Characterization of Alloantigen Specific Human Suppressor T Cells Generated in Mixed Leukocyte Culture (MLC)

The mixed leukocyte culture (MLC) extended to 11 days provides the best source of allospecific suppressor T cell (Ts) as these cultures no longer autostimulate fresh autologous responder cells and have little cytotoxic activity. The suppressor assay is performed by adding these culture primed Ts to flat-bottom microwell cultures of fresh autologous lymphocytes responding to the same stimulator cells used for Ts induction. These Ts are radioresistant similar to the naturally occurring human Ts of the MLC. The phenotype of the Ts generated in this model is CD2+, CD8+ and 9.3+. No suppressor activity is found in the lymphocyte subset bearing the CD4 antigen. Studies on the antigen specificity of these alloactivated Ts povide formal evidence that not only Class II but also Class I HLA antigens can suffice as the target antigen(s). Preliminary data is provided to suggest that there are HLA antigens to which a given individual will easily make Ts and HLA antigens to which that individual will not readily produce Ts. It is suggested that this may be due to the genetic background of the responder and thus may be under Ir gene control as in the mouse. The antigen specificity of these Ts has been demonstrated by their failure to suppress the response of autologous lymphocytes to stimulator cells bearing unrelated alloantigens present in the same cultures. However, suppression of the response to unrelated alloantigens can be produced by presentation of those antigen(s) on the same cell bearing the suppressor inducer target antigen.