOs:.16 or 26. Further, any transmembrane domain derived from a myeloid receptor protein, e.g. derived from SEQ ID NOs: 16, 26, 66, 68, 70, 72, 74, 76, 78 or 80 (and particularly SEQ ID NOs: 16 or 26) may be used within the first (or third/further) polypeptides of the invention. Thus, a portion or variant of the transmembrane domain of a myeloid receptor protein, e.g. as set forth in SEQ ID NOs: 16, 26, 66, 68, 70, 72, 74, 76, 78 or 80 may be used. A portion refers to a part or a truncation of the transmembrane domain, where for example, at least 1, 2, 3, 4, 5, or 6 amino acids may be truncated from the sequence. A variant of the transmembrane domain of a myeloid receptor protein, (e.g. as set forth in SEQ ID NOs: 16, 26, 66, 68, 70, 72, 74, 76, 78 or 80) may comprise at least 70, 80, 90, 95 or 99% sequence identity to the wildtype transmembrane domain sequence of the same myeloid receptor protein, e.g. to SEQ ID NOs: 16, 26, 66, 68, 70, 72, 74, 76, 78 or 80. Typically, as discussed previously, any such variant or portion of a transmembrane domain of a myeloid receptor protein should be capable of binding to either DAP10 or DAP12. Thus, preferably any portion or variant will retain any positively charged amino acid residues which are required for binding. With regard to variants or portions of SEQ ID NOs: 16 or 26, these will typically retain the positively charged lysine. DAP10 (alternatively known as hematopoietic cell signal transducer, HCST or DNAX- Activating Protein 10) as used herein refers to a protein having an amino acid sequence as set forth in SEQ ID NO: 29. DAP10 comprises a transmembrane domain having a sequence of SEQ ID NO: 30. The extracellular domain of DAP10 comprises the sequence of SEQ ID NO: 31 and includes a signal sequence of SEQ ID NO: 32. The cytoplasmic domain of DAP10 comprises the sequence as set forth in SEQ ID NO: 33. DAP12 (alternatively known as TYROBP, KARAP or DNAX-Activating Protein 12) as used herein refers to a protein having an amino acid sequence as set forth in SEQ ID NO: 34. DAP12 comprises a transmembrane domain having a sequence of SEQ ID NO: 35. The extracellular domain of DAP12 comprises the sequence of SEQ ID NO: 36 which includes a signal sequence as set out in SEQ ID NO: 37. The cytoplasmic domain of DAP12 comprises the sequence as set forth in SEQ ID NO: 38. As discussed previously, the second polypeptide of the multichain chimeric receptor of the invention comprises a transmembrane domain derived from DAP10 or DAP12 which is capable of binding to a TREM protein. A transmembrane domain derived from DAP10 or DAP12 (also referred to herein as a second transmembrane domain), may comprise or consist of SEQ ID NO: 30 or SEQ ID NO: 35. Further, any transmembrane domain derived from DAP10 or DAP12, e.g. derived from SEQ ID NOs: 30 or 35 may be used within the second polypeptide of the invention. Thus, a portion or variant of the transmembrane domain of DAP10 or DAP12, e.g. as set forth in SEQ ID NOs: 30 or 35 may be used. A portion refers to a part or a truncation of the transmembrane domain, where for example, at least 1, 2, 3, 4, 5, or 6 amino acids may be truncated from the sequence. A variant of the transmembrane domain of DAP10 or DAP12, (e.g. as set forth in SEQ ID NOs: 30 or 35) may comprise at least 70, 80, 90, 95 or 99% sequence identity to the wildtype transmembrane domain sequence of DAP10 or DAP12, e.g. to SEQ ID NOs: 30 or 35. Typically, as discussed previously, any such variant or portion of a transmembrane domain of DAP10 or DAP12 should be capable of binding to TREM (e.g. to TREM1 or TREM2). Thus, preferably any portion or variant will retain the negatively charged amino acid residues which are required for binding. With regard to variants or portions of SEQ ID NOs: 30 or 35, these will typically retain the negatively charged aspartic acid residue (amino acid residue 9 of SEQ ID NO: 30 and amino acid residue 10 of SEQ ID NO: 35). In one particular aspect, the invention may utilise a transmembrane domain within the second polypeptide which is negatively charged. The negative charge of the transmembrane domain will allow binding to the positively charged TM in the first polypeptide chain. Such a TM domain may be artificially synthesised and may for example comprise a poly leucine TM. It will be appreciated by a skilled person that “derived” as used herein refers both to sequences which are artificially synthesised (e.g. which are encoded by artificially synthesised nucleic acid) or which have been obtained by manipulation of naturally occurring nucleic acids. A skilled person will be readily able to determine whether a second polypeptide comprising a transmembrane domain derived from DAP10 or DAP12 binds to a TREM protein (e.g. to TREM1 or TREM2, or to a polypeptide comprising a transmembrane domain of TREM1 or TREM2) by using any of the assays described previously including ToxR, TOXCAT, GALLEX or FRET. Preferably, a second polypeptide comprising a transmembrane domain derived from DAP10 or DAP12 of the present invention should be capable of binding to a TREM protein (e.g. to a sequence of SEQ ID NO: 11 or 22, or to a sequence comprising the transmembrane domains of TREM1 or TREM2, e.g. to sequences comprising SEQ ID NOs: 16 or 26) with at least 50, 60, 70, 80, 90, 95 or 99% of the affinity of wildtype DAP10 or DAP12. In one aspect, it is possible that a transmembrane domain derived from DAP10 or DAP12 of the invention (when comprised within a second polypeptide) may have an increased ability to bind to a TREM protein (e.g. to TREM1 or TREM2 or to a polypeptide comprising the transmembrane domains of TREM1 or TREM2), e.g. it may have a 2, 3, 4, 5 or 10 fold affinity for TREM1 or TREM2 (or to the transmembrane domains of TREM1 or TREM2) as compared to a wildtype DAP10 or DAP12. An endodomain as used herein refers to the portion of a polypeptide which is generally present inside the cell. The endodomain typically is found at the C terminus of the transmembrane domain of a polypeptide. Both the first (and third/further) and second polypeptides of the invention may comprise an endodomain. In this respect, although the first polypeptide of the multichain chimeric receptor of the invention may further comprise an endodomain, this domain may also be absent when the second polypeptide comprises a heterologous protein sequence (i.e. when the second polypeptide comprises sequence which is not derived from DAP10 or DAP12). Thus, when the second polypeptide comprises at least one heterologous costimulatory domain and/or at least one heterologous intracellular signalling domain (i.e. not derived from DAP10 or DAP12), or when the second polypeptide comprises a heterologous extracellular portion, in one embodiment, the first polypeptide chain may not comprise an endodomain e.g. comprising at least one costimulatory domain and/or at least on intracellular signalling domain. In another embodiment however, the first polypeptide may comprise an endodomain, e.g. comprising at least one costimulatory domain and/or at least one intracellular signalling domain. Alternatively viewed, when the second polypeptide consists of a sequence from DAP10 or DAP12, the first polypeptide comprises an endodomain comprising at least one costimulatory domain and/or at least one intracellular signalling domain. It will be appreciated by a skilled person that the endodomain of the first polypeptide may comprise all or a portion of the cytoplasmic domain of a myeloid receptor protein, particularly of the myeloid receptor protein from which the transmembrane domain of the first polypeptide is derived, e.g. TREM protein, e.g. all or a portion of SEQ ID NOs: 17 or 27. A portion may be at least 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 amino acids of the cytoplasmic domain of a myeloid receptor protein, particularly of the myeloid receptor protein from which the transmembrane domain of the first polypeptide is derived, e.g. a TREM protein (e.g. of SEQ ID NOs: 17 or 27). The second polypeptide of the multichain chimeric receptor of the invention comprises an endodomain comprising at least one costimulatory domain and/or at least one intracellular signalling domain. It will be appreciated by a skilled person that the endodomain of the second polypeptide may comprise all or a portion of the cytoplasmic domain of DAP10 or DAP12, e.g. all or a portion of SEQ ID NOs: 33 or 38. A portion may be at least 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 amino acids of the cytoplasmic domain of DAP10 or DAP12 (e.g. of SEQ ID NOs: 33 or 38). Further, it will be appreciated by a skilled person that the second polypeptide may comprise any part or all of the extracellular domain of DAP10 or DAP12, e.g. as set out in SEQ ID NOs: 31 or 36. The at least one costimulatory domain as used herein refers to the portion of the endodomain comprising the intracellular domain of a co-stimulatory molecule. Co-stimulatory molecules are cell surface molecules other than antigen receptors or Fc receptors that provide a second signal that is typically required for efficient activation and function of an immune cell (e.g. a T-cell) upon binding to antigen. Examples of such co-stimulatory molecules include CD27, CD28, 4- IBB (CD137), OX40 (CD134), CD30, CD40, ICOS (CD278), LFA-1, CD2, CD7, LIGHT, NKD2C, B7-H2 and a ligand that specifically binds CD83, more particularly the intracellular domains of such molecules. Preferably the molecules are human. Accordingly, in some preferred embodiments, a co-stimulatory domain is derived from derived from 4-1BB, CD28 or OX40 (CD134), although other co- stimulatory domains are contemplated for use with the chimeric receptors described herein. The co-stimulatory domains may be used singly or in combination (i.e. one or more co- stimulatory domains may be included, e.g. two costimulatory domains). The inclusion of one or more co-stimulatory signalling domains may enhance the efficacy and expansion of immune cells expressing the chimeric receptor. The endodomain of a polypeptide chain of the invention may comprise the following CD28 costimulatory domain: RSKRSRLLHSDYMNMTPRRPGPTRKHYQPYAPPRDFAAYRS (SEQ ID NO: 39) In one embodiment, the costimulatory domain has at least 85, 90, 95, 97, 98 or 99% identity to SEQ ID NO: 39. The endodomain of a polypeptide chain of the invention may comprise the following CD27 signaling domain: QRRKYRSNKGESPVEPAEPCHYSCPREEEGSTIPIQEDYRKPEPACSP (SEQ ID NO: 40). In one embodiment, the costimulatory domain has at least 85, 90, 95, 97, 98 or 99% identity to SEQ ID NO: 40. Illustrative sequences for OX40, 4-1BB, ICOS and TNFRSF25 costimulatory domains are shown below as SEQ ID NOs: 41-44. The polypeptide endodomains may also comprise one or more of SEQ ID NOs: 41-44 or a variant of SEQ ID NOs: 41-44. OX40 signalling domain (SEQ ID NO: 41): ALYLLRRDQRLPPDAHKPPGGGSFRTPIQEEQADAHSTLAKI 41BB signalling domain (SEQ ID NO: 42): KRGRKKLLYIFKQPFMRPVQTTQEEDGCSCRFPEEEEGGCEL ICOS signalling domain (SEQ ID NO: 43): CWLTKKKYSSSVHDPNGEYMFMRAVNTAKKSRLTDVTL TNFRSF25 signalling domain (SEQ ID NO: 44): TYTYRHCWPHKPLVTADEAGMEALTPPPATHLSPLDSAHTLLAPPDSSEKICTVQLVGNSW TPGYPETQEALCPQVTWSWDQLPSRALGPAAAPTLSPESPAGSPAMMLQPGPQLYDVMD AVPARRWKEFVRTLGLREAEIEAVEVEIGRFRDQQYEMLKRWRQQQPAGLGAVYAALERM GLDGCVEDLRSRLQRGP The polypeptide endodomain may comprise a variant of one or more of SEQ ID NOs: 41-44 which has at least 85, 90, 95, 97, 98 or 99% identity to any one of SEQ ID NOs: 41- 44. In this respect, as described in WO2020/044055 (incorporated herein by reference in its entirety), it may be advantageous to include a domain in the endodomain of the first (or third/further) and/or second polypeptide that comprises a STAT5 association motif and a JAK1- and/or a JAK2-binding motif. This may be particularly helpful when the chimeric receptor is expressed in a T cell (e.g. a Treg) as such receptors address the problem associated with the high IL-2 dependence of adoptively transferred Tregs without requiring exogenous IL-2 to be administered and by providing a productive IL-2 signal in an antigen- specific manner. “Signal Transducer and Activator of Transcription 5” (STAT5) is a transcription factor involved in the IL-2 signalling pathway that plays a key role in Treg function, stability and survival by promoting the expression of genes such as FOXP3, IL2RA and BCLXL. In order to be functional and translocate into the nucleus, STAT5 needs to be phosphorylated. IL-2 ligation results in STAT5 phosphorylation by activating the JAK1/JAK2 and JAK3 kinases via specific signalling domains present in the IL-2Rβ and IL-2Rγ chain, respectively. Although JAK1 (or JAK2) can phosphorylate STAT5 without the need of JAK3, STAT5 activity is increased by the transphosphorylation of both JAK1/JAK2 and JAK3, which stabilizes their activity. “STAT5 association motif” as used herein refers to an amino acid motif which comprises a tyrosine and is capable of binding a STAT5 polypeptide. Any method known in the art for determining protein:protein interactions may be used to determine whether an association motif is capable of binding to STAT5. For example, co-immunoprecipitation followed by western blot. Suitably, the endodomain of a polypeptide of the invention (e.g. the endodomain of the first or second polypeptide) may comprise two or more STAT5 association motifs as defined herein. For example, the endodomain may comprise two, three, four, five or more STAT5 association motifs as defined herein. Preferably, the endodomain may comprise two or three STAT5 association motifs as defined herein. Suitably, the STAT5 association motif may exist endogenously in a cytoplasmic domain of a transmembrane protein. For example, the STAT5 association motif may be from an interleukin receptor (IL) receptor endodomain or a hormone receptor. The endodomain may comprise an amino acid sequence selected from any chain of the interleukin receptors where STAT5 is a downstream component, for example, the cytoplasmic domain comprising amino acid numbers 266 to 551 of IL-2 receptor β chain (NCBI REFSEQ: NP_000869.1, SEQ ID NO: 45), amino acid numbers 265 to 459 of IL-7R α chain (NCBI REFSEQ: NP_002176.2, SEQ ID NO: 46), amino acid numbers 292 to 521 of IL-9R chain (NCBI REFSEQ: NP_002177.2, SEQ ID NO: 47), amino acid numbers 257 to 825 of IL-4R α chain (NCBI REFSEQ: NPJD00409.1, SEQ ID NO: 48), amino acid numbers 461 to 897 of IL-3Rβ chain (NCBI REFSEQ: NP_000386.1, SEQ ID NO: 49), amino acid numbers 314 to 502 of IL-17R β chain (NCBI REFSEQ: NP_061195.2, SEQ ID NO: 50) or a truncated form of IL-7R α chain (SEQ ID NO: 51) may be used. The entire region of the cytoplasmic domain of interleukin receptor chain may be used. The endodomain of a polypeptide may comprise a STAT5 association motif that comprises an amino acid sequence shown as SEQ ID NOs: 45-51, or a variant which is at least 80, 85, 90, 95, 96, 97, 98 or 99% identical to SEQ ID NOs: 45-51. For example, the variant may be capable of binding STAT5 to at least 10%, at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, or at least 90% of the level of an amino acid sequence shown as one of SEQ ID NOs: 45-51. The variant or derivative may be capable of binding STAT5 to a similar or the same level as one of SEQ ID NOs: 45- 51 or may be capable of binding STAT5 to a greater level than an amino acid sequence shown as one of SEQ ID NOs: 45-51 (e.g. increased by at least 10%, at least 20%, at least 30%, at least 40% or at least 50%). For example, the STAT5 association motif may be from IL2Rβ, IL7Rα, IL-3Rβ (CSF2RB), IL-9R, IL-17Rβ, erythropoietin receptor, thrombopoietin receptor, growth hormone receptor and prolactin receptor. “JAK1- and/or a JAK2-binding motif” as used herein refers to BOX motif which allows for tyrosine kinase JAK1 and/or JAK2 association. Suitable JAK1- and JAK2-binding motifs are described, for example, by Ferrao & Lupardus (Frontiers in Endocrinology; 2017; 8(71); which is incorporated herein by reference). The JAK1- and/or JAK2-binding motif may occur endogenously in a cytoplasmic domain of a transmembrane protein. For example, the JAK1- and/or JAK2-binding motif may be from Interferon lambda receptor 1 (IFNLR1), Interferon alpha receptor 1 (IFNAR), Interferon gamma receptor 1 (IFNGR1), IL10RA, IL20RA, IL22RA, Interferon gamma receptor 2 (IFNGR2) or IL10RB. The JAK1-binding motif may comprise an amino acid motif shown as SEQ ID NOs: 52-58 or a variant therefore which is capable of binding JAK1. The variant of SEQ ID NOs: 52-58 may comprise one, two or three amino acid differences compared to any of SEQ ID NOs: 52-58 and retain the ability to bind JAK1. The variant may be at least 80, 85, 90, 95, 96, 97, 98 or 99% identical to any one of SEQ ID NOs: 52-58 and retain the ability to bind JAK1. In a preferred embodiment, the JAK1-binding domain comprises SEQ ID NO: 21 or a variant thereof which is capable of binding JAK1. For example, the variant may be capable of binding JAK1 to at least 10%, at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, or at least 90% of the level of a corresponding, reference sequence. The variant or derivative may be capable of binding JAK1 to a similar or the same level as a corresponding, reference sequence or may be capable of binding JAK1 to a greater level than a corresponding, reference sequence (e.g. increased by at least 10%, at least 20%, at least 30%, at least 40% or at least 50%). The JAK2-binding motif may comprise an amino acid motif shown as SEQ ID NOs: 59-61 or a variant therefore which is capable of binding JAK2. The variant of SEQ ID NOs: 59-61 may comprise one, two or three amino acid differences compared to any of SEQ ID NOs: 59-61 and retain the ability to bind JAK2. For example, the variant may be capable of binding JAK2 to at least 10%, at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, or at least 90% of the level of a corresponding, reference sequence. The variant or derivative may be capable of binding JAK2 to a similar or the same level as a corresponding, reference sequence or may be capable of binding JAK2 to a greater level than a corresponding, reference sequence (e.g. increased by at least 10%, at least 20%, at least 30%, at least 40% or at least 50%). Any method known in the art for determining protein:protein interactions may be used to determine whether a JAK1- or JAK2-binding motif is capable of binding to a JAK1 or JAK2. For example, co-immunoprecipitation followed by western blot. The endodomain of the chimeric receptor of the invention may further comprise a JAK3-binding motif. “JAK3-binding motif” as used herein refers to BOX motif which allows for tyrosine kinase JAK3. Suitable JAK3-binding motifs are described, for example, by Ferrao & Lupardus (Frontiers in Endocrinology; 2017; 8(71); which is incorporated herein by reference). Any method known in the art for determining protein:protein interactions may be used to determine whether a motif is capable of binding to JAK3. For example, co- immunoprecipitation followed by western blot. The JAK3-binding motif may occur endogenously in a cytoplasmic domain of a transmembrane protein. For example, the JAK3-binding motif may be from an IL-2Rγ polypeptide. The JAK3-binding motif may comprise an amino acid motif shown as SEQ ID NO: 62 or SEQ ID NO: 63 or a variant therefore which is capable of binding JAK3. The variant may be at least 80, 85, 90, 95, 96, 97, 98 or 99% identical to SEQ ID NO: 62 or SEQ ID NO: 63. In a particular embodiment, the endodomain comprises one or more JAK1-binding domains and at least one JAK3-binding domain. In a further particular embodiment, the endodomain of the first polypeptide (or of a third or further polypeptide) may comprise a domain comprising at least one STAT5 association motif and at least one JAK1- and/or a JAK2-binding motif, and the endodomain of the second polypeptide may comprise at least one JAK3-binding domain, or vice versa. In this regard, the invention further provides a multichain chimeric receptor comprising: (a) a first polypeptide comprising (i) an extracellular domain comprising an antigen binding domain, (ii) a first transmembrane domain which is capable of associating with DAP10 or DAP12 and (iii) an endodomain comprising at least one STAT5 association motif and at least one JAK1- and/or a JAK2-binding motif; and (b) a second polypeptide comprising (i) a second transmembrane domain derived from DAP10 or DAP12 which is capable of associating with the first transmembrane domain and (ii) an endodomain comprising (1) at least one JAK3-binding domain and (2) at least one co-stimulatory domain and/or at least one intracellular signalling domain. Alternatively, the invention provides a multichain chimeric receptor comprising: (a) a first polypeptide comprising (i) an extracellular domain comprising an antigen binding domain, (ii) a first transmembrane domain which is capable of associating with DAP10 or DAP12 and (iii) an endodomain comprising at least one JAK3-binding domain; and (b) a second polypeptide comprising (i) a second transmembrane domain derived from DAP10 or DAP12 which is capable of associating with the first transmembrane domain and (ii) an endodomain comprising (1) at least one STAT5 association motif and at least one JAK1- and/or a JAK2-binding motif and (2) at least one co- stimulatory domain and/or at least one intracellular signalling domain. In a further embodiment, the invention provides a multichain chimeric receptor comprising: (a) a first polypeptide comprising (i) an extracellular domain comprising an antigen binding domain, (ii) a first transmembrane domain which is capable of associating with DAP10 or DAP12 and (iii) optionally an endodomain comprising at least one JAK3-binding domain; and (b) a second polypeptide comprising (i) a second transmembrane domain derived from DAP10 or DAP12 which is capable of associating with the first transmembrane domain and (ii) an endodomain comprising (1) at least one STAT5 association motif and at least one JAK1- and/or a JAK2- binding motif, (2) optionally at least one JAK3-binding domain and (3) at least one co- stimulatory domain and/or at least one intracellular signalling domain. In these embodiments, a skilled person will appreciate that the transmembrane domain of the first polypeptide may be any transmembrane domain from any protein which has a transmembrane domain, and which is capable of binding to DAP10 or DAP12. This includes the first transmembrane domains as described previously, or transmembrane domains from receptors expressed upon non-myeloid cells, such as natural killer cells (NK cells), including transmembrane domains from receptors such as KIR and NKG2D. Any artificial transmembrane domains are also encompassed which bind to DAP10 or DAP12. Typically, any such transmembrane domain may include a positively charged amino acid residue. In one specific embodiment, the invention provides a polypeptide comprising (i) a transmembrane domain derived from DAP10 or DAP12 which is capable of associating with a TREM protein and (ii) an endodomain comprising (1) at least one STAT5 association motif and at least one JAK1- and/or a JAK2-binding motif, (2) optionally at least one JAK3-binding domain and (3) at least one co-stimulatory domain and/or at least one intracellular signalling domain. The intracellular signalling domain of the invention refers to the part of the endodomain that participates in transducing the message of effective chimeric receptor binding to a target antigen (i.e. of the antigen binding domain of the first polypeptide or of the third or further polypeptides) into the interior of a particular cell, e.g. an immune cell to elicit cell function, e.g. activation, cytokine production, proliferation or other cellular responses elicited with antigen binding to the antigen binding domain of the extracellular domain of the chimeric receptor. The intracellular signalling domain is comprised within the endodomain of the receptor. The term "cell function" refers to a specialized function of a cell. Cell function of a T cell, for example, may be cytolytic activity or helper activity including the secretion of a cytokine or immunosuppressive activity. Thus, the term "intracellular signalling domain" refers to the portion of a protein that transduces a function signal and that directs a cell to perform a specialized function. While the entire intracellular signalling domain of a protein can be employed, in many cases it is not necessary to use the entire domain. To the extent that a truncated portion of an intracellular signalling domain is used, such truncated portion may be used in place of the entire domain as long as it transduces the effector function signal. The term intracellular signalling domain therefore includes any truncated portion of an intracellular signalling domain sufficient to transduce a function signal. The intracellular signalling domain is also known as the "signal transduction domain," and is typically derived from portions of the human CD3ζ or FcRy chains. Alternatively, or additionally, the signal transduction domain may be derived from DAP12/DAP10. It will be appreciated that the chimeric receptors of the invention may be introduced into cells, such as precursor or progenitor cells where the intracellular signalling domain may not be capable of inducing a cell function. However, the chimeric receptor should be capable of signalling once expressed within an appropriate cell type, e.g. an immune cell, e.g. a T cell. Additionally, as described previously, to allow or to augment full activation of the cell, e.g. the immune cell, the first polypeptide (or third/further polypeptides) and/or the second polypeptide may be provided with one or more secondary or co-stimulatory domains within the endodomain. Thus, the endodomain may initiate antigen dependent primary activation through the at least one intracellular signalling domain (i.e. may be a primary cytoplasmic signalling sequence) and the at least one co-stimulatory domain may act in an antigen independent manner to provide a secondary or co-stimulatory signal (secondary cytoplasmic signalling sequence(s)). Primary cytoplasmic signalling sequences may regulate primary activation, including in an inhibitory way. The intracellular signalling domain providing a primary signal may contain signalling motifs which are known as immunoreceptor tyrosine- based activation motif or ITAMs. In some embodiments, the primary signalling domain is a signalling domain from a protein selected from a receptor tyrosine kinase (RTK), an M-CSF receptor, CSF-1R, Kit, TIE3, an ITAM-containing protein, DAP12, DAP10, an Fc receptor, FcR-gamma, FcR- epsilon, FcR-beta, TCR-zeta, CD3-gamma, CD3-delta, CD3-epsilon, CD3-zeta, CD3-eta, CD5, CD22, CD79a, CD79b, CD66d, TNF-alpha, NF-KappaB, a TLR (toll-like receptor), TLR5, Myd88, TOR/CD3 complex, lymphocyte receptor chain, IL-2 receptor, IgE, IgG, CD16α, FcγRIII, FcγCD28, 4-1BB, and any combination thereof. In some embodiments, the signalling domain is a signalling domain selected from a 4-1BB intracellular domain, a CD3- zeta ITAM domain, a CD3-zeta intracellular domain, a CSF-1R receptor tyrosine kinase (RTK) intracellular domain, a DAP12 intracellular domain, a TCR-zeta intracellular domain, a TLR5 intracellular domain, a CD28 intracellular domain, a DAP10 intracellular domain, an FcR-gamma intracellular domain, and any combination thereof. Examples of ITAM containing primary cytoplasmic signalling sequences that may be used in the invention include those derived from TCRζ, FcRy, FcRβ, CD3γ, CD3δ, CD3ε, CD5, CD22, CD79a, CD79b and CD66d. In some embodiments, the intracellular signalling domain is derived from CD3ζ or FcRγ, preferably human CD3ζ or FcRγ. In a particular embodiment, the intracellular signalling domain is derived from DAP10 and/or DAP12. In a preferred representative embodiment, the intracellular signalling domain is preferably a human CD3ζ domain, more preferably a human CD3ζ domain having the amino acid sequence of SEQ ID NO: 64 or an amino acid sequence having at least 95% sequence identity thereto. In a further preferred embodiment, the intracellular signalling domain is preferably a DAP10 signalling domain, more preferably a DAP10 signalling domain having the amino acid sequence of SEQ ID NO: 33 or an amino acid sequence having at least 95% identity thereto. In a further preferred embodiment, the intracellular signalling domain is preferably a DAP12 signalling domain, more preferably a DAP12 signalling domain having the amino acid sequence of SEQ ID NO: 38 or an amino acid sequence having at least 95% identity thereto. It will be appreciated by a skilled person that intracellular signalling domains which comprise more than one ITAM sequence may be modified to optimise the number of ITAM sequences within the multichain receptor. Thus, intracellular signalling domains may be modified to comprise fewer ITAM sequences, e.g. to delete one or more of the ITAM sequences present, or to modify or mutate (e.g. substitute) the amino acid residues which constitute one or more of the ITAM sequences to prevent their signalling. Preferably, at least one or two functional ITAM sequences may be retained within an intracellular signalling domain. In a particular embodiment, an intracellular signalling domain of CD3zeta or a portion thereof may be modified to delete or to substitute one or two of the ITAM sequences. The signalling portion of CD3zeta comprises three ITAM sequences and in one embodiment, it may be desirable to utilise CD3zeta or a portion thereof which only comprises one or two functional ITAMs, particularly when CD3zeta or a portion thereof is used in direct combination with another intracellular signalling domain, e.g. with an intracellular signalling domain from DAP10 or DAP12. In particular, second polypeptide chains comprising a truncated CD3zeta portion are as set forth in SEQ ID NOs: 203-204, 206-207, 211-212, 214- 215, 218-219, 221-222, and 226-227. As discussed previously, more than at least one intracellular signalling domain may be used in the multichain chimeric receptor of the invention. Thus, at least one, two, three or four intracellular signalling domains may be present, which may be from the same or different proteins. Multiple different combinations of costimulatory and intracellular signalling domains may be used in the present invention. For example, the second polypeptide may comprise of consist of the transmembrane and cytoplasmic domains of DAP10 or DAP12, optionally modified with at least one costimulatory domain (e.g. CD28) and at least one intracellular signalling domain (e.g. derived from CD3zeta), or may comprise or consist of the transmembrane domain of DAP10 or DAP12, in combination with at least one costimulatory domain (e.g. CD28) and at least one heterologous intracellular signalling domain (e.g. derived from CD3zeta). The second polypeptide may therefore be a chimeric polypeptide comprising domains derived from different proteins. However, the following combinations are particularly preferred: 1. First polypeptide comprising a costimulatory domain (e.g. from CD28) and the second polypeptide comprising an intracellular signalling domain (e.g. from DAP10 or DAP12). 2. First polypeptide comprising an intracellular signalling domain (e.g. from CD3zeta) and the second polypeptide comprising a costimulatory domain (e.g. from CD28). 3. First polypeptide comprising a costimulatory domain (e.g. from CD28) and the second polypeptide comprising an intracellular signalling domain from CD3zeta. 4. First polypeptide not comprising a costimulatory domain or an intracellular signalling domain and the second polypeptide comprising both a costimulatory domain (e.g. from CD28) and an intracellular signalling domain, e.g. from CD3zeta. In particular embodiments, the first polypeptide chain may comprise a sequence of any one of SEQ ID NOs: 81 to 200. Further, the second polypeptide chain may comprise a sequence of any one of SEQ ID NOs: 201 to 230. In one embodiment, the invention further provides a (first) polypeptide comprising (i) an extracellular domain comprising an antigen binding domain and (ii) a transmembrane domain derived from TREM2 which is capable of binding to DAP10 or DAP12 wherein said antigen binding domain is heterologous to the transmembrane domain. Further, the invention provides a (first) polypeptide comprising (i) an extracellular domain comprising an antigen binding domain, (ii) a transmembrane domain derived from a myeloid receptor protein which is capable of binding to DAP10 or DAP12 wherein said antigen binding domain is heterologous to the transmembrane domain and (iii) an endodomain comprising at least one co-stimulatory domain and/or at least one intracellular signalling domain. In this regard, it will be appreciated by a skilled person that it may be possible in some circumstances for a cell to endogenously provide a second polypeptide of the invention. For example, Tregs express endogenous DAP10. Thus, it may only be necessary in such situations to introduce and express the first polypeptide within the cell. Accordingly, in a further aspect, the invention provides a nucleic acid molecule encoding a multichain chimeric receptor as defined herein or a polypeptide as described above. Sequence identity may be determined by any suitable means known in the art, e.g. using the SWISS-PROT protein sequence databank using FASTA pep-cmp with a variable pamfactor, and gap creation penalty set at 12.0 and gap extension penalty set at 4.0, and a window of 2 amino acids. Other programs for determining amino acid sequence identity include the BestFit program of the Genetics Computer Group (GCG) Version 10 Software package from the University of Wisconsin. The program uses the local homology algorithm of Smith and Waterman with the default values: Gap creation penalty - 8, Gap extension penalty = 2, Average match = 2.912, Average mismatch = -2.003. The nucleic acid, when expressed by a cell, causes the encoded polypeptide (i.e. multichain chimeric receptor, or a polypeptide as described above) to be expressed at the cell-surface of the cell. The nucleic acid molecule may be RNA or DNA, such as cDNA. The nucleic acid molecule may be introduced into a cell, particularly an immune cell, as mRNA or as DNA for expression in the cell. Vectors may be used to transfer the nucleic acid molecule into the cell or to produce the nucleic acid for transfer (e.g. to produce mRNA for transfer, or to produce a nucleic acid molecule for preparation of an expression vector for transfer into a cell). Thus, in a further aspect, the invention provides a vector comprising the nucleic acid molecule of the invention. In some embodiments, the vector is capable of transfecting or transducing a cell (e.g. Treg), such that it expresses the polypeptide (i.e. the multichain chimeric receptor or polypeptide described above). The vector may be a non-viral vector such as a plasmid. Plasmids may be introduced into cells using any well-known method of the art, e.g. using calcium phosphate, liposomes, or cell penetrating peptides (e.g. amphipathic cell penetrating peptides). The vector may be a viral vector, such as a retroviral, e.g. a lentiviral vector or a gamma retroviral vector. Vectors suitable for delivering nucleic acids for expression in mammalian cells are well-known in the art and any such vector may be used. Vectors may comprise one or more regulatory elements, e.g. a promoter. Delivery systems are also available in the art which do not rely on vectors to introduce a nucleic acid molecules into a cell, for example, systems based on transposons, CRISPR/TALEN delivery and mRNA delivery. Any such system can be used to deliver a nucleic acid molecule according to the present invention. The multichain chimeric receptor of the invention generally requires the expression of more than one polypeptide in the cell (e.g. of the first and the second polypeptides). In a representative embodiment, as discussed above, the multichain chimeric receptor of the invention comprises at least a first and a second polypeptide which may bind e.g. which may heterodimerise with each other. Whilst in some embodiments, the second polypeptide may be present in the host cell (e.g. in embodiments where DAP10 or DAP12 comprise a DAP10 or DAP12 intracellular signaling domain, i.e. where the second polypeptide consists of the sequence of DAP10 or DAP12), in most embodiments, it may be advantageous to modify the cell to express the second polypeptide, e.g. where the cell does not endogenously produce the second polypeptide (e.g. where the second polypeptide comprises heterologous costimulatory and/or intracellular signaling domains) or does so at low levels. Thus, in some embodiments, a nucleic acid molecule (e.g. a vector) encoding at least the first and the second polypeptides may be introduced (e.g. transfected or transduced) into a cell. Thus, the vector may comprise at least a nucleic acid encoding the first polypeptide and a nucleic acid encoding the second polypeptide. The vector may comprise the nucleic acid molecules as separate entities, or as a single nucleotide sequence. If they are present as a single nucleotide sequence, they may comprise one or more internal ribosome entry site (IRES) sequences or other translational coupling sequences between the two encoding portions to enable the downstream sequence to be translated. A cleavage site such as a 2A cleavage site (e.g. T2A, F2A or P2A) may be encoded by a nucleic acid. Alternatively, the nucleic acid encoding at least the first polypeptide and the nucleic acid encoding at least the second polypeptide may be introduced to a cell as separate entities, e.g. on different vectors. Other polypeptides may further be encoded by a nucleic acid or vector of the invention, for example, a third or further polypeptide as discussed above, or a polypeptide that may be capable of inducing cell lysis upon activation to provide a safety switch feature. The present invention also provides a cell that expresses the multichain chimeric receptor of the invention. The cell may co-express the first polypeptide and the second polypeptide at the cell surface. The present invention also provides a cell comprising a nucleic acid molecule or vector encoding a multichain chimeric receptor of the invention, or of a polypeptide as described above. The cell may be a cell into which a nucleic acid molecule or vector as described herein has been introduced. The cell may have been transduced or transfected with a vector according to the invention. The cell may be suitable for adoptive cell therapy. The cell may be any cell but particularly may be an immune cell or a precursor thereof. A precursor cell may also be termed a progenitor cell, and the two terms are used synonymously herein. Precursors of immune cells include pluripotent stem cells, e.g. induced PSC (iPSC), or more committed progenitors including multipotent stem cells, or cells which are committed to a lineage. Precursor cells can be induced to differentiate into immune cells in vivo or in vitro. In one aspect, a precursor cell may be a somatic cell which is capable of being transdifferentiated to an immune cell. Most notably the cell may be an immune cell, such as an NK cell, a dendritic cell, a NKT cell, a MDSC, a neutrophil, a macrophage or a T cell, such as a cytotoxic T lymphocyte (CTL; CD8+ T cells), helper T cells (HTLs; CD4+ T cells) or a regulatory T cell (Treg cell). Memory or naïve T cell populations may be used. The T cell may have an existing specificity. For example, it may be an Epstein-Barr virus (EBV)-specific T cell. Alternatively, the T cell may have a redirected specificity, for example, by introduction of an exogenous or heterologous TCR or a chimeric receptor, e.g. CAR. In a preferred embodiment the immune cell is a Treg cell. “Regulatory T cells (Treg) or T regulatory cells” are immune cells with immunosuppressive function that control cytopathic immune responses and are essential for the maintenance of immunological tolerance. As used herein, the term Treg refers to a T cell with immunosuppressive function. Suitably, immunosuppressive function may refer to the ability of the Treg to reduce or inhibit one or more of a number of physiological and cellular effects facilitated by the immune system in response to a stimulus such as a pathogen, an alloantigen, or an autoantigen. Examples of such effects include increased proliferation of conventional T cell (Tconv) and secretion of proinflammatory cytokines. Any such effects may be used as indicators of the strength of an immune response. A relatively weaker immune response by Tconv in the presence of Tregs would indicate an ability of the Treg to suppress immune responses. For example, a relative decrease in cytokine secretion would be indicative of a weaker immune response, and thus indicative of the ability of Tregs to suppress immune responses. Tregs can also suppress immune responses by modulating the expression of co-stimulatory molecules on antigen presenting cells (APCs), such as B cells, dendritic cells and macrophages. Expression levels of CD80 and CD86 can be used to assess suppression potency of activated Tregs in vitro after co-culture. Assays are known in the art for measuring indicators of immune response strength, and thereby the suppressive ability of Tregs. In particular, antigen-specific Tconv cells may be co-cultured with Tregs, and a peptide of the corresponding antigen added to the co- culture to stimulate a response from the Tconv cells. The degree of proliferation of the Tconv cells and/or the quantity of the cytokine IL-2 they secrete in response to addition of the peptide may be used as indicators of the suppressive abilities of the co-cultured Tregs. Antigen-specific Tconv cells co-cultured with Tregs as described herein may proliferate 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 90%, 95% or 99% less than the same Tconv cells cultured in the absence of Tregs as described herein. Antigen-specific Tconv cells co-cultured with Tregs may express at least 10%, at least 20%, at least 30%, at least 40%, at least 50%, or at least 60% less effector cytokine than corresponding Tconv cells cultured in the absence of Tregs. The effector cytokine may be selected from IL-2, IL-17, TNFα, GM-CSF, IFN-γ, IL-4, IL-5, IL-9, IL-10 and IL-13. Suitably the effector cytokine may be selected from IL-2, IL-17, TNFα, GM-CSF and IFN-γ. Several different subpopulations of Tregs have been identified which may express different or different levels of particular markers. Tregs generally are T cells which express the markers CD4, CD25 and FOXP3 (CD4⁺CD25⁺FOXP3⁺). “FOXP3” is the abbreviated name of the forkhead box P3 protein. FOXP3 is a member of the FOX protein family of transcription factors and functions as a master regulator of the regulatory pathway in the development and function of regulatory T cells. Tregs may also express CTLA-4 (cytotoxic T-lymphocyte associated molecule-4) or GITR (glucocorticoid-induced TNF receptor). A Treg may be identified using the cell surface markers CD4 and CD25 in the absence of or in combination with low-level expression of the surface protein CD127 (CD4⁺CD25⁺CD127⁻ or CD4⁺CD25⁺CD127^low). The use of such markers to identify Tregs is known in the art and described in Liu et al. (JEM; 2006; 203; 7(10); 1701-1711), for example. A Treg may be a CD4⁺CD25⁺FOXP3⁺ T cell, a CD4⁺CD25⁺CD127⁻ T cell, or a CD4⁺CD25⁺FOXP3⁺CD127^−/low T cell. A Treg may have a demethylated Treg-specific demethylated region (TSDR). The TSDR is an important methylation-sensitive element regulating FOXP3 expression (Polansky, J.K., et al., 2008. European journal of immunology, 38(6), pp.1654-1663). Different subpopulations of Tregs are known to exist, including naïve Tregs (CD45RA⁺FOXP3^low), effector/memory Tregs (CD45RA-FOXP3^high) and cytokine-producing Tregs (CD45RA-FOXP3^low). “Memory Tregs” are Tregs which express CD45RO and which are considered to be CD45RO⁺. These cells have increased levels of CD45RO as compared to naïve Tregs (e.g. at least 10, 20, 30, 40, 50, 60, 70, 80 or 90% more CD45RO) and which preferably do not express or have low levels of CD45RA (mRNA and/or protein) as compared to naïve Tregs (e.g. at least 80, 90 or 95% less CD45RA as compared to naïve Tregs). “Cytokine-producing Tregs” are Tregs which do not express or have very low levels of CD45RA (mRNA and/or protein) as compared to naïve Tregs (e.g. at least 80, 90 or 95% less CD45RA as compared to naïve Tregs), and which have low levels of FOXP3 as compared to Memory Tregs, e.g. less than 50, 60, 70, 80 or 90% of the FOXP3 as compared to Memory Tregs. Cytokine-producing Tregs may produce interferon gamma and may be less suppressive in vitro as compared to naïve Tregs (e.g. less than 50, 60, 70, 80 or 90% suppressive than naïve Tregs. Reference to expression levels herein may refer to mRNA or protein expression. Particularly, for cell surface markers such as CD45RA, CD25, CD4, CD45RO etc, expression may refer to cell surface expression, i.e. the amount or relative amount of a marker protein that is expressed on the cell surface. Expression levels may be determined by any known method of the art. For example, mRNA expression levels may be determined by Northern blotting/array analysis, and protein expression may be determined by Western blotting, or preferably by FACS using antibody staining for cell surface expression. Particularly, the Treg may be a naïve Treg. “A naïve regulatory T cell, a naïve T regulatory cell, or a naïve Treg” as used interchangeably herein refers to a Treg cell which expresses CD45RA (particularly which expresses CD45RA on the cell surface). Naïve Tregs are thus described as CD45RA⁺. Naïve Tregs generally represent Tregs which have not been activated through their endogenous TCRs by peptide/MHC, whereas effector/memory Tregs relate to Tregs which have been activated by stimulation through their endogenous TCRs. Typically, a naïve Treg may express at least 10, 20, 30, 40, 50, 60, 70, 80 or 90% more CD45RA than a Treg cell which is not naïve (e.g. a memory Treg cell). Alternatively viewed, a naïve Treg cell may express at least 2, 3, 4, 5, 10, 50 or 100-fold the amount of CD45RA as compared to a non-naïve Treg cell (e.g. a memory Treg cell). The level of expression of CD45RA can be readily determined by methods of the art, e.g. by flow cytometry using commercially available antibodies. Typically, non-naïve Treg cells do not express CD45RA or low levels of CD45RA. Particularly, naïve Tregs may not express CD45RO, and may be considered to be CD45RO-. Thus, naïve Tregs may express at least 10, 20, 30, 40, 50, 60, 70, 80 or 90% less CD45RO as compared to a memory Treg, or alternatively viewed at least 2, 3, 4, 5, 10, 50 or 100 fold less CD45RO than a memory Treg cell. Although naïve Tregs express CD25 as discussed above, CD25 expression levels may be lower than expression levels in memory Tregs, depending on the origin of the naïve Tregs. For example, for naïve Tregs isolated from peripheral blood, expression levels of CD25 may be at least 10, 20, 30, 40, 50, 60, 70, 80 or 90% lower than memory Tregs. Such naïve Tregs may be considered to express intermediate to low levels of CD25. However, a skilled person will appreciate that naïve Tregs isolated from cord blood may not show this difference. Typically, a naïve Treg as defined herein may be CD4⁺, CD25⁺, FOXP3⁺, CD127^low, CD45RA⁺. Low expression of CD127 as used herein refers to a lower level of expression of CD127 as compared to a CD4⁺ non-regulatory or Tcon cell from the same subject or donor. Particularly, naïve Tregs may express less than 90, 80, 70, 60, 50, 40, 30, 20 or 10% CD127 as compared to a CD4⁺ non-regulatory or Tcon cell from the same subject or donor. Levels of CD127 can be assessed by methods standard in the art, including by flow cytometry of cells stained with an anti-CD127 antibody. Typically, naïve Tregs do not express, or express low levels of CCR4, HLA-DR, CXCR3 and/or CCR6. Particularly, naïve Tregs may express lower levels of CCR4, HLA- DR, CXCR3 and CCR6 than memory Tregs, e.g. at least 10, 20, 30, 40, 50, 60, 70, 80 or 90% lower level of expression. Naïve Tregs may further express additional markers, including CCR7⁺ and CD31⁺. Isolated naïve Tregs may be identified by methods known in the art, including by determining the presence or absence of a panel of any one or more of the markers discussed above, on the cell surface of the isolated cells. For example, CD45RA, CD4, CD25 and CD127 low can be used to determine whether a cell is a naïve Treg. Methods of determining whether isolated cells are naïve Tregs or have a desired phenotype can be carried out as discussed below in relation to additional steps which may be carried out as part of the invention, and methods for determining the presence and/or levels of expression of cell markers are well-known in the art and include, for example, flow cytometry, using commercially available antibodies. In some embodiments, the nucleic acid molecule encoding the multichain chimeric receptor or polypeptide described above is transferred to the cell e.g. the immune cell (e.g. Treg) using a viral vector, for example, a retroviral vector. In this way, a large number of antigen-specific cells (e.g. immune cells) can be generated for adoptive cell transfer. When the multichain chimeric receptor binds the target-antigen, this results in the transmission of an activating signal to the immune cell (e.g. Treg) it is expressed on. Thus, the multichain chimeric receptor directs the specificity of the cell (e.g. immune cell) (e.g. Treg) towards cells expressing the targeted antigen. Accordingly, the cell comprising the nucleic acid molecule of the invention may be viewed as an “engineered cell”. An “engineered cell” as used herein means a cell which has been modified to comprise or express a polynucleotide that is not naturally encoded by the cell. Methods for engineering cells are known in the art and include, but are not limited to, genetic modification of cells, e.g. by transduction such as retroviral or lentiviral transduction, transfection (such as transient transfection – DNA or RNA based) including lipofection, polyethylene glycol, calcium phosphate and electroporation. Any suitable method may be used to introduce a nucleic acid molecule into a cell. Non-viral technologies such as amphipathic cell penetrating peptides may be used to introduce a nucleic acid molecule in accordance with the present invention. Accordingly, the nucleic acid molecule of the invention is not naturally expressed by a corresponding, unmodified cell. Suitably, an engineered cell is a cell which has been modified e.g. by transduction or by transfection. Suitably, an engineered cell is a cell which has been modified or whose genome has been modified, e.g. by transduction or by transfection. Suitably, an engineered cell is a cell that has been modified or whose genome has been modified by retroviral transduction. Suitably, an engineered cell is a cell which has been modified or whose genome has been modified by lentiviral transduction. As used herein, the term “introduced” refers to methods for inserting foreign DNA or RNA into a cell. As used herein the term introduced includes both transduction and transfection methods. Transfection is the process of introducing nucleic acids into a cell by non-viral methods. Transduction is the process of introducing foreign DNA or RNA into a cell via a viral vector. Engineered cells according to the present invention may be generated by introducing DNA or RNA encoding a chimeric receptor as described herein by one of many means including transduction with a viral vector, or transfection with DNA or RNA. Cells may be activated and/or expanded prior to, or after, the introduction of a polynucleotide encoding the multichain chimeric receptor as described herein, for example by treatment with an anti-CD3 monoclonal antibody or both anti-CD3 and anti-CD28 monoclonal antibodies. Tregs may also be expanded in the presence of anti-CD3 and anti-CD28 monoclonal antibodies in combination with IL-2. Suitably, IL-2 may be substituted with IL-15. Other components which may be used in a Treg expansion protocol include, but are not limited to rapamycin, all-trans retinoic acid (ATRA) and TGFβ. As used herein “activated” means that a cell has been stimulated, causing the cell to proliferate. As used herein “expanded” means that a cell or population of cells has been induced to proliferate. The expansion of a population of cells may be measured for example by counting the number of cells present in a population. The phenotype of the cells may be determined by methods known in the art such as flow cytometry. The cell (e.g. Treg) in which the multichain chimeric receptor or a polypeptide as discussed above is to be expressed may be derived from a patient, that is from a subject to be treated. For example, the cell may have been removed from a subject and then transduced or transfected ex vivo with a vector according to the present invention to provide an engineered cell. Alternatively, the cell may be a donor cell, for transfer to a recipient subject, or from a cell line., e.g. an NK cell line. The cell may further be a pluripotent cell (e.g. an iPSC) which may be differentiated to a desired target cell type, e.g. to a T cell, particularly to a Treg. T cell populations which are suitable for ACT include: bulk peripheral blood mononuclear cells (PBMCs), CD8+ cells (for example, CD4-depleted PBMCs); PBMCs that are selectively depleted of T-regulatory cells (Tregs); isolated central memory (Tern) cells; EBV-specific CTLs; and tri-virus-specific CTLs and Treg cell preparations and populations as discussed above. The present invention also comprises a cell population comprising a cell according to the present invention (e.g. an engineered Treg cell). The cell population may have been transduced with a vector according to the present invention. A proportion of the cells of the cell population may express a multichain chimeric receptor or a polypeptide according to the invention at the cell surface. The cell population may be ex vivo patient-derived cell population. It will be appreciated that not all cells within a cell population may express the multichain chimeric receptor or polypeptide of the invention. However, in a particular embodiment, at least 50, 60, 70, 80, 90, 95 or 99% of cells express the multichain chimeric receptor or polypeptide of the invention. Adoptive transfer of genetically modified cells (e.g. immune cells) (i.e. engineered cells) such as T cells is an attractive approach for generating desirable immune responses, such as an anti-tumour immune response, or to suppress or prevent an unwanted immune response. Thus, in a further aspect the invention provides a pharmaceutical composition comprising a cell or cell population of the invention (i.e. an engineered cell such as an engineered Treg, expressing a multichain chimeric receptor or polypeptide of the invention, or a cell population comprising an engineered cell). A pharmaceutical composition is a composition that comprises or consists of a therapeutically effective amount of a pharmaceutically active agent, i.e. the cell or cell population of the invention. It preferably includes a pharmaceutically acceptable carrier, diluent or excipient (including combinations thereof). Acceptable carriers or diluents for therapeutic use are well-known in the pharmaceutical art, and are described, for example, in Remington's Pharmaceutical Sciences, Mack Publishing Co. (A. R. Gennaro edit.1985). The choice of pharmaceutical carrier, excipient or diluent can be selected with regard to the intended route of administration and standard pharmaceutical practice. The pharmaceutical compositions may comprise as - or in addition to - the carrier, excipient or diluent any suitable binder(s), lubricant(s), suspending agent(s), coating agent(s) or solubilising agent(s). By “pharmaceutically acceptable” is included that the formulation is sterile and pyrogen free. The carrier, diluent, and/or excipient must be “acceptable” in the sense of being compatible with the cell (e.g. Treg) and not deleterious to the recipients thereof. Typically, the carriers, diluents, and excipients will be saline or infusion media which will be sterile and pyrogen free, however, other acceptable carriers, diluents, and excipients may be used. Examples of pharmaceutically acceptable carriers include, for example, water, salt solutions, alcohol, silicone, waxes, petroleum jelly, vegetable oils, polyethylene glycols, propylene glycol, liposomes, sugars, gelatin, lactose, amylose, magnesium stearate, talc, surfactants, silicic acid, viscous paraffin, perfume oil, fatty acid monoglycerides and diglycerides, petroethral fatty acid esters, hydroxymethyl-cellulose, polyvinylpyrrolidone, and the like. The pharmaceutical composition according to the present invention may be administered in a manner appropriate for treating and/or preventing the disease described herein. The quantity and frequency of administration will be determined by such factors as the condition of the subject, and the type and severity of the subject's disease, although appropriate dosages may be determined by clinical trials. The pharmaceutical composition may be formulated accordingly. The pharmaceutical composition of the invention can be administered parenterally, for example, intravenously, or they may be administered by infusion techniques. The pharmaceutical composition may be administered in the form of a sterile aqueous solution which may contain other substances, for example, enough salts or glucose to make the solution isotonic with blood. The aqueous solution may be suitably buffered (preferably to a pH of from 3 to 9). The pharmaceutical composition may be formulated accordingly. The preparation of suitable parenteral formulations under sterile conditions is readily accomplished by standard pharmaceutical techniques well-known to those skilled in the art. The pharmaceutical composition may comprise cells of the invention in infusion media, for example sterile isotonic solution. The pharmaceutical composition may be enclosed in ampoules, disposable syringes or multiple dose vials made of glass or plastic. The pharmaceutical composition may be administered in a single or in multiple doses. Particularly, the pharmaceutical composition may be administered in a single, one off dose. The pharmaceutical composition may be formulated accordingly. The pharmaceutical composition may further comprise one or more active agents. The pharmaceutical composition may further comprise one or more other therapeutic agents, such as lympho-depletive agents (e.g. thymoglobulin, campath-1H, anti-CD2 antibodies, anti-CD3 antibodies, anti-CD20 antibodies, cyclophosphamide, fludarabine), inhibitors of mTOR (e.g. sirolimus, everolimus), drugs inhibiting costimulatory pathways (e.g. anti-CD40/CD40L, CTAL4Ig), and/or drugs inhibiting specific cytokines (IL-6, IL-17, TNFalpha, IL18). Depending upon the disease and subject to be treated, as well as the route of administration, the pharmaceutical composition may be administered at varying doses (e.g. measured in cells/kg or cells/subject). The physician in any event will determine the actual dosage which will be most suitable for any individual subject and it will vary with the age, weight and response of the particular subject. Typically, however, for cells (e.g. Tregs) of the invention, doses of 5x10⁷ to 3x10⁹ cells, or 10⁸ to 2x10⁹ cells per subject may be administered. The cells may be appropriately modified for use in a pharmaceutical composition. For example, cells (e.g. Tregs) may be cryopreserved and thawed at an appropriate time, before being infused into a subject. The invention further includes the use of kits comprising the nucleic acid, vector, cell and/or pharmaceutical composition of the present invention. Preferably said kits are for use in the methods and uses as described herein, e.g., the therapeutic methods as described herein. Preferably said kits comprise instructions for use of the kit components. The present invention further provides a method for treating and/or preventing a disease or condition in a subject, which comprises the step of administering a cell, cell population or pharmaceutical composition according to the invention to the subject. The method may comprise the step of administering a population of cells to a subject. The method may involve the following steps: (i) taking a sample of cells, such as a blood sample from a patient, (ii) extracting the immune cell, e.g. T-cells, (iii) introducing into the cells (e.g. transducing or transfecting the cells) a vector or a nucleic acid of the present invention encoding the chimeric receptor of the invention, (iv) expanding the cells comprising the nucleic acid or vector (i.e. the modified or engineered cells) ex-vivo, and (v) returning the cells to the subject. In some embodiments, steps (i) and (ii) may be viewed as providing a cell-containing sample (e.g. Treg sample), particularly obtained from a subject. The modified (i.e. engineered) cells may possess a desired therapeutic property such as immunosuppressive activity or specific targeting and killing of target cells. It will be appreciated by the skilled person that the cells may be allogeneic or autologous to the subject to be treated. Thus, in a further aspect, the invention provides a cell, cell population or pharmaceutical composition as defined herein for use in therapy. Where the cell or cell population comprises a Treg comprising a nucleic acid or vector of the invention and particularly where the antigen binding domain of the first polypeptide specifically binds to an antigen present or expressed at a site of inflammation, at a site of autoimmune disease, or by a transplanted organ, the cell, cell population and pharmaceutical composition of the invention may find particular utility in the treatment of inflammatory disorders (e.g. neurological disorders such as Alzheimer’s Disease and ALS) and/or autoimmune disorders (such as type I diabetes) or in the prevention of transplant rejection. In one embodiment, the present invention provides a method for inducing tolerance to a transplant; treating and/or preventing cellular and/or humoral transplant rejection; treating and/or preventing graft-versus-host disease (GvHD), an autoimmune or allergic disease; or to promote tissue repair and/or tissue regeneration; or to ameliorate chronic inflammation secondary to metabolic disorders which comprises the step of administering an engineered Treg or a pharmaceutical composition of the invention to a subject. As used herein, “inducing tolerance to a transplant” refers to inducing tolerance to a transplanted organ in a recipient. In other words, inducing tolerance to a transplant means to reduce the level of a recipient’s immune response to a donor transplant organ. Inducing tolerance to a transplanted organ may reduce the amount of immunosuppressive drugs that a transplant recipient requires, or may enable the discontinuation of immunosuppressive drugs. For example, the engineered Tregs may be administered to a subject with a disease in order to lessen, reduce, or improve at least one symptom of disease such as jaundice, dark urine, itching, abdominal swelling or tenderness, fatigue, nausea or vomiting, and/or loss of appetite. The at least one symptom may be lessened, reduced, or improved by at least 10%, at least 20%, at least 30%, at least 40%, or at least 50%, or the at least one symptom may be completely alleviated. The engineered Tregs may be administered to a subject with a disease in order to slow down, reduce, or block the progression of the disease. The progression of the disease may be slowed down, reduced, or blocked by at least 10%, at least 20%, at least 30%, at least 40%, or at least 50% compared to a subject in which the engineered Tregs are not administered, or progression of the disease may be completely stopped. In one embodiment, the subject is a transplant recipient undergoing immunosuppression therapy. Suitably, the subject is a mammal. Suitably, the subject is a human. The transplant may be selected from a liver, kidney, heart, lung, pancreas, intestine, stomach, bone marrow, vascularized composite tissue graft, and skin transplant. Suitably, the CAR may comprise an antigen binding domain which is capable of specifically binding to a HLA antigen that is present in the graft (transplant) donor but not in the graft (transplant) recipient. Suitably, the transplant is a liver transplant. In embodiments where the transplant is a liver transplant, the antigen may be a HLA antigen present in the transplanted liver but not in the patient, a liver-specific antigen such as NTCP, or an antigen whose expression is up- regulated during rejection such as CCL19, MMP9, SLC1A3, MMP7, HMMR, TOP2A, GPNMB, PLA2G7, CXCL9, FABP5, GBP2, CD74, CXCL10, UBD, CD27, CD48, CXCL11. Suitably, the antigen may be HLA-A2. The present invention further provides a method for treating and/or preventing graft- versus-host disease (GvHD), an autoimmune or allergic disease; or to promote tissue repair and/or tissue regeneration; or to ameliorate chronic inflammation secondary to metabolic disorders. A method for treating a disease relates to the therapeutic use of the cells of the present invention. In this respect, the cells may be administered to a subject having an existing disease or condition in order to lessen, reduce or improve at least one symptom associated with the disease and/or to slow down, reduce or block the progression of the disease. Suitably, treating and/or preventing cellular and/or humoral transplant rejection may refer to administering an effective amount of a Treg of the invention such that the amount of immunosuppressive drugs that a transplant recipient requires is reduced, or may enable the discontinuation of immunosuppressive drugs. Preventing a disease relates to the prophylactic use of the cells of the present invention. In this respect, the cells may be administered to a subject who has not yet contracted the disease and/or who is not showing any symptoms of the disease to prevent the disease or to reduce or prevent development of at least one symptom associated with the disease. The subject may have a predisposition for, or be thought to be at risk of developing, the disease. The autoimmune or allergic disease may be selected from inflammatory skin diseases including psoriasis and dermatitis (e.g. atopic dermatitis); responses associated with inflammatory bowel disease (such as Crohn's disease and ulcerative colitis); dermatitis; allergic conditions such as food allergy, eczema and asthma; rheumatoid arthritis; systemic lupus erythematosus (SLE) (including lupus nephritis, cutaneous lupus); diabetes mellitus (e.g. type 1 diabetes mellitus or insulin dependent diabetes mellitus); multiple sclerosis and juvenile onset diabetes. Suitably, the engineered Treg may be administered in combination with one or more other therapeutic agents, such as lympho-depletive agents (e.g. thymoglobulin, campath-1H, anti-CD2 antibodies, anti-CD3 antibodies, anti-CD20 antibodies, cyclophosphamide, fludarabine), inhibitors of mTOR (e.g. sirolimus, everolimus), drugs inhibiting costimulatory pathways (e.g. anti-CD40/CD40L, CTAL4Ig), and/or drugs inhibiting specific cytokines (IL-6, IL-17, TNFalpha, IL18). The engineered Treg may be administered simultaneously with or sequentially with (i.e. prior to or after) the one or more other therapeutic agents. Suitably the subject is a mammal. Suitably the subject is a human. Tregs may be activated and/or expanded prior to, or after, the introduction of a polynucleotide encoding the multichain chimeric receptor or polypeptide as described herein, for example by treatment with an anti-CD3 monoclonal antibody or both anti-CD3 and anti- CD28 monoclonal antibodies. The Tregs may also be expanded in the presence of anti-CD3 and anti-CD28 monoclonal antibodies in combination with IL-2. Suitably, IL-2 may be substituted with IL-15. Other components which may be used in a Treg expansion protocol include, but are not limited to rapamycin, all-trans retinoic acid (ATRA) and TGFβ. As used herein “activated” means that a Treg or population of Tregs has been stimulated, causing the Treg(s) to proliferate. As used herein “expanded” means that a Treg or population of Tregs has been induced to proliferate. The expansion of a population of Tregs may be measured for example by counting the number of Tregs present in a population. The phenotype of the Tregs may be determined by methods known in the art such as flow cytometry. The Tregs may be washed after each step of the method, in particular after expansion. The population of engineered Treg cells according to the present invention may be further enriched by any method known to those of skill in the art, for example by FACS or magnetic bead sorting. The steps of the method of production may be performed in a closed and sterile cell culture system. The invention will now be further described by way of Figures and Examples, which are meant to serve to assist one of ordinary skill in the art in carrying out the invention and are not intended in any way to limit the scope of the invention. Figures 5 to 9 show results of experiments performed with various constructs (SEQ ID NOs: 231-252) that are dual chain CARs comprising (a) a first polypeptide comprising an extracellular domain comprising an antigen binding domain based on a receptor protein, and a first transmembrane domain derived from a myeloid receptor protein (e.g., TREM2), and (b) a second polypeptide comprising a second transmembrane domain derived from DAP10 or DAP12 which is capable of associating with TREM2. Figure 1 shows schematics for different multichain chimeric receptors of the invention. The first polypeptides have an extracellular domain comprising an antigen binding domain based on an scFv, followed by a stalk or hinge derived from TREM2 or TREM1, and a TREM2 or a TREM1 transmembrane domain. In the first example, the first polypeptide comprises an endodomain comprising a costimulatory domain from CD28, and the second polypeptide is DAP12. In the second example, the first polypeptide comprises an endodomain comprising an intracellular signaling domain from CD3zeta and the second polypeptide comprises a truncated DAP12 molecule comprising the DAP12 transmembrane domain and a costimulatory domain from CD28. In the third example, the first polypeptide comprises an endodomain comprising a costimulatory domain from CD28, and the second polypeptide comprises a truncated DAP12 molecule comprising the DAP12 transmembrane domain and an intracellular signaling domain derived from CD3zeta. In the fourth example, the first polypeptide does not comprise an endodomain and the second polypeptide comprises a truncated DAP12 molecule comprising the DAP12 transmembrane domain, a costimulatory domain from CD28 and an intracellular signaling domain derived from CD3zeta. Figure 2 shows schematics for different multichain chimeric receptors of the invention. The first polypeptides have an extracellular domain comprising an antigen binding domain based on a receptor protein, followed by a stalk or hinge derived from TREM2 or TREM1, and a TREM2 or a TREM1 transmembrane domain. In the first example, the first polypeptide comprises an endodomain comprising a costimulatory domain from CD28, and the second polypeptide is DAP12. In the second example, the first polypeptide comprises an endodomain comprising an intracellular signaling domain from CD3zeta and the second polypeptide comprises a truncated DAP12 molecule comprising the DAP12 transmembrane domain and a costimulatory domain from CD28. In the third example, the first polypeptide comprises an endodomain comprising a costimulatory domain from CD28, and the second polypeptide comprises a truncated DAP12 molecule comprising the DAP12 transmembrane domain and an intracellular signaling domain derived from CD3zeta. In the fourth example, the first polypeptide does not comprise an endodomain and the second polypeptide comprises a truncated DAP12 molecule comprising the DAP12 transmembrane domain, a costimulatory domain from CD28 and an intracellular signaling domain derived from CD3zeta. In the fifth example, the first polypeptide does not comprise an endodomain and the second polypeptide comprises a truncated DAP12 molecule comprising the DAP12 transmembrane domain, a costimulatory domain from CD28 and an intracellular signaling domain derived from CD3zeta, wherein one ITAM sequence has been deleted. Figure 3 shows schematics for different multichain receptors used in the experiments shown in Figures 5 to 9. The first polypeptides have an extracellular domain comprising an antigen binding domain based on a receptor protein and a TREM2 transmembrane domain. The first example comprises a first polypeptide comprising a CD3zeta intracellular signalling domain and a second polypeptide comprising DAP10. The second example shows a first polypeptide comprising a CD3zeta intracellular signalling domain and a second polypeptide comprising DAP10 and a CD28 costimulatory domain. The third example shows a first polypeptide with no intracellular signalling sequence or costimulatory domains, and a second polypeptide comprising DAP10 and an intracellular signalling domain of CD3zeta. Figure 4 shows schematics for different multichain receptors used in the experiments shown in Figures 5 to 9. The first polypeptides have an extracellular domain comprising an antigen binding domain based on a receptor protein and a TREM2 transmembrane domain. The first example comprises a first polypeptide comprising a CD28 costimulatory domain and a second polypeptide comprising DAP12. The second example shows a first polypeptide comprising a CD28 costimulatory domain and a second polypeptide comprising DAP12 and a CD3zeta intracellular signalling domain. The third example shows a first polypeptide with no intracellular signalling sequence or costimulatory domains, and a second polypeptide comprising DAP12 and a CD28 costimulatory domain. Figure 5 shows the expression of various constructs (SEQ ID NOs: 235-247) that are dual chain CARs comprising an extracellular domain comprising an antigen binding domain based on a receptor protein and a TREM2 transmembrane domain. The constructs were expressed in Jurkat cells after transduction using two different concentrations of virus and expression was detected using an antibody to the receptor protein. Figure 6 shows the activation of Jurkat cells transduced with various chimeric constructs (SEQ ID NOs: 235-245) that are dual chain CARs comprising an extracellular domain comprising an antigen binding domain based on a receptor protein and a TREM2 transmembrane domain. The Jurkat cells were activated using an antibody to the receptor protein. Figure 7 shows the activation of Jurkat cells transduced with various chimeric constructs (SEQ ID NOs: 235-245) that are dual chain CARs comprising an extracellular domain comprising an antigen binding domain based on a receptor protein and a TREM2 transmembrane domain. The Jurkat cells were activated using necrotic K562 cells. Figure 8 shows the activation of Jurkat cells transduced with various chimeric constructs (SEQ ID NOs: 235-245) that are dual chain CARs comprising an extracellular domain comprising an antigen binding domain based on a receptor protein and a TREM2 transmembrane domain. The Jurkat cells were activated using HEK cell debris. Figure 9 shows the expression of various chimeric constructs (SEQ ID NOs: 248- 252), which are dual chain CARs comprising an extracellular domain comprising an antigen binding domain based on a receptor protein and a TREM2 transmembrane domain, in Treg cells after transduction. SEQ ID NOs: 248, 249, 250, 251 and 252 correspond to SEQ ID NOs: 235, 236, 237, 239 and 240, except that they comprise an additional 2A cleavage sequence and eGFP sequence. Example 1a: Screening of split CAR constructs Different constructs of the split CAR were cloned into a lentiviral backbone encoding a puromycin resistance gene. Here, anti-HLA-A*02 scFv or anti-CD19 scFv are used to confer specificity to the CAR construct. Viral vectors are produced and used for the transduction of the Jurkat T cell line. Two days after transduction, Jurkat cells are selected with 4 μg/ml puromycin for one week. Cells are counted and 0.5*10⁶ cells are stained with the HLA-A*02 dextramer to determine the level of CAR expression. Similarly, cells were stained with an CD19-Fc fusion protein, followed by staining with an anti-Fc conjugated antibody. CAR expression was assessed by flow cytometry. As above, constructs used in the experiments shown in Figures 5 to 9 (encoding SEQ ID NOs: 235-247) were cloned into a lentiviral backbone encoding a puromycin resistance gene, where the ligand binding domain of a receptor protein (WT or mutated) was used to confer specificity to the CAR construct. Viral vectors were produced and used for the transduction of the Jurkat T cell line. Two days after transduction, Jurkat cells were selected with 4 μg/ml puromycin for one week. Cells were counted and 0.5*106 cells were stained with an antibody to the receptor protein to determine the level of CAR expression. CAR expression was assessed by flow cytometry and expression of the constructs can be seen in Figure 5. Example 1b: Screening of constructs – activation with antibody Jurkat cells were transduced as described in Example 1a with constructs encoding SEQ ID NOs: 235 to 245, except that the lentiviral backbone did not include a puromycin resistance gene and Jurkat cells were not selected for using puromycin. Transduced cells were activated with an antibody against the receptor protein. CAR-dependent activation levels were assessed by flow cytometry using CD69 staining and can be seen in Figure 6. Example 1c: Screening of constructs – activation with dead cells or cell debris Jurkat cells were transduced as described in Example 1a with constructs encoding either SEQ ID NOs: 235-245 (Figure 7) or SEQ ID NOs: 235-247 (Figure 8), except that the lentiviral backbone did not include a puromycin resistance gene and Jurkat cells were not selected for using puromycin. Transduced cells were either co-cultured with RPMI as a control and with necrotic K562 cells to activate the cells (Figure 7) or co-cultured with RPMI as control and with HEK cell debris for 24 or 48 hours to activate the cells (Figure 8). CAR- dependent activation levels were assessed by flow cytometry using CD69 staining and can be seen in Figures 7 and 8, respectively. Example 2: NFAT/NfkB/STAT5 signaling of CAR constructs Different constructs of the split CAR were cloned into a lentiviral backbone encoding a puromycin resistance gene. Here, anti-HLA-A2 scFv or anti-CD19 scFv are used to confer specificity to the CAR construct. Viral vectors are produced and used for the transduction of a NFAT, NfkB and STAT5 Jurkat reporter cell line. Here, the NFAT, NfkB or STAT5 response element control the activity of a luc2 reporter gene. Two days after transduction, Jurkat cells are selected with 4 μg/ml puromycin for one week. Cells are then activated with K562 wild-type cells, as a negative control, or K562 cells expressing HLA-A*02 or CD19 protein on their cell surface. Eight hours after activation luciferase is assessed in the different reporter cell lines using ONE-Glo™ Luciferase Assay System (Promega). Fold induction of the reporter is calculated based on K562 wild-type control cells. Example 3a: Generation of regulatory T cells expressing the split CAR Regulatory T cells are purified and FACS sorted as CD4+ CD25+ CD127- cells from healthy donors. Cells are activated using Human T-Activator CD3/CD28 Dynabeads™ (ThermoFisher Scientific) in X-Vivo medium (Lonza) in the presence of Interleukin-2 (1000 IU/ml). After 48 hours of activation, cells are transduced with lentiviral particles, encoding anti-HLA-A*02 classical or split CAR constructs. Cells are further expanded, and expansion rate is compared between the different conditions. At day 14 cells are harvested and cryopreserved for further analysis. To assess CAR expression, cells are counted, and 0.5*106 cells are stained with the HLA-A*02 dextramer to determine the level of CAR expression. CAR expression was assessed by flow cytometry. The Treg phenotype is assessed by surface staining with anti-CD4, anti-CD25, anti-CD127, anti-CD8, anti-GITR, anti-CD39, anti-CD45RA, anti-CD45RO, anti-ICOS and intracellular staining with anti- FOXP3 and anti-HELIOS, following fixation and permeabilization (Transcription Factor Staining Buffer Set, ThermoFisher Scientific). Example 3b: Generation of regulatory T cells expressing multichain CAR constructs Regulatory T cells were purified and FACS sorted as CD4+ CD25+ CD127- cells from healthy donors. Cells were activated using Human T-Activator CD3/CD28 Dynabeads™ (ThermoFisher Scientific) in X-Vivo medium (Lonza) in the presence of Interleukin-2 (1000 IU/ml). After 48 hours of activation, cells were transduced with lentiviral particles, encoding the multichain CAR constructs, or encoding a control construct that comprises HLA-A2. All constructs also encoded eGFP. Cells were further expanded, and expansion rate was compared between the different conditions. At day 14 cells were harvested and cryopreserved for further analysis. To assess CAR expression, cells were counted, and 0.5*106 cells were stained with an antibody to the receptor protein to determine the level of CAR expression. The level of CAR expression and transduction efficiency was assessed by flow cytometry looking at the percentage of antibody to the receptor protein and percentage of GFP expression, respectively. The Treg phenotype was assessed by surface staining with anti-CD4, anti-CD25, anti-CD127, anti-CD8, anti-GITR, anti-CD39, anti-CD45RA, anti-CD45RO, anti-ICOS and intracellular staining with anti- FOXP3 and anti-HELIOS, following fixation and permeabilization (Transcription Factor Staining Buffer Set, ThermoFisher Scientific). Figure 9 shows the expression of various multichain CAR constructs in regulatory T cells. Regulatory T cells were transduced with a control construct comprising HLA-A2 or with constructs comprising SEQ ID NOs: 248, 249, 250, 251 or 252. Example 4: Treg suppressive activity For assessing the ability of Treg to suppress effector T cell activation, Teff cells are labeled with CFSE dye. Teff cells are co-cultured with different concentrations of Treg cells (ratios Treg:Teff of 1:1, 1:2, 1:4, 1:8, 1:16, 1:32, 1:64, 1:124) or no Treg cells. For activation, CD3/28 Beads (1:100) are added. For CAR-dependent activation, HLA-A*02 positive or negative irradiated B cells are added.72h after activation, cells are harvested and analyzed by flow cytometry. CFSE dilution is used as a surrogate marker for Teff cell proliferation. Example 5: Treg activation assay For analysis of CAR-dependent Treg activation, Treg are cultured in the presence of HLA-A*02 positive or negative K562 cells. Here, 0.1*10⁶ Treg are co-cultured with 0.1*10⁶ irradiated HLA-A*02 positive or negative K562 cells. As a negative control, Treg are cultured in the absence of K562 cells. As a positive control, Treg are cultured in the presence of CD3/CD28 activation beads. After 24h cells are harvested and stained with anti-CD4, anti- CD25, anti-CD69, anti-CD137 and anti-GARP antibodies. Cells are acquired on a flow cytometer and percentage of CD69, CD137 and GARP up-regulation after stimulation are calculated. Example 6: generation of effector CAR-T cells For the generation of Teff CAR-T cells, PBMCs were activated with anti-CD3 antibody (OKT3) for 48h. After activation, cells are washed and transduced with lentiviral vector encoding the different CAR and split-CAR constructs, with an anti-CD19 scFv.48h after transduction, cells are washed and seeded for expansion until day 10. At day 10 cells are harvested and cryopreserved for further analysis. To assess CAR expression, cells are counted, and 0.5*106 cells are stained with the CD19-Fc fusion protein, followed by staining with anti-Fc Alexa-647 conjugated antibody to determine the level of CAR expression. CAR expression was assessed by flow cytometry. Cell phenotype was assessed by flow cytometry staining with anti-CD4, anti-CD8, anti-CD45RA, anti-CD45RO, anti-CD62L, anti- CCR7, anti-CD25 and anti-CD69 antibodies. Example 7: cytotoxic potency of T effector CAR-T cells In order to assess cytotoxic activity of anti-CD19 CAR-T cells, cells are co-cultured with the CD19-positive RAJI and NALM6 cell lines.0.1*10⁶ CAR-T cells are co-cultured with 0.1*10⁶ in a 96 well plate. As a control, mock transduced T cells are used. After 24, 48 and 72 hours the number of RAJI and NALM6 cells is assessed by flow cytometry. Relative killing of RAJI and NALM6 cells is calculated over time for the different CAR constructs. Example 8: cytokine production of T effector CAR-T cells In order to assess cytokine production of anti-CD19 CAR-T cells after activation, cells are co-cultured with the CD19-positive RAJI and NALM6 cell lines.0.1*10⁶ CAR-T cells are co-cultured with 0.1*10⁶ in a 96 well plate. As a control, mock transduced T cells are used. After 24 hours the supernatant is harvested. ELISA for IFNg and IL2 in the supernatant are used to assess the activity of the different CAR constructs.

Claims

Claims 1. A multichain chimeric receptor comprising: (a) a first polypeptide comprising (i) an extracellular domain comprising an antigen binding domain, (ii) a first transmembrane domain derived from a myeloid receptor protein which is capable of associating with DAP10 or DAP12, wherein said antigen binding domain is heterologous to said first transmembrane domain and (iii) optionally an endodomain optionally comprising at least one co-stimulatory domain and/or at least one intracellular signalling domain; and (b) a second polypeptide comprising (i) a second transmembrane domain derived from DAP10 or DAP12 which is capable of associating with a TREM protein, and (ii) an endodomain comprising at least one co-stimulatory domain and/or at least one intracellular signalling domain, wherein said first polypeptide and/or said second polypeptide comprise at least one heterologous co-stimulatory domain and/or at least one heterologous intracellular signalling domain.

2. The multichain chimeric receptor of claim 1, wherein said myeloid receptor protein is an Immunoglobulin superfamily receptor.

3. The multichain chimeric receptor of claim 1 or 2, wherein said myeloid receptor protein is a TREM protein.

4. The multichain chimeric receptor of claim 3, wherein said TREM protein is TREM1 or TREM2.

5. The multichain chimeric receptor of claim 4, wherein the first transmembrane domain comprises a sequence as set forth in SEQ ID NO.16 or 26 or a sequence having at least 70% identity thereto.

6. The multichain chimeric receptor of claim 1, wherein said myeloid receptor protein is selected from anyone of CD300E, CD300B, Clec5A, Siglec14, Siglec15, Siglec16, SirpB1, or PiLRB.

7. The multichain chimeric receptor of claim 6, wherein the first transmembrane domain comprises a sequence as set forth in any one of SEQ ID Nos, 66, 68, 70, 72, 74, 76, 78 or 80 or a sequence having at least 70% identity thereto.

8. The multichain chimeric receptor of any one of claims 1 to 7, wherein said first polypeptide comprises an endodomain.

9. The multichain chimeric receptor of claim 8, wherein said endodomain comprises a co-stimulatory domain and/or at least one intracellular signalling domain.

10. The multichain chimeric receptor of claim 9, wherein said co-stimulatory domain is derived from CD28.

11. The multichain chimeric receptor of claim 9, wherein said intracellular signalling domain is derived from CD3zeta.

12. The multichain chimeric receptor of any one of claims 1 to 11, wherein said second transmembrane domain comprises an amino acid sequence as set out in SEQ ID Nos 30 or 35, or a sequence having at least 70% identity thereto.

13. The multichain chimeric receptor of any one of claims 1 to 12, wherein said endodomain of said second polypeptide comprises a co-stimulatory domain derived from CD28.

14. The multichain chimeric receptor of any one of claims 1 to 13, wherein said endodomain of said second polypeptide comprises an intracellular signalling domain derived from DAP10, DAP12 and/or CD3zeta.

15. The multichain chimeric receptor of any one of claims 1 to 14, wherein said first polypeptide comprises an endodomain comprising at least one co-stimulatory domain, optionally a CD28 costimulatory domain, and said second polypeptide comprises a sequence as set forth in SEQ ID NO.29 or 34, or a sequence having at least 70% identity thereto.

16. The multichain chimeric receptor of any one of claims 1 to 14, wherein said first polypeptide comprises an endodomain comprising at least one intracellular signalling domain (optionally an intracellular signalling domain from CD3zeta) and said second polypeptide comprises an endodomain comprising a costimulatory domain (optionally, a costimulatory domain from CD28).

17. The multichain chimeric receptor of any one of claims 1 to 14, wherein said first polypeptide comprises an endodomain comprising at least one costimulatory domain (optionally a costimulatory domain from CD28) and said second polypeptide comprises an endodomain comprising at least one intracellular signalling domain (optionally, an intracellular signalling domain from CD3zeta).

18. The multichain chimeric receptor of any one of claims 1 to 14, wherein said first polypeptide does not comprise an endodomain comprising at least one costimulatory domain and/or at least one intracellular signalling domain, and said second polypeptide comprises an endodomain comprising at least one costimulatory domain (optionally from CD28) and at least one intracellular signalling domain (optionally an intracellular signalling domain from CD3zeta).

19. The multichain chimeric receptor of any one of claims 1 to 18, wherein said first polypeptide comprises a hinge between said antigen binding domain and said first transmembrane domain.

20. The multichain receptor of any one of claims 1 to 19, wherein said first polypeptide or said second polypeptide comprises an endodomain comprising at least one STAT5 association motif and at least one JAK1 and/or JAK2 binding motif.

21. The multichain receptor of claim 20, wherein: (a) said first polypeptide comprises an endodomain comprising at least one STAT5 association motif and at least one JAK1 and/or JAK2 binding motif and said second polypeptide comprises an endodomain comprising at least one JAK3 binding motif; (b) said first polypeptide comprises an endodomain comprising at least one JAK3 binding motif and said second polypeptide comprises an endodomain comprising at least one STAT5 association motif and at least one JAK1 and/or JAK2 binding motif; or (c) said first polypeptide or said second polypeptide comprise an endodomain comprising at least one STAT5 association motif and at least one JAK1 and/or JAK2 binding motif and at least one JAK3 binding motif.

22. A polypeptide comprising (i) an extracellular domain comprising an antigen binding domain and (ii) a transmembrane domain derived from TREM2 which is capable of binding to DAP10 or DAP12 wherein said antigen binding domain is heterologous to the transmembrane domain.

23. A polypeptide comprising (i) an extracellular domain comprising an antigen binding domain, (ii) a transmembrane domain derived from a myeloid receptor protein which is capable of binding to DAP10 or DAP12 wherein said antigen binding domain is heterologous to the transmembrane domain and (iii) an endodomain comprising at least one co- stimulatory domain and/or at least one intracellular signalling domain.

24. A nucleic acid molecule comprising a polynucleotide sequence encoding the multichain chimeric receptor of any one of claims 1 to 21 or a polypeptide of claim 22 or 23.

25. A vector comprising the nucleic acid molecule of claim 24.

26. A cell which expresses the multichain chimeric receptor of any one of claims 1 to 21 or the polypeptide of claim 22 or 23; and/or which comprises a nucleic acid molecule of claim 24 or a vector of claim 25.

27. The cell of claim 26, wherein said cell is an immune cell.

28. The cell of claim 27, wherein said cell is a T cell, particularly a Treg.

29. A cell population comprising a cell of any one of claims 26 to 28.

30. A pharmaceutical composition comprising a cell of any one of claims 26 to 28 or a cell population of claim 29.

31. A method for producing a cell of any one of claims 26 to 28 comprising introducing a nucleic acid of claim 24 or a vector of claim 25 into a cell.

32. A cell of any one of claims 26 to 28, a cell population of claim 29, or a pharmaceutical composition of claim 30 for use in therapy.

33. A method for treating and/or preventing a disease or condition in a subject, which comprises the step of administering a cell of any one of claims 26 to 28, a cell population of claim 29 or pharmaceutical composition of claim 30 to the subject.