Functional analysis of human T and B cells developed in NOD/SCID/IL2rγ^nullrecipients. (A) Production of OVA-specific human immunogloblins. Two weeks after immunization with OVA, sera of 5 independent recipients were sampled, and were evaluated for the concentration of OVA-specific human IgM (□) and IgG (▦) by ELISA. Sera of 3 nonimmunized NOD/SCID/IL2rγ^null recipients were used as controls. O.D. indicates optical density. (B) Cytotoxic activity of human T cells generated in NOD/SCID/IL2rg-null mice. hCD4⁺ and hCD8⁺ T-cell clones derived from the recipient spleen were cocultured with allogeneic target cells (TAK-LCLs). KIN-LCLs that do not share any HLA type with effector cells or TAK-LCLs (X) were used as negative controls. Both hCD4⁺ and hCD8⁺ T-cell lines displayed cytotoxic activity against TAK-LCL in a dose-dependent manner. In hCD4⁺ T-cell clones, this effect was blocked by anti–HLA-DR antibodies (▴), whereas in hCD8⁺ T-cell clones, the effect was blocked by anti–HLA class I antibodies (▪). ♦ indicates cytotoxic response to TAK-LCLs without addition of antibodies.