In vitro-generated MART-1-specific CD8 T cells display a broader T cell receptor repertoire than naïve ex vivo and tumor infiltrating lymphocytes.

The differentiation of human hematopoietic stem cells into CD8 T cells can be achieved in vitro with the OP9-DL4 system. We considered that in the absence of medullary thymic epithelial cells, which serve to restrict the breath of the T-cell receptor (TCR) repertoire by expressing tissue-restricted antigens, a distinct repertoire would be generated in vitro. To test this notion, we compared the TCR-V alpha/V beta (TRAV/TRBV) gene usage of major histocompatibility complex-restricted antigen (MART-1)-specific T cells generated in vitro to that from ex vivo naive T cells and tumor-infiltrating lymphocytes (TILs) using high-throughput DNA sequencing. In contrast to naive T cells and TILs, which showed the expected narrow TRAV repertoire, in vitro-generated MART-1-specific T cells used almost all TRAV gene families and displayed unique CDR3 lengths. Our work demonstrates that the OP9-DL4 system supports the creation of a broad antigen-specific TCR repertoire, suggesting that T cells generated in vitro may undergo a different set of selection events that otherwise constrains the TCR repertoire of thymus-derived T cells.