It has been well established that immune surveillance plays critical roles in preventing the occurrence and progression of tumor. More and more evidence in recent years showed the host anti-tumor immune responses also play important roles in the chemotherapy and radiotherapy of cancers. Our previous study found that tumor- targeting therapy of anti-HER2/neu mAb is mediated by CD8(+) T cell responses. However, we found here that enhancement of CD8(+) T cell responses by combination therapy with IL-15R/IL-15 fusion protein or anti-CD40, which are strong stimultors for T cell responses, failed to promote the tumor therapeutic effects of anti-HER2/neu mAb. Analysis of tumor microenviornment showed that tumor tissues were heavily infiltrated with the immunosuppressive macrophages and most tumor infiltrating T cells, especially CD8(+) T cells, expressed high level of inhibitory co-signaling receptor PD-1. These data suggest that tumor microenvironment is dominated by the immunosuppressive strategies, which thwart anti-tumor immune responses. Therefore, the successful tumor therapy should be the removal of inhibitory signals in the tumor microenvironment in combination with other therapeutic strategies.
Animals ; Antibodies, Monoclonal ; immunology ; therapeutic use ; Breast Neoplasms ; drug therapy ; immunology ; pathology ; Cell Line, Tumor ; Female ; Humans ; Immune Tolerance ; immunology ; Mice ; Mice, Inbred BALB C ; Neoplasm Transplantation ; Receptor, ErbB-2 ; immunology ; Tumor Microenvironment ; immunology

Objective: To investigate the function of anti-PD-1 (scFv)/IL-15/IL-15Rα-sushi fusion protein (PD-S15) to specifically bind to PD-1 in vitro and to explore its effect on NK/T cell proliferation. Methods: The human anti-PD-1 (scFv) gene sequence and human IL-15/IL-15Rα-sushi fusion gene sequence were synthesized chemically. The recombinant expression plasmid pUC57-PD-S15 was constructed by enzyme digestion and ligation of the two target genes, and then transiently transfected into HEK293T cells by lipofectamineTM 2000. The supernatants of cell culture medium were acquired, and the expression of PD-S15 fusion protein in cell culture supernatants was detected by Wb assay. PBMCs and TILs were cultured in mediums with different proportion of PD-S15/X-VIVOTM15, respectively. Then, the capacity of PD-S15 fusion protein to bind to PD-1 in vitro and its effect on the proliferation of PBMCs and the proportion of CD3+CD8+, CD3+CD4+ and CD3-CD56+ subsets were detected by flow cytometry. The effect of PD-S15 fusion protein on the proliferation of TILs was detected by cytometry. Results: The successful construction of pUC57-PD-S15 eukaryotic expression plasmid was confirmed by double enzyme digestion and sequencing, and then successfully transfected into HEK293T cells. The relative molecular weight of the target protein was approximately 55 000, and was in line with expectations. PD-S15 fusion protein could specifically combine with PD-1 in vitro (P<0.05) and stimulate NK/T cell proliferation (P<0.05). Compared with classical TILs culture method, the efficiency of activation and amplification of T cells in vitro by PD-S15 culturemethodwasbetter (P<0.01). Conclusion: PD-S15 fusion protein can specifically target PD-1 and rapidly expand NK/T cells in vitro, which lays a foundation for the selective expansion of CD8+PD-1+ antigen-specific T lymphocytes from tumor tissues and even peripheral blood.