Purpose: To investigate potential immunotherapeutic strategies in B lymphocytic malignancies we looked for CTLs recognizing CD19 and CD20 epitopes.
Experimental design: Three CD19 and CD20 peptides binding to HLA-A*0201 were identified and used to detect peptide specific CTLs by a quantitative real-time PCR to measure IFN-gamma mRNA expression in 23 healthy individuals and 28 patients (18 chronic lymphocytic leukemia (CLL), 7 follicular lymphoma, 2 acute lymphocytic leukemia, and 1 large cell lymphoma). Peptide-specific CTLs were expanded in culture with CD40-activated B cells to test lytic activity in three patients.
Results: In healthy individuals, CD8+ T-cell responses were detected in one to CD19(74-82), in three to CD20(127-135), and three to CD20(188-196). Seven of 27 patients (6 with CLL) had CD8+ T cells recognizing CD19(74-82). Seven patients responded to CD20(127-135) and three to CD20(188-196). All were CLL patients. CD19(74-82)-specific CTLs from three patients were expanded over 4 weeks. These cells were HLA-A*0201 specific and lytic for peptide-loaded antigen-presenting cells but not to malignant or unpulsed B cells.
Conclusions: CTLs that recognize CD19 and CD20 epitopes exist in healthy individuals and may be increased in CLL patients. They are of low avidity and require high doses of peptide for activation. Strategies to increase T-cell avidity would be necessary for T-cell immunotherapeutic approaches using the peptides studied.