We describe the biochemical properties and cell surface distributions of three human T cell antigens (Leu-1, Leu-2a, and Leu-2b) which we postulate to be the homologues of the Lyt-1, Lyt-2, and Lyt-3 antigens that distinguish functional T cell subsets in the mouse. Leu-l, like Lyt-1, is on all thymocytes and peripheral T cells and is present in greater amounts on the helper/inducer subset than on the cytotoxic/suppressor subset. Both antigens increase in parallel fashion during T cell maturation in the thymus and each antigen is carried on a single 67,000-molecular weight (relative) (M(r)) polypeptide chain. Surprisingly, Leu-1 and Lyt-1 each are also expressed in readily detectable amounts on some B celI Ieukemias but not detectably so on normal B cells. Leu-2a and Leu-2b are antigens found only on suppressor/cytotoxic cells in the human and are very similar to the murine Lyt-2 and Lyt-3 antigens. In both species, the two antigens are on the same disulfide- linked multimeric molecules. Disulfide-bond reduction in both species yields subunits of similar size and charge. Lyt-3 and Leu-2b are extremely sensitive to trypsin digestion on viable cells whereas Lyt-2 and Leu-2a are much less so. A different membrane antigen, Leu-3, is an exclusive marker of the helper/inducer subset in man. No mouse homologue for this 55,000-M(r) protein is known. The maintenance of the homologous molecules on functionally distinct T cell subpopulations in two evolutionarily distant species suggests that the Lyt and Leu antigens perform essential functions for the cells on which they are found.

We analyzed the effects of T-cell depletion on the outcome of HLA- identical sibling bone marrow transplants for leukemia by comparing 731 T-cell-depleted transplants with 2,480 non-T-cell-depleted transplants. T-cell depletion decreased acute graft-versus-host disease (GVHD) (relative risk [RR] 0.45; P less than .0001) and chronic (GVHD) (RR 0.56; P less than .0001). However, it increased graft failure (RR 9.29; P less than .0001). Leukemia relapse also was increased. In first remission acute leukemia or chronic phase chronic myelogenous leukemia, leukemia relapse was 2.75 times more likely after T-cell-depleted transplants (P less than .0001). T-cell depletion increased the risk of treatment failure (RR 1.35; P less than .0003) and decreased leukemia- free survival. We also studied controllable variables associated with outcome of T-cell-depleted transplants. The unique findings were that among recipients of T-cell-depleted transplants for early leukemia, radiation doses greater than or equal to 11 Gy (RR 0.54; P less than .01), dose rates greater than 14 cGy/min (RR 0.56; P less than .002), and additional posttransplant immune suppression with cyclosporine alone (RR 0.53; P less than .0006) or cyclosporine plus methotrexate (RR 0.36; P less than .01) were associated with fewer treatment failures. Use of monoclonal antibodies rather than physical techniques for T-cell depletion (RR 2.01; P less than .03) and fractionated radiation (RR 1.69; P less than .05) were associated with increased treatment failure and lower leukemia-free survival. These data may be useful in designing strategies to improve results of T-cell-depleted transplants.

Graft failure was analyzed in 625 patients receiving allogeneic bone marrow transplants from HLA-identical sibling donors as treatment for severe aplastic anemia. Sixty-eight (11%) had no or only transient engraftment. Second bone marrow transplants were successful in achieving extended survival in 16 of 27 patients with transient initial engraftment but in none of ten patients with no sign of engraftment after the first transplant. The major factors associated with a reduced risk of graft failure were use of radiation for pretransplant immunosuppression and use of cyclosporine rather than methotrexate or T- cell depletion of the donor bone marrow for prophylaxis against graft-v- host disease (GVHD). Among 266 patients prepared for transplantation with cyclophosphamide alone, the risk of graft failure was increased in patients who received previous transfusions and reduced in those who received corticosteroids for previous therapy. Neither cell dose nor administration of donor buffy coat cells affected the probability of engraftment. Although use of radiation in conditioning reduced graft failure, survival was not improved. Posttransplant treatment with cyclosporine and avoidance of pretransplant blood transfusions were associated with improved survival.

Chronic graft-versus-host disease (GVHD) is an important complication of bone marrow transplantation. We analyzed risk factors for chronic GVHD in 2,534 recipients of HLA-identical sibling transplants surviving at least 90 days after transplantation. The actuarial probability of developing chronic GVHD within three years posttransplant was 46% +/- 3% (95% confidence interval). The most important risk factor for chronic GVHD was acute GVHD. The 3-year probabilities of chronic GVHD were 28% +/- 3%, 49% +/- 5%, 59% +/- 6%, 80% +/- 9%, and 85% +/- 15% for persons with grades 0, I, II, III, and IV acute GVHD, respectively (P less than .0001). Among patients with no or grade I acute GVHD, recipient age greater than 20 years, use of non-T-cell depleted bone marrow, and alloimmune female donors for male recipients predicted a higher risk of chronic GVHD. When all three adverse risk factors were present, the probability of chronic GVHD was 62% among persons with no prior acute GVHD and 85% among those with grade I acute GVHD. Among patients with grade II through IV acute GVHD, no other risk factor predicted chronic GVHD. These data identify individuals who might benefit from treatment strategies aimed at changing the incidence of chronic GVHD.

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