Melan‐A‐specific T cells derived from A2+ or A2‐umbilical cord blood (UCB) units proliferate and exhibit specific cytolytic function following in vitro stimulation

UCB is increasingly used as a source of haematopoietic progenitors to treat a variety of blood disorders requiring bone marrow transplantation. Advantages of UCB include availability and reduced HLA matching requirements as compared with bone marrow. To characterize functional properties of UCB T cells in the context of allogeneic UCB transplant, naïve CD8+ T cells specific for the HLA‐A2‐restricted Melan‐A‐derived peptide ELAGIGILTV were sorted from A2+ and A2− UCB units using A2/Melan‐A tetramers and were cultured in the presence of IL‐2, IL‐7, PHA, and peptide. Microcultures were phenotyped and tested for Melan‐A‐specific cytotoxicity by 51Cr‐release assay. Clonal diversity was estimated by T cell receptor (TCR) β chain sequencing. 83.3% (15/18) of clinical units tested were positively stained by tetramers (median frequency of 0.11% regardless of HLA type). Following in vitro stimulation, the median frequency of tetramer+ T cells was increased (p<0.0001), T cell microcultures exhibited Melan‐A‐specific cytolytic activity (median = 11.98% of positive cultures at an input of 1000 cells/well), and the TCR β chain repertoire showed evidence of oligoclonality consistent with antigen‐driven expansion. This study will bring new light on the ability of the preimmune T cell repertoire to participate in antitumoral and antiviral activity following UCB transplantation. Supported by FRSQ/Héma‐Québec.