Redirecting Human T Lymphocytes toward Tumor-Associated Antigens by T Cell Receptor (TCR) Replacement.

The gene transfer of alpha and beta chains derived from a defined TCR has been successfully applied to endow T cells with specificities directed against tumor-associated antigens. However, it is still unclear if the transfer of TCR genes into T cells that already express an endogenous TCRalpha and beta chain leads to engineered T cells expressing four different TCR complexes on their cell surface. Mixed TCR heterodimers composed of endogenous and exogenous TCR chains may acquire new specificities, which may cause unwanted reactions in patients following adoptive T cell transfer. We examined the possibility of mixed TCR heterodimer formation using defined conditions of single TCR chain transfer into human cytotoxic T cell (CTL) clones specific for CMV and Melan-A, respectively. After stimulation for three days CTLs were retrovirally transduced with the beta chain derived from a gp100-specific TCR. The expression of the exogenous (transduced) and the endogenous beta chain was distinguished by flow cytometry using antibodies against the different Vbeta motives. Indeed, CTLs that had been transduced with the single beta chain expressed this chain on the cell surface indicating the formation of mixed TCRs, because the expression of the exogenous TCRbeta chain requires the pairing with the endogenous TCRalpha chain. Furthermore, we transduced the CTL clones with both the TCRalpha and beta chain derived from a gp100-specific TCR. The transduced T cells were positively stained with an A2/gp100 multimer documenting the correct formation of the exogenous TCR chains. Functionality of transduced CTL clones was tested by antigen-specific IFN-gamma release and cytolytic activity. The TCR-transduced T cells were sorted with the A2/gp100 multimer and expanded for two weeks. Double staining with HLA multimers for the endogenous and the transduced TCRs showed the downregulation of the endogenous TCRs in three different CTL clones. In one CTL clone, the endogenous TCR was even replaced by the exogenous TCR as documented by flowcytometry and antigen-specific T cell function. In conclusion, transfer of single TCR chains in CTL clones can result in the formation of TCR heterodimers. However, our results also show that complete TCRs are predominantly expressed or can even replace other TCRs following transfer. The development of dominant TCRs will facilitate the therapeutical approaches of adoptive transfer regimens based on TCR-transduced T cells, because dominant TCRs can be selected or TCRs can be modified to be more dominant.