CD4+ T Cell Dependent B Cell Recovery and Function After Autologous Hematopoietic Stem Cell Transplantation.

Introduction: High-dose chemotherapy followed by autologous hematopoietic stem cell transplantation (auto-HSCT) represents a standard treatment regime for multiple myeloma (MM) patients. Common and potentially fatal side effects after auto-HSCT are infections due to a severely compromised immune system with hampered humoral and cellular immunity. This study delineates in depth the quantitative and functional B cell defects and investigates underlying extrinsic or intrinsic drivers. Methods: Peripheral blood of MM patients undergoing high-dose chemotherapy and auto-HSCT (before high-dose chemotherapy and in early reconstitution after HSCT) was studied. Absolute numbers and distribution of B cell subsets were analyzed ex vivo using flow cytometry. Additionally, B cell function was assessed with T cell dependent (TD) and T cell independent (TI) stimulation assays, analyzing proliferation and differentiation of B cells by flow cytometry and numbers of immunoglobulin secreting cells in ELISpots. Results: Quantitative B cell defects including a shift in the B cell subset distribution occurred after auto-HSCT. Functionally, these patients showed an impaired TD as well as TI B cell immune response. Individual functional responses correlated with quantitative alterations of CD19+, CD4+, memory B cells and marginal zone-like B cells. The TD B cell function could be partially restored upon stimulation with CD40L/IL-21, successfully inducing B cell proliferation and differentiation into plasmablasts and immunoglobulin secreting cells. Conclusion: Quantitative and functional B cell defects contribute to the compromised immune defense in MM patients undergoing auto-HSCT. Functional recovery upon TD stimulation and correlation with CD4+ T cell numbers, indicate these as extrinsic drivers of the functional B cell defect. Observed correlations of CD4+, CD19+, memory B and MZ-like B cell numbers with the B cell function suggest that these markers should be tested as potential biomarkers in prospective studies.

Cytotoxic Effects of Rabbit Anti-thymocyte Globulin Preparations on Primary Human Thymic Epithelial Cells.

BACKGROUND: Graft-versus-host disease (GvHD) presents a major cause for morbidity and mortality after allogeneic hematopoietic stem cell transplantation. Rabbit-derived antithymocyte globulin (rATG) treatment reduces the incidence of GvHD after allogeneic hematopoietic stem cell transplantation. However, delayed immune reconstitution following rATG treatment, partly caused by hampered thymic function, is being discussed. The present study aims at elucidating possible cytotoxic effects of 2 commonly used rATG preparations on cultured human thymic stroma, especially thymic epithelial cells (TECs). METHODS: A primary TEC culture was established and the binding and cytotoxicity of 2 rATG preparations to the aforementioned cells were assessed by flow cytometry and immunofluorescence analyses. The release of several cytokines by cultured thymic stroma cells in response to rATG was analyzed via multiplex enzyme-linked immunosorbent assays. RESULTS: Both preparations showed a comparable dose-dependent binding to TECs and exerted a similar complement-independent, dose-dependent cytotoxicity. rATG exposure further resulted in hampered secretion of interleukin (IL)-7, IL-15, and IL-6, cytokines being involved in thymic T cell development and proliferation. Pretreatment with keratinocyte growth factor diminished rATG-induced cytotoxicity of TECs and restored their IL-7 and IL-15 secretion. CONCLUSIONS: Cytotoxic effects on TECs link the rATG-induced thymic damage to the delayed T cell reconstitution, witnessed after rATG treatment. Our data support a combination treatment of rATG and thymus-protective strategies such as keratinocyte growth factor to simultaneously offer sufficient GvHD prophylaxis and overcome delayed T cell reconstitution caused by thymic damage.