Identification and modification of an HLA-A*0201-restricted cytotoxic T lymphocyte epitope from Ran antigen

Ran is considered to be a promising target for tumor-specific immunotherapy because its protein is exclusively expressed in tumor tissues, though its mRNA can be expressed in most normal tissues. In our study, we obtained four candidate wild-type epitopes designated Ran1, Ran2, Ran3, and Ran4, derived from the Ran antigen with the highest predicted affinity with MHC-I, indicated by affinity prediction plots and molecular dynamics simulation. However, in vitro affinity assays of these epitopes showed only a moderate affinity with MHC-I. Thus, we designed altered peptide ligands (APLs) derived from Ran wild-type epitopes with preferred primary and auxiliary HLA-A*0201 molecule anchor residue replacement. Of the eight tested peptides, the 1Y analog had the strongest binding-affinity and lowest-dissociation rate to HLA-A*0201. Additionally, we investigated the CTLs activities induced by Ran wild-type peptides and the APLs in human PBMCs and in HLA-A*0201/K^b transgenic mice. Ran1 1Y was superior to other APLs and wild-type peptides in eliciting epitope-specific CTL immune responses both in vitro and in vivo. In summary, a wild-type epitope of the tumor-specific antigen Ran, expressed broadly in many tumors, was identified and designated Ran1. An APL of Ran1, Ran1 1Y, was further designed and verified in vitro and in vivo and found to elicit a stronger Ran-specific CTL response, indicating a potential anti-tumor application in the future.