Identification of novel CTL epitopes of CMV-pp65 presented by a variety of HLA alleles

Cytomegalovirus (CMV)-specific T-cell immunity plays an important role in protection from CMV disease in immunocompromised patients. Identification of cytotoxic T-lymphocyte (CTL) epitopes is essential for monitoring T-cell immunity and also for immunotherapy. In this and previous studies, CMV-pp65-specific CTL lines were successfully generated from all of 11 CMV-seropositive healthy donors, using pp65-transduced CD40-activated B (CD40-B) cells as antigen-presenting cells. By use of enzyme-linked immunospot (ELISPOT) assays, individual CTL epitopes could be mapped with truncated forms of the pp65 gene. For human leukocyte antigen (HLA) alleles with a known binding motif, CTL epitopes within the defined regions were predicted by computer algorithm. For HLA alleles without a known binding motif (HLA-Cw*0801, -Cw*1202, and -Cw*1502), the epitopes were alternatively identified by step-by-step truncations of the pp65 gene. Through this study, a total of 14 novel CTL epitopes of CMV-pp65 were identifled. Interestingly, 3 peptides were found to be presented by 2 different HLA class I alleles or subtypes. Moreover, use of CD40-B cells pulsed with a mixture of synthetic peptides led to generation of pp65-specific CTL lines from some of seronegative donors. The study thus demonstrated an efficient strategy for identifying CTL epitopes presented by a variety of HLA alleles.