Engineered Antigen-Specific Human Regulatory T Cells Suppress Both FVIII-Specific T- and B-Cell Responses

Expansion of human regulatory T cells (Tregs) for clinical applications offers great promise for the treatment of undesirable immune responses in autoimmunity, transplantation, allergy and anti-drug antibody responses, including inhibitor responses in hemophilia A patients. However, polyclonal Tregs are “nonspecific” and therefore their therapeutic application could potentially cause global immunosuppression. To avoid this undesirable outcome, the generation of antigen-specific Tregs would represent a significant advance. In this study, we demonstrate the production and properties of engineered antigen-specific Tregs created by transduction of a recombinant T-cell receptor into expanded human FoxP3+ Tregs. The DNA sequence of this T cell receptor was obtained from a FVIII-specific T cell clone that had been expanded from blood donated by a hemophilia A subject. The resulting engineered FVIII-specific Tregs efficiently suppressed both proliferation and cytokine production of FVIII-specific CD4 T effector cells. Moreover, studies with an HLA-transgenic, FVIII-deficient mouse model demonstrated that antibody production from FVIII-primed spleen cells in vitro was profoundly inhibited in the presence of these FVIII-specific Tregs, suggesting that this novel approach has translational potential for the prevention and/or reversal of inhibitor responses in hemophilia A patients. Furthermore, these FVIII-specific Tregs successfully cross-suppressed unrelated, bystander T effector cells (specific for a myelin peptide) only in the presence of FVIII and the unrelated, stimulatory myelin peptide. These data strongly imply that such FVIII-specific Tregs would be effective at suppressing multiple effector cells, e.g., CD4 T effector cells specific for other FVIII epitopes besides that recognized by the Tregs expressing the engineered TCR, in the local milieu when FVIII is present. Thus, we propose that FVIII-specific Tregs have potential as a therapeutic tool to induce tolerance to FVIII, by preventing or reversing inhibitor formation in hemophilia A patients.

Supported by NIH RO1-HL061883 (DWS), funding from Bayer and CSL Behring (KPP) and intramural support from NIAID (EMS). We thank the Puget Sound Blood Center for enrolling hemophilia A patients and we thank all blood donors.