Murine bone marrow chimeras developing autoimmunity after CTLA-4-blockade show an expansion of T regulatory cells with an activated cytokine profile

Abstract

Autoimmune adverse events are a concern in patients treated with blocking anti-CTLA-4-mAb for solid and hematological tumors. Patient and mouse data on the contribution of a quantitative or qualitative defect of regulatory T cells (T reg) in this autoimmune phenomenon are conflicting. We have previously shown that a treatment course with blocking anti-CTLA-4-mAb in murine allogeneic bone marrow chimeras induces an antileukemic response in close association with systemic autoimmunity. Here, we used this model to investigate the effect of CTLA-4-blocking therapy on the kinetics of T reg frequency and function. As previously published, CTLA-4-blocking treatment, initiated on day 20 after bone marrow transplantation, led to overt autoimmunity by day 35. CD4 +Foxp3 + T reg frequency was determined (flowcytometry) on day 21, 23, 25 and 35: treated chimeras showed an expansion of CD4 +Foxp3 + T reg frequencies on day 25 and 35, without a prior frequency decrease. The T reg expansion occurred selectively in the recipient-derived CD4+ T-cell compartment. In vitro, purified CD4 +CD25 +FR4 high T reg from ‘day 35’ autoimmune and control chimeras showed equal suppressive effects towards self-antigen-specific autoimmune T cells. Purified CD4 +CD25 highFR4 high T reg from ‘day 35’ treated chimeras showed increased IL-10 and IFN-γ mRNA-expression (RT-PCR) relative to control chimeras. In this model of CTLA-4-blockade-induced autoimmunity after allogeneic bone marrow transplantation, anti-CTLA-4-mAb gives rise to a progressive expansion – without a prior transient reduction – of T reg cells. T reg of autoimmune animals do not show a defect in in vitro suppressive function but show an in vivo activated cytokine profile, suggesting that the expansion occurs as a compensatory phenomenon to control autoimmunity.