Aberrant germinal center formation, follicular T-helper cells, and germinal center B-cells were involved in chronic graft-versus-host disease.

Chronic graft-versus-host disease (cGVHD) is an important complication after allogeneic hematopoietic stem cell transplantation (HSCT). To define the roles of T-cells and B-cells in cGVHD, a murine minor histocompatibility complex-mismatched HSCT model was used. Depletion of donor splenocyte CD4(+) T-cells and B220(+) B-cells alleviated cGVHD. Allogeneic recipients had significantly increased splenic germinal centers (GCs), with significant increases in follicular T-helper (Tfh) cells and GC B-cells. There were increased expressions in Tfh cells of inducible T-cell co-stimulator (ICOS), interleukin (IL)-4 and IL-17, and in GC B-cells of B-cell activating factor receptor and ICOS ligand. Depletion of donor splenocyte CD4(+) T-cells abrogated aberrant GC formation and suppressed Tfh cells and GC B-cells. Interestingly, depletion of donor splenocyte B200(+) B-cells also suppressed Tfh cells in addition to GC B-cells. These results suggested that in cGVHD, both Tfh and GC B-cells were involved, and their developments were mutually dependent. The mammalian target of rapamycin (mTOR) inhibitor everolimus was effective in suppressing cGVHD, Tfh cells, and GC B-cells, either as a prophylaxis or when cGVHD had established. These results implied that therapeutic targeting of both T-cells and B-cells in cGVHD might be effective. Signaling via mTOR may be another useful target in cGVHD.