CD4 and graft versus host disease: Within an ongoing clinical trial, initiated in the Leiden University Medical Center, treating patients 3 months after TCD alloSCT with an HLA-identical sibling donor with purified donor CD4 T-cells with primary aim to improve immune reconstitution (34), we observed hematopoiesis restricted immune responses, as illustrated by conversion from mixed to full donor chimerism, without GVHD in four patients.