Use of monoclonal antibodies to quantitate T lymphocyte subpopulations in human cardiac allografts.

T cell subsets have been quantitated in 40 human cardiac biopsies to characterize the surface phenotype of T lymphocytes involved in acute rejection. Seventeen biopsies were from patients receiving conventional immunosuppression, and 18 were from patients receiving cyclosporine (Cys) as the major immunosuppressive drug. Five biopsies were from nontransplanted hearts. Frozen sections were treated with monoclonal antibodies of the Leu series and an immunoperoxidase technique to determine numbers of Leu 4 (T3 or pan-T-cell), Leu 2a (T8 or suppressor/cytotoxic), and Leu 3a (T4 or helper/inducer) positive cells. Biopsies from patients on conventional immunosuppression during rejection contained 68.3 +/- 10 infiltrating leukocytes/0.048 mm2 of the biopsy, of which 47 +/- 7.4% were T cells. Most of the T cells (86%) were of the 2a/T8 phenotype. In contrast, nonrejecting hearts contained substantially fewer infiltrating leukocytes (43.3 +/- 18.8/0.048 mm2), of which only 12.6% were T cells. There was no predominance of the 2a/T8 subset in nonrejecting biopsies. It is concluded that in patients receiving conventional immunosuppression, rejection is associated with an influx of T cells, most of which are 2a/T8-positive, into the cardiac allograft. In contrast, biopsies from patients on Cys contained large numbers of infiltrating leukocytes that did not appear to correlate with the histological assessment of rejection. However, in these patients, rejection was associated with an increase in the number of T cells with no consistent pattern of subset distribution. Biopsies from nontransplanted hearts contained few infiltrating leukocytes (31.5 +/- 9.4/0.048 mm2), and none of them were T cells.