Improvement of the defect in influenza virus immunity by stem cell targeted gene transfer. (A) Percentage of splenic CD8⁺ T cells positive for influenza NP antigen–specific receptors following secondary influenza challenge. Eight to 9 weeks following primary inoculation,¹⁰  gene-corrected and several control animals received a secondary challenge with influenza. Eight to 9 days later, splenic T cells were harvested. WT indicates wild type; WASP^—, hemizygous deficient male animal; MG, control GFP encoding vector; MWG, bicistronic vector encoding WASP and GFP; and n, number of animals in each group. The difference in the percentage of NP-specific cells between the WASP^—/MG and WASP^—/MWG groups is statistically significant (P < .02). (B) Cytokine production by gene-corrected and control splenic T lymphocytes after stimulation with influenza-specific NP peptide following secondary influenza challenge. Splenic CD8⁺ cells were cultured in the presence of Brefeldin A and NP peptide and then analyzed by flow cytometry as described in “Materials and methods.” IFN-γ and TNF-α production by stimulated CD8⁺ splenic T cells from a gene-corrected animal killed 9 days after secondary influenza challenge were measured as described in “Materials and methods.” (C) Summary of cytokine secretion by splenic T cells of gene-corrected and control animals. Abbreviations are as defined in the legend to Figure 6. n indicates the number of animals included in each group. The difference in the percentage of double-positive cells between the WASP^—/MG and WASP^—/MWG groups is statistically significant (P < .03).