Azacitidine-induced reconstitution of the bone marrow T cell repertoire is associated with superior survival in AML patients

Hypomethylating agents (HMA) like azacitidine are licensed for the treatment of acute myeloid leukemia (AML) patients ineligible for allogeneic hematopoietic stem cell transplantation. Biomarker-driven identification of HMA-responsive patients may facilitate the choice of treatment, especially in the challenging subgroup above 60 years of age. Since HMA possesses immunomodulatory functions that constitute part of their anti-tumor effect, we set out to analyze the bone marrow (BM) immune environment by next-generation sequencing of T cell receptor beta (TRB) repertoires in 51 AML patients treated within the RAS-AZIC trial. Patients with elevated pretreatment T cell diversity (11 out of 41 patients) and those with a boost of TRB richness on day 15 after azacitidine treatment (12 out of 46 patients) had longer event-free and overall survival. Both pretreatment and dynamic BM T cell metrics proved to be better predictors of outcome than other established risk factors. The favorable broadening of the BM T cell space appeared to be driven by antigen since these patients showed significant skewing of TRBV gene usage. Our data suggest that one course of AZA can cause reconstitution to a more physiological T cell BM niche and that the T cell space plays an underestimated prognostic role in AML.