Immunological reconstitution after bone marrow transplant with Campath-1 treated bone marrow.

Immunological reconstitution after allogeneic bone marrow transplant (BMT) was studied in 20 patients who received Campath-1 treated bone marrow. The peripheral blood lymphocyte phenotype was analysed with a panel of monoclonal antibodies at 3, 6 and 12 months. T cell proliferative capacity was evaluated by stimulation with PHA and Con A and in the mixed lymphocyte reaction (MLR). Natural killer (NK) cell activity was analysed against the K562 cell line at specified times after BMT in nine patients. Absolute numbers of T lymphocytes were reduced in all patients at 3 and 6 months. A marked decrease in the number of CD4+ cells persisted beyond 12 months. CD8+ cells regenerated more rapidly and reached normal at 6 months. No correlation was found between changes in lymphocyte subpopulations and the presence of graft-versus-host disease or cytomegalovirus infection. B cells recovered rapidly and maintained normal numbers throughout the study. A moderate increase in HNK1+ (Leu7) cells was observed at 3 and 6 months simultaneously with a low expression of NK15 (Leu11) and OKM1 antigens at 3 and 6 months, suggesting the presence of immature NK cells early after the transplant. A profound decrease of T cell proliferative capacity was observed both after mitogen stimulation and in the mixed lymphocyte reaction. NK cell activity was raised during the first month after transplant in all but one patient but no correlation was found with the presence of GVHD or cell marker analysis.