Reconstitution of B cell immunity following bone marrow transplantation

Bone marrow transplant recipients are known to be immunodeficient in cellular and humoral immune responses for months to years. Mechanisms underlying the post-transplant immunodeficiency are mostly unknown and therefore it has been difficult to design therapeutic strategies to address this problem. Here, we review studies of post-transplant B cell (humoral) immunity including B cell blood counts, phenotype, function and origin, and the morphology of lymphoid organs. We postulate that the aetiology of post-transplant humoral immunodeficiency is multifactorial, involving: B cell immaturity due to recapitulation of their ontogenesis, and, in some patients, insufficient T cell help and/or exaggerated CD8+ T cell/NK cell suppression. Implications for clinical practice are outlined, e.g. hypersensitivity reactions and autoimmune diseases as part of the differential diagnosis of post-transplant disorders, questionable diagnostic benefit of serologic studies, and usefulness of prophylactic intravenous immunoglobulin.