Depletion and repopulation of epidermal dendritic cells after allogeneic bone marrow transplantation in humans.

We have observed marked depletion of epidermal dendritic cells, defined by monoclonal antibodies directed against HLA-DR (Ia-like) and T6 antigens, after allogeneic bone marrow transplantation. To more precisely characterize this observation, we examined a total of 39 sequential biopsies from 15 patients both before and after allogeneic bone marrow transplantation. Profound depletion of HLA-DR and T6-positive epidermal dendritic cells was observed early after transplantation (1-4 weeks), followed by gradual and variable repopulation. Transmission electron microscopy confirmed absence of dendritic cells in selected biopsies. Depletion of dendritic cells did not appear to be related to development of clinical or histologic evidence of graft-versus-host disease, suggesting that depletion may relate to pretransplant conditioning regimens. The rate of return of these cells, however, may be influenced by the presence or persistence of clinical disease. Repopulation of epidermal dendritic cells after initial depletion in bone marrow transplantation represents a human model relevant to studies concerned with the origin and kinetics of Langerhans cells.