Increase in FOXP3⁺ Regulatory T Cells in GVHD Skin Biopsies Is Associated with Lower Disease Severity and Treatment Response

In animal models, CD4⁺/CD25⁺ T-regulatory cells (Tregs) have been reported to prevent/delay the onset of graft-versus-host disease (GVHD). Recently, an insufficient upregulation of Tregs was found in target organ (intestinal) biopsies from patients with GVHD. We have analyzed by immunohistochemistry the number of CD3⁺ T lymphocytes and FOXP3⁺ Tregs in skin biopsies from (1) recipients of allogeneic hematopoietic stem cell transplantation (HSCT, n = 26), (2) nontransplanted patients diagnosed with cutaneous drug reaction (n = 12), and (3) healthy donors (n = 10). Infiltrating CD3⁺ cells were significantly higher in both transplanted patients showing acute GVHD (aGVHD) and drug reaction when compared to healthy donors and patients without GVHD. Tregs number in aGVHD was higher than in patients without GVHD or healthy subjects and lower than in drug reaction. Interestingly, the number of infiltrating FOXP3⁺ Tregs was significantly higher in patients responding to GVHD treatment and with a low GVHD grade. Increase in FOXP3⁺ Tregs in GVHD skin biopsies correlates with less severe GVHD and is associated with response to GVHD treatment. Larger studies are required to confirm that evaluation of Tregs in minimally invasive skin biopsies assists the diagnosis and prognosis of GVHD patients.