Comparative delineation of T cell clonotypes in coexisting syngeneic B16 melanoma

 B16 is a murine melanoma of C57Bl/6 origin, which rapidly develops as a tumor when inoculated into syngeneic immunocompetent hosts. Nevertheless, B16 tumors are considered to be immunogenic since tumor regression can be induced by means of immunotherapeutic intervention. Furthermore, B16 melanoma cells express several melanoma-associated antigens that may serve as targets for autologous T cells. To study the in vivo T cell response against B16, with particular emphasis on diversity and systemic involvement, we ex- amined the spectra of T cell clonotypes in coexisting B16 melanoma lesions in C57Bl/6 mice. Three tumors from each animal (n = 8) were examined for the presence of clonotypic T cells using the highly sensitive T cell receptor (TCR) clonotype mapping technology. Systematic analysis of the TCRB variable regions 1–16 revealed from 19 to more than 30 clonotypic TCR transcripts in each tumor. To study intra- and inter-individual variations in the T cell response further, more than 600 clono-typic TCR transcripts were compared for sequence identity. Overall, approximately 2% of the T cell clonotypes were detected in more than one tumor from the same animal. Furthermore, none of the detected clonotypes was present in more than one animal, arguing against recurrent or “public” T cell responses against B16 melanoma. Our data strongly suggest that anti-melanoma T cell responses in this murine model encompass mainly localized T cells, and that systemic involvement is limited.