T-cell receptor CDR3 size distribution analysis to evaluate specific T-cell response to cancer vaccines

To evaluate immunization procedures in cancer patients, it is important to define which biological parameters reflecting a specific immune response to the vaccine should be followed. One of these may be the recruitment or expansion of clonally amplified T-cell subpopulations previously primed by tumor-specific antigen that could be detected in tiny samples by CDR3 length analysis of T-cell receptor Vbeta transcripts. To evaluate this procedure, we studied one patient with metastatic colorectal adenocarcinoma who had received 4 intradermal injections of irradiated autologous tumor cells plus IL-2 on days 1, 8, 15 and 36. Skin tests for delayed type hypersensitivity (DTH) reaction to irradiated autologous tumor cells were performed on days 1 and 43. Although no change was observed in day 43 PBMCs, some recurrent transcripts were detected with similar CDR3 size patterns in both vaccine and DTH sites. Fine analysis of these Vbeta-Cbeta PCR products with Jbeta primers confirmed that transcripts with similar length were recruited in both vaccine and DTH sites. Induction of an inflammatory response in both DTH and vaccine sites may therefore be associated with the recruitment of few T-cell clonotypes. In addition, a Vbeta15-Jbeta2.5 transcript similar to those detected in vaccine and DTH sites was also identified in enzymatically dissociated tumor cells and in a tumor fragment. Sequencing confirmed that an identical junctional sequence was shared by Vbeta15-Jbeta2.5 transcripts from both DTH and tumor samples. Our results indicate that a T-cell clone similar to the one amplified in the tumor was recruited at the vaccine and DTH reaction sites. We therefore suggest that such an approach would be useful in assessing specific expansion of T-cell clones induced by cancer vaccines.