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 l acked adequate sensitivity and specificity for wide clinical applicati on. In this study, limiting dilution analysis (LDA) was used to quanti tate the number of donor alloantigen-reactive helper T lymphocytes (HT Ls) in the peripheral blood of cardiac transplant recipients. Cadaveri c donor splenocytes were cryopreserved, providing a source of donor al loantigenic stimulation for these assays. Peripheral blood mononuclear cells were harvested from cardiac transplant recipients before transp lantation and at the time of EMB. LDA of donor-reactive HTLs was condu cted simultaneously on all time points to minimize experimental variat ion, and these data were related to EMB scores. Frequencies of donor-r eactive HTLs in pretransplant samples were highly variable, ranging fr om 1/1381 to <1/200,000, and correlated poorly with the degree of HLA disparity. During episodes of moderate rejection, donor-specific HTL f requencies increased an average of 6 times their posttransplant baseli ne frequency. Additionally, 10-fold increases in HTL frequencies were seen preceding EMB-diagnosed rejection in several individuals. These d ata indicate that episodes of allograft rejection are associated with increases in the number of circulating donor-reactive HTL which are fr equently detected before the development of histologically defined rej ection. Thus, monitoring HTL frequencies may serve as a noninvasive me thod for detecting and predicting cardiac allograft rejection. Further more, this assay may provide a valuable means of assessing the in vivo efficacy of various immunosuppressive therapies.