WO2023161648A1

WO2023161648A1 - Novel use and method comprising il-2 and a tissue- or organ-specific targeting moiety

Info

Publication number: WO2023161648A1
Application number: PCT/GB2023/050424
Authority: WO
Inventors: Adrian LISTON; James Dooley; Matthew Holt; Lidia YSHII; Emanuela PASCIUTO; Ludo Van Den Bosch
Original assignee: Babraham Institute; Vib Vzw; Katholieke Universiteit Leuven
Priority date: 2022-02-25
Filing date: 2023-02-24
Publication date: 2023-08-31
Also published as: GB202202628D0

Abstract

The invention relates to a pharmaceutical composition for use in a method of treating and/or preventing amyotrophic lateral sclerosis (ALS), said composition comprising IL-2 and a targeting moiety specific for a tissue or organ of a subject, such as the central nervous system and the brain. Also provided are methods for treating and/or preventing ALS, said methods comprising expanding a population of regulatory T cells and/or administration of a pharmaceutical composition as defined herein.

Description

NOVEL USE AND METHOD COMPRISING IL-2 AND A TISSUE- OR ORGAN-SPECIFIC TARGETING MOIETY FIELD OF THE INVENTION The invention relates to a pharmaceutical composition for use in a method of treating and/or preventing amyotrophic lateral sclerosis (ALS), said composition comprising IL-2 and a targeting moiety specific for a tissue or organ of a subject, such as the central nervous system and the brain. Also provided are methods for treating and/or preventing ALS, said methods comprising expanding a population of regulatory T cells and/or administration of a pharmaceutical composition as defined herein. BACKGROUND OF THE INVENTION Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease characterised by a progressive loss of motor neurons (Jaarsma et al. (2008) J. Neurosci, 28:2075-2088, doi: https://doi.org/10.1523/JNEUROSCI.5258-07.2008 and Clement et al. (2003) Science, 302:113-117, doi: https://doi.org/10.1126/science.1086071) and denervation of muscle fibres, resulting in muscle weakness and paralysis. With an incidence of 2.7 cases per 100,000 individuals (Logroscino, et al. (2010) J. Neurol. Neurosurg. Psychiatry, 81:385-390, doi: https://doi.org/10.1136/jnnp.2009.183525), it is the most common form of motor neuron disease. Due to the lack of a medical cure, average life expectancy is limited to 2-3 years post-diagnosis. 10% of ALS cases are familial, of which 20% are caused by mutations in SOD1 and 40% in C9orf72, for which ALS mouse models are available (Gurney et al. (1994) Science, 264:1772-1775, doi: https://doi.org/10.1126/science.8209258, O’Rourke et al. (2016) Science, 351:1324-1329, doi: https://doi.org/10.1126/science.aaf1064 and O’Rourke et al. (2015) Neuron, 88:892-901, doi: https://doi.org/10.1016/j.neuron.2015.10.027). As disease progression is indistinguishable between familial (fALS) and sporadic ALS (sALS), shared disease mechanisms are expected. ALS is a multifactorial disease, with multiple processes contributing to motor neuron degeneration in ALS, including protein aggregation, excitotoxicity and neuroinflammation (Robberecht & Philips (2013) Nat. Rev. Neurosci., 14:248-264, doi: https://doi.org/10.1038/nrn3430). Two drugs are currently available for persons with ALS in the USA, riluzole (Miller et al. (2012) Cochrane Database Syst Rev., CD001447, doi: https://doi.org/10.1002/14651858.CD001447.pub3) and radicava (Rothstein, JD (2017) Cell, 171:725, doi: https://doi.org/10.1016/j.cell.2017.10.011), of which neither provide a robust therapeutic effect, illustrating the remaining large and urgent unmet medical need in ALS. ALS pathophysiology is non-cell autonomous (Ilieva et al. (2009) J. Cell Biol. 187:761-772, doi: https://doi.org/10.1083/jcb.200908164). An inflammatory component to disease causation is proposed, with astrogliosis, microgliosis and increased expression of several cytokines observed in patient tissue (Aebischer et al. (2012) Eur. J. Neurol., 19:752-759, e45-46, doi: https://doi.org/10.1111/j.1468-1331.2011.03623.x) and in rodent models of the disease (O’Rourke et al. (2016) and Beers et al. (2011) Brain Behav. Immun., 25:1025-1035, doi: https://doi.org/10.1016/j.bbi.2010.12.008). Moreover, increased inflammation drives disease progression in ALS models (Gowing et al. (2009) Exp. Neurol., 220:267-275, doi: https://doi.org/10.1016/j.expneurol.2009.08.021, Nguyen et al. (2004) J. Neurosci., 24:1340- 1349, doi: https://doi.org/10.1523/JNEUROSCI.4786-03.2004 and Staats et al. (2016) Hum. Mol. Genet., doi: https://doi.org/10.1093/hmg/ddw190), and is a disease-modifier in patients with ALS (Robberecht & Philips (2013), McCauley & Baloh (2019) Acta Neuropathol., 137:715- 730, doi: https://doi.org/10.1007/s00401-018-1933-9, Lall & Baloh (2017) J. Clin. Invest., 127:3250-3258, doi: https://doi.org/10.1172/JCI90607 and Thonhoff et al. (2018) Curr. Opin. Neurol., 31:635-639, doi: https://doi.org/10.1097/ WCO.0000000000000599). As neuroinflammation is detrimental in ALS, immune regulatory processes that reverse or mitigate this inflammation have potential therapeutic use. Among the most potent of immune regulatory agents are regulatory T cells (Tregs), based on their capacity to sense the inflammatory milieu and respond through a cocktail of anti-inflammatory mediators. Tregs have been proposed to have neuroprotective functions in neuroinflammatory diseases ranging from multiple sclerosis to stroke (Dombrowski et al. (2017) Nat Neurosci, 20:674-680, doi: https://doi.org/10.1038/nn.4528 and Ito et al. (2019) Nature, 565:246-250, doi: https://doi.org/ 10.1038/s41586-018-0824-5). Dysfunctional Tregs have been described in ALS and their replacement has been proposed to be protective in ALS (Thonhoff et al. (2018)). A small population of Tregs are resident in the central nervous system (CNS) of even healthy mice and humans (Pasciuto et al. (2020) Cell, 182:625-640, e24, doi: https://doi.org/10.1016/ j.cell.2020.06.026), with the number present limited by low levels of interleukin 2 (IL2) (unpublished data). IL-2 is intimately linked to Treg homeostasis, with IL-2 signalling critical for Tregs to overcome a propensity to programmed apoptosis (Pierson et al. (2013), doi: https://doi.org/10.1038/ ni.2649), in a negative feedback circuit that limits the immunosuppressive impact of Tregs (Liston & Gray (2014) Nature Reviews Immunol., 14:154- 165, doi: https://doi.org/10.1038/ nri3605). An increase of IL-2 is observed in ALS mouse models (Angelini et al. (2020) Front Immunol., 11:575792, doi: https://doi.org/10.3389/fimmu.2020.575792) and ALS patients (Tortelli et al. (2020) Front. Neurol., 11:552295, doi: https://doi.org/10.3389/ fneur.2020.552295), in both sera and cerebrospinal fluid (CSF). Interestingly, an increase in IL-2 levels in the blood of ALS patients was associated with a protective effect on the odds of ALS diagnosis (Prado et al. (2018) J. Neurol. Sci., 394:69-74, doi: https://doi.org/10.1016/ j.jns.2018.08.033), suggesting a beneficial effect of IL-2 in ALS. However whether this putative effect can be amplified via therapeutic methods, and whether the effect is mediated via peripheral or CNS expression, remains unknown. There is therefore a great unmet need for a therapy for ALS, such as a targeted therapy which may be used to treat/relieve neuroinflammation associated with the disease. SUMMARY OF THE INVENTION According to a first aspect of the invention, there is provided a pharmaceutical composition comprising IL-2 and a targeting moiety specific for a tissue or organ of a subject for use in a method of treating and/or preventing amyotrophic lateral sclerosis (ALS), wherein said tissue or organ is the central nervous system. In another aspect, there is provided a method of expanding a population of regulatory T cells in a tissue or organ of a subject in need thereof for treating and/or preventing ALS, said method comprising administering to the subject the pharmaceutical composition defined herein, wherein said tissue or organ is the central nervous system. According to a further aspect of the invention, there is provided a method of treating and/or preventing ALS in a subject in need thereof, said method comprising administering to the subject the pharmaceutical composition defined herein. In certain embodiments, the tissue or organ is the brain. BRIEF DESCRIPTION OF THE FIGURES Figure 1: Schematic figures showing IL-2 gene delivery. A) Viral vector schematic with control elements shown. B) Time-course of cargo expression following AAV-based delivery in healthy mice. C) Time-course of treatment in SOD1^G93A mice. Figure 2: Gene delivery of IL-2 delays end point disease progression in. A) Kaplan- Meir curve of SOD1^G93A mice treated with PHP.B.GFAP-IL-2 (n=9) or with the control vector PHP.B.GFAP-GFP (n=9). Log-rank testing p=0.031. B) Age at which SOD1^G93A mice reached clinical end-point (n=9 per group). Parametric t-test p=0.026. Mean ± standard deviation. DETAILED DESCRIPTION OF THE INVENTION According to a first aspect of the invention, there is provided a pharmaceutical composition comprising IL-2 and a targeting moiety specific for a tissue or organ of a subject for use in a method of treating and/or preventing amyotrophic lateral sclerosis (ALS), wherein said tissue or organ is the central nervous system. In one embodiment, the pharmaceutical composition leads to the expansion of a population of regulatory T cells in the tissue or organ targeted by the targeting moiety, i.e. the central nervous system, for the treatment and/or prevention of ALS. Thus in a further aspect of the invention, there is provided a method of expanding a population of regulatory T cells in a tissue or organ of a subject in need thereof for treating and/or preventing ALS, wherein said tissue or organ is the central nervous system. In certain embodiments, the method comprises administration of a pharmaceutical composition comprising IL-2 and a targeting moiety specific for said tissue or organ as described herein. In one embodiment, the methods defined herein comprise expanding a population of cells, such as a population of regulatory T cells. In a further embodiment, said expanding of a population of cells, such as a population of regulatory T cells, is in a tissue or organ of a subject in need thereof, such as a particular tissue or organ of interest. In particular embodiments, said expanding of a population of cells is in the central nervous system (e.g. the brain). References herein to the terms “expanding”, “expansion” and “expanded” or to the phrases “expanding a population of regulatory T cells” and “expanded population of regulatory T cells” include references to populations of cells which are larger than or comprise a larger number of cells than a non-expanded population. It will thus be appreciated that such an “expanded” population comprises a larger number of cells than a population which has not been subjected to IL-2. Thus in certain embodiments, the expanded population of cells, such as an expanded population of regulatory T cells, comprises a larger number of cells compared to a reference population of cells. In one embodiment, the reference population of cells may be a population of cells not subjected to or administered with IL-2. In one embodiment, the expanded population of cells, such as an expanded population of regulatory T cells, comprises a larger number of cells than the population prior to any administration of IL-2. In further embodiments, the reference population of cells may be located in a different tissue or organ to the expanded population of cells. In a further embodiment, the expanded population of cells, such as an expanded population of regulatory T cells, is an expanded population in a tissue or organ of a subject and comprises a larger number of cells compared to a population of cells not located in said tissue or organ of interest. In a further embodiment, the expanded population of cells, such as an expanded population of regulatory T cells, is located in a tissue or organ separated from other tissues or organs by a barrier (such as the blood-brain barrier) and comprises a larger number of cells compared to a population of cells not located with said barrier-separated tissue or organ. Thus in some embodiments, the expanded population of cells is in the central nervous system (e.g. the brain) and comprises a larger number of cells compared to a population of cells located in a tissue or organ other than the central nervous system (e.g. the peripheral nervous system). In one embodiment, the expanded population of cells, such as an expanded population of regulatory T cells, comprises a population at least 2-fold, at least 3-fold, at least 4-fold, at least 5-fold, at least 6-fold, at least 7-fold, at least 8-fold, at least 9-fold, at least 10-fold, at least 11- fold, at least 12-fold, at least 13-fold, at least 14-fold or more larger than a population of cells which has not been subjected to or administered with IL-2. In a further embodiment, the expanded population of cells, such as an expanded population of regulatory T cells, comprises a population at least 2-fold, at least 3-fold, at least 4-fold, at least 5-fold, at least 6-fold, at least 7-fold, at least 8-fold, at least 9-fold, at least 10-fold, at least 11-fold, at least 12-fold, at least 13-fold, at least 14-fold or more larger than a population of cells not located in the tissue or organ of interest. In a particular embodiment, the expanded population of cells is at least 2- fold, at least 4-fold, at least 5-fold, at least 6-fold, at least 7-fold, at least 8-fold, at least 12- fold, at least 13-fold or at least 14-fold larger than a reference population, such as a population of cells in the tissue or organ of interest which has not been subjected to or administered with IL-2 or a population of cells not located in the tissue or organ of interest. In some embodiments, the expanded population of cells, such as an expanded population of regulatory T cells, comprises a larger proportion of cells which make up a subset of the population (e.g. a larger proportion of regulatory T cells within the total population of T cells in the tissue or organ). Therefore, it will be appreciated that the expanded population of regulatory T cells as defined herein may be expanded in a manner which is dependent on the dose of IL-2 administered. Thus in certain embodiments, the expanded population of regulatory T cells as defined herein comprises a population which is larger than a reference population by a factor which is IL-2 dose-dependent. In further embodiments, the expanded population of regulatory T cells comprises a population of cells which have increased survival. Thus in one embodiment, the expanded population of regulatory T cells comprises increased survival. In a further embodiment, the expanded population of regulatory T cells comprises decreased, or reduced, cell death. In a yet further embodiment, the expanded population of regulatory T cells comprise increased proliferation. Thus in one embodiment, the expanded population of regulatory T cells is larger than a reference population (e.g. a population of regulatory T cells not subjected to or administered with IL-2 or a population of cells not located in the tissue or organ of interest) because of increased survival of the expanded population of regulatory T cells. In a further embodiment, the expanded population of regulatory T cells is larger than a reference population because of decreased, or reduced, cell death in the expanded population of regulatory T cells. In a yet further embodiment, the expanded population of regulatory T cells is larger than a reference population because of increased proliferation. In a still further embodiment, the expanded population of regulatory T cells is larger than a reference population because of a combination of one or more of increased survival, decreased/reduced cell death and increased proliferation. It will be appreciated that references herein to an “expanded population”, such as an “expanded population of regulatory T cells”, may also include a population of cells which are activated. References herein to “expanding” may therefore include the activation of a population of cells, such as a population of regulatory T cells. Similarly, “expanding” also includes the expansion of an activated population of regulatory T cells, for example, a population which is already activated prior to administration of IL-2. Such activation of the population of cells, such as a population of regulatory T cells, may be independent of an expansion or may be concomitant with an expansion of said population. Thus in one embodiment, the expanded population of regulatory T cells comprises activated regulatory T cells. In a further embodiment, the expanded population of regulatory T cells is an activated population of regulatory T cells. In an alternative embodiment, references herein to “expanding” or an “expanded population” do not include activating said population or an activated population of cells. Thus according to this embodiment, the expanded population of cells, such as an expanded population of regulatory T cells, does not comprise an activated phenotype. In a further embodiment, the expanded population of regulatory T cells does not comprise activated regulatory T cells. Thus in a yet further embodiment, the expanded population of regulatory T cells comprises the phenotype, such as the surface phenotype, of a population of regulatory T cells which have not been subjected to or administered with IL-2. Regulatory T cells (also known as Tregs) are a subpopulation of T cells that modulate the immune system, maintain tolerance and prevent autoimmune disease. They generally suppress or downregulate the activation and/or proliferation of effector T cells and have been shown to have utility in immunosuppression. As such, regulatory T cells are highly potent cells that combine multiple immunosuppressive and regenerative capabilities and there is great interest in using exogenous regulatory T cells as a cell therapy or exogenous factors which stimulate, activate or expand endogenous regulatory T cells. The inventors have previously demonstrated that regulatory T cells exist in the healthy brain (see Fig.1 of WO2021/044175, the contents of which are hereby incorporated in their entirety and Pasciuto et al. (2020)), despite the traditional view that the brain is a tissue which is isolated from the immune system (e.g. because of the blood-brain barrier), and thus may be a valid target for immunosuppressive treatment, such as anti-inflammatory treatment, in the brain. Thus in one embodiment, the expanded population of regulatory T cells comprises an increased anti-inflammatory potential. Such increased anti-inflammatory potential may be compared to a non-expanded population of regulatory T cells, such as a non-expanded population of regulatory T cells present in the tissue or organ, or to a population of regulatory T cells present at another location other than the tissue or organ of interest. In one embodiment, the expanded population of regulatory T cells comprises a phenotype similar to non-expanded regulatory T cells within the tissue or organ of interest or to regulatory T cells from a location other than the tissue or organ of interest. Such phenotypes may include surface marker phenotype, transcriptomic phenotype/signature (e.g. gene expression signature), gene and/or protein expression profile and cytokine expression profile. Thus in a particular embodiment, the expanded population of regulatory T cells comprises or retains the anti-inflammatory potential of a non-expanded population of regulatory T cells or the expanded population of regulatory T cells prior to expansion. In a further embodiment, the expanded population of regulatory T cells comprises or retains the anti-inflammatory potential of a population of regulatory T cells from another location other than the tissue or organ of interest. References herein to the phrase “in a tissue or organ” refer to a discrete location in the subject such as in a particular tissue or organ. It will be appreciated that such terms do not relate to wherein an effect is produced systemically or outside of the tissue or organ of interest, or wherein a cell type or cell population not located in the tissue or organ of interest is affected (e.g. expanded or activated). Thus in one embodiment the population of regulatory T cells is affected (e.g. expanded) in a particular tissue or organ, i.e. locally. In a further embodiment, the population of regulatory T cells is affected (e.g. expanded) in a particular tissue or organ only. In a yet further embodiment, the population of regulatory T cells located outside or not in the tissue or organ of interest is not affected (e.g. expanded). Thus in particular embodiments, the systemic or peripheral population of regulatory T cells is not affected (e.g. expanded). In a further embodiment, the population of regulatory T cells is affected (e.g. expanded) in the central nervous system only. In a yet further embodiment, the population of regulatory T cells is not affected (e.g. expanded) outside of the central nervous system, such as is not affected in the peripheral nervous system or systemically. Tissues or organs as defined herein comprise a discrete location of the body or of an organism. For example, the tissue or organ may comprise a compartment of the body such as the central nervous system (e.g. the brain). In a particular embodiment, the tissue or organ is separated from other tissues or organs by a barrier, such as the blood-brain barrier. Thus in one embodiment, the tissue or organ is the central nervous system. In a further embodiment, the tissue or organ is the brain. IL-2 is a key population control factor for regulatory T cells. Regulatory T cells have a naturally high turnover frequency compared to other T cells, with rapid proliferation and high apoptosis rates. IL-2 is able to increase the frequency of regulatory T cells through the induction of the anti-apoptotic protein Mcl1, which in turn reduces the Bim-dependent apoptotic rate (Pierson et al. (2013)). Increased IL-2 levels can therefore expand the size of the regulatory T cell population (Liston and Gray (2014)). IL-2 delivery has been shown to be a potent anti- inflammatory agent via the expansion of this regulatory T cell population in multiple pre-clinical studies, and optimisation of IL-2 delivery is being clinically investigated. Therefore, in the context of the brain, for the potential use of IL-2 as an anti-inflammatory mediator, the systemic delivery of IL-2 should, in theory, drive an increase in regulatory T cell numbers in the brain as this population is seeded by regulatory T cells in the circulation (see Pasciuto et al. (2020) and Fig.2 of WO2021/044175). In practice, however, systemic expansion of regulatory T cells through provision of IL-2 disproportionately increases the naïve regulatory T cell population which seeds the brain at approximately 10-fold lower levels of efficiency (see Fig.2E of WO2021/044175). Therefore, the levels of systemic IL-2 provision that create a substantial increase in anti-inflammatory potential in the periphery do not create notable increases in regulatory T cell numbers in the brain. This finding presented in WO2021/044175 and Pasciuto et al. (2020) indicates that while IL-2 has a high potential as a therapeutic for inflammation in the brain, such as neuroinflammation, systemic delivery in the physiological range required to boost brain regulatory T cell numbers is highly likely to induce systemic immunosuppression. By contrast, brain-specific expansion or increase in regulatory T cell numbers could induce the anti- inflammatory properties of regulatory T cells locally, without the detrimental effects of systemic immunosuppression. Thus according to certain embodiments described herein, there is provided a method of expanding a population of regulatory T cells in a tissue or organ of a subject in need thereof, wherein the tissue or organ is separated from other tissues or organs by a barrier, such as the blood-brain barrier. It will therefore be appreciated that the disclosures herein provide for the expansion of a population of regulatory T cells within a tissue or organ which, due to the presence of a barrier such as the blood-brain barrier, is difficult to achieve with systemic delivery of IL-2. For example, due to the presence of said barrier any dose of IL-2 sufficient to affect a population of cells present in the tissue or organ would have to be at a level high enough to give wide-spread peripheral or systemic effects. In the case of a population of regulatory T cells expanded in a tissue or organ using IL-2 as described herein, the resulting wide-spread peripheral or systemic immunosuppression would be untenable to patients due to an increased risk of infection. In one embodiment, the methods described herein, such as methods of treating and/or preventing ALS, comprise administration of IL-2. References herein to “administration” will be appreciated to refer to the providing or the making available of IL-2 at a discrete location or site of the organism, such as a particular tissue or organ (i.e. the central nervous system and/or brain). Such administration will therefore be likened with the definitions of “in a tissue or organ” as previously described herein. Thus in one embodiment, administration of IL-2 comprises administration to or in a particular tissue or organ. In particular embodiments, administration of IL-2 comprises expression of IL-2 in a particular tissue or organ (i.e. the nervous system and/or brain). In one embodiment, administration comprises expression of a gene encoding for IL-2 in a particular tissue or organ (i.e. the nervous system and/or brain). Thus in one embodiment, the method of treating and/or preventing ALS comprises tissue- or organ-specific expression of IL-2 in said tissue or organ of the subject. In a further embodiment, expression of IL-2 is not detectable outside the tissue or organ of interest, such as in the periphery. In a yet further embodiment, expression of IL-2 is expression which is restricted to the particular tissue or organ of interest. In a further embodiment, expression of IL-2 is tissue- or organ-specific expression. In certain embodiments, administration or expression of IL-2 may be in more than one related tissue or organ of interest (e.g. related tissues or organs of the central nervous system). In one embodiment, administration or expression of IL-2 is in one, two, or more tissues or organs of the central nervous system, such as in the brain and the spinal cord. Furthermore, references herein to “administration” and “expression” also refer to wherein IL-2 is provided to a population of cells in a tissue or organ. Such provision of IL-2 may, in one embodiment, comprise administration of IL-2 in protein or peptide form to or in the tissue or organ of interest, i.e. locally. In a further embodiment, the provision of IL-2 comprises the expression of IL-2 in the cells of the tissue or organ of interest. Thus in a particular embodiment, expression of IL-2 comprises the cells of the tissue or organ of interest, such as those cells which make up said tissue or organ (e.g. neurons), expressing IL-2. In some embodiments, expression of IL-2 comprises neurons, oligodendrocytes and/or astrocytes. In one embodiment, expression of IL-2 comprises astrocytes. The expression of IL-2 by/in astrocytes will be appreciated to provide several advantages: 1) astrocytes are efficient secretory cells which are widely distributed across the brain; 2) astrocytes are well represented in the spinal cord, providing the possibility of administration or expression of IL-2 in the spinal cord; 3) astrocytes demonstrate temporal and spatial numerical increases during neuroinflammatory events such as traumatic brain injury; and 4) expression of the astrocyte- specific promoter GFAP is upregulated in response to injury and disease (see Pasciuto et al. (2020) and Fig. 5B of WO2021/044175). In a further embodiment, expression of IL-2 comprises expression in cells other than the regulatory T cells which make up the expanded population of regulatory T cells. Thus in a yet further embodiment, expression of IL-2 is not in a population of regulatory T cells. In one embodiment, administration or expression of IL-2 comprises expression from the endogenous IL-2-encoding gene of cells of the tissue or organ of interest. According to this embodiment, expression of IL-2 in the cells of the tissue or organ does not comprise transfection, transduction or introduction of exogenous sequence. Thus in one embodiment, expression of IL-2 in the cells of the tissue or organ comprises tissue- or organ-specific stimulation using a compound which upregulates or “turns on” expression of the gene encoding for IL-2 only in those cells of the tissue or organ of interest. It will be appreciated that, according to this embodiment, stimulation of expression of the endogenous gene encoding IL-2 is specific and localised only to the tissue or organ of interest. In an alternative embodiment, administration or expression of IL-2 comprises introducing into the cells of the tissue or organ (i.e. the central nervous system and/or brain) exogenous sequence encoding IL-2. Thus in one embodiment, administration or expression of IL-2 comprises expression from an exogenous sequence. In a further embodiment, administration or expression of IL-2 comprises expression from a transgene. In a yet further embodiment, the transgene comprises a gene or an element encoding for IL-2. In a particular embodiment, the exogenous sequence is an IL-2 encoding sequence. In a further embodiment, the transgene comprises an IL-2 encoding sequence or gene. In one embodiment, the exogenous sequence encoding IL-2 is in the form of a transgene comprising a tissue- or organ-specific promoter. Such tissue- or organ-specific promoters are known in the art and include promoters which drive the expression of tissue- or organ-specific genes. In one embodiment, the transgene comprises a tissue- or organ-specific promoter which specifically drives expression in the tissue or organ of interest. In a further embodiment, the transgene comprises a tissue- or organ-specific promoter which does not lead to expression in a tissue or organ other than the tissue or organ of interest. Thus in one embodiment, the transgene comprises a promoter which drives expression specifically in neurons. In a further embodiment, the transgene comprises a promoter which drives expression specifically in cells of the central nervous system. In a yet further embodiment, the transgene comprises a promoter which drives expression in the central nervous system but not in the peripheral nervous system. In one embodiment, the transgene comprises a promoter which drives expression specifically in the brain. In a particular embodiment, the transgene comprises a promoter which drives expression specifically in astrocytes. In a further embodiment, the transgene comprises a GFAP promoter. In a yet further embodiment, the transgene comprises a minimal GFAP promoter. In alternative embodiments, the transgene comprises a PLP or CaMKIIa promoter. In a further embodiment, administration or expression of IL-2 comprises a transgene which comprises an element which promotes or induces the expression of IL-2 in the presence of an exogenous compound. Such elements which promote or induce expression are known in the art and include, for example, tetracycline (Tet)-inducible systems. Tet-inducible systems provide reversible control of transcription and utilise a tetracycline-controlled transactivator (tTA) which binds tetracycline operator (TetO) sequences contained in a tetracycline response element (TRE) placed upstream of the gene/coding region of interest (and its promoter, such as a tissue-specific promoter). They may either be TetOff or TetOn systems. The TetOff system of inducible expression (also known as the tTA-dependent system) uses a tTA protein created by fusing the tetracycline repressor (TetR), found in Escherichia coli bacteria, with the activation domain of another protein, VP16, found in the Herpes Simplex Virus. The resulting tTA is able to bind TetO sequences within the TRE in the absence of tetracycline and promote expression of the downstream gene/coding region. In the presence of tetracycline, tTA binding to the TetO sequences is prevented, resulting in reduced gene expression. Conversely, the TetOn system (also known as the rtTA-dependent system) uses a reverse Tet repressor (rTetR) to create a reverse tetracycline-controlled transactivator (rtTA) protein which relies on the presence of tetracycline to promote expression. Therefore, rtTA only binds to TetO sequences within the TRE and promotes expression in the presence of tetracycline. Specific examples of TetOn systems include, but are not limited to, TetOn Advanced, TetOn 3G and the T-REx system from Life Technologies. Derivatives and analogues of tetracycline may be used with either the TetOff or TetOn systems and include, without limitation, doxycycline and minocycline (e.g. minomycin). Such derivatives/analogues will be appreciated to provide significant advantages compared to tetracycline such as increased stability in the case of doxycycline and/or the ability to cross the blood-brain barrier in the case of minocycline (Chtarto et al. 2003, doi: https://doi.org/10.1016/j.neulet.2003.08.067). Thus in certain embodiments, the exogenous sequence encoding IL-2, such as the transgene comprising a tissue- or organ-specific promoter, further comprises a tetracycline response element (TRE). As such, in one embodiment administration or expression of IL-2 is tetracycline-dependent or tetracycline-inducible. In a further embodiment, administration or expression of IL-2 comprises introducing into the cells of the tissue or organ exogenous sequence encoding a reverse tetracycline-controlled transactivator (rtTA). In one embodiment, the exogenous sequence encoding an rtTA comprises a tissue- or organ-specific promoter, i.e. expression of the rtTA-encoding sequence is under the control of a tissue- or organ-specific promoter as disclosed herein. Thus in a further embodiment, the exogenous sequence encoding an rtTA comprises a promoter specific for the nervous system, such as the central nervous system (e.g. the brain). In a yet further embodiment, expression of the rtTA-encoding sequence is under the control of a promoter specific for the nervous system, such as the central nervous system (e.g. the brain). In a particular embodiment, the exogenous sequence encoding an rtTA comprises a promoter which drives expression specifically in astrocytes, such as a GFAP promoter or a minimal GFAP promoter. Such an rtTA-encoding exogenous sequence may be a separate sequence to the exogenous sequence encoding IL-2, e.g. it may be separate from the IL-2 transgene comprising a tissue- or organ-specific promoter. Alternatively, such an rtTA-encoding exogenous sequence may be comprised together with the IL-2-encoding sequence, e.g. it may be comprised in the same transgene. Thus in some embodiments, administration or expression of IL-2 comprises a TetOn system. It will therefore be appreciated that in one embodiment, administration or expression of IL-2 comprises the administration of tetracycline or a derivative/analogue of tetracycline, such as doxycycline or minocycline. In a particular embodiment, administration or expression of IL-2 comprises administration of minocycline, such as administration of minomycin. The use of tetracycline-dependent or tetracycline-inducible administration or expression of IL-2 provides another level of control and allows the administration or expression of IL-2 to be ‘switched’ on or off. Such switching will be appreciated to be advantageous in the methods described herein by allowing the expansion of a population of regulatory T cells in a tissue or organ to be temporally controlled. For example, expression of IL-2 may be switched ‘on’ by administering tetracycline or a derivative/analogue thereof when inflammation of the central nervous system, such as neuroinflammation and/or inflammation of the brain, is detected/diagnosed. Expression of IL-2 may then be switched ‘off’ by removal of tetracycline or a derivative/analogue thereof when inflammation, such as neuroinflammation, is no longer detected or has reduced. Said use of tetracycline-dependent or tetracycline-inducible administration or expression of IL-2 further provides dose-dependent IL-2 administration of expression. For example, the level and/or amount of IL-2 administration or expression may be altered and/or titrated in the tissue or organ to depend on the level and/or amount of inflammation, such as neuroinflammation, in the tissue or organ. Therefore, expression of IL-2 may be switched ‘on’ by administering a particular dose of tetracycline or a derivative/analogue thereof when inflammation of the central nervous system, such as neuroinflammation and/or inflammation of the brain, is detected/diagnosed and said dose may be increased if the inflammation persists. Similarly, said dose may be decreased if the inflammation decreases following initial administration of tetracycline or a derivative/analogue thereof. In another example, the level and/or amount of IL-2 administration or expression may be altered and/or titrated in the tissue or organ to depend on the severity of motor neuron loss, denervation of muscle fibres, muscle weakness and/or paralysis in a subject diagnosed with ALS (such as the subject in need of treatment as described herein). According to this example, expression of IL-2 may be switched ‘on’ by administering a particular dose of tetracycline or a derivative/analogue thereof when motor neuron loss, denervation of muscle fibres, muscle weakness and/or paralysis is detected or when ALS is diagnosed and said dose may be increased if the motor neuron loss, denervation of muscle fibres, muscle weakness and/or paralysis persists. Similarly, said dose may be decreased if the motor neuron loss, denervation of muscle fibres, muscle weakness and/or paralysis decreases following initial administration of tetracycline or a derivative/analogue thereof. In one embodiment, the transgene as defined herein is introduced into the cells of the tissue or organ of interest by transduction, such as transduction using a virus or viral vector. In a particular embodiment, the transduction uses an adeno-associated virus. Thus in one embodiment, administration of IL-2 comprises transduction, such as viral transduction. In a further embodiment, administration of IL-2 comprises adeno-associated virus transduction. In one embodiment, transduction of the transgene as defined herein utilises a viral vector which specifically targets or infects the cells of the tissue or organ of interest. Thus in one embodiment, transduction of the transgene as defined herein specifically targets or infects the cells of the tissue or organ of interest. According to this embodiment, it will be appreciated that transduction using a viral vector of the transgene as defined herein does not target or infect a population of regulatory T cells. In a further embodiment, transduction of the transgene as defined herein comprises a viral vector which is capable of accessing the tissue or organ of interest and is capable of crossing a barrier which separates the tissue or organ of interest from other tissues, organs or the rest of the organism. Thus in one embodiment, transduction comprises a viral vector capable of specifically targeting or infecting the nervous system. In a further embodiment, transduction comprises a viral vector capable of targeting or infecting the central nervous system. In a yet further embodiment, transduction comprises a viral vector capable of targeting or infecting the brain. In a particular embodiment, transduction comprises a viral vector capable of crossing the blood-brain barrier. In one embodiment, transduction comprises a blood-brain barrier- crossing adeno-associated virus. Thus in one embodiment, transduction comprises a neurotropic virus or viral vector. In another embodiment, the viral vector is a neurotropic virus or viral vector. Examples of neurotropic viruses and viral vectors capable of crossing the blood-brain barrier include, but are not limited to, AAVrh.8, AAVrh10 and AAV9 as well as its variants and derivatives (e.g. AAVhu68 and PHP.B). In certain embodiments, the transgene as defined herein is comprised in a viral vector, such as a neurotropic virus or viral vector and/or an adeno-associated virus vector. In a further embodiment, transduction comprises the adeno-associated virus variant AAV9 and its derivatives, such as PHP.B. In a yet further embodiment, transduction comprises a PHP.B viral vector. In another embodiment, the transgene as defined herein is comprised in a PHP.B viral vector. Thus in one embodiment, the transduction and/or the viral vector comprises PHP.B-GFAP-IL2, which is the PHP.B derivative of AAV9 comprising a transgene which contains an IL-2 encoding sequence and the astrocyte-specific promoter, GFAP. Viral vectors may be used to integrate the target sequence, such as a transgene, into the host cell genome, such as the genome of a cell of the tissue or organ of interest. Thus in certain embodiments, transduction comprises integration of the transgene as defined herein into the genome of a cell of the tissue or organ of interest such that long-term expression of the transgene in the tissue or organ is achieved. Viral vectors, such as neurotropic viruses or viral vectors and adeno-associated viral vectors, may also be used to enable stable or long-term expression without integration of the target sequence into the host cell genome. Thus in one embodiment, the transgene and/or target sequence are stably maintained outside the host cell genome. References herein to a “virus” and/or “viral vector” include a virus which is non-lytic or lysogenic. Such viruses will be appreciated to achieve infection of a cell, such as a cell of the tissue or organ of interest, or introduction of a transgene into a cell without death or destruction of said cell. It will be appreciated from the disclosures presented herein that combination of a virus or viral vector which specifically targets or infects cells of the tissue- or organ of interest (e.g. a neurotropic virus or viral vector) and a promoter which drives expression specifically in cells of the tissue or organ of interest, provides exceptional specificity. Such specificity provides a so-called ‘dual lock’, restricting both the cells into which the transgene is targeted or infected and in which cells the transgene is expressed. Thus in one embodiment, the combination of a tissue- or organ-specific viral vector and tissue- or organ-specific promoter as defined herein provides that only those cells of the tissue or organ of interest comprise the transgene as defined herein and only those cells of the tissue or organ of interest are capable of expressing said transgene. In a further embodiment, the combination of a tissue- or organ-specific viral vector and tissue- or organ-specific promoter as defined herein provides that only those cells of the tissue or organ of interest comprise an IL-2-encoding gene and only those cells of the tissue or organ of interest are capable of expressing said gene. In a yet further embodiment, the combination of a tissue- or organ-specific viral vector and tissue- or organ-specific promoter as defined herein together with an inducible element, such as a tetracycline-inducible element, provides that only those cells of the tissue or organ of interest comprise the transgene as defined herein and only those cells of the tissue or organ of interest are capable of expressing said transgene when an activator of the inducible element is administered (e.g. tetracycline, doxycycline or minocycline/minomycin). In one embodiment, the combination of a tissue- or organ-specific viral vector and tissue- or organ- specific promoter as defined herein together with an inducible element, such as a tetracycline- inducible element, provides that only those cells of the tissue or organ of interest comprise an IL-2-encoding gene and only those cells of the tissue or organ of interest are capable of expressing said gene when an activator of the inducible element is administered (e.g. tetracycline, doxycycline or minocycline/minomycin). In a further embodiment, said combination provides that only those cells of the tissue or organ of interest comprise an inducible IL-2-encoding gene and only those cells of the tissue or organ of interest are capable of expressing a reverse tetracycline-controlled transactivator (rtTA) which leads to the expression of IL-2 when an activator of the inducible element is administered (e.g. tetracycline, doxycycline or minocycline/minomycin). Administration of IL-2 as defined herein may further comprise administration of IL-2 directly to the tissue or organ of interest. Examples of direct administration include injection directly into the tissue or organ of interest, such as by intracranial injection, or utilise a suitable delivery device. Such delivery devices are known in the art and, according to the present disclosures, allow for the controlled and/or sustained administration of IL-2 for the duration of treatment (e.g. chronically or for duration of treatment of an acute inflammatory disease or disorder). The duration of IL-2 administration as defined herein can be altered to depend on the treatment and the characteristics of the ALS to be treated and/or prevented by the pharmaceutical compositions and methods described herein. For example, administration of IL-2 may be chronic. Alternatively, administration of IL-2 may be for the duration of treatment for the ALS. Thus in certain embodiments, the duration of administration or expression of IL-2 depends on the ALS to be treated or on the duration of the treatment. In one embodiment, administration or expression of IL-2 is acute. In an alternative embodiment, administration or expression of IL-2 is chronic. It will be appreciated that IL-2 and a targeting moiety specific for a tissue or organ may be combined or co-administered. Therefore, the administration of IL-2 may comprise expression of IL-2 in the tissue or organ of interest as defined herein (e.g. tissue- or organ-specific expression) and can be combined with a targeting moiety specific for the tissue or organ of the subject. Furthermore, administration of IL-2 may comprise administration of IL-2 in protein or peptide form and can be combined with a targeting moiety specific for the tissue or organ of the subject. References herein to the term “targeting moiety” refer to any moiety that provides for the tissue- or organ-specific administration or expression of IL-2 as defined herein. Furthermore, said targeting moiety will be appreciated to provide for the localised administration or expression of IL-2 as defined herein. Thus in one embodiment of the present invention, the methods defined herein, such as methods of treating and/or preventing ALS, comprise administration of a targeting moiety specific for the tissue or organ of the subject, wherein said tissue or organ is the central nervous system. In a further embodiment, the targeting moiety specific for the tissue or organ of the subject localises IL-2 in or to the tissue or organ of interest (i.e. the central nervous system). Thus in one embodiment, the targeting moiety specific for the tissue or organ of the subject localises IL-2 only in or to the tissue or organ of interest. In a further embodiment, the targeting moiety specific for the tissue or organ of the subject prevents localisation of IL-2 to other tissues or organs other than the tissue or organ of interest, or localises IL-2 away from tissues or organs other than the tissue or organ of interest. In another embodiment, the targeting moiety provides for expression of IL-2 in the tissue or organ of interest. Thus in one embodiment, the targeting moiety specific for the tissue or organ of the subject provides for expression of IL-2 only in the tissue or organ of interest. Such references herein to “in the tissue or organ of interest” further include wherein said effect is in the cells which make up said tissue or organ (e.g. neurons and/or astrocytes). In one embodiment, the targeting moiety specific for the tissue or organ of the subject is a virus or viral vector as defined herein. In a further embodiment, said virus or viral vector specifically targets or infects the tissue or organ of interest or specifically targets or infects cells of the tissue or organ of interest (i.e. the central nervous system). Thus according to this embodiment, said targeting moiety specific for the tissue or organ of interest which is a virus or viral vector does not target or infect cells in other tissues or organs other than the tissue or organ of interest, or target or infect cells which make up a tissue or organ other than the tissue or organ of interest. Also according to this embodiment, it will be appreciated that said targeting moiety specific for the tissue or organ as defined herein does not target or infect a population of regulatory T cells. In a further embodiment, the targeting moiety specific for the tissue or organ of a subject as defined herein comprises a virus or viral vector which is capable of accessing the tissue or organ of interest and is capable of crossing a barrier which separates the tissue or organ of interest from other tissues, organs or the rest of the subject. Thus in one embodiment, the targeting moiety specific for a tissue or organ comprises a virus or viral vector capable of specifically targeting or infecting the nervous system, such as a neurotropic virus or viral vector. In a further embodiment, the targeting moiety specific for a tissue or organ comprises a virus or viral vector capable of targeting or infecting the central nervous system. In a yet further embodiment, the targeting moiety specific for a tissue or organ comprises a virus or viral vector capable of targeting or infecting the brain. In a particular embodiment, the targeting moiety specific for a tissue or organ comprises a virus or viral vector capable of crossing the blood-brain barrier. In one embodiment, the targeting moiety specific for a tissue or organ comprises a blood-brain barrier-crossing adeno- associated virus. Thus in certain embodiments, the targeting moiety specific for a tissue or organ comprises a neurotropic virus or viral vector. In one embodiment, the targeting moiety is selected from a neurotropic virus or viral vector, such as AAVrh.8, AAVrh10 or AAV9 and variants and derivatives (e.g. AAVhu68 and PHP.B). In a further embodiment, the targeting moiety specific for a tissue or organ comprises the adeno-associated virus variant PHP.B. In certain embodiments, the transgene as defined herein is comprised in a targeting moiety specific for a tissue or organ, such as an adeno-associated virus vector, which is comprised within an adeno-associated virus as defined herein. In one embodiment, the transgene as defined herein is comprised in a neurotropic virus or viral vector, such as a PHP.B viral vector. Thus in a further embodiment, the transgene which contains an IL-2 encoding sequence and the astrocyte-specific promoter, GFAP or minimal GFAP, is comprised in the AAV9 derivative PHP.B virus/viral vector and the virus/viral vector is PHP.B-GFAP-IL2. According to a further aspect, there is provided a method for the expansion of a population of regulatory T cells in a tissue or organ in vivo for treating and/or preventing ALS, wherein said tissue or organ is the central nervous system, such as the brain. In another aspect, there is provided a pharmaceutical composition for use in a method of expanding a population of regulatory T cells in a tissue or organ in vivo for treating and/or preventing ALS, wherein said tissue or organ is the central nervous system, such as the brain. Embodiments of the present aspects will be appreciated to be equivalent and comparable to all embodiments previously described herein. Thus in certain embodiments, the term “of a subject” as described herein is synonymous with “in vivo”. In one embodiment, the method for expanding a population of regulatory T cells in a tissue or organ in vivo comprises administration of IL-2 as described herein. In a further embodiment, the method for expanding a population of regulatory T cells in a tissue or organ in vivo comprises administration of a targeting moiety specific for the tissue or organ of a subject in vivo. In a yet further embodiment, the method for expanding a population of regulatory T cells in a tissue or organ in vivo comprises administration of a pharmaceutical composition as described herein. In one embodiment, the administration of IL-2, which may comprise expression of IL-2, is combined with a targeting moiety specific for a tissue or organ in vivo. In a further embodiment, the method for expanding a population of regulatory T cells in a tissue or organ in vivo comprises a virus or viral vector which comprises an IL-2-encoding gene. In one embodiment, said virus or viral vector is capable of targeting or infecting a tissue or organ of interest (i.e. the central nervous system). In a particular embodiment, said virus or viral vector capable of targeting or infecting a tissue or organ of interest, specifically targets or infects cells of a tissue or organ of interest. In a further embodiment, the method for expanding a population of regulatory T cells in a tissue or organ in vivo comprises a virus or viral vector which comprises a tissue- or organ-specific promoter. Thus in a particular embodiment, the method for expanding a population of regulatory T cells in a tissue or organ in vivo comprises administration of a targeting moiety specific for the tissue or organ of interest, wherein said targeting moiety is a virus or viral vector which crosses the blood-brain barrier as defined herein. In a further embodiment, the method for expanding a population of regulatory T cells in a tissue or organ in vivo comprises administration of a targeting moiety specific for the tissue or organ of interest, wherein said targeting moiety is specific for the central nervous system, such as the brain. In a yet further embodiment, the targeting moiety specific for a tissue or organ of interest is specific for astrocytes. In another embodiment, the method for expanding a population of regulatory T cells in a tissue or organ in vivo comprises administration of a neurotropic virus or viral vector containing the transgene as defined herein, such as administration of PHP.B-GFAP-IL2. According to another aspect, there is provided a population of regulatory T cells expanded according to or obtained by the methods or the pharmaceutical composition (e.g. by administration of said pharmaceutical composition) as described herein. Thus in one embodiment, there is provided an expanded population of regulatory T cells which have been expanded in a tissue or organ of a subject by administration of IL-2 and a targeting moiety specific for said tissue or organ for use in the treatment and/or prevention of ALS, wherein said tissue or organ is the central nervous system (e.g. the brain). In a further embodiment, the methods of treating and/or preventing ALS as described herein comprise the expanded population of regulatory T cells in the central nervous system (e.g. in the brain) as described herein. Pharmaceutical Compositions According to a particular aspect of the invention, there is provided a pharmaceutical composition comprising IL-2 and a targeting moiety specific for a tissue or organ of a subject, wherein said tissue or organ is the central nervous system. In one embodiment, the pharmaceutical composition comprises IL-2 which promotes the expansion of a population of regulatory T cells. In a yet further embodiment, the pharmaceutical composition comprises a targeting moiety specific for a tissue or organ of a subject (i.e. the central nervous system, such as the brain). In one embodiment, the targeting moiety specific for a tissue or organ of a subject is a virus or viral vector which specifically targets or infects cells of the tissue or organ and drives tissue- or organ-specific expression of IL-2 as described herein. Thus according to this aspect of the invention, there is provided a pharmaceutical composition comprising a tissue- or organ-specific viral vector which expands a population of regulatory T cells in said tissue or organ of the subject (i.e. the central nervous system). In particular embodiments, the pharmaceutical composition expands a population of regulatory T cells specifically or locally in a tissue or organ of interest in a subject. In one embodiment, the pharmaceutical composition as defined herein comprises a targeting moiety capable of crossing a barrier which separates a tissue or organ of interest from other tissues or organs or from the rest of the organism. Thus in one embodiment, the pharmaceutical composition as defined herein comprises a blood-brain barrier crossing virus or viral vector, such as an adeno-associated virus and/or a neurotropic virus or viral vector. In a further embodiment, the pharmaceutical composition as defined herein comprises the adeno-associated virus variant AAV9 or its derivatives, such as PHP.B. In a further embodiment, the viral vector comprised in the pharmaceutical composition as defined herein comprises a gene, such as a transgene, which encodes for IL-2. In a yet further embodiment, the transgene comprised in the viral vector of the pharmaceutical composition further comprises a tissue- or organ-specific promoter as defined herein. Thus in certain embodiments, the pharmaceutical composition as defined herein comprises a tissue- or organ-specific virus or viral vector capable of targeting or infecting cells of the tissue or organ of interest (i.e. the central nervous system), comprising an IL-2-encoding gene, expression of which is driven by a tissue- or organ-specific promoter. In one particular embodiment, the pharmaceutical composition as defined herein comprises a viral vector, such as an adeno-associated virus (e.g. AAV9 or its derivatives, such as PHP.B), which specifically targets or infects neurons or the nervous system, such as the brain, (i.e. a neurotropic virus or viral vector) which comprises an IL-2-encoding gene, expression of which is driven by a tissue- or organ-specific promoter. In a further embodiment, the pharmaceutical composition as defined herein comprises the adeno-associated virus AAV9, which comprises an IL-2- encoding gene, expression of which is driven locally in a neuron/astrocyte or in the nervous system by a GFAP promoter or a minimal GFAP promoter. In a yet further embodiment, the adeno-associated virus is a derivative of AAV9, such as PHP.B. Thus in one embodiment, the pharmaceutical composition comprises PHP.B-GFAP-IL2. According to some embodiments, the pharmaceutical composition, in addition to a tissue- or organ-specific virus or viral vector as defined herein, further comprises one or more pharmaceutically acceptable excipients. Generally, the present pharmaceutical compositions will be utilised with pharmacologically appropriate excipients or carriers. Typically, these excipients or carriers include aqueous or alcoholic/aqueous solutions, emulsions or suspensions, including saline and/or buffered media. Parenteral vehicles include sodium chloride solution, Ringer's dextrose, dextrose and sodium chloride and lactated Ringer's. Suitable physiologically-acceptable adjuvants, if necessary to keep a composition comprising the targeting moiety specific for a tissue or organ as defined herein in a discrete location (e.g. within a tissue or organ of interest), may be chosen from thickeners such as carboxymethylcellulose, polyvinylpyrrolidone, gelatine and alginates. Intravenous vehicles include fluid and nutrient replenishers and electrolyte replenishers, such as those based on Ringer's dextrose. Preservatives and other additives, such as antimicrobials, antioxidants, chelating agents and inert gases, may also be present (Mack (1982) Remington's Pharmaceutical Sciences, 16^th Edition). Therapeutic Uses and Methods It will be appreciated from the disclosures presented herein that the method of expanding a population of regulatory T cells, pharmaceutical compositions and methods of treatment described herein will find particular utility in the treatment and/or amelioration of diseases or disorders mediated by inflammation and/or in the reduction of inflammation. It will be further appreciated that a population of regulatory T cells expanded according to the methods and disclosures presented herein will also find utility in the treatment and/or amelioration of diseases or disorders mediated by inflammation and/or in the reduction of inflammation. However, as demonstrated by the results presented herein, the methods and pharmaceutical compositions described herein surprisingly also find utility in treating and/or preventing ALS, i.e. the methods and pharmaceutical compositions described herein surprisingly also find utility in treating and/or preventing a neurodegenerative disease/disorder considered to be non-inflammatory. Thus according to one aspect of the invention, there is provided a method for expanding a population of regulatory T cells in a tissue or organ of a subject for use in the treatment and/or prevention of ALS, wherein said tissue or organ is the central nervous system. In some embodiments, the ALS is associated with and/or related to neurological ageing. According to a further aspect of the invention, there is provided the pharmaceutical composition as defined herein for use in the treatment of ALS, wherein said tissue or organ is the central nervous system. In another aspect of the invention, there is provided a method of treating and/or preventing ALS, said method comprising administering to a subject in need thereof the pharmaceutical composition as defined herein. In some embodiments, the ALS is related to neurological ageing. Thus in further embodiments, there is provided a method of treating ALS related to neurological ageing, wherein said tissue or organ is the central nervous system. In a further aspect, there is provided a population of expanded regulatory T cells in a tissue or organ of a subject produced according to the methods defined herein or by administration of the pharmaceutical composition defined herein for use in the treatment and/or prevention of ALS, wherein said tissue or organ is the central nervous system. In one embodiment, the expanded population of regulatory T cells in a tissue or organ of a subject produced according to the methods defined herein has been expanded by administration of IL-2 and a targeting moiety specific for said tissue or organ. In a further embodiment, the population of expanded regulatory T cells in a tissue or organ of a subject produced according to the methods defined herein has been expanded by tissue- or organ-specific expression of IL-2 as defined herein. In another embodiment, the population of expanded regulatory T cells in a tissue or organ of a subject has been expanded by tissue- or organ-specific expression of IL-2 promoted or induced by an inducible element, such as a tetracycline-inducible element. In a further embodiment, the population of expanded regulatory T cells has been expanded by administration of the pharmaceutical composition as defined herein. In one embodiment, the methods defined herein, such as methods of treating and/or preventing ALS, comprise administering a virus or viral vector comprising a gene encoding IL-2 as defined herein to a subject in need thereof. In one embodiment, the methods defined herein comprise administering to a subject in need thereof a virus or viral vector which specifically targets or infects a tissue or organ affected by ALS (i.e. the central nervous system). In certain embodiments, the methods defined herein further comprise administering to a subject in need thereof a virus or viral vector comprising a gene encoding IL-2, expression of which is driven by a tissue- or organ-specific promoter. In a further embodiment, the methods defined herein comprises administering to a subject in need thereof a virus or viral vector comprising a gene encoding IL-2, expression of which is driven by a tissue- or organ- specific promoter and an inducible element, such as a tetracycline-inducible element. In an alternative embodiment, the methods comprise administering to a subject a virus or viral vector comprising a gene encoding IL-2, expression of which is driven by an inducible element, such as a tetracycline-inducible element, under the control of a tissue- or organ-specific promoter. In further embodiments, the methods defined herein comprise administering to a subject in need thereof a neurotropic virus comprising a gene encoding IL-2, expression of which is driven by a tissue- or organ-specific promoter, such as administering PHP.B-GFAP-IL2. In certain embodiments, said subject in need thereof is an aged individual. Thus in further embodiments, the subject in need thereof is suffering from ALS related to neurological ageing. In still further embodiments, the ALS is considered to be inflammatory. In a further embodiment, the ALS comprises loss of motor neurons, denervation of muscle fibres, muscle weakness and/or paralysis. Therefore in a further aspect of the invention, there is provided a method of treating, preventing and/or reducing the loss of motor neurons, denervation of muscle fibres, muscle weakness and/or paralysis in a subject in need thereof, said method comprising administering to the subject the pharmaceutical composition defined herein. In some embodiments, the method of treating, preventing and/or reducing the loss of motor neurons, denervation of muscle fibres, muscle weakness and/or paralysis comprises the methods of expanding a population of regulatory T cells in the central nervous system of a subject as defined herein. Thus in one embodiment, the method of treating, preventing and/or reducing the loss of motor neurons, denervation of muscle fibres, muscle weakness and/or paralysis comprises administering IL-2, such as tissue- or organ-specific expression of IL-2 in the central nervous system as described herein. In certain embodiments, the subject in need thereof is suffering from ALS. Thus in further embodiments, the method of treating, preventing and/or reducing the loss of motor neurons, denervation of muscle fibres, muscle weakness and/or paralysis comprises treating and/or preventing ALS. It will be understood that all embodiments described herein may be applied to all aspects of the invention. Other features and advantages of the present invention will be apparent from the description provided herein. It should be understood, however, that the description and the specific examples while indicating preferred embodiments of the invention are given by way of illustration only, since various changes and modifications will become apparent to those skilled in the art. The invention will now be described using the following, non-limiting examples: EXAMPLES Example 1: Materials and Methods Mice High-copy number SOD1^G93A mice on a C57BL/6 background were obtained from The Jackson Laboratory (JAX; Bar Harbor, USA). All mice were housed in standard conditions in the conventional housing facility of the University of Leuven with food and water ad libitum. SOD1^G93A mice were monitored longitudinally following AAV treatment at age 80 days. End stage was determined when mice were unable to rear themselves within 30 seconds when placed on their back. At end stage mice were humanely euthanized by the guidelines in place by the local animal science committee. Mice were assessed in comparison to their littermate controls. Experiments performed at the University of Leuven were performed according to the guidelines of the University of Leuven and have received ethical committee approval. All animal experiments met the standards required by the Belgian Council for Laboratory Animal Science (BCLAS) guidelines and the EU Directive 2010/63/EU for animal experiments. AAV Design, Production and Treatment AAV-PHP.B production was performed by VectorBuilder (Neu-Isenburg, Germany) with subsequent vector titration performed using qPCR-based (Fripont et al. (2019), J Vis Exp 143:e58960, doi: https://dx.doi.org/10.3791/58960 and Rincon et al. (2018) Gene Ther, 25(2): 83-92, doi: https://doi.org/10.1038/s41434-018-0005-z). AAV-PHP.B.GFAP-IL2 and control AAV-PHP.B.GFAP-GFP were cloned as described previously (Pasciuto et al. (2020), doi: https://doi.org/10.1016/j.cell.2020.06.026). AAV was delivered intravenously at a single dose of 10¹⁰ vg. Statistics Survival was determined by age at end stage and was plotted by a Kaplan-Meir curve with Log Rank testing with statistical significance set at p<0.05. Example 2: Gene Delivery of IL-2 Delays End Point Disease Progression in a Mouse Model of ALS To test the potential of IL-2 gene delivery to mitigate disease progression in ALS, the gold standard ALS mouse, SOD1^G93A high-copy mice were used (Gurney, et al. (1994) Science, 264:1772–1775, doi: https://doi.org/10.1126/science.8209258). An IL-2 gene delivery AAV- based vector was used, based on the PHP.B serotype and the GFAP promoter (Figure 1A), which, in combination, result in astrocyte-specific cargo production (Pasciuto et al. (2020)). SOD1^G93A transgenic mice were injected with PHP.B.GFAP-IL2 or the control PHP.B.GFAP- GFP, at age 80 days by intravenous injection (Figure 1B). Daily monitoring of the mice indicated that they tolerated the treatment well, and no animals were lost before the onset of disease symptoms at P80. ALS progression was measured through motor capacity upon challenge, with end-point ALS reached based on inability to right themselves. Treatment of SOD1^G93A mice with PHP.B.GFAP-IL2 lead to a moderate yet statistically significant delay of ALS end point by 7 days, compared to mice treated with the control PHP.B.GFAP-GFP (Figures 2A and 2B). These results indicate that directed gene delivery of IL-2 expression is well tolerated, neuroprotective, and can delay terminal neurodegeneration even in an aggressive ALS mouse model such as the SOD1^G93A mouse.

Claims

CLAIMS 1. A pharmaceutical composition comprising IL-2 and a targeting moiety specific for a tissue or organ of a subject for use in a method of treating and/or preventing amyotrophic lateral sclerosis (ALS), wherein said tissue or organ is the central nervous system.

2. The pharmaceutical composition for use of claim 1, wherein the tissue or organ is the brain.

3. The pharmaceutical composition for use of claim 1 or claim 2, wherein the method of treating and/or preventing ALS comprises administration of IL-2, such as tissue- or organ- specific expression of IL-2 in said tissue or organ of the subject.

4. The pharmaceutical composition for use of claim 3, wherein tissue- or organ-specific expression of IL-2 is driven by a tissue- or organ-specific promoter.

5. The pharmaceutical composition for use of claim 4, wherein the tissue- or organ- specific promoter is a brain-specific promoter, such as the GFAP, PLP or CaMKIIa promoter.

6. The pharmaceutical composition for use of any one of claims 3 to 5, wherein administration of IL-2 or tissue- or organ-specific expression of IL-2 in said tissue or organ comprises an exogenous IL-2 encoding sequence.

7. The pharmaceutical composition for use of any one of claims 1 to 6, wherein the targeting moiety specific for the tissue or organ comprises a viral vector.

8. The pharmaceutical composition for use of claim 7, wherein the viral vector is an adeno-associated virus which specifically targets or infects the tissue or organ.

9. The pharmaceutical composition for use of any one of claims 1 to 8, wherein the targeting moiety specific for the tissue or organ or the viral vector crosses a barrier which separates the tissue or organ from other tissues or organs of the subject, such as the blood- brain barrier.

10. The pharmaceutical composition for use of any one of claims 7 to 9, wherein the viral vector is a neurotropic virus or viral vector.

11. The pharmaceutical composition for use of claim 10, wherein the neurotropic virus or viral vector is an adeno-associated virus selected from AAVrh.8, AAVrh10 or AAV9 and variants and derivatives thereof, such as AAVhu68 and PHP.B.

12. The pharmaceutical composition for use of claim 11, wherein the neurotropic virus or viral vector is the adeno-associated virus variant PHP.B.

13. A method of expanding a population of regulatory T cells in a tissue or organ of a subject in need thereof for treating and/or preventing ALS, said method comprising administering to the subject the pharmaceutical composition of any one of claims 1 to 12, wherein said tissue or organ is the central nervous system.

14. A method of treating and/or preventing ALS in a subject in need thereof, said method comprising administering to the subject the pharmaceutical composition of any one of claims 1 to 12.