Increased effector-target cell conjugate formation due to HLA restricted specific antigen recognition

The T cell receptor (TCR) orchestrates T cell mediated-cytotoxicity through a complex interaction that results in an antigen-specific effector-target cell conjugate formation. While it is well recognized that specific TCR/antigen interactions generate the immunological synapse, their direct contribution to the effector-target cell conjugate has not been conclusively demonstrated. Moreover, since human cytotoxic T lymphocyte (CTL) clones are also susceptible to antigen-independent adhesion to target cells, it remains unclear whether effector-target cell conjugate formation can serve as an indicator of specific antigen recognition by the TCR. To address this question, a well-characterized epitope-specific CTL clone recognizing the melanoma-associated antigen epitope gp100:209-217 in association with HLA-A*0201 was tested against melanoma cell lines lacking or expressing the HLA-A*0201 allele and/or gp100. In this model, TCR/HLA/antigen interactions cooperated with accessory/adhesion molecules to facilitate effector-target cell conjugate formation. HLA-restricted antigen recognition played a dominant role resulting in up to 2-fold increases in conjugate frequency, and a 50% increase of CTL binding to tumor cells over background. The increased number of CTL contained in conjugates correlated with the number of IFN-gamma producing CTL. These results warrant further investigation to evaluate conjugate assays as a potential tool to detect and isolate viable and functionally active CTL. Since conjugate formation analysis does not require knowledge of the target antigen, this assay could potentially be used for enrichment of CTL directed against novel antigens.