CD4 and graft versus host disease: The hypothesis of peripheral conversion into CD4+CD25−Lag-3+ IL-10-secreting regulatory T cells can also explain why a combination WT-CD4 and Lag-3−/−CD8 T cells did not cause an increase in GVHD pathogenicity while the combination of Lag-3−/−CD4 and WT-CD8 T cells did (Fig. 2G).