Background: Despite tremendous clinical success of adeno-associated virus (AAV) vectors for in vivo gene therapy, immunological barriers remain a major challenge that limits their security and efficacy. The viral vector, and sometimes the transgene, are foreign antigens against which the patient presents little or no tolerance at all, thus, leading to the rejection of the transduced cells. Our team has developed a new strategy to overcome the immune activation induced by AAV vectors. We have shown that the co-transduction of the liver, a known tolerogenic organ, in parallel to that of the muscle, induces a robust immune tolerance that prevents the clearance of transduced muscle cells. Foxp3⁺ regulatory T cell (Treg)-mediated tolerance has been implicated after liver gene transfer. However, little is known about the fate of the transgene specific CD4⁺ T cells in this context.
Methods: Here, we used a hepatotropic AAV₈ vector encoding the single CD4⁺ T cell epitope DBY₆₀₈ . To follow the response after AAV-mediated gene transfer into the liver, we made use of either DBY₆₀₈-specific tetramer or an adoptive transfer model of physiological numbers of DBY₆₀₈-specific transgenic CD4⁺T cells (DBY-Tconv).
Results: Transgene-specific T cells were activated in the liver and liver draining lymph nodes 24h following AAV intravenous administration and showed thereafter an initial 10 days expansion followed by a rapid retraction. Surprisingly, DBY-Tconv acquired a Th1-like profile characterized by high T-bet expression and IFN-gamma secretion, the absence of the FR4⁺CD73⁺ anergic markers and very few Foxp3⁺ Tregs. Finally, no hepatotoxicity was observed and DBY-Tconv were able to mediate a partial tolerance against transgene-expressing cells.
Conclusion: Numerous populations of tolerant CD4+ T cells have previously been described (anergic FR4⁺ CD73⁺, Foxp3⁺, Tr1 and recently Tfh-like cells…). Here we describe a new phenotype, having a dysfunctional Th1-like profile, induced after antigen targeting to the liver.