Increased frequency of alloantigen-reactive helper T lymphocytes is associated with human cardiac allograft rejection.

Endomyocardial biopsy (EMB) is the standard method of monitoring heart transplant recipients for the development of allograft rejection. To date, noninvasive methods to detect cardiac allograft rejection have lacked adequate sensitivity and specificity for wide clinical application. In this study, limiting dilution analysis (LDA) was used to quantitate the number of donor alloantigen-reactive helper T lymphocytes (HTLs) in the peripheral blood of cardiac transplant recipients. Cadaveric donor splenocytes were cryopreserved, providing a source of donor alloantigenic stimulation for these assays. Peripheral blood mononuclear cells were harvested from cardiac transplant recipients before transplantation and at the time of EMB. LDA of donor-reactive HTLs was conducted simultaneously on all time points to minimize experimental variation, and these data were related to EMB scores. Frequencies of donor-reactive HTLs in pretransplant samples were highly variable, ranging from 1/1381 to < 1/200,000, and correlated poorly with the degree of HLA disparity. During episodes of moderate rejection, donor-specific HTL frequencies increased an average of 6 times their post-transplant baseline frequency. Additionally, 10-fold increases in HTL frequencies were seen preceding EMB-diagnosed rejection in several individuals. These data indicate that episodes of allograft rejection are associated with increases in the number of circulating donor-reactive HTL which are frequently detected before the development of histologically defined rejection. Thus, monitoring HTL frequencies may serve as a non-invasive method for detecting and predicting cardiac allograft rejection. Furthermore, this assay may provide a valuable means of assessing the in vivo efficacy of various immunosuppressive therapies.