Immunogenic HLA-B7-restricted peptides of hTRT

Abstract

Telomerase reverse transcriptase (TRT) is the first bona fide common tumor antigen. While several 9mer peptides of the human TRT have been identified for HLA-A2, little information exists on peptides for the remaining HLA types. Here, we used a multi-step approach to select and characterize a panel of HLA-B7 9mer peptides as candidate immunogens. In sequence, we used algorithm-based predictions, in vivo immunization of HLA-B7 transgenic (Tg) mice, in vitro immunization of human blood lymphocytes from two normal donors and two cancer patients, in vivo processing in HLA-B7 Tg mice and HLA-B7 supertype binding. We found a correlation between the in vivo immunogenicity and the actual HLA-B7 binding avidity of the seven predicted peptides. Furthermore, endogenous processing correlated with in vitro immunogenicity in human PBMC and HLA-B7 supertype binding. Peptide (1123)LPSDFKTIL(1131) (p1123) with the wider spectrum of supertype binding displayed the highest immunogenicity overall and was endogenously processed in several human lymphoblastoid cells. Since no single step of the screening/selection process could substitute for the whole approach, we conclude that the identification of MHC class I-restricted peptides for potential vaccination of cancer patients remains, by and large, an empirical process.

A novel minigene scaffold for therapeutic cancer vaccines

“…Previous studies have explored minigene vaccines comprising multiple contiguous minimal murine CTL epitopes 47 or contiguous dominant HLA-A*0201 and HLA-A*11-restricted epitopes from the polymerase, envelope, and core proteins of hepatitis B virus and HIV, together with the PADRE (pan-DR epitope) universal T-cell epitope and an endoplasmic reticulum-translocating signal sequence 48 . However, processing of individual epitopes in these minigenes is not assured due to the non-specific nature of proteasomal processing 49 . The approach of inserting AAY spacers between the epitopes and the use of ubiquitin as a protein-targeting sequence was previously tested in the context of minigenes containing CTL epitopes derived from MPT64 and 38 kDa proteins of Mycobacterium tubercolosis 32 .…”

Is telomerase a viable target in cancer?

“…The immune response can be induced by exposure to antigen presenting cells that either overexpress immunogenic hTERT fragments [92] or have been pulsed with immunogenic hTERT peptides. To date, 26 different hTERT peptides have been utilized to elicit an anti-telomerase immune response [88,97,101,102,104–111]. Vaccination studies using the I540–548 peptide have produced functional anti-tumor responses in prostate, breast and melanoma patients [89,96,112].…”

A second chance for telomerase reverse transcriptase in anticancer immunotherapy

“…Thus, p540 might be expressed at only the low end of natural antigen-presentation levels (~10 copies per cell) 22,23 . Over the years, further evidence showed that TERT is processed endogenously, and that TERT peptides are presented by cancer cells that express HLA-A*03, HLA-A*24, and HLA-B*7 MHC I molecules [24][25][26][27][28] .…”

“…This finding is important because immunization does not result in the de novo creation of antigenspecific T cells, but rather the selective expansion of reactive clones that pre-exist in the T-cell repertoire 15,16,24,26,28,33 . The in vivo immunogenicity of TERT has also been interrogated in preclinical models using a variety of approaches, including synthetic TERT peptides 15,24,28 , dendritic cells (DCs) transfected with TERT mRNA [34][35][36] , and DCs transduced with TERT-adenovirus 37 , TERT-encoding lentivirus vectors 38 , and plasmid DNA encoding TERT 39 . In selected instances, the induction of T-cell responses was associated with inhibition of tumour growth 34,[38][39][40][41] .…”