T Regulatory Cells in Graft-Versus-Host Disease of the Skin

FoxP3+ CD25+ T regulatory (T_reg) cells are known to be present in normal skin. T_reg cell functional deficiency resulting in loss of suppression of activation, differentiation or expansion of effector T cells could conceivably contribute to the pathophysiology of graft-versus- host disease (GVHD). Rezvani et al. suggest that levels of peripheral blood T_reg cells in donors and recipients may predict the risk of acute GVHD. Rieger et al. found a significantly lower number of T_reg cells in human colonic biopsies with GVHD versus CMV colitis or normal samples. There are no reports that evaluate tissue T_reg cells in human skin affected by GVHD. This study was conducted to evaluate the distribution of T_reg cells in skin affected by acute GVHD versus chronic GVHD. Archived samples from patients previously reported by routine histopathological methods as acute or chronic GVHD were collected, coded and entered into a database. For immunostaining, 4-μm thick serial sections were cut and deparaffinized. Immunohistochemical stains for CD4 (Neomarkers, 1:20), CD8 (Dako, prediluted), CD25 (Dako, 1:100), and Foxp3 (Serotec, 1:250) were performed using standard techniques. The dermatopathologist evaluating the samples was blinded to the clinical outcomes. Results were scored as 0 (<10% of lymphocytes positive), 1+ (10–25% positive), 2+ (26–50% positive), and 3+ (≥50% positive). Fourteen patients with acute skin GVHD and seventeen with chronic GVHD were identified from a database of patients who had undergone nonmyeloablative allogeneic peripheral blood transplantation in the recent past. The average scores for each immunostain were calculated and are summarized in table 1. The average FoxP3 score in acute GVHD specimens was significantly lower than that in chronic GVHD specimens (average, 0.57 versus 1.41; p-value = 0.011). The average scores of CD3, CD4, CD8 and CD25 immunostains were not significantly different between acute and chronic GVHD biopsies. These findings represent the initial observation of a distinction between the distribution of regulatory T cells in acute and chronic GVHD of the skin. These observations should be confirmed in a larger sample, supported by functional assays of T_reg cells, and correlated with clinical outcomes. Such studies may help to elucidate the role of T_reg cells in acute and chronic skin GVHD.

Table 1.