Sequences and repertoire of the human T cell receptor α and β chain variable region genes in thymocytes

To compare and contrast the human T cell antigen receptor (TcR) α and β chain messages found in human thymocytes to those previously isolated from human peripheral blood T lymphocytes and other nonthymic sources, 13 TcR α and 13 TcR β cDNA were isolated from a human thymocyte library and the nucleotide sequences were determined. The data indicate that, as was found in the peripheral T lymphocytes, the majority of the TcR α and TcRβ chain thymocyte cDNA were derived from potentially functional messages. Although the thymocyte‐derived TcR cDNA do not contain any unique structural features when compared to TcR cDNA from mature T lymphocytes, 4 new J_α segments, 17 new V‐gene segments (9 V_α; 8 Vβ) and 7 additional V‐gene families (4 V_α and 3 Vβ) and sequences had been identified. The exon C_βO, found in many murine thymocyte TcR β messages, was not found in over 75 human β chain messages. Based on these new data, a revised estimate of human TcR V_α, J_α and Vβ repertoires is calculated. The most significant change has been the increase in the estimated number of human TcR Vβ‐gene segments to a total of about 100 distributed among about 18 families. The V_α families are now revised upward to 16, with a total number of V_α segments of 50. The estimate of the J_α segments in humans remains between 50–100.