Alternative Transgene Expression for rAAV Vector Based

Potential treatments for T1D involve the dampening of the autoreactive Teff population and/or expansion of the FoxP3+ Treg pool to re-establish self tolerance. IL-2, which preferentially accomplishes the latter goal, is one of many molecules that has shown efficacy for the treatment of T1D (2, 7, 17, 18). While each molecule offers unique pros and cons in relation to others, a “magic bullet” has yet to be discovered. Therefore, the exploration for alternative approaches is continually warranted.

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Interleukin-35 (IL-35) is a recently identified cytokine composed of Epstein-Barr- virus-induced gene 3 and the interleukin-12 α chain that is secreted by FoxP3+ Treg, but not CD4+ Teff (19, 20). The secretion of IL-35 from FoxP3+ Treg is shown to inhibit Teff cell proliferation in vitro (19, 21). Furthermore, IL-35, in combination with IL-10, is capable of inducing an “iTR35” population, which is characterized by a lack of FoxP3 expression, but constitutive expression of IL-35 (22). This iTR35 cell type is thought to contribute to immune regulation and has been shown to be a stable lineage both in vitro and in vivo (22). IL-35 is beneficial for the treatment of various autoimmune diseases, including IBD and arthritis (19, 23). In addition, a recent study that linked ecoptic expression of IL-35 to β cells through coupling to the rat insulin promoter II showed substantial long term protection from T1D in NOD mice (24). This protection was defined by reduced Teff infiltration and proliferation into the islets, particularly by autoreactive IGRP-specific CD8+ T cells. Interestingly, however, proliferation of FoxP3+ Treg was also reduced in the islets of IL-35 expressing animals, as determined by BrdU incorporation (24).

An AAV8mIP vector encoding IL-35 (AAV8mIP-IL35) would offer an alternative approach to IL-2 mediated treatment, since IL-35 preferentially dampens the Teff population, while IL-2 promotes FoxP3+ Treg. Therefore, the efficacy of AAV8mIP-IL35 treatment in NOD mice for the prevention of T1D could address the feasibility of directly altering islet Teff. In addition, coupling AAV8mIP-IL35 vaccination, with either AAV8mIP- IL2 or AAV8mIP-IL10 treatment may also produce novel results by directly influencing both sides of the autoreactive immune response. For IL-2, the potential dampening of

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the islet FoxP3+ Treg pool by IL-35 could be offset by localized IL-2 expression.

Alternatively, co-administration of IL-10 is particularly noteworthy given that IL-35 and IL-10 collectively induce iTR35 (22). Importantly, the ability of different rAAV vectors to transduce and efficiently secrete different transgenes, especially within the restricted β cell mass found in recent onset diabetics, would have to be investigated prior.

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