CD5-positive B cells after T cell depleted bone marrow transplantation.

CD5 is an antigen normally found on T cells and on a minority subpopulation of B cells in fetal spleen and tonsil and on the majority of cells in B-chronic lymphocytic leukaemia. Recent reports described the occurrence of large numbers of CD5-positive B cells in the peripheral blood after bone marrow transplantation (BMT). We examined the peripheral blood for CD5-positive B cells in 21 patients who underwent allogeneic BMT for leukaemia with marrow first depleted of T cells using anti-T monoclonal antibodies and complement mediated lysis. Twenty-six samples were obtained from patients 24-644 days after BMT and examined for the existence of blood-borne CD5-positive B cells by immunofluorescence analysis microscopically and by flow cytometry. The number of CD5-positive B cells was consistently lower than 2%. The absence of CD5-positive B cells in this series may be due to the method of T cell depletion of the marrow or to methodological differences in the analysis of the cells.