Human B cell growth and differentiation in the spleen of immunodeficient mice

Human mAbs (HumAbs) have therapeutic potential against infectious diseases and cancer, Heretofore, their production has been hampered by ethical const raints preventing the isolation of Ag-specific activated B cells by in vivo immunization. Alternatively, severe combined immune deficient (SCID) mice, transplanted i.p. with human (Hu)-PBLs, allow the in vivo stimulation of h uman Ab responses without the usual constraints. Unfortunately, human B cel ls only represent a minor fraction of the surviving graft, they are scatter ed all over the animal body, and thus are hard to isolate for subsequent im mortalization procedures. To prevent this dispersion and to provide the hum an B cells with a niche for expansion and maturation, SCID mice were engraf ted with Hu-PBL directly into the spleen. Simultaneously endogenous murine NK cell activity was depleted by treatment with an anti-mouse IL-2 receptor beta -chain Ab. During engraftment, human B lymphocytes became activated, divided intensely, and differentiated into plasmacptoid tells. In vivo expo sure to a recall Ag after cell transfer induced expansion of Ag-specific B cell clones. One week after inoculation, human B cells mere abundant in the spleen and could easily be recovered for fusion with a heteromyeloma line. This resulted in the formation of stable hybridoma cell lines that secrete d Ag-specific HumAbs. Thus transplantation of human lymphoid cells in the s pleens of immune deficient mice represents a model for the study of human T cell-dependent B cell activation and proves to be an excellent tool for th e successful production of HumAbs.