Withdrawal of sex steroids reverses age- and chemotherapy-related defects in bone marrow lymphopoiesis.

A significant decline in immune function is characteristic of aging. Along with the involution of the thymus and associated impaired architecture, which contributes to profound loss of naive T cell production, there are also significant declines in B cell development and the progenitors that support lymphopoiesis. These collectively lead to a reduced peripheral immune repertoire, increase in opportunistic infections, and limited recovery following cytoablation through chemo- or radiotherapy. We have previously shown that sex steroid ablation (SSA) causes a major reversal of age-related thymic atrophy and improves recovery from hematopoietic stem cell transplant. This study focused on the impact of SSA on the B cell compartment and their progenitors in middle-aged and cyclophosphamide-treated mice. In both models, SSA enhanced the number of lymphoid progenitors and developing B cells in the bone marrow (BM) as well as reversing age-related defects in the cycling kinetics of these cells. Enhanced BM lymphopoiesis was reflected in the periphery by an increase in recent BM emigrants as well as immature and mature plasma cells, leading to an enhanced humoral response to challenge by hepatitis B vaccine. In conclusion, SSA improves lymphoid progenitor and B cell recovery from age- and chemotherapy-induced immunodepletion, complimenting the effects on T cells. Since SSA has been achieved clinically for over 25 years, this provides a novel, rational basis for approaching the need for immune recovery in many clinical conditions.