Summary:Cyclosporin A (CsA) can induce graft-versus-host disease (GVHD) following autologous bone marrow transplantation (ABMT) and autologous peripheral blood stem cell transplantation (APBSCT) in adults. We investigated whether GVHD can be induced following ABMT and APBSCT in childhood, and which cells are involved in the pathogenesis of this syndrome. We conducted a prospective study of 20 children and adolescents with hematological malignancies receiving CsA after ABMT and APBSCT. Skin biopsies were obtained on day 21 after transplantation or in the event of a rash. Immunophenotypic analysis of peripheral blood lymphocytes was performed on days 14, 21, 28 and 60 after transplantation. Clinical GVHD of the skin, confirmed by histological criteria, occurred in five patients. Five patients had no clinical GVHD but had acute GVHD alterations on routine skin biopsy. In all 10 patients with a positive skin biopsy for GVHD, CD4 + lymphocytes were the predominant cells in the epidermis. Immunophenotypic analysis of peripheral blood lymphocytes revealed a significantly increased CD4/CD8 ratio in patients with a positive skin biopsy (P Ͻ 0.01). Our findings indicate that it is possible to induce acute GVHD following ABMT and APBSCT in childhood. In addition, CD4 + lymphocytes play an important role in the pathogenesis of CsA-induced GVHD. Keywords: cyclosporin A; graft-versus-host disease; bone marrow transplantation; hematopoietic stem cell transplantation Despite the increased morbidity and mortality in patients with graft-versus-host disease (GVHD) after allogeneic bone marrow transplantation (BMT), GVHD is associated with a clinically significant antitumor effect. 1,2 It has been shown that mature T cells from the donor contaminating the bone marrow inoculum are responsible for the development of GVHD. 3 T cell depletion of donor marrow for allogeneic BMT leads to a markedly reduced incidence of GVHD in the marrow recipients. Unfortunately, T cell depletion is also associated with an increased incidence of marrow graft failure and an increase in relapse rate. 4 The procedure-related toxicity is lower after autologous bone marrow transplantation (ABMT) than after allogeneic BMT. In contrast, the higher relapse rates after autologous and syngeneic BMT than after allogeneic BMT are at least partly due to the absence of graft-versus-tumor effect associated with GVHD. 5,6 A syndrome that clinically resembles acute GVHD has been observed spontaneously in 8% of patients receiving autologous or syngeneic BMT. 7 This syndrome appears to involve only the skin, is generally mild, and is self-limiting. Due to the rarity of this phenomenon, it has not been possible to determine its effects on leukemic relapse rates.In ABMT, further significant dose escalation with the current conditioning protocols is limited due to unacceptable toxicity. Therefore, interest has focused on methods stimulating immunologically mediated antitumor activity. In animal models, GVHD was induced by treatment with cyclosporin A (CsA) in rats or mice un...