Fas (CD95) expression on EBV+ LCLs generated from human EBV⁺ B-cell tumors of hu-PBL-SCID mice. The solid peak represents staining with the FITC-conjugated anti-Fas MoAb, while the dashed line represents staining with an FITC-conjugated nonreactive isotype control MoAb. Eighteen LCLs generated from 18 individual human EBV⁺ B-cell tumors from hu-PBL-SCID mice demonstrated virtually identical reactivity for Fas expression as that shown here. The COLO 205 cell line lacks Fas expression and was used as a negative control and the Jurkat T-cell line was used as a positive control (not shown).44