Low Efficiency of a Newly Introduced High-Density Microparticles Method for B Cell Depletion in Multiple Myeloma Patients Undergoing Autologous Hematopoietic Stem Cell Transplantation

Autologous peripheral blood stem cell (PBSC) transplantation proved to increase complete remission (CR) and DFS in multiple myeloma (MM) patients. CD34+ cell selection has been used to reduce possible myeloma cell contamination in the graft, but it has not been showed to offer substantial advantages when compared to unpurged grafts; on the contrary, an increase of infectious complications was observed. We investigated the feasibility of a new negative-selection method in this setting. B cell negative selection was performed by using Eligix® B cell HDM method. B cell contamination in the yield and in the final product was investigated by now cytometry. Three patients with newly diagnosed MM entered the study. CD34+ cell recovery in the three procedures was 73, 97, and 106%, and CD3+ cell recovery was 88, 86, and 102%, respectively. CD20+ cell depletion was 100% in all procedures, while CD19+ cell depletion was 0.37, 1.21, and 0.07 log, respectively. We found an unexpected unreliability and a low efficiency in this B cell depletion method and suggest the need for further extensive testing before its introduction in the preclinical and clinical settings, at least in MM patients. In fact, reasons of such unsatisfactory results are still controversial: platelet contamination/activation in the preselection product, plasma protein interference, reduced CD19 antigen expression on immature B cells, lack of specificity of anti-CD19 monoclonal antibodies, instable binding between anti-CD19-coated high-density microparticles (HDM) and CD19 antigen may, alone or in combination, be involved in the system's low performance.