Characterization of novel CD25 antibodies that deplete human regulatory T cells in humanized mouse model

Abstract

Abstract Regulatory T cells (Tregs) are key players in the suppression of immune responses and in the maintenance of immune homeostasis. Due to their central role in pathogenesis of multiple conditions, Tregs are an attractive target for immunomodulatory drug development. Tregs exhibit an activated phenotype and share the expression of many activation antigens with activated conventional T cells (Tconv). Our goal in this project was to generate and characterize monoclonal antibodies (mAbs) that would specifically react with human Tregs. mAbs were raised in mice by immunization with purified, in vitro expanded human Tregs. In contrast to widely available anti-CD25 mAbs that equally bound both activated Tregs and activated Tconv, we identified several mAbs that bound CD25 on expanded Tregs, but failed to bind to CD25 on expanded Tconv. To determine whether a similar selective binding could be demonstrated in vivo, we used the xeno-GVHD model in which NOD-SCID-γc−/− (NSG) mice are engrafted with human peripheral blood mononuclear cells (PBMCs). Several of the mAbs bound to CD25 expressed on Tregs, but not to CD25 expressed on activated Tconv. To test the effect of in vivo administration of the Treg specific mAbs, one of the clones, 2B010, was selected and injected intravenously (i.v) 2 weeks after PBMCs engraftment. Injection of 2B010 resulted in markedly reduced Tregs frequencies and numbers, much less depletion of CD25+ activated Tconv, and no reduction of CD25+CD8+ T cells. Further studies will address the effect of these mAbs at reversing the Treg-mediated protection of xeno-GVHD and enhancing tumor immunity in reconstituted NSG recipients bearing transplanted tumors.