Correlation of in vitro CD4⁺T helper cell function with clinical graft status in immunosuppressed kidney transplant recipients

We recently identified three distinct T helper pathways which contribute to interleukin-2 (IL-2) production by human peripheral blood lymphocytes following stimulation with HLA alloantigens. In two of these pathways, CD4⁺T helper cells respond to alloantigen using either self antigen-presenting cells (sAPC)* or allogeneic antigen-presenting cells (aAPC). A third pathway involves CD8⁺T helper cells using aAPC. Previous in vitro studies have shown that the T helper pathway dependent on CD4⁺T helper cells and sAPC (CD4-sAPC) is the most susceptible to suppression by cyclosporine. In the present study, we measured alloantigen-stimu- lated IL-2 production by PBL from 42 kidney transplant recipients to characterize the strength of the three T helper-APC pathways. In 58% of patients, a loss of the CD4-sAPC pathway was identified and was correlated with cyclosporine treatment. However, several patients not receiving cyclosporine also exhibited a similar loss of T helper cell function, suggesting that cyclosporine is not the only factor involved. Of 27 patients exhibitingdepressed CD4-sAPC function, none had evidence of ongoing/recent graft rejection. In contrast, of 11 patients with no defects in the three pathways of in vitro T helper cell function, 6 had evidence of chronic graft rejection. Of considerable interest are the data obtained from a separate group of 4 patients who had episodes of acute rejection during the study. In each case, at the time of the rejection episode, all exhibited an intact CD4- sAPC pathway. However, samples tested prior to the rejection episode or after successful treatment of the rejection episode showed a depressed CD4-sAPC pathway. These results suggest that depression of the CD4- sAPC pathway represents adequate immunosuppression for graft retention and that patients not exhibiting such suppression are at increased risk for both acute and chronic graft rejection. These data may have relevance for diagnosis and/or prediction of graft rejection and may provide an in vitro method of monitoring the functional degree of immunosuppression in transplant recipients.