Anti-CD3 antibodies modulate anti-factor VIII immune responses in hemophilia Amice after factor VIII plasmid-mediated gene therapy

One major obstacle in gene therapy is the generation of immune responses directed against transgene product. Five consecutive anti-CD3 treatments concomitant with factor VIII (FVIII) plasmid injection prevented the formation of inhibitory antibodies against FVIII and achieved persistent, therapeutic levels of FVIII gene expression in treated hemophilia A mice. Repeated plasmid gene transfer is applicable in tolerized mice without eliciting immune responses. Anti-CD3 treatment significantly depleted both CD4(+) and CD8(+) T cells, whereas increased transforming growth factor-beta levels in plasma and the frequency of both CD4(+)CD25(+) FoxP3(+) and CD4(+)CD25(-)Foxp3(+) regulatory T cells in the initial few weeks after treatment. Although prior depletion of CD4(+)CD25(+) cells did not abrogate tolerance induction, adoptive transfer of CD4(+) cells from tolerized mice at 6 weeks after treatment protected recipient mice from anti-FVIII immune responses. Anti-CD3-treated mice mounted immune responses against both T-dependent and T-independent neo-antigens, indicating that anti-CD3 did not hamper the immune systems in the long term. Concomitant FVIII plasmid + anti-CD3 treatment induced long-term tolerance specific to FVIII via a mechanism involving the increase in transforming growth factor-beta levels and the generation of adaptive FVIII-specific CD4(+)Foxp3(+) regulatory T cells at the periphery. Furthermore, anti-CD3 can reduce the titers of preexisting anti-FVIII inhibitory antibodies in hemophilia Amice. (Blood. 2009;114:4373-4382)