We previously discovered one particular
HLA-A*02:01 mutant that enhanced
peptide-specific cytotoxic T lymphocyte (CTL) recognition in vitro compared to wild-type
HLA-A*02:01. This mutant contains a single amino acid substitution from
histidine to
leucine at position 74 (H74L) that is located in the
peptide-binding groove. To investigate the effect of the H74L mutation on the in vivo CTL priming, we took advantage of the technology of the HLA class I single-chain trimer (SCT) in which three components involving a
peptide, β2 microglobulin and the HLA class I heavy chain are joined together via flexible linkers. We generated recombinant adenovirus expressing SCT comprised
influenza A matrix
protein (
FMP)-derived
peptide, β2 microglobulin and the H74L heavy chain.
HLA-A*02:01 transgenic mice were immunized with the adenovirus, and the induction of
peptide-specific CTLs and antitumor immunity was investigated. It was clearly shown that the H74L mutation enabled the
HLA-A*02:01 SCT molecule to dramatically enhance both in vivo priming of
FMP-specific CTLs and protection against a lethal challenge of
tumor cells expressing
FMP. These data present the first evidence that a simple point mutation in the HLA class I heavy chain of SCT is beneficial for improving CTL-based
immunotherapy and prophylaxis to control
tumors.