b12-IgA transgene expression in B cells and plasma cells in mucosal and lymphoid tissues. (A) Human B cell (CD45⁺CD19⁺)–specific expression of transgene in hu-BLT mice. Gut-homing lymphocytes were isolated from the epithelia and lamina propria of the small and large intestine and genital tract-homing lymphocytes were isolated from the entire genital tract except the testis or ovary. Flow cytometry of the ZsGreen reporter gene expression of the lymphocytes isolated from PBMC, spleen, lymph node, gut and genital tract. The ZsGreen fluorescence of CD19⁻ cells (filled histogram) and CD19⁺ (solid lines) was analyzed after gating on CD45⁺ human leukocytes. (B) Percent transgene expression of CD19⁻ (black) and CD19⁺ (white) cells from peripheral blood of hu-BLT mice transduced with Luc-ZsGreen vector or b12-IgA-ZsGreen vector (n = 4-5, mean ± SEM). (C) Enzyme-linked immunosorbent assay of the secreted b12-IgA in plasma of hu-BLT mice transduced with Luc-ZsGreen vector (black) or b12-IgA-ZsGreen vector (white) at 10 weeks posttransplantation of human HSPCs (n = 6-8, mean ± SEM). (D) Plasma cell development from transplanted human HSPCs in hu-BLT mice transduced with b12-IgA-ZsGreen and transgene expression in long-lived plasma cells. Flow cytometry of bone marrow mononuclear cells (Di-iii) and gut lymphocytes (Div-Dvi) isolated from 22 to 24 week posttransplanted hu-BLT mice, with gating on CD45⁺ cells. The contour plots (Di,iv) show CD138⁺CD45^int plasma cells (R1) and CD138⁺CD45^hi (R2) plasma cells. R1 and R2 cell populations were then separately plotted by CD38 and CD138 expression (Dii,v). Histograms (Diii,vi) display reporter gene ZsGreen expression in CD45^hiCD138⁺CD38⁻ cells, CD45^hiCD138⁺CD38⁺ early plasma cells and CD45^intCD138⁺CD38⁺ mature plasma cells.