The B-cell population in hu-mice expressing mBAFF or hBAFF. hu-mice were generated by transplanting CB CD34⁺ cells into BRGS or hBAFFKI-BRGS mice and these animals were analyzed 23 to 24 weeks after transplantation. (A) Representative flow cytometric analysis of bone marrow (top) and spleen (bottom) cells from BRGS (mBAFF) and hBAFFKI-BRGS (hBAFF) hu-mice. The human leukocyte (hCD45⁺) population was measured within the combined mouse and hCD45⁺ cell fraction of both bone marrow and spleen. The frequency of human B cells (CD19⁺ in bone marrow and CD20⁺ in spleen) was measured within the hCD45⁺ cell fraction. (B) Frequencies of hCD45⁺ cells in the combined mouse and human leukocyte population of bone marrow and spleen of BRGS (□) and hBAFFKI-BRGS (▪) hu-mice. (C) Frequencies of B cells within the hCD45⁺ cell populations (top) and absolute numbers (bottom) in bone marrow and spleen of BRGS and hBAFFKI-BRGS hu-mice. Each symbol in panels B and C represents a mouse; bars are mean and SEM. N = 14 to 23 mice per group and 3 to 4 different CB groups. **P < .01.