Systematic analysis of mucosal‐associated invariant T cells in haematological malignancies

Abstract Mucosal‐associated invariant T‐cells (MAIT) are unconventional T‐cells with cytotoxic and pro‐inflammatory properties. Previous research has reported contradictory findings on their role in cancerogenesis with data being even scarcer in haematological malignancies. Here, we report the results of a systematic analysis of MAIT cells in treatment‐naïve patients with a broad range of haematological malignancies. We analysed peripheral blood of 204 patients and 50 healthy subjects. The pool of haematological patients had a statistically significant lower both the absolute value (median values, 0.01 × 10 9 /L vs. 0.05 × 10 9 /L) of MAIT cells and their percentage (median values 0.94% vs. 2.56%) among T‐cells compared to the control group. Separate analysis showed that the decrease in the absolute number of MAIT cells is significant in patients with acute myeloid leukaemia, myeloproliferative neoplasms, plasma cell myeloma, B‐cell non‐Hodgkin lymphomas, otherwise not specified, diffuse large B‐cell lymphoma, follicular lymphoma, mantle cell lymphoma, marginal zone lymphoma compared to the control population. Furthermore, in haematological malignancies, MAIT cells overexpress PD‐1 (average values, 51.7% vs. 6.7%), HLA‐DR (average values, 40.2% vs. 7%), CD38 (average values, 25.9% vs. 4.9%) and CD69 (average values, 40.2% vs. 9.2%). Similar results were obtained when comparing patients with individual malignancies to the control population. Our data show that the depletion of circulating MAIT cells is a common observation in a broad spectrum of haematological malignancies. In addition to their reduced numbers, MAIT cells acquire an activated/exhausted phenotype.