Nonredundant roles of IL-10 and TGF-Β in suppression of immune responses to hepatic AAV-factor IX gene transfer

Hepatic gene transfer using adeno-associated viral (AAV) vectors has been shown to efficiently induce immunological tolerance to a variety of proteins. Regulatory T-cells (Treg) induced by this route suppress humoral and cellular immune responses against the transgene product. In this study, we examined the roles of immune suppressive cytokines interleukin-10 (IL-10) and transforming growth factor-Β (TGF-Β) in the development of tolerance to human coagulation factor IX (hF.IX). Interestingly, IL-10 deficient C57BL/6 mice receiving gene transfer remained tolerant to hF.IX and generated Treg that suppressed anti-hF.IX formation. Effects of TGF-Β blockade were also minor in this strain. In contrast, in C3H/HeJ mice, a strain known to have stronger T-cell responses against hF.IX, IL-10 was specifically required for the suppression of CD8⁺ T-cell infiltration of the liver. Furthermore, TGF-Β was critical for tipping the balance toward an regulatory immune response. TGF-Β was required for CD4⁺ CD25⁺ FoxP3⁺ Treg induction, which was necessary for suppression of effector CD4⁺ and CD8 T-cell responses as well as antibody formation. These results demonstrate the crucial, nonredundant roles of IL-10 and TGF-Β in prevention of immune responses against AAV-F.IX-transduced hepatocytes.