Epidermal Langerhans cells after allogeneic bone marrow transplantation: Depletion by chemotherapy conditioning regimen alone

Depletion of Langerhans cells (LC) is known to follow bone marrow transplantation (BMT) and is thought to be mainly related to pretransplant radiation and chemotherapy conditioning regimens. We studied sequential biopsies of clinically normal skin of 22 thalassemic and leukemic patients undergoing allogeneic BMT who had received only chemotherapy (busulfan and cyclophosphamide) as conditioning regimen. LC were identified immnunohistochemically using antibodies against CD1a and HLA-DR antigens, and their number expressed per square mm of epidermal vertical section, the latter measured by computerixed image analysis. After the preparatory regimen, the number of LC decreased progressively in both leukemic and thalassemic patients. CD1a⁺ and HLA-DR⁺ epidermal cells were reduced, respectively, to 68.5% and 64.5% of their original number around Day 2, and to 23.1% and to 18.2% around Day 17. By this time, electron microscopic examination of selected biopsies confirmed the depletion of L.C. Variable repopulation was observed between Days 40 and 60. Our results indicate that a conditioning regimen based exclusively on high dose chemotherapy depletes epidermal LC early after BMT, and that such depletion is not related to the development of acute graft-versus-host disease.