Effects of different immunogenic amino acids in PD-L1 vaccine on the differentiation of T cell subsets

To compare the effects of endogenous 3-nitrotyrosine and non-natural 4-nitrophenylalanine in PD-L1 vaccine on the differentiation of T cell subsets, two immunogenic amino acids were introduced into the same site of PD-L1 vaccine. Two PD-L1 mutants with 3-nitrotyrosine and 4-nitrophenylalanine were obtained, respectively, using genetic code expansion technology. Mice were immunized with these two mutants, and their effects on the differentiation of T cell subsets in spleen were analyzed. The results of flow cytometry showed that the introduction of 4-nitrophenylalanine in PD-L1 vaccine could promote the polarization of Th1 cells while reducing the proportion of Treg cells; the introduction of 3-nitrotyrosine had no effect on the polarization of Th1 cells, while significantly increasing the proportion of Treg and Th17 cells. The introduction of both into PD-L1 vaccine could promote the response of CD8⁺ T cells in spleen, and the response of PD-L1 mutant containing 4-nitrophenylalanine was stronger. In summary, the non-natural 4-nitrophenylalanine is more suitable for the design of tumor vaccines as compared with endogenous 3-nitrotyrosine.