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Regulatory T cells in graft-versus-host disease.

To the Editor: Koreth et al. (Dec. 1 issue)1 clearly show that low-dose interleukin-2 was effective for suppression of manifestations of chronic graft-versus-host disease (GVHD). However, in the present study, there was no significant difference in CD4+ regulatory T (Treg)-cell counts between patients with a response and those without a response, suggesting that the response to treatment might be dependent on factors other than CD4+ Treg cells. Recently, CD8+ Treg cells have been reported to play a critical role in the maintenance of selftolerance.2,3 In mice, autoimmune disease results when CD8+ Treg cells are defective.2 Interestingly, CD8+ Treg cells are also positive for CD122 (interleukin-2 receptor β chain), CD44, and inducible costimulator ligand.2 In the present study, although the number of total CD8+ T cells (including both effector T cells and Treg cells) did not increase significantly, it would be interesting to examine whether the specific CD8+ Treg-cell fraction increased after treatment with low-dose interleukin-2. CD8+ Treg cells could participate in suppressing GVHD. Shigeo Masuda, M.D., Ph.D.