MHC restriction and cytolytic pathways of the T cells. (A) Inhibition of T-cell–mediated cytotoxicity against SP53 lymphoma cells by mAbs against MHC class I (HLA-ABC), MHC class II (HLA-DR), or HLA-A*0201 (HLA-A2). Isotypic IgG and cultures with medium without addition of the mAbs or isotypic IgG served as controls. An effector:target (E:T) ratio of 10:1 was used. (B) Flow cytometry analysis showing the expression of FasL, granzyme B, granzyme A, perforin, and CD45RO by HLA-A*0201-Py101 tetramer+ T cells. Shown are the results of gated CD8+ T cells of a T-cell line generated from a HLA-A*0201+ blood donor. Similar results were obtained with other Py101 peptide-specific T-cell lines from HLA-A*0201+ blood donors or MCL patients.