A potential role for B cells in suppressed immune responses in cord blood transplant recipients

We evaluated immune reconstitution in 58 adults who received hematopoietic stem cell transplants from allogeneic siblings (allosib), matched unrelated donors (MUD), or cord blood (CB) at 90-day intervals for one year post-transplant. CB recipients had a higher incidence of infections in the first 100 days compared to allosib and MUD recipients. The number of circulating T cells was lower in CB recipients compared to MUD recipients at 90 days and compared to allosib recipients at 180 days. Spectratype analysis of the TCR Vβ complementarity determining region 3 (CDR3) of patient lymphocytes revealed that the TCR repertoire remained poorly diversified even at 360 days in nearly all patients. In contrast, the number of circulating B cells was significantly elevated in CB recipients compared to allosib recipients throughout the first year post-transplant and compared to MUD recipients at 9-12 months. Spectratype analysis of the B cell receptor V(H) CDR3 showed that the B cell repertoire was diversified in most patients by 90 days. CD5(pos) B cells from assayed CB recipients expressed intracellular IL-10 early post-transplant. Our data suggest that B cells, in addition to T cells, may play a role in impaired immune responses in CB transplant patients.