GB2606693A

GB2606693A - Fusion protein

Info

Publication number: GB2606693A
Application number: GB2105044.8A
Authority: GB
Inventors: Robert Edgar James; Trowsdale John; Young Lesley; Lo Matthew
Original assignee: Exosis Inc
Current assignee: Exosis Inc
Priority date: 2021-04-08
Filing date: 2021-04-08
Publication date: 2022-11-23
Also published as: GB202105044D0; WO2022216949A1

Abstract

The fusion protein comprises a tetraspanin exosomal protein and one or more immunogenic proteins. The tetraspanin may be CD63, CD9 or CD81, or a fragment or variant thereof. The protein may be capable of eliciting an immune response against a SARS-CoV-2 protein, such as the spike protein. Also claimed is an exosome or membrane preparation comprising the fusion protein, a vaccine composition comprising the exosome or membrane preparation, a nucleic acid molecule, an expression vector and a cell comprising the fusion protein. Also claimed is a method of preventing or ameliorating an infection comprising providing the subject with a therapeutically effective amount of the exosome, membrane preparation or vaccine composition. The exosome may comprise a DC receptor ligand and/or an immune enhancing moiety.

Description

FUSION PROTEIN

Field of the Invention

The present invention relates to a fusion protein comprising an exosomal protein and one or more immunogenic protein, wherein the exosomal protein is a tetraspanin protein. The present invention also relates to an exosome comprising said fusion protein. Further, the present invention relates to a vaccine composition comprising an exosome of the invention. The present invention also relates to a nucleic acid molecule encoding said fusion protein, and an expression vector comprising said nucleic acid molecule. The present invention further relates to a cell comprising said fusion protein, exosome, nucleic acid molecule, and/or expression vector. The invention also relates to the exosome and the vaccine composition for use as a medicament. The invention also relates to the exosome and and/or the vaccine composition for use in the prevention or amelioration of an infection in a subject. Furthermore, the invention relates to a method of preventing or ameliorating an infection in a subject, the method comprising providing the subject in need thereof with a therapeutically effective amount of an exosome and/or a vaccine composition of the invention.

Background

SARS-CoV-2 is a recently emerging coronavirus responsible for the Covid-19 epidemic. The virus causes significant pathology, in some cases death, in a fraction of patients, in particular those with associated comorbidities and has an unprecedented gradient of severity in relation to older age. Severity may extend from extremely mild (or even asymptomatic) to life-threatening.

The virus binds to the ACE2 receptor in cells of the airways, including pneumocytes and alveolar macrophages. It infects and destroys alveoli in the lungs. Mild cases may make neutralising antibodies that stop the virus early in its development in the individual. One way it becomes problematic is by interfering with the production of interferon. Disease may be due to the body's response to the pathogen, specifically over-reaction of immunity. If inflammation and tissue damage become too severe the infected person may die or end up with significant organ damage, not only to the lungs. Multiple organs may be affected by mechanisms such as excessive clotting.

The SARS-CoV-2 pandemic has resulted in a desperate need for a vaccine against the virus. However, it has also highlighted a desperate need for new vaccine approaches that may be useful in the context of other pathogens, not just SARS-CoV2. The present invention aims to address some of these problems.

Summary of Invention

In one aspect, provided herein is a fusion protein comprising: i) an exosomal protein, wherein the exosomal protein is a tetraspanin protein; and ii) one or more immunogenic protein.

In an embodiment, the tetraspanin is selected from the group consisting of CD63, CD9, and CD81 or a fragment, or variant thereof.

In an embodiment, the one or more immunogenic protein is capable of eliciting an immune response against a SARS-CoV-2 protein.

In an embodiment, the SARS-CoV-2 protein is selected from the group consisting of spike protein (S), nucleoprotein (N), membrane protein (M), envelope protein (E), Open reading frame (ORF) 3a protein, ORF 3b protein, ORF 6 protein, ORF 7a protein, ORF 7b protein, ORF 8 protein, ORF 9b protein, ORF 9c protein, and ORF 10 protein, optionally wherein when the SARS-CoV-2 protein is spike protein (S) it is the extracellular domain of spike protein (S).

In an embodiment, the one or more immunogenic protein is capable of eliciting a B-cell and a T-cell immune response.

In an embodiment, the one or more immunogenic protein is capable of eliciting a T-cell immune response.

In an embodiment, the protein comprises a first one or more immunogenic protein capable of eliciting a B-cell and a T-cell immune response and a second one or more immunogenic protein capable of eliciting a T-cell immune response.

In an embodiment, the first one or more immunogenic protein capable of eliciting a B-cell and T-cell immune response is incorporated into a luminal loop of the exosomal protein.

In an embodiment, the second one or more immunogenic protein capable of eliciting a T-cell immune response is incorporated near or at the N-terminus of the exosomal protein, and/or is incorporated into an intravesicular loop of the exosomal protein.

In an embodiment, the first one or more immunogenic protein is capable of eliciting a B-cell and T-cell immune response against the SARS-CoV-2 spike protein (S), optionally against the extracellular domain of spike protein (S).

In an embodiment, the second one or more immunogenic protein is capable of eliciting a T-cell immune response against the SARS-CoV-2 protein selected from the group consisting of nucleoprotein (N), membrane protein (M), envelope protein (E), ORF 3a protein, ORF 3b protein, ORF 6 protein, ORF 7a protein, ORF 7b protein, ORF 8 protein, ORF 9b protein, ORF 9c protein, and ORF 10 protein, optionally wherein when the SARS-CoV-2 protein is spike protein (S) it is the extracellular domain of spike protein (S).

In an embodiment, the first one or more immunogenic protein capable of eliciting a B-cell and a T-cell immune response is incorporated into the first and/or second luminal loop of the tetraspanin, optionally wherein the tetraspanin is CD63.

In an embodiment, the second one or more immunogenic protein capable of eliciting a T-cell immune response is incorporated near or at the N-terminus of the tetraspanin, optionally wherein the tetraspanin is CD63.

In an embodiment, the one or more immunogenic protein shares at least 75% identity with a SARS-CoV-2 protein or protein variant, or a fragment thereof. Optionally, when the SARS-CoV-2 protein is spike protein (S), the fragment is the receptor binding domain (RBD) (SEQ ID NO: 4). Optionally wherein the SARS-CoV-2 protein is membrane protein (M) the fragment is according to SEQ ID NO: 57 or 58. Optionally, wherein the SARS-CoV-2 protein is nucleoprotein (N) the fragment is according to SEQ ID NO: 56.

In an embodiment, the SARS-CoV-2 protein is selected from the group consisting of the extracellular domain of spike protein (S) (SEQ ID NO: 1), nucleoprotein (N) (SEQ ID NO: 2), membrane protein (M) (SEQ ID NO: 3), envelope protein (E) (SEQ ID NO: 46), ORF 3a protein (SEQ ID NO: 47), ORF 3b protein (SEQ ID NO: 48), ORF 6 protein (SEQ ID NO: 49), ORF 7a protein (SEQ ID NO: 50), ORF 7b protein (SEQ ID NO: 51), ORF 8 protein (SEQ ID NO: 52), ORF 9b protein (SEQ ID NO: 53), ORF 9c protein (SEQ ID NO: 54), and ORF 10 protein (SEQ ID NO: 55).

In an embodiment, the fusion protein shares at least 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identity with SEQ ID NO: 5, SEQ ID NO: 6, SEQ ID NO: 7, SEQ ID NO: 8, SEQ ID NO: 9, SEQ ID NO: 10, SEQ ID NO: 11, SEQ ID NO: 12, SEQ ID NO: 13, SEQ ID NO: 14, SEQ ID NO: 15, SEQ ID NO: 16, SEQ ID NO: 17, SEQ ID NO: 18, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, SEQ ID NO: 25, or SEQ ID NO: 26., In one embodiment, the fusion protein shares at least 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% with SEQ ID NO: 5 or SEQ ID NO: 6. Suitably, the fusion protein shares at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identity with SEQ ID NO: 5. Suitably, the fusion protein shares at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identity with SEQ ID NO: 6. More suitably, the fusion protein is according to SEQ ID NO: 5 or SEQ ID NO: 6.

In an embodiment, the exosomal protein and the one or more immunogenic protein is separated by a linker sequence.

In one aspect, provided herein is an exosome comprising the fusion protein of the invention or a membrane preparation comprising the fusion protein of the invention.

In an embodiment, the exosome or membrane preparation comprises a DC receptor ligand and/or an immune enhancing moiety, optionally wherein the immune enhancing moiety is selected from the group consisting of a molecule with a pathogen-associated molecular pattern (PAMP), DNA oligonucleotide containing an CpG motif, a STING agonist (such as cyclic GMP-AMP), and a TLR9 (Toll-like Receptor) agonist.

In one aspect, provided herein is a vaccine composition comprising an exosome or membrane preparation of the invention.

In one aspect, provided herein is nucleic acid molecule encoding a fusion protein of the invention.

In one aspect, provided herein is an expression vector comprising the nucleic acid molecule of the invention.

In an embodiment, the vector is a lentivirus expression vector.

In one aspect, provided herein is a cell comprising a fusion protein, an exosome, a membrane preparation, a nucleic acid, and/or an expression vector if the invention, optionally wherein the cell is an isolated cell.

In an embodiment, the transformed cell line is a HeLa cell or a LCL721 cell.

In an embodiment, the cell is modified to enhance the production of exosomes. In an embodiment, the cell has reduced expression of tetherin (Bst2).

In one aspect, provided herein is an exosome, a membrane preparation, or vaccine composition of the invention, for use as a medicament.

In one aspect, provided herein is an exosome, a membrane preparation, or a vaccine composition of the invention, for use in the prevention or amelioration of an infection.

In an embodiment, the infection is a viral, bacterial or fungal infection. Optionally, wherein the viral infection is a SARS-CoV-2 infection.

In one aspect, provided herein is a method of preventing or ameliorating an infection in a subject, the method comprising providing the subject in need thereof with a therapeutically effective amount of an exosome, a membrane preparation, or a vaccine composition of the invention. The infection may be a viral, bacterial or fungal infection. Optionally, the viral infection is a SARS-CoV-2 infection.

Except for where the context requires otherwise, the considerations set out in this disclosure should be considered to be applicable to all aspects of the invention. Merely by way of example, any consideration set out with reference to the fusion protein will be applicable to the exosome, nucleic acid molecule, expression vector, vaccine composition, cell, uses and treatment methods of the invention.

Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of them mean "including but not limited to", and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps.

Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise. Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.

Various aspects of the invention are described in further detail below. Brief Description of the Figures The invention is described in detail with reference to the following figures. Figure 1. A schematic representation of a SARS-CoV-2 virus particle Figure 2. A schematic representation of exemplary fusion polypeptides of the invention (A). Orientation of luminal and intravesicular loops for native CD63 protein and CD63 fusion protein (B). Schematic representation of CD63 fusion constructs (C).

Figure 3. A schematic representation of an exemplary expression vector of the invention.

Figure 4. Shows the results of a restriction digest. Minipreps 1+3 were both found to have the correct sized insert by test digest, and the CD63-FLAG-SpikeRBD was confirmed by sanger sequencing (SEQ ID NO: 19 to 22 -restriction sites highlighted in red. Start codon in bold and italics. CD63 sequence underlined. FLAG in bold text. Linkers are italics. SpikeRBD in underlined text.

Figure 5. A photo showing immunofluorescence assay results. To check the FLAGCD63Spike insert was not disrupting CD63 trafficking, pLVX-EF1alpha-CD63-FLAGSpikeRBD-IRES-Puro DNA was transiently transfected to HeLa cells and subject to immunofluorescence.

Figure 6. An image showing immunofluorescence results. FLAG signal was confirmed to be in CD63-positive compartments as shown by co-localisation of signal, and CD63 localisation remained in punctate organelles in transfected cells (as is also observed in non-transfected cells).

Figure 7. An image showing immunofluorescence assay results. An antibody against SpikeRBD showed similar pattern of staining, and colocalised with FLAG -confirming that Spike and FLAG are together localised in CD63-positive, late endosomal compartments. Together, these data indicate that Spike RBD and FLAG are localised to late endocytic compartments as expected.

Figure 8. An image showing Western Blot results. Whole cell lysates were collected from untransduced and transduced WT and Bst2K0 HeLa cells. Lysates were probed with antibodies against CD63, and both transduced cell lines displayed enhanced staining, and at a higher molecular weight -reflecting additional molecular mass given from the addition of FLAG-SpikeRBD (A). Antibodies against FLAG were similarly used to blot whole cell lysates, and a positive band was observed at the correct molecular weight in transduced stable cell lines, and not in untransduced controls. Exosome-enriched fractions were generated from cells and subject to Western blotting. Exosomes from tetherin KO HeLa cells + CD63-FLAG-SpikeRBD displayed a band at the correct molecular weight as expected (B).

Figure 9. Electron microscopy images confirming that exosomes from transduced cells contained FLAG-SpikeRBD. An antibody against FLAG displays labelling specifically to exosomes. Labelling was not present in untransduced cells.

Detailed Description of the Invention

The present invention is based on the inventors' development of fusion proteins that may be useful in the context of vaccines, in particular anti-SARS-CoV-2 vaccines. As shown in the examples section of the present description, the inventors have developed fusion proteins that may have the ability to strongly activate T-cells rendering the fusion proteins especially useful in the context of vaccines. The fusion proteins of the invention comprise an exosomal protein, which enables it to be localised on exosomes. Importantly, the inventors have shown that the fusion proteins of the invention do not prevent exosonnal biogenesis and/or processing, allowing for exosomes expressing the fusion proteins to be released by cells to which a vector encoding the fusion proteins has been provided.

Exosomes comprising the fusion proteins of the invention may be provided to a subject and elicit an immune response that may prevent or ameliorate the symptoms and disease associated with a pathogen infection, such as for example SARS-CoV-2. Without wishing to be bound by this hypothesis, the inventors believe that providing a subject with exosomes comprising the fusion proteins of the invention may be associated with a number of advantages compared to other vaccination approaches currently investigated. For example, exosomes have the ability to taken up by antigen presenting cells or directly fuse to the plasma membrane of antigen presenting cells. This may be beneficial because it may enable efficient uptake of antigens to cells key to immune stimulation (such as dendritic cells). Exosomes may be packed with a payload of multiple viral antigens allowing the stimulation of B-cell immune and/or 1-cell immune responses. Indeed, as explained in more detail hereinbelow, some of the fusion proteins of the invention comprise immunogenic proteins capable of eliciting B-cell immune and/or T-cell immune responses.

Fusion protein The terms "fusion protein" and "fusion polypeptide" are used herein interchangeably, and refer to an artificial protein comprising amino acid sequences of at least two different proteins or protein variants, or fragments thereof. The fusion protein of the invention comprises an exosomal protein and one or more immunogenic protein.

The term "exosomal protein" as used herein refers to any polypeptide that is enriched in a vesicular structure. The exosomal protein may therefore be utilised to transport the fusion protein of the invention to the vesicular structure. Suitably, the vesicular structure is an exosome, suitably a human exosome. Accordingly, the exosomal protein may be a human exosomal protein.

Suitably, the exosomal protein is a tetraspanin. Suitably, the tetraspanin is selected from the group consisting of CD63 (SEQ ID NO: 43), CD9 (SEQ ID NO: 44) and CD81 (SEQ ID NO: 45) or a fragment, or variant thereof.

Suitably the tetraspanin variant may share at least 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, identity with SEQ ID NO: 43, SEQ ID NO: 44 or SEQ ID NO: 45. Suitably the tetraspanin variant may share at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, identity with SEQ ID NO: 43, SEQ ID NO: 44 or SEQ ID NO: 45. More suitably the tetraspanin variant may share at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, identity with SEQ ID NO: 43.

Suitably the tetraspanin fragment may comprise or consist of at least 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% contiguous amino acids of SEQ ID NO: 43, SEQ ID NO: 44 or SEQ ID NO: 45. More suitably, the fragment may comprise or consist of at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% contiguous amino adds of SEQ ID NO: 43, SEQ ID NO: 44 or SEQ ID NO: 45. More suitably, the fragment may comprise or consist of at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% contiguous amino adds of SEQ ID NO: 43. Most suitably, the tetraspanin protein is CD63 (SEQ ID NO: 43).

Similarly to other tetraspanins, CD63 protein has four transmennbrane domains, and three loops. Two of the loops are luminal loops, meaning that they extend outward from the vesicular structure (such as exosonne). One of the loops is intravesicular, meaning that it extends into the vesicular structure (such as exosome). In the present specification, in the context of tetraspanins, (for example CD63), the luminal loop that is closer to the N-terminal of the protein is referred to as the first (I) luminal loop, and the luminal loop that is closer to the C-terminal of the protein is referred to as the second (II) lumina! loop. Suitably, amino acids 33 to 51 of the human CD63 protein (SEQ ID NO: 43) define the I lumina! loop. Suitably, amino acids 103 to 203 of the human CD63 protein (SEQ ID NO: 43) define the II lumina! loop.

The ten-n "immunogenic protein" as used herein refers to a polypeptide that is capable of eliciting an immune response. Suitably, the immunogenic protein may be capable of eliciting a protective immune response in a host. Such a protective immune response may establish or improve the host's immunity to a pathogen. Suitably, the pathogen may be selected from the group consisting of a virus, a bacterium, and a fungus. More suitably the virus may be SARS-CoV-2. Suitably, the host may be a mammal, preferably human.

The immunogenic protein may elicit a B-cell and/or T-cell immune response.

The phrase "elicit a B-cell immune response" as used herein refers to the immunogenic protein's ability to trigger a humoral immune response, meaning that the immunogenic protein may cause cells of the subject's immune system to produce antibodies that bind specific protein targets. Suitably, the protein targets may correspond to the immunogenic protein. For example, if the protein target to which the antibodies are produced is SARS-CoV-2 spike protein (S), variant, or fragment thereof, the immunogenic protein may have a sequence corresponding to that SARS-CoV-2 spike protein (5) or variant, or fragment thereof.

The phrase "elicit a B-cell immune response" as used herein refers to the immunogenic protein's ability to trigger a cellular immune response, meaning that the immunogenic protein may trigger the selection, expansion and maturation of B-cells producing antibodies capable of binding the antigen. Some of these antibodies are neutralizing antibodies that are capable of blocking the infection of host cells by the SARS-CoV-2 virus.

The phrase "elicit a T-cell immune response" as used herein refers to the immunogenic protein's ability to trigger a cellular immune response, meaning that the immunogenic protein may trigger the selection and expansion of specific helper and/or cytotoxic T-lymphocytes capable of directly eliminating the cells that contain the antigen. A T-cell immune response may be initiated when the immunogenic protein is presented as an antigen on the surface of the exosome.

It will be appreciated that whether the immunogenic protein elicits a B-cell and/or 1-cell immune response may depend upon the immunogenic protein's location with respect to the exosomal protein. As explained in more detail elsewhere in the present specification, by way of example, immunogenic proteins incorporated into a luminal loop of an exosomal protein, may elicit a B-cell and 1-cell immune response. Notably, antigens designed to elicit a B-cell response are constructed in the luminal loop of the fusion protein in order to orient the antigen epitope on the outside (lumina!) of the exosome. Immunogenic proteins incorporated into intravesicular loops, or at or near the N-terminal of an immunogenic protein may elicit a 1-cell immune response. "At the N-terminal" as used herein means attached to the first amino acid of a sequence encoding a protein that would normally have a free amine group. "Near the N-terminal" as used herein means attached to an amino acid that is several amino acids away from the first amino acid of a sequence encoding a protein. For example, the immunogenic protein may be referred to as being near the N-terminal if it is attached to an amino acid located 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or more amino acids away from the first amino acid of a sequence encoding a protein.

Suitably, the immunogenic protein may be capable of eliciting a B-cell and/or T-cell immune response against a SARS-CoV-2 protein, variant, or fragment thereof. Suitably, the SARS-CoV-2 protein against which the immunogenic protein elicits an immune response may be selected from the group consisting of spike protein (S), nucleoprotein (N), membrane protein (M), envelope protein (E), ORF 3a, ORF 3b protein, ORF 6 protein, ORF 7a protein, ORF 7b protein, ORF 8 protein, ORF 9b protein, ORF 9c protein and ORF 10 protein.

The spike protein (S) plays a key role in the receptor recognition and cell membrane fusion process, and is composed of two subunits, Si and S2. The Si subunit contains a receptor-binding domain (RBD) that recognises and binds to the host receptor angiotensin-converting enzyme 2 (ACE2), while the S2 subunit mediates viral cell membrane fusion by forming a six-helical bundle via the two-heptad repeat domain.

The nucleoprotein (N) (also known as the nucleocapsid protein) packages the positive strand viral genome RNA into a helical ribonucleocapsid (RNP) and plays a fundamental role during virion assembly through its interactions with the viral genome and membrane protein (M).

The membrane protein (M) is a component of the viral envelope that plays a central role in virus morphogenesis and assembly via its interactions with other viral proteins.

The envelope protein (E) plays a central role in virus morphogenesis and assembly. The protein acts as a viroporin and self-assembles in host membranes forming pentameric protein-lipid pores that allow ion transport. It also plays a role in the induction of apoptosis.

The ORF 3a protein Forms homotetrarneric potassium sensitive ion channels (viroporin) and may modulate virus release.

The ORF 3b protein is potent interferon antagonist, suppressing the induction of type I interferon.

The ORF6 protein disrupts cell nuclear import complex formation by tethering karyopherin alpha 2 and karyopherin beta I to the membrane, The ORF 7a protein plays a role as antagonist of host tetherin (BST2), disrupting its antiviral effect, It acts by binding to BST2 thereby interfering with its glycosylation. The ORF 7a protein may also facilitate the disassembly of the Golgi apparatus, The ORF 7b protein is transmembrane protein postulated to have the potential to interfere with important cellular processes that involve leucine-zipper formation by rnultimerizing with phosphoiarnban and with E-cadherins.

The ORF 8 protein is believed to play a role in modulating host immune response and may play a role in blocking host 11_17 cytokine by its interaction with host 11_17RA.

The ORF 9b protein plays a role in the inhibition of host innate immune response by targeting the mitochondrial-associated adapter MAVS.

The ORF 9c protein is postulated to enhance the host proteasome activity thereby affect immune evasion, virulence and pathogenesis of the SARS-CoV2 virus.

The ORF 10 protein is postulated to bind Coffin ubiquitin ligase complex and hijack it for ubiquitination and degradation of restriction factors.

Suitably, the immunogenic protein capable of eliciting an immune response against a SARS-CoV-2 protein may have an amino acid sequence that shares at least 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% sequence identity with a SARS-CoV-2 protein, variant, or a fragment thereof.

Thus, suitably, the immunogenic protein capable of eliciting an immune response against a SARS-CoV-2 spike protein (S) may have an amino acid sequence that shares at least 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% sequence identity with a SARS-CoV-2 spike protein (S), variant, or a fragment thereof.

Suitably, in the context of the spike protein (S), the fragment may comprise or consist of the extracellular domain of the spike protein (S). Accordingly, the immunogenic protein may have an amino acid sequence that shares at least a 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% sequence identity with the extracellular domain of the spike protein (S) or variant, or fragment thereof.

Suitably, in the context of spike protein (S), the fragment may comprise or consist of the receptor binding domain (RBD). Accordingly, the immunogenic protein may have an amino acid sequence that shares at least a 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% sequence identity with the receptor binding domain (RBD) (SEQ ID NO: 4), or variant, or fragment thereof. More suitably, the fragment is according to SEQ ID NO: 4.

Suitably, the immunogenic protein capable of eliciting an immune response against a SARS-CoV-2 nucleoprotein (N) may have an amino acid sequence that shares at least 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% sequence identity with a SARS-CoV-2 nucleoprotein (N) (SEQ ID NO: 2), variant, or a fragment thereof. Suitably, the fragment may share at least 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% sequence identity with SEQ ID NO: 56. More suitably, the fragment is according to SEQ ID NO: 56.

Suitably, the immunogenic protein capable of eliciting an immune response against a SARS-CoV-2 membrane protein (M) may have an amino acid sequence that shares at least 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% sequence identity with a SARS-CoV-2 membrane protein (M) (SEQ ID NO: 3), variant, or a fragment thereof. Suitably, the fragment may share at least 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% sequence identity with SEQ ID NO:57 or SEQ ID NO: 58. More suitably, the fragment is according to SEQ ID NO:57 or SEQ ID NO: 58.

Suitably, the immunogenic protein capable of eliciting an immune response against a SARS-CoV-2 envelope protein (E) may have an amino acid sequence that shares at least 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% sequence identity with a SARS-CoV-2 envelope protein (E), variant, or a fragment thereof.

Suitably, the immunogenic protein capable of eliciting an immune response against a SARS-CoV-2 ORF3a may have an amino acid sequence that shares at least 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% sequence identity with a SARS-CoV-2 ORF3a, variant, or a fragment thereof.

Suitably, the immunogenic protein capable of eliciting an immune response against a SARS-CoV-2 ORF3b may have an amino acid sequence that shares at least 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% sequence identity with a SARS-CoV-2 ORF3b, variant, or a fragment thereof.

Suitably, the immunogenic protein capable of eliciting an immune response against a SARS-CoV-2 ORF6 may have an amino acid sequence that shares at least 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% sequence identity with a SARS-CoV-2 ORF6, variant, or a fragment thereof.

Suitably, the immunogenic protein capable of eliciting an immune response against a SARS-CoV-2 ORF7a may have an amino acid sequence that shares at least 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% sequence identity with a SARS-CoV-2 ORF7a, variant, or a fragment thereof.

Suitably, the immunogenic protein capable of eliciting an immune response against a SARS-CoV-2 ORF7b may have an amino acid sequence that shares at least 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% sequence identity with a SARS-CoV-2 ORF7b, variant, or a fragment thereof.

Suitably, the immunogenic protein capable of eliciting an immune response against a SARS-CoV-2 ORF8 may have an amino acid sequence that shares at least 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% sequence identity with a SARS-CoV-2 ORF8, variant, or a fragment thereof.

Suitably, the immunogenic protein capable of eliciting an immune response against a SARS-CoV-2 ORF9b may have an amino acid sequence that shares at least 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% sequence identity with a SARS-CoV-2 ORF9b, variant, or a fragment thereof.

Suitably, the immunogenic protein capable of eliciting an immune response against a SARS-CoV-2 ORF9c may have an amino acid sequence that shares at least 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% sequence identity with a SARS-CoV-2 ORF9c, variant, or a fragment thereof.

Suitably, the immunogenic protein capable of eliciting an immune response against a SARS-CoV-2 ORF10 may have an amino acid sequence that shares at least 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% sequence identity with a SARS-CoV-2 ORF10, variant, or a fragment thereof.

Suitably, the fusion protein may comprise one, two, three, or more immunogenic proteins. Suitably, the fusion protein may comprise one immunogenic protein. Suitably, the fusion protein may comprise two immunogenic proteins. Suitably, the fusion protein may comprise three immunogenic proteins.

In an embodiment where the fusion protein comprises one immunogenic protein, the immunogenic protein may elicit a B-cell and a T-cell immune response, or a 1-cell immune response. As mentioned elsewhere in the present specification, the type of immune response elicited may depend on the localisation of the immunogenic protein in the exosome. Suitably, the immunogenic protein that elicits a B-cell and a T-cell immune response, elicits a response against the SARS-CoV-2 spike protein (S). Suitably, the immunogenic protein that elicits a T-cell response, elicits a response against the nucleoprotein (N) or membrane protein (M).

In an embodiment where the fusion protein comprises two or more immunogenic proteins, it will be appreciated that some or all of the immunogenic proteins may be the same or different. By different it is meant that the immunogenic proteins may have a sequence corresponding to different proteins, or a sequence that corresponds to different parts of the same protein (the different parts may be overlapping or non-overlapping).

Merely by way of example, in an embodiment where the fusion protein comprises two different immunogenic proteins, the first immunogenic protein may elicit a B-cell and a T-cell immune response, and the second immunogenic protein may elicit a T-cell immune response. In such an example, the immunogenic protein that elicits a B-cell and a 1-cell immune response, may elicit a response against the SARS-CoV-2 spike protein (S). The immunogenic protein that elicits a T-cell response, may elicit a response against the nucleoprotein (N) or membrane protein (M).

Merely by way of another example, in an embodiment where the fusion protein comprises two different immunogenic proteins, each one of the immunogenic proteins may elicit a T-cell response. In such an example, the first immunogenic protein may elicit a response against the SARS-CoV-2 nucleoprotein (N), whereas the second immunogenic protein elicits a response against membrane protein (M).

Merely by way of another example, in an embodiment where fusion protein comprises three different immunogenic proteins, it may comprise one or two immunogenic proteins that elicit a T-cell immune response, and one or two immunogenic proteins that elicit a B-cell and 1-cell immune response. For example, the fusion protein may comprise two immunogenic proteins that elicit a T-cell immune response against the nucleoprotein (N) or membrane protein (M), and an immunogenic protein that elicits a B-cell and T-cell immune response against SARS-CoV-2 spike protein (S).

As mentioned elsewhere in the present specification, the type of immune response elicited by the immunogenic protein may be dictated by the immunogenic protein's location with respect to the exosomal protein.

Immunogenic proteins incorporated into a luminal loop of an exosomal protein (for example a tetraspanin, such as CD63), may elicit a B-cell and a 1-cell immune response. Suitably, the immunogenic protein that is incorporated into the luminal loop may be one that elicits a response against SARS-CoV-2 spike protein (S). Such an immunogenic protein may be incorporated into the first and/or second lumina! loop. Suitably, in the context of CD63, the immunogenic protein may be incorporated between amino acids Q36 and L37 (thereby incorporated into loop I) and/or between amino acids R108-D109 (thereby incorporated into loop II).

Immunogenic proteins incorporated into intravesicular loops, or at or near the N-terminal of an exosomal protein (for example a tetraspanin, such as CD63), may elicit a T-cell immune response. Suitably, an immunogenic protein that is incorporated into the intravesicular loop and/or at or near the N-terminal of an exosomal protein may be one that elicits a response against SARS-CoV-2 nucleoprotein (N) or membrane protein (M).

The fusion protein of the invention may comprise a linker. The linker may be between the immunogenic protein and exosomal protein sequence. Suitably, the linker may be on one or both side of the immunogenic protein. When the fusion protein comprises more than one immunogenic protein, a linker may be present between some, or all, of the immunogenic proteins and exosomal protein sequence. Suitably, when the fusion protein comprises two or more immunogenic proteins adjacent to one another, there may be a linker between some, or all, of the immunogenic proteins.

Suitably the linker may be 20 or fewer amino acids in length. Suitably, the linker may be about 18, about 16, about 14, about 12 or about 10 amino acids in length. Suitably the linker may be about 9, about 8, about 7, about 6, about 5, about 4, about 3, about 2 or 1 amino acid in length. More suitably the linker may be from 6 to 2 amino acids long.

Suitably the linker may be a flexible or a rigid linker. More suitably the liker is flexible. Merely by way of example a flexible linker may have the sequence GGSG, GGGSG, GGGGS, GGG, or CC. Other suitable linkers will be known to those skilled in the art. It will be appreciated that the linker may be used to enable or enhance correct immunogenic protein folding and/or stability.

Table 1 Exemplary fusion polypeptides of the invention Fusion protein Fusion protein arrangement * SEQ ID NO: name V1 CD63-FLAG-SpikeRBD 5 V2 CD63-FLAG-Spike (full in loop 1) 7 V3 FLAG-N-CD63 9 V4 FLAG-M-CD63 11 V5 FLAG-N-M-CD63 13 V6 CD63-FLAG-Spike (full in loop 2) 15 V7 N-M-CD63-FLAG-SpikeRBD 17 V12 CD63-M17-FLAG-SpikeRBD 19 V13 FLAG-Nfrags-CD63 21 V14 CD9-FLAG-SpikeRBD 23 V15 CD81-FLAG-SpikeRBD 25 it will be appreciated that the presence of FLAG is optional in each of these exemplary fusion protein arrangements In a suitable embodiment, the fusion protein comprises CD63 and the extracellular domain of the SARS-CoV-2 spike protein (S), variant, or a fragment thereof. Suitably, the extracellular domain of the SARS-CoV-2 spike protein (S), variant, or a fragment thereof is incorporated into the first lumina! of CD63. Suitably, the extracellular domain of the spike protein (S), variant, or fragment thereof may be incorporated between amino acids 036 and L37 of C063. Suitably the extracellular domain of the SARSCoV-2 spike protein (S) may have a sequence sharing at least 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identity with SEQ ID NO: 1. Suitably the fragment may have a sequence sharing at least 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identity with SEQ ID NO: 4. Suitably, a linker may be incorporated between both sides of the immunogenic protein and exosomal protein. In a suitable embodiment, the fusion protein comprises or consists of a sequence sharing at least 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identity with SEQ ID NO:5, SEQ ID NO:6, SEQ ID NO:7 or SEQ ID NO:8. More suitably, the fusion protein comprises or consists of SEQ ID NO:5, SEQ ID NO:6, SEQ ID NO:7 or SEQ ID NO:8.

In a suitable embodiment, the fusion protein comprises CD63 and the extracellular domain of the SARS-CoV-2 spike (S) protein or a fragment thereof. Suitably, the extracellular domain of the SARS-CoV-2 spike (S) protein or a fragment thereof is incorporated into the second lumina! of CD63. Suitably, the extracellular domain of the spike protein (S), variant, or fragment thereof may be incorporated between amino acids R108 and D109 of CD63. Suitably the extracellular domain of the SARS-CoV-2 spike (S) protein have a sequence sharing at least a 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identity with SEQ ID NO: 1. Suitably the fragment may have a sequence sharing at least a 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identity with SEQ ID NO: 4. Suitably, a linker may be incorporated between both sides of the immunogenic protein and exosomal protein. In a suitable embodiment, the fusion protein comprises or consists of a sequence sharing at least 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identity with SEQ ID NO:15 or SEQ ID NO:16. More suitably, the fusion protein comprises or consists of SEQ ID NO:15 or SEQ ID NO:16.

In a suitable embodiment, the fusion protein comprises CD9 and the extracellular domain of the SARS-CoV-2 spike protein (S), variant, or a fragment thereof. Suitably, the extracellular domain of the SARS-CoV-2 spike protein (S), variant, or a fragment thereof is incorporated into the first lumina! of 0D9. Suitably, the extracellular domain of the spike protein (S), variant, or fragment thereof may be incorporated between amino acids N50 and N51 of CD9. Suitably the extracellular domain of the SARS-CoV2 spike protein (S) may have a sequence sharing at least 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identity with SEQ ID NO: 1. Suitably the fragment may have a sequence sharing at least 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identity with SEQ ID NO: 4. Suitably, a linker may be incorporated between both sides of the immunogenic protein and exosomal protein. In a suitable embodiment, the fusion protein comprises or consists of a sequence sharing at least 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identity with SEQ ID NO:23 or SEQ ID NO:24. More suitably, the fusion protein comprises or consists of SEQ ID NO:23 or SEQ ID NO:24.

In a suitable embodiment, the fusion protein comprises CD81 and the extracellular domain of the SARS-CoV-2 spike protein (S), variant, or a fragment thereof Suitably, the extracellular domain of the SARS-CoV-2 spike protein (S), variant, or a fragment thereof is incorporated into the first lumina! of CD81. Suitably, the extracellular domain of the spike protein (S), variant, or fragment thereof may be incorporated between amino acids L49 and G50 of CD81. Suitably the extracellular domain of the SARSCoV-2 spike protein (S) may have a sequence sharing at least 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identity with SEQ ID NO: 1. Suitably the fragment may have a sequence sharing at least 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identity with SEQ ID NO: 4. Suitably, a linker may be incorporated between both sides of the immunogenic protein and exosomal protein. In a suitable embodiment, the fusion protein comprises or consists of a sequence sharing at least 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identity with SEQ ID NO:25 or SEQ ID NO:26. More suitably, the fusion protein comprises or consists of SEQ ID NO:25 or SEQ ID NO:26.

In a suitable embodiment, the fusion protein comprises CD63 and SARS-CoV-2 nucleoprotein (N) and/or membrane protein (M), or fragment thereof. Suitably, the SARS-CoV-2 nucleoprotein (N) and/or membrane protein (M), or fragment thereof is incorporated near or at the N-terminal of CD63. Suitably the SARS-CoV-2 nucleoprotein (N) protein has a sequence sharing at least a 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identity with SEQ ID NO: 2. Suitably the SARS-CoV-2 membrane protein (M) protein has a sequence sharing at least a 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identity with SEQ ID NO: 3. Suitably, the fragment of nucleoprotein (N) and has a sequence that is sharing at least a 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identity with SEQ ID NO: 56. Suitably, the fragment of membrane protein (M) has a sequence that is sharing at least a 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identity with SEQ ID NO: 57 or 58, more suitably SEQ ID NO: 58. Suitably, a linker may be incorporated between the immunogenic protein and the exosomal protein. Suitably, when both the nucleoprotein (N) and membrane protein (M) are incorporated into the fusion protein the membrane protein (M) may be incorporated at the N-terminal of the exosomal protein, followed by the nucleoprotein (N). In such an embodiment, the nucleoprotein (N) and membrane protein (M) may or may not be separated by a linker. In a suitable embodiment, the fusion protein comprises or consists of a sequence sharing at least 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identity with SEQ ID NO:9, SEQ ID NO:10, SEQ ID NO:11, SEQ ID NO:12, SEQ ID NO:13, or SEQ ID NO:14. More suitably, the fusion protein comprises or consists of SEQ ID NO:9, SEQ ID NO:10, SEQ ID NO:11, SEQ ID NO:12, SEQ ID NO:13, or SEQ ID NO:14.

In a suitable embodiment, the fusion protein comprises CD63 and SARS-CoV-2 nucleoprotein (N) or membrane protein (M), or fragment thereof. Suitably, the SARSCoV-2 nucleoprotein (N) or membrane protein (M), or fragment thereof is incorporated near or at the N-terminal of CD63. Suitably the SARS-CoV-2 nucleoprotein (N) protein has a sequence sharing at least a 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identity with SEQ ID NO: 2. Suitably, the fragment of nucleoprotein (N) and has a sequence that is sharing at least a 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identity with SEQ ID NO: 56. Suitably the SARS-CoV-2 membrane protein (M) protein has a sequence sharing at least a 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identity with SEQ ID NO: 3. Suitably, the fragment of membrane protein (M) has a sequence that is sharing at least a 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identity with SEQ ID NO: 57 or 58, more suitably SEQ ID NO: 58. Suitably, a linker may be incorporated between the immunogenic protein and the exosomal protein. In a suitable embodiment, the fusion protein comprises or consists of a sequence sharing at least 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identity with SEQ ID NO:9, SEQ ID NO:10, SEQ ID NO:11 or SEQ ID NO:12. More suitably, the fusion protein comprises or consists of SEQ ID NO:9, SEQ ID NO:10, SEQ ID NO:11 or SEQ ID NO:12.

In a suitable embodiment, the fusion protein comprises CD63 and the extracellular domain of the SARS-CoV-2 spike (S) protein or a fragment thereof, and nucleoprotein (N) and/or membrane protein (M) or fragment thereof. Suitably, the extracellular domain of the SARS-CoV-2 spike (S) protein or a fragment thereof is incorporated into the first or second lumina! of CD63. Suitably, the extracellular domain of the SARSCoV-2 nucleoprotein (N) and/or membrane protein (M), or fragment thereof is incorporated near or at the N-terminal of CD63. Suitably the extracellular domain of the SARS-CoV-2 spike (S) protein has a sequence sharing at least a 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identity with SEQ ID NO: 1. Suitably the fragment may have a sequence sharing at least a 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identity with SEQ ID NO: 4. Suitably the SARS-CoV-2 nucleoprotein (N) protein has a sequence sharing at least a 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identity with SEQ ID NO: 2. Suitably the SARS-CoV-2 membrane protein (M) protein has a sequence sharing at least a 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identity with SEQ ID NO: 3. Suitably, the membrane protein (M) fragment has a sequence sharing at least a 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identity with SEQ ID NO: 58 (RLFARTRSMWSFNPETN ILLNVPLHGTILTRPLLESELVIGAVILRGHLRIA GH H LGRCD IKDLPKE ITVATSRTLSYYKLGASQRVAGDSGFAAYSRYRIGNYKLNTD HSSSSDNIALLVQ). In a suitable embodiment, the fusion protein comprises or consists of a sequence sharing at least 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identity with SEQ ID NO:17 or SEQ ID NO:18. More suitably, the fusion protein comprises or consists of SEQ ID NO:17 or SEQ ID NO:18.

In a suitable embodiment, the fusion protein comprises CD63 and SARS-CoV-2 membrane protein (M), variant, or a fragment thereof, and extracellular domain of the SARS-CoV-2 spike protein (S), variant, or a fragment thereof. Suitably, the fragment of the membrane protein (M) may have a sequence sharing at least 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identity with SEQ ID NO: 57. More suitably, the fragment is according to SEQ ID NO: 57 (MADSNGTITVEELKKLLEQ). Suitably, the membrane protein (M), variant or fragment is incorporated into a luminal loop of CD63. Suitably the extracellular domain of the SARS-CoV-2 spike protein (S) may have a sequence sharing at least 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identity with SEQ ID NO: 1. Suitably the fragment of the spike protein (S) may have a sequence sharing at least 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identity with SEQ ID NO: 4. Suitably, the fragment of the spike protein (S) is according to SEQ ID NO: 4. Suitably, a linker may be incorporated between both sides of the immunogenic protein and exosomal protein. In a suitable embodiment, the fusion protein comprises or consists of a sequence sharing at least 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identity with SEQ ID NO:19 or SEQ ID NO:20. More suitably, the fusion protein comprises or consists of an amino acid sequence according to SEQ ID NO:19 or SEQ ID NO:20.

As used herein, the terms "homology" and "identity" are used interchangeably. Calculations of sequence homology or identity between sequences may be performed as follows. To determine the percent identity of two amino acid sequences, or of two nucleic acid sequences, the sequences are aligned for optimal comparison purposes (e.g., gaps can be introduced in one or both of a first and a second amino acid or nucleic acid sequence for optimal alignment and non-homologous sequences can be disregarded for comparison purposes). In a preferred embodiment, the length of a reference sequence aligned for comparison purposes is at least 30%, preferably at least 40%, more preferably at least 50%, even more preferably at least 60%, and even more preferably at least 70%, 75%, 80%, 82%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% of the length of the reference sequence. The amino acid residues or nucleotides at corresponding amino acid positions or nucleotide positions are then compared. When a position in the first sequence is occupied by the same amino acid residue or nucleotide as the corresponding position in the second sequence, then the molecules are identical at that position (as used herein amino acid or nucleic acid "identity" is equivalent to amino acid or nucleic acid "homology"). The percent identity between the two sequences is a function of the number of identical positions shared by the sequences, taking into account the number of gaps, and the length of each gap, which need to be introduced for optimal alignment of the two sequences.

The comparison of sequences and determination of percent identity between two sequences can be accomplished using a mathematical algorithm. In a preferred embodiment, the percent identity between two amino acid sequences is determined using the Needleman et al. (1970) 1 MoL Biol. 48:444-453) algorithm which has been incorporated into the GAP program in the GCG software package (available at http://www.gcg.com), using either a BLOSUM 62 matrix or a PAM250 matrix, and a gap weight of 16, 14, 12, 10, 8, 6, or 4 and a length weight of 1, 2, 3, 4, 5, or 6. In yet another preferred embodiment, the percent identity between two nucleotide sequences is determined using the GAP program in the GCG software package (available at http://www.gcg.com), using a NWSgapdna. CMP matrix and a gap weight of 40, 50, 60, 70, or 80 and a length weight of 1, 2, 3,4, 5, or 6. A particularly preferred set of parameters (and the one that should be used if the practitioner is uncertain about what parameters should be applied to determine if a molecule is within a sequence identity or homology limitation of the invention) are a BLOSUM 62 scoring matrix with a gap penalty of 12, a gap extend penalty of 4, and a frameshift gap penalty of 5.

Alternatively, the percent identity between two amino acid or nucleotide sequences can be determined using the algorithm of Meyers et al. (1989) CAB1OS 4:11-17) which has been incorporated into the ALIGN program (version 2.0), using a PAM120 weight residue table, a gap length penalty of 12 and a gap penalty of 4. Other methods of determining sequence identity will be known to those skilled in the art.

As mentioned elsewhere in the present specification, the fusion proteins of the invention are artificial proteins comprising amino acid sequences of at least two different proteins or protein variants, or fragments thereof. Specifically, the fusion proteins of the invention comprise an exosomal protein or an exosomal protein variant, or a fragment thereof, and one or more immunogenic protein or immunogenic protein variant, or fragment thereof. It will be appreciated that in the context of the present speciation, when reference is made to a "protein", for example an exosomal protein or immunogenic protein, this also refers to the protein variant, or fragment of the protein or protein variant. The term "variant" as used herein refers to a polypeptide that shares a partial sequence identity with the amino acid encoding the exosomal protein or the immunogenic protein. The term "fragment" as used herein refers to a polypeptide that shares 100% identity with the corresponding portion of the amino acid sequence of the exosomal or immunogenic protein or variant, but that consist of a truncation in the amino acid sequence encoding the exosomal protein (for example a tetraspanin, such as CD63) or immunogenic protein (for example a protein selected from the group consisting of spike protein (S), nucleoprotein (N), and membrane protein (M) of SARSCoV-2).

Exosomes In one aspect the present invention provides exosomes comprising the fusion proteins of the invention. An "exosome", as used herein, is a membrane-bound extracellular vesicle between 30-150 nanometers in size. In vivo, exosomes are shed into the blood, urine, cerebrospinal fluid and other bodily fluids from cells, and may contain some of the proteins and functional ribonucleic acid (RNA) molecules from their cells of origin. In vitro, exosomes may be shed into the cell culture media. The cells of origin as per the present invention may be selected from a wide range of cells. Merely by way of example the cells may be HeLa cells. Methods of purifying exosomes from cell culture media are well known in the art. Merely by way of example, exosomes may be purified using the Total Exosome Isolation Reagent (InvitrogenTm) following the manufacturer's instructions.

In the context of vaccines, exosomes may be advantageous because they can be efficiently taken up by dendritic cells (DCs). DCs are proficient at antigen processing and presentation and promotion of an active and beneficial T-cell immune response. Antigens (such as the immunogenic proteins of the fusion protein of the invention) taken up by DCs, as well as unprocessed antigens, travel through the lymph to the nearest draining node to stimulate antigen specific T-cells. This leads to a cellular response, invoking both CD8 cytotoxic and CD4 helper T-cells, as well as humoral responses leading to production of specific antibodies.

In some cases, this process may be made even more efficient by enhancing targeting of the exosomes to DCs. DCs express receptors on their surface, including C-type lectin receptor, mannose receptor, DEC-205 or Dectin-1 that trigger DC activation. To facilitate this process ligands for these receptors may be expressed on the exosomes. Accordingly, the exosomes of the invention may further comprise a DC receptor ligand. The ligand may be a natural biological ligand, or a nanobody or related structure designed to bind to the receptor.

It will be appreciated that the ligand may be encoded by a polypeptide forming part of the fusion protein, or a separate polypeptide. Suitably, the fusion protein of the invention may further comprise a polypeptide encoding a DC receptor ligand.

In a suitable embodiment, the exosomes of the invention may comprise an immune enhancing moiety. Merely by way of example, such an immune enhancing moiety may be selected from the group consisting of a molecule with a pathogen-associated molecular pattern (PAMP), DNA oligonucleotides containing the CpG motif, a STING agonist (such as cyclic GMP-AMP) and a TLR9 (Toll-like Receptor) agonist.

A molecule with a pathogen-associated molecular pattern (PAMP) may be advantageous as it may help the exosomes induce a potent Thl response. Examples of adjuvants include synthetic CpG (a TLR9 agonist) or poly-ICLC (a TLR3 ligand). DNA oligonucleotides containing the CpG motif may be advantageous as they may help stimulate cells of the immune system leading to the production of cytokines such as type-I interferon, IL-6, TNF and IL-12. A STING agonist (such as cyclic GMP-AMP) may be advantageous as it may help stimulate cells of the immune system leading to the production of cytokine such as type I interferon.

Methods for producing exosomes are well known in the art. Methods for producing exosomes expressing fusion proteins are also well known in the art. Suitably the exosomes may be produced by cells modified (for example, genetically modified) to enhance the production of exosomes. Suitably, exosomes may be produced in cells which have reduced expression of proteins which retain exosomes, such as tetherin (bone marrow stromal antigen 2) protein. By reduced expression it is meant that the expression levels are lower (for example by 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 99% or 100%) as compared to a suitable control. A suitable control may be, for example, a cell in which a gene encoding a protein that retains exosomes (such as tetherin) is not knocked out. Techniques for knocking out an undesirable gene, such as the gene encoding tetherin are also known in the art. The inventors believe that a reduction of tetherin expression in a cell may increase exosomal production by about 4-fold.

Accordingly, in a further aspect, provided herein is a cell that has reduced expression of tetherin. Suitably, the cell may be isolated. Provided herein is also the use of a cell with reduced expression of tetherin in the production of an exosome. Suitably, the exosome may be genetically modified. Suitably, such a genetically modified exosome may be the exosome of the invention. Suitably, such a genetically modified exosome may comprise the fusion protein of the invention.

Expression Vectors In one aspect the invention provides an expression vector comprising an expressible nucleic acid encoding the fusion proteins herein described. In one embodiment the vector may be any vector capable of transferring DNA to a cell. Suitably, the vector is an integrating vector or an episomal vector.

Preferred integrating vectors include recombinant retroviral vectors. A recombinant retroviral vector will include DNA of at least a portion of a retroviral genome which portion is capable of infecting the target cells. The term "infection" is used to mean the process by which a virus transfers genetic material to its host or target cell. Suitably, the retrovirus used in the construction of a vector of the invention is also rendered replication-defective to remove the effect of viral replication of the target cells. In such cases, the replication-defective viral genome can be packaged by a helper virus in accordance with conventional techniques. Generally, any retrovirus meeting the above criteria of infectiousness and capability of functional gene transfer can be employed in the practice of the invention. Suitably, the retroviral vector may be a lentiviral vector. Lentiviral vectors are well known in the art, and have been used to deliver genes to numerous cell types, including HeLa or B lymphoid cells. Other vectors useful in the present invention include adenovirus, adeno-associated virus, SV40 virus, vaccinia virus, HSV and poxvirus vectors.

Preferred episomal vectors include transient non-replicating episomal vectors and self-replicating episomal vectors with functions derived from viral origins of replication such as those from EBV, human papovavirus (BK) and BPV-1. Such integrating and episomal vectors are well known to those skilled in the art and are fully described in the body of literature well known to those skilled in the art. In particular, suitable episomal vectors are described in W098/07876.

Mammalian artificial chromosomes can also be used as vectors in the present invention. The use of mammalian artificial chromosomes is discussed by Cabs (1996 Trends in Genetics 12: 463-466).

In a preferred embodiment, the vector of the present invention is a plasmid. The plasmid may be a non-replicating, non-integrating plasmid.

The term "plasmid" as used herein refers to any nucleic acid encoding an expressible gene and includes linear or circular nucleic acids and double or single stranded nucleic acids. The nucleic acid can be DNA or RNA and may comprise modified nucleotides or ribonucleotides, and may be chemically modified by such means as methylation or the inclusion of protecting groups or cap-or tail structures.

A non-replicating, non-integrating plasmid is a nucleic acid which when transfected into a host cell does not replicate and does not specifically integrate into the host cell's genome (i.e. does not integrate at high frequencies and does not integrate at specific sites). Replicating plasmids can be identified using standard assays including the standard replication assay of Ustav eta! (1991 EMBO J 10: 449-457).

The present invention also provides a cell transformed or transfected with (i.e. comprising) the expression vector of the present invention. The present invention also provides a cell comprising the fusion protein of the invention or exosome of the invention. Suitably the cell is an isolated cell. Suitably the cell is a mammalian cell. Suitably, the cell is a HeLa cell. Suitably, the cell may be modified to produce increased amounts of exosomes as compared to control cells.

Numerous techniques are known and are useful according to the invention for delivering the vectors described herein to cells, including the use of nucleic acid condensing agents, electroporation, complexing with asbestos, polybrene, DEAE cellulose, Dextran, liposomes, cationic liposomes, lipopolyamines, polyornithine, particle bombardment and direct microinjection (reviewed by Kucherlapati and Skoultchi (1984 Crit. Rev. Biochenn 16:349-379); Keown et al (1990 Methods Enzymol 185:527-37).

A vaccine composition Provided herein is a vaccine composition comprising the exosome of the invention or a membrane preparation comprising the fusion protein of the invention. Suitably, the vaccine is anti-SARS-CoV-2. The term "vaccine composition" and "composition" are used herein interchangeably and refer to a composition comprising, in addition to comprising the exosome of the invention, a pharmaceutically acceptable excipient, adjuvant, diluent and/or carrier. As used herein, "vaccine" is defined broadly to refer to any type of biological agent in an administrable form capable of stimulating an immune response (for example a B-cell immune and/or 1-cell immune response) in an animal (for example human) inoculated with the vaccine. Suitably, the vaccine prevents or ameliorates the symptoms of a disease, such as an infection (for example COVID-19). Thus, reduction in the incidence or severity of characteristic symptoms of COVID-19 in comparison to non-immunized subjects may be termed a vaccine for the purposes of this invention.

The term "membrane preparation" as used herein refers to a composition comprising membrane fragments from cells which express the fusion protein (for example HeLa cells or LCL721 cells). Methods for obtaining a membrane preparation are well known in the art. Suitably, the fusion protein is attached to the membrane fragments in the membrane preparation. Suitably, the fusion protein is attached to the membrane fragments by the exosomal protein (such as tetraspanin). In the one aspect, the present invention provides a membrane preparation comprising the fusion protein of the invention.

Compositions may routinely contain pharmaceutically acceptable concentrations of salt, buffering agents, preservatives, compatible carriers, supplementary immune potentiating agents such as adjuvants and cytokines and optionally other therapeutic agents or compounds.

As used herein, "pharmaceutically acceptable" refers to a material that is not biologically or otherwise undesirable, i.e., the material may be administered to an individual along with the selected binding protein without causing any undesirable biological effects or interacting in a deleterious manner with any of the other components of the pharmaceutical composition in which it is contained.

Excipients are natural or synthetic substances formulated alongside an active ingredient (e.g. fusion protein or exosome of the invention), included for the purpose of bulking-up the formulation or to confer a therapeutic enhancement on the active ingredient in the final dosage form, such as facilitating drug absorption or solubility. Excipients can also be useful in the manufacturing process, to aid in the handling of the active substance concerned such as by facilitating powder flowability or non-stick properties, in addition to aiding in vitro stability such as prevention of denaturation over the expected shelf life. Pharmaceutically acceptable excipients are well known in the art. A suitable excipient is therefore easily identifiable by one of ordinary skill in the art. By way of example, suitable pharmaceutically acceptable excipients include water, saline, aqueous dextrose, glycerol, ethanol, and the like.

Diluents are diluting agents. Pharmaceutically acceptable diluents are well known in the art. A suitable diluent is therefore easily identifiable by one of ordinary skill in the art.

Carriers are non-toxic to recipients at the dosages and concentrations employed and are compatible with other ingredients of the formulation. The term "carrier denotes an organic or inorganic ingredient, natural or synthetic, with which the active ingredient is combined to facilitate the application. Pharmaceutically acceptable carriers are well known in the art. A suitable carrier is therefore easily identifiable by one of ordinary skill in the art.

Provided herein is the exosome or vaccine composition of the invention for use as a medicament. Said medicament may be used for human or animal therapy of various diseases or disorders in a therapeutically effective dose. Suitably the disease may be an infection. The medicament can be formulated by various techniques dependent on the desired application purposes. Formulations described herein in connection to the vaccine composition of the invention are exemplary formulations of the medicament.

Also provided herein is the exosome or vaccine composition of the invention for use in the prevention or amelioration of an infection in a subject. The term "infection" as used herein refers to the undesirable presence of a microorganism in or on the subject's body. Suitably, the microorganism is pathogenic. Such an undesirable presence of a microorganism may be symptomatic or asymptomatic. It will be appreciated that whether the infection is symptomatic or asymptomatic may depend on the subject and/or type of microorganism. It will also be appreciated where an infection is symptomatic, the type of symptoms and their severity may depend on the subject and/or type of microorganism. Suitably the infection may be a viral, bacterial or fungal infection. Merely by way of example, if the infection is caused by SARS-CoV-2, the symptoms may include fever, cough, and/or loss of taste and/or smell.

Also provided is a method of eliciting an anti-SARS-CoV-2 immune response in a mammal comprising administering the exosome or a vaccine composition comprising the exosome of the invention to a subject.

Also provided herein is a method for preventing or ameliorating an infection in a subject, the method comprising providing the subject in need thereof with a therapeutically effective amount of an exosome or vaccine composition of the invention.

"Therapeutically effective amount" as used herein refers to the amount of exosomes or vaccine composition of the invention that elicit a biological response in a tissue or system of a subject such that the infection is prevented or ameliorated. Methods of establishing a therapeutically effective amount will be known to those skilled in the art and merely by way of example can include performing a dose response assay.

The term "subject" will be understood to refer to a warm-blooded animal, particularly a mammal. Non-limiting examples of animals within the scope and meaning of this term include humans, non-human primates, dogs, cats, guinea pigs, rats, mice, horses, goats, cattle, sheep, and zoo animals.

The present invention provides novel vaccine compositions comprising the exosomes of the invention for controlling SARS-CoV-2 infection in mammalian, most preferably human, subjects. The present vaccine compositions are useful in providing immune resistance against the strain(s) of SARS-CoV-2 used for preparation of the fusion proteins of the invention, as well as against strains which are different from those used in the preparation of the fusion proteins.

In certain embodiments vaccines of the invention are administered prophylactically. In certain embodiments, a vaccine of the invention is administered therapeutically. In an embodiment, the vaccine is administered to a patient with an active SARS-CoV-2 infection to both treat the active infection and/or prevent recurrence of a SARS-CoV2.

EXAMPLES Example 1 Constructs Constructs are designed to integrate fragments, or whole parts of SARS-CoV-2 genes CD63.

SARS-CoV-2 genes are: - Tagged to the N terminus of CD63; - Inserted into lumina! loops 1; and/or - Inserted into lumina! loop 2.

This may depend on the antigen. For example, N and M will be N terminal, Spike or ACE2 constructs will be within the loops.

For inserts to lumina! loop 1 inserts are between Q36 and L37 of CD63. For inserts to lumina! loop 2, inserts will be between R108-D109 of CD63.

CD63-FLAG-SpikeRBD was synthesised by GeneWiz and cDNA was flanked by a 5' EcoRl and a 3' BamHI site. These were ligated to pLVX-EF1alpha-IRES-Puro and transduced to competent cells. Minipreps were picked, analysed by test digests and potential colonies sequenced by Sanger sequencing (GeneWiz).

Results The data below have been performed for the construct v1 -CD63-FLAG-SpikeRBD.

CD63-FLAG-SpikeRBD cDNA was synthetically synthesised and cloned to the lentiviral vector pLVX-EF1alpha-IRES-Puro. Miniprepped DNA was subject to test digest and potential clonal DNA selected and sent for sanger sequencing (GeneWiz). Minipreps 1+3 were both found to have the correct sized insert by test digest, and the CD63-FLAG-SpikeRBD was confirmed by sanger sequencing (Fig 5).

To check the FLAG-CD63Spike insert was not disrupting CD63 trafficking, pLVXEF1alpha-CD63-FLAG-SpikeRBD-IRES-Puro DNA was transiently transfected to HeLa cells and subject to immunofluorescence (Fig 6). FLAG signal was confirmed to be in CD63-positive compartments as shown by colocalisation of signal, and CD63 localisation remained in punctate organelles in transfected cells (as is also observed in non-transfected cells).

After confirming expression of CD63-FLAG-SpikeRBD DNA was tolerated by cells, and localised to the correct intracellular compartments, stable cell lines were generated. Briefly, HEK293T cells were transfected with pLVX-EF1alpha-CD63-FLAG-SpikeRBD-IRES-Puro and the lentiviral packaging plasmids pCMVR8.91 ("199") and pMD.G (VSV-G) ("200") using TransIT-293 (Mirus Bio, USA). Viral supernatants were collected 48 h after transfection, passed through 0.45 pm filters and both wild-type and tetherin KO HeLa cells transduced by spinfection'-viral supernatants were centrifuged at 1800 rpm in a benchtop centrifuge at 37 °C for 3 h to enhance viral transduction.

After 48 hours, transduced WT HeLa and Bst2K0 HeLa cells were selected with 1ug/m1 Puromycin for 5 days. WT and Bst2K0 stable HeLa cell lines were confirmed to express CD63-FLAG-SpikeRBD using immunofluorescence, again using anti-FLAG antibodies, but also using a human monoclonal antibody raised against SARS-CoV-2 Spike-RBD (PO6DHu, ThermoFisher) (Fig 7). FLAG staining colocalised to CD63, a marker for multivesicular endosomes -the compartment where intraluminal vesicles (and therefore exosomes) are generated. The increase in CD63 staining in transduced cells reflects the additional, ectopic copy of CD63, rather than just the endogenous CD63.

An antibody against SpikeRBD showed similar pattern of staining, and colocalised with FLAG -confirming that Spike and FLAG are together localised in CD63-positive, late endosomal compartments. Together, these data indicate that Spike RBD and FLAG are localised to late endocytic compartments as expected (Fig 8).

Whole cell lysates were collected from untransduced and transduced WT and Bst2K0 HeLa cells. Lysates were probed with antibodies against CD63, and both transduced cell lines displayed enhanced staining, and at a higher molecular weight -reflecting additional molecular mass given from the addition of FLAG-SpikeRBD (Fig 9A).

Antibodies against FLAG were similarly used to blot whole cell lysates, and a positive band was observed at the correct molecular weight in transduced stable cell lines, and not in untransduced controls. Exosome-enriched fractions were generated from cells and subject to Western blotting. Exosomes from tetherin KO HeLa cells + CD63-FLAG-SpikeRBD displayed a band at the correct molecular weight as expected (Fig 9B).

Further evidence of expression of FLAG-SpikeRBD in the CD63 fusion protein was obtained by mass spectrometry analysis. I-leLa cells stably expressing CD63-FLAGSpikeRBD were lysed, ran on a NuPage (Invitrogen) protein gel and stained with InstantBlue Commassie Stain. A gel band between 50 and 70 kDa was excised, digested with Trypsin and subject to proteomic analysis. Liquid chromatography-mass spectrometry identified a number of unique peptides within CD63-FLAG-SpikeRBD (SEQ ID NO: 5) as follows:

Table 2

Molecular mass Level Deduced Peptide Sequence + Species Experimental Calculated Ppm 885.4213 885.4232 -2.14 K.IADYNYK.L 898.4855 898.4872 -1.91 R.QTAPGQTGK./ 898.4865 898.4872 -0.76 R.QIAPGQTGICI 898.4876 898.4872 0.40 R.()I.APGQTGE.I 910.4213 910.4219 -0.61 E.CYGUSPTILL 1052.4552 1052.4597 -4.28 R.MMENYPK.N + Oxidation (M) 1052.4570 1052.4597 -2.53 R.00MENYPK.N + Oxidation (M) 1052.4574 1052.4597 -2.19 R.QaMENYPK.N + Oxidation (M) 1052.4577 1052.4597 -1.83 R.QQMENYPK.N + Oxidation (M) 1112.5411 1112.5403 0.71 R.FASVYANNR.K 1217.5819 1217.5829 -0.83 K.VGGNYNYLYR.L 1256.5652 1256.5608 3.48 K.VMSEENNNFR.Q 1272.5553 1272.5557 -0.35 K.VMSEENNNFR.Q + Oxidation 00 1272.5553 1272.5557 -0.35 K.VMSEFNNNFR.Q + Oxidation 00 1272.5567 1272.5557 0.80 K.VMSEENNNFR.Q + Oxidation 00 2045.9747 2045.9881 -6.53 K.LNDLCFTNVYADSFVIR.G 2265.0296 2265.0372 -3.35 K.LPDDFTGCVIAWNSMILDSR.V 2265.0440 2265.0372 3.02 K.LPDDFTGCVIAWNSENLDSK.V 2372.0700 2372.0995 -12.43 R.ISNCVADYSVLYNSASPSTER.0 The sequence of the theoretical CD63-FLAG-SpikeRBD sequence is shown in SEQ ID NO: 5. Of the identified unique peptides identified, several were identified which originate from the SpikeRBD. The identified unique peptides, and their position within CD63-FLAG-SpikeRBD and amino acid position were defined as shown below:

Table 3

Location in Position in Peptide Fragment Identified Theoretical Protein Theoretical Protein By Mass Spectrometry K.IADYNYR.L Spike RED Spike RED Spike RED 149-157 140-150 110-119 361-370 78-87 176-187 351-362 118-136 156-177 89-112 R.QIAPGQTGR.I K.CYGVSPTK.L R.QQMENYPK.N + Oxidation 00 R.FASVYAWNR.K K.VGGNYNYLYR.L K.VMSEFNNNFR.Q K.LNDLCFTNVYADSIVIR.G CD63 post-insert Spike RED Spike RED K.LPDOFTGCVIAWNSWNLDSK.V R.ISNCVADYSVLYNSASFSTFR.0 CD63 post-insert Spike RED Spike RED Spike RED Finally, to confirm that exosomes from transduced cells contained FLAG-SpikeRBD, we performed surface labelling innmunogold electron microscopy, making use of the FLAG epitope that is exposed on the outside of exosomes. Briefly, transduced and untransduced WT HeLa cells were treated with Bafilomycin Al for 16 hours to induce exosome release as previously described (Edgar et al., eLife 2016;5:e17180 DOI: 10.7554/ELIFE.17180). Cells were fixed before being labelled with antibodies against FLAG. lOnm Protein-A gold was then used to detect anti-FLAG antibodies. Cells were then re-fixed with glutaraldehyde before being processed for electron microscopy. Ultrathin sections were cut, stained with heavy metals and imaged. Immunogold labelling was only observed in transduced cells and was specifically seen on surface-associated exosomes as expected.

Together, these data confirm that CD63-FLAG-SpikeRBD is trafficked to late endosomes, and to exosomes (Fig 10A, B).

Antibodies SARS-CoV-2 Spike-RBD (PO6DHu, human monoclonal, ThermoFisher, 1:100 for IF) Anti-FLAG; (L5, rat monoclonal, BioLegend, 1:200 for IF), (anti-DYKDDDDK, D6W5B, rabbit monoclonal, Cell Signalling Technology, 1:200 for IF)), (M2, mouse monoclonal, Sigma Aldrich, 1:1000 for Wester blotting).

CD63 (H5C6, mouse monoclonal, BDBiosciences, 1:200 for IF) GAPDH (14C10, rabbit monoclonal, Cell Signalling Technology, 1:1000 for Western blotting).

Example 2

The aim of the following example is to demonstrate that SARS-CoV2 spike protein containing exosomes (RBD region) elicit recognition by T-cells specific to epitopes with SARS-CoV-2 Spike. A polyclonal T-cell culture from a donor with reactivity to the RBD region of SARS-CoV-2 spike was used. Reactivity was demonstrated by incubating some of the culture with overlapping peptides spanning the RBD region of the SARS-CoV-2 spike protein (commercially available PepMixTm, JPT Peptide Technologies). Autologous Lymphoblastoid Cell Lines (LCL) were established from B cells isolated from the same donor and transformed with Epstein-Barr virus (EBV) into permanent cell lines. These LCLs serve as targets of T-cells in assays. Membranes prepared from HeLa cells expressing the SpikeRBD fusion protein were used as a positive control.

Method The autologous LCL cells were washed once with serum-free AIM-V medium, then dispensed into 10 different 15 ml tubes (150,000 cells/tube in volume of 50u1). One tube was left untreated (negative control) and one had 0.5 ul RBD pepmix added (positive control). To the remaining tubes, 50 ul or 5 ul of the different exosome or membrane preparations was added. LCL cells were then incubated at 37°C 5% 002, with intermittent agitation to keep cells suspended. During the incubation, polyclonal T-cells were counted, washed and resuspended to 250,000 T-cells per ml. Aliquots (100 ul) were added to a 96 well plate. After one hour each tube of LCL cells were washed once with 8m1 LCL media, resuspended in 200 ul of LCL medium and pipetted into appropriate wells of a 96U bottom plate containing T-cells. Outer wells of each plate were filled with saline to reduce evaporation and plates were incubated at 37°C 5% CO2. After 24 and 48hr incubation, 60 ul of supernatant from each well were dispensed into separate wells of a 96 well plate and stored at 4°C.

The interferon gamma (IFN-y) concentration of each aliquot of supernatant was tested using an IFN-y capture ELISA, with doubling dilutions of recombinant IFN-y included for quantitation of IFN-y concentration in the samples.

Whole cell membranes from HeLa cells expressing CD63-FLAG-SpikeRBD were prepared in cold hypotonic buffer and mechanically lysed. The homogenate was centrifuged at 25,000 xg, 20mins, 4°C and the resulting cell membrane pellets were resuspended in PBS. An aliquot was used as a positive control in the T cell assay.

Results The polyclonal T-cell culture did not produce any interferon-gamma when co-cultured with the autologous LCL, but produced large quantities of the cytokine when co-cultured with the same LCL that had been exposed to SARS-CoV-2 spike RBD pepmix. This demonstrates that the polyclonal culture contains T-cells specific to epitopes within the RBD region. The lack of any recognition of the autologous LCL allows this polyclonal culture to be used to investigate exosome and membrane preparations.

This polyclonal culture produced large quantities of interferon-gamma when co-cultured with autologous LCL exposed to the SARS-CoV-2 spike exosomes, but not the control exosomes. The same pattern was seen for LCL exposed to the membrane fractions. These results are shown in Table 4.

These results demonstrates that the Spike RBD containing exosomes elicit strong activation of RBD-specific T-cells. Control exosomes not containing Spike RBD did not non-specifically activate T-cells.

Table 4 T-cell activation results Tube No: Condition: Result mean (+/-SD of triplicate wells) 1 media (T-cells alone -neg control) -89 (61)

2 LCL (background control) 114 (70)

3 LCL + 50 ul control exosomes 278 (97) 4 LCL + 5 ul control exosomes 158 (72) LCL + 50 ul RBD exosomes 18,478 (471) 6 LCL + 5 ul RBD exosomes 11,074 (1371) 7 LCL + 50 ul control membrane prep 201 (171) 8 LCL + 5 ul control membrane prep 151 (60) 9 LCL + 50 ul RBD membrane prep 14,173 (552) LCL + 5 ul RBD membrane prep 15,551 (1251) 11 LCL + RBD Pepmix (positive control) 26,591 (288) Note -all conditions were tested with T-cells. Therefore No.1 represents T-cells alone, No.2 represents T-cells incubated with unmanipulated autologous LCL -the background level of interferon-gamma in the assay. No.? and 8 represent positive controls using membranes prepared from HeLa cells expressing CD63-FLAG-SpikeRBD.

Claims

CLAIMS1. A fusion protein comprising: i) an exosomal protein, wherein the exosomal protein is a tetraspanin protein; and ii) one or more immunogenic protein.
2. The fusion protein of claim 1, wherein the tetraspanin is selected from the group consisting of CD63, CD9, and CD81, or a fragment, or variant thereof.
3. The fusion protein of claims 1 or 2, wherein the one or more immunogenic protein is capable of eliciting an immune response against a SARS-CoV-2 protein.
4. The fusion protein of claim 3, wherein the SARS-CoV-2 protein is selected from the group consisting of spike protein (S), nucleoprotein (N), membrane protein (M), envelope protein (E), Open reading frame (ORF) 3a protein, ORF 3b protein, ORF 6 protein, ORF 7a protein, ORF 7b protein, ORF 8 protein, ORF 9b protein, ORF 9c protein, and ORF 10 protein, optionally wherein when the SARS-CoV-2 protein is spike protein (S) it is the extracellular domain of spike protein (S).
5. The fusion protein of any one of the preceding claims, wherein the one or more immunogenic protein is capable of eliciting a B-cell and a T-cell immune response.
6. The fusion protein of any one of the preceding claims, wherein the one or more immunogenic protein is capable of eliciting a 1-cell immune response.
7. The fusion protein of the preceding claims, wherein the protein comprises a first one or more immunogenic protein capable of eliciting a B-cell and a 1-cell immune response and a second one or more immunogenic protein capable of eliciting a T-cell immune response.
8. The fusion protein of any one of claims 5 to 7, wherein the first one or more immunogenic protein capable of eliciting a B-cell and 1-cell immune response is incorporated into a luminal loop of the exosomal protein.
9. The fusion protein of any one of claims 5 to 8, wherein the second one or more immunogenic protein capable of eliciting a T-cell immune response is incorporated near or at the N-terminus of the exosomal protein, and/or is incorporated into an intravesicular loop of the exosomal protein.
10. The fusion protein of any one of claims 5 to 9, wherein first the one or more immunogenic protein is capable of eliciting a B-cell and T-cell immune response against the SARS-CoV-2 spike protein (S), optionally the extracellular domain of spike protein (S).
11. The fusion protein of any one of claims 5 to 10, wherein the second one or more immunogenic protein is capable of eliciting a T-cell immune response against the SARS-CoV-2 M and/or N protein, and/or ORF proteins, and/or E protein.
12. The fusion protein of any one of claims 3 to 11, wherein the first one or more immunogenic protein capable of eliciting a B-cell and a T-cell immune response is incorporated into the first and/or second luminal loop of the tetraspanin, optionally wherein the tetraspanin is CD63, or CD9 or CD81.
13.The fusion protein of any one of claims 2 to 12, wherein the second one or more immunogenic protein capable of eliciting a T-cell immune response is incorporated near or at the N-terminus of the tetraspanin, optionally wherein the tetraspanin is CD63, or CD9 or CD81.
14. The fusion protein of any one of the preceding claims, wherein the one or more immunogenic protein shares at least 75% identity a SARS-CoV-2 protein or protein variant, or a fragment thereof.
15. The fusion protein of claim 14 wherein the SARS-CoV-2 protein is selected from the group consisting of the extracellular domain of spike protein (S) (SEQ ID NO: 1), nucleoprotein (N) (SEQ ID NO: 2), and membrane protein (M) (SEQ ID NO: 3).
16. The fusion protein of claim 15, wherein the fragment of the spike protein (S) is the receptor binding domain (RBD) (SEQ ID NO: 4), the fragment of the membrane protein (M) is according to SEQ ID NO: 57 or 58, and/or the fragment of the nucleoprotein (N) is according to SEQ ID NO: 56.
17. The fusion protein of any one of the preceding claims, sharing at least 75%, at least 80%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99% or 100% identity with SEQ ID NO: 5, SEQ ID NO: 6, SEQ ID NO: 7, SEQ ID NO: 8, SEQ ID NO: 9, SEQ ID NO: 10, SEQ ID NO: 11, SEQ ID NO: 12, SEQ ID NO: 13, SEQ ID NO: 14, SEQ ID NO: 15, SEQ ID NO: 16, SEQ ID NO: 17, SEQ ID NO: 18, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, SEQ ID NO: 25, or SEQ ID NO: 26.
18. The fusion protein of any one of the preceding claims, wherein the exosomal protein and the one or more immunogenic protein is separated by a linker sequence.
19. An exosome or membrane preparation comprising a fusion protein of any one of claims 1 to 18.
20. The exosome or membrane preparation according to claim 19, wherein the exosome further comprises a DC receptor ligand and/or an immune enhancing moiety, optionally wherein the immune enhancing moiety is selected from the group consisting of a molecule with a pathogen-associated molecular pattern (PAMP), DNA oligonucleotide containing an CpG motif, a STING agonist (such as cyclic GMP-AMP), and a TLR9 (Toll-like Receptor) agonist.
21. A vaccine composition comprising an exosome or membrane preparation of claim 19 or 20.
22. A nucleic acid molecule encoding a fusion protein of any one of claims 1 to 18.
23. An expression vector comprising the nucleic acid molecule of claim 22.
24. The expression vector of claim 23, wherein it is a lentivirus expression vector.
25. A cell comprising a fusion protein of any one of claims 1 to 18, an exosome or membrane preparation of claim 19 or 20, a nucleic acid of claim 22, and/or an expression vector of claim 23 or 24, optionally wherein the cell is an isolated cell.
26. The cell of claim 25, wherein the transformed cell line is a HeLa cell or a LCL721 cell.
27. The cell of claim 25 or 26, wherein the cell is modified to enhance the production of exosomes.
28. The cell of any one of claims 25 to 27, wherein the cell has reduced expression of tetherin.
29. The exosome or membrane preparation of claim 19 or 20, or the vaccine composition according to claim 21, for use as a medicament.
30. The exosome or membrane preparation of claim 19 or 20, or the vaccine composition according to claim 21, for use in the prevention or amelioration of an infection.
31. The exosome, membrane preparation, or vaccine composition for use according to claim 30, wherein the infection is a viral, bacterial or fungal infection.
32. A method of preventing or ameliorating an infection in a subject, the method comprising providing the subject in need thereof with a therapeutically effective amount of an exosome or membrane preparation of claim 19 or 20, or a vaccine composition according to claim 21.
33. The method of claim 32, wherein the infection is a viral, bacterial or fungal infection.
34. The method of claim 33, wherein the viral infection is a SARS-CoV-2 infection.