HLA-DR expression in epidermal keratinocytes after allogeneic bone marrow transplantation. Relationship to histology, rash, marrow purging, and systemic graft-versus-host disease.

HLA-DR expression on epidermal keratinocytes was studied in leukemic recipients of allogeneic marrow in order to clarify its relationship to GVHD, investigate its diagnostic value, and gain insight into the pathogenetic mechanisms. Using frozen-section immunohistological techniques, positive keratinocytes were encountered in a small minority of normal donors and in a few recipients prior to transplantation. In patients receiving marrow unpurged of T lymphocytes, keratinocyte HLA-DR staining was found in the majority of patients with, and in about one third of those without, histological evidence of GVHD. Positivity was strongly related to the presence of a rash and was more likely to be found if the interval between the onset of the rash and biopsy exceeded 24 hr. There was a strong association between the presence of positive cells and the subsequent development of systemic GVHD, indicating that staining for HLA-DR on keratinocytes may be a useful adjunct to conventional morphological analysis in the interpretation of post-transplant skin biopsies. Positivity was not observed in patients who received marrow depleted of T lymphocytes, indicating a crucial role for these cells in stimulating keratinocyte HLA-DR expression. Sequential studies, however, showed that keratinocyte positivity preceded lymphocytic infiltration of the epidermis.