Transitional B cells in humans: Characterization and insight from B lymphocyte reconstitution after hematopoietic stem cells transplantation

Transitional B cells have been recently identified in human peripheral blood. However, their precise rote in human B cell differentiation has not been established. Therefore, besides characterizing them further in the blood of healthy adults and children and cord blood, we used the immune reconstitution after hematopoietic stem cell transplantation (HSCT) model. to define their role in human B cell development. Human transitional B cells are reliably identified as CD19+ CD24(high) CD38(high) lwymphocytes and represent approximately 4% of B cells in healthy adult peripheral blood. In contrast, they are abundant in cord blood (near 50% of B cells) and their percentage progressively decreases during infancy. Similary, after HSCT all. B cells first appearing in peripheral blood are transitional B cells; afterwards, the transitional B cell percentage progressively decreases white the mature naive B cell proportion rises. Our results now formally demonstrate that transitional B cells are necessary developmental intermediates for human mature B cell. generation. (C) 2007 Etsevier Inc. All rights reserved.