Potential limitations of IL-2 administration for the treatment of experimental acute graft-versus-host disease.

Low-dose IL-2 administration can control autoimmunity by specifically activating CD4(+) Foxp3(+) regulatory T cells (Tregs). Here, we studied IL-2-based immunotherapy in experimental graft-versus-host disease (GVHD). IL-2 administration to donor mice induced a dose-dependent expansion of Tregs in the graft but was insufficient to control GVHD. IL-2 administration to allogeneic-grafted recipient mice activated T-conventional cells (Tcons) and did not prevent GVHD. This loss of IL-2 selectivity toward Tregs was explained by an IL-2-induced increase in the IL-2 receptor α-chain expression on Tcons. Finally, in xeno-GVHD generated by human PBMCs transplanted into immunodeficient mice, low-dose IL-2 increased Treg frequencies but did neither control pro-inflammatory cytokine production by pathogenic Tcons, nor prevented GVHD. Furthermore, combination of low-dose IL-2 with rapamycin was ineffective in this model. Our results indicate that limitations on the use of IL-2 during acute GVHD are likely due to the massive activation of the allogeneic T cells unique to this setting.