Using monoclonal antibodies and flow cytometry, we serially monitored lymphocyte subpopulations in renal-allograft recipients treated with either conventional immunosuppression or a monoclonal antibody. In 29 patients given conventional suppression, highly significant correlations between changes in T-cell subsets and rejection were noted. Normal or elevated ratios of OKT4 (helper/inducer) to OKT8 (suppressor/cytotoxic) cells were associated with rejection unless the donor was HLA identical or the total number of T cells was extremely low. In patients with low ratios, rejection seldom occurred. Two patients treated with OKT3 monoclonal antibody for acute rejection had rapid disappearance of OKT3-reactive cells from the peripheral blood and prompt reversal of rejection.

The use of monoclonal antibodies allows the precise determination of changes in T-cell subsets and promises the development of therapeutic protocols that can be designed to manipulate selected lymphocyte populations. (N Engl J Med. 1981; 305:308–14.)