MELANOCYTE MODIFICATIONS UPON BONE-MARROW TRANSPLANTATION

Human skin undergoes relevant changes upon the conditioning regimen pr eceding bone marrow transplantation (BMT) and during acute graft-versu s-host disease (aGVHD). It is not known whether melanocytes participat e in the skin response to cytostatic treatment and/or to aGVHD in BMT recipients, neither is it clear why such patients develop cutaneous hy perpigmentation. As a first step to address these issues, we used immu nohistochemistry and electron microscopy to analyze melanocytes in bio psies from: (1) clinically healthy skin of 8 allogeneic BMT patients w ithout any rash; (2) lesional skin of 2 allogeneic BMT patients with a GVHD; (3) normal skin of 6 healthy controls. Biopsies were obtained 0- 28 days after BMT. In the thinned skin of patients without aGVHD, mela nocytes appeared round, small, and often protruding into the dermis. I n the lesional, normally thick skin of patients with aGVHD, melanocyte s were large, with only a small area of contact with the basement memb rane, and expressed the 100/7 kDa activation antigen. These findings i ndicate that melanocytes show morphological changes induced by BMT and by the conditioning regimen preceding it. This effect is transiently reversed during aGVHD suggesting that infiltrating leukocytes might di rectly or indirectly stimulate melanocytes. Minor modifications observ ed in the melanocyte/basal keratinocyte ratio suggest a trophic balanc e between these cells. The hyperpigmentation observed after the transp lant conditioning regimen does not seem due to a change in melanocyte number or activity and may stem from an unmasking of melanin in the ba sal epidermal layer as a result of epidermal atrophy. During aGVHD epi dermal atrophy is reverted and hyperpigmentation may be due to an acti vated state of melanocytes and perhaps to some dermal pigmentary incon tinence. The epidermis after BMT may provide information on melanocyte -keratinocyte interactions in vivo.