Targeting the TNF/IAP pathway synergizes with anti-CD3 immunotherapy in T-Cell Acute Lymphoblastic Leukemia.

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematological malignancy. Current treatments, based on intensive chemotherapy regimens provide overall survival rates of ~85% in children and <50% in adults, calling the search of new therapeutic options. We previously reported that targeting the T cell receptor (TCR) in T-ALL with anti-CD3 (CD3) mAbs enforces a molecular program akin to thymic negative selection, a major developmental checkpoint in normal T-cell development, induces leukemic cell death and impairs leukemia progression to ultimately improve host survival. However, CD3 monotherapy resulted in relapse. To find out actionable targets able to re-enforce leukemic cells vulnerability to CD3 mAbs, including the clinically relevant Teplizumab, we identified the molecular program induced by CD3 mAbs in PDXs-derived from T-ALL cases. Using large-scale transcriptomic analysis, we found prominent expression of TNF, LT and multiple components of the "TNF⍺ via NFκB signaling" pathway in anti-CD3-treated T-ALL. We show in vivo that Etanercept, a sink for TNF/LTenhancesCD3 anti-leukemic properties, indicating that TNF/TNFR survival pathways interferes with TCR-induced leukemic cell death. However, suppression of TNF-mediated survival and switch to TNFR-mediated cell death through inhibition of c-IAP1/2 with the SMAC mimetic Birinapant synergized with -CD3 to impair leukemia expansion in a RIPK1-dependent manner and improve mice survival. Thus, our results advocate the use of either TNFa/LTa inhibitors, or Birinapant/other SMAC mimetics to improve anti-CD3 immunotherapy in T-ALL.