Impaired humoral immune responses in X-SCID/JAK3–deficient patients correlates with reduced generation of total and class-switched memory B cells. (A-B) PBMCs from age-matched controls (n = 11 [total B cells]; n = 18 [memory B cells]) or transplanted X-SCID/JAK3–deficient patients with either donor-derived B cells (group 1; n = 13) or autologous host B cells (n = 15 [total B cells]; n = 11 [memory B cells]; group 2) were labeled with mAb against CD19 (or CD20) and CD27. The frequencies of total B cells (A) or memory B cells (B) were then determined by flow cytometry. The plots are from representative donors and patients, with the values representing the mean of each group. The graphs show data points for all donors and patients examined, with the horizontal line representing the mean. ns indicates not significant (*P < .05; **P < .01). (C-D) Memory (CD20⁺CD27⁺) B cells from age-matched controls (n = 11) or group 1 (n = 6) or group 2 (n = 8) X-SCID/JAK3–deficient patients were labeled with mAb specific for IgM, IgG, or IgA. The frequency of memory B cells that were IgM⁺, IgG⁺, or IgA⁺ was then determined. (C) Histogram plots show IgG and IgA expression on memory B cells from representative patients corresponding to group 1 (gray-filled histogram) or group 2 (dashed black histogram). (D) Data points for all donors and patients examined, with the horizontal line representing the mean (*P < .05; ***P < .005).