Prevention and reversal of adverse humoral immune response by BAR-transduced regulatory T cells

Abstract

Abstract Antigen-specific elimination of unwanted immune response, such as anti-FVIII neutralizing antibody formation in hemophilia A patients, is highly desirable but remains a challenge. Analogous to the chimeric antigen receptor (CAR) strategy successfully used in cancer immunotherapy, we have created a chimeric receptor comprising a protein antigen or its domain, linked with the transmembrane and signal transduction domains, CD28-CD3ζ. We termed it “BAR” for B-cell-targeting antibody receptor. CD4+CD25hiCD127low human Tregs were retrovirally transduced to express a BAR containing the immunodominant FVIII C2 (C2 BAR) or A2 domain (A2 BAR). Control human Tregs were transduced to express a BAR containing chicken ovalbumin (OVA BAR). FACS sorted, BAR transduced human CD4+ Tregs have been successfully expanded in vitro, and shown to maintain phenotypic Treg markers in terms of co-expression of Foxp3 and Helios. Pretreatment of naïve hemophilia A mice with a mixture of C2 BAR plus A2 BAR human Tregs completely prevented anti-FVIII antibody development in response to FVIII/IFA immunization for as long as 8 weeks. More importantly, BAR human Tregs also effectively suppressed anti-FVIII antibody formation in primed animals with detectible pre-existing anti-FVIII antibodies. Further mechanistic studies suggest that the FVIII-specific B cell response were directly suppressed while the T cell response remained intact. Taking together, we report here a successful proof of principle strategy utilizing FVIII-specific BAR Tregs to directly target FVIII-specific B cells, an approach which could be adapted to address other adverse immune responses as well.