Submitted May 11, 2009
Accepted August 31, 2009
Anti-CD3 antibodies modulate anti-factor VIII immune responses in hemophilia A mice after factor VIII plasmid-mediated gene therapy
Baowei Peng, Peiqing Ye, David J. Rawlings, Hans D. Ochs, and Carol H. Miao*
Department of Pediatrics, Seattle Children's Research Institute and University of Washington, Seattle, WA, United States
* Corresponding author; email: miao{at}u.washington.edu.
One of the major obstacles 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-level 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 in treated mice, while increased TGF-
levels in plasma and the frequency of both CD4+CD25+FoxP3+ and CD4+CD25-Foxp3+ regulatory T cells (Tregs) in the initial few weeks post treatment. Although prior depletion of CD4+CD25+ cells did not abrogate tolerance induction, adoptive transfer of CD4+ cells from tolerized mice at 6 weeks post 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 anti-CD3 did not hamper the immune systems for long-term. Concomitant FVIII plasmid+anti-CD3 treatment induced long-term tolerance specific to FVIII via a mechanism involving the increase in TGF- levels and the generation of adaptive FVIII-specific CD4+Foxp3+Tregs at the periphery. Furthermore, anti-CD3 can reduce the titers of pre-existing anti-FVIII inhibitory antibodies in hemophilia A mice.
