materials and methods statistical analysis the data were described as mean ± standard deviation ( sd ) and the statistical significance was determined by one - way anova before lsd test for multiple comparisons and independent - sample t - test for comparison between the two groups. the level of p * * * results * * * discussion the host immune system exerts immunosurveillance to control cancer development. by inducing the expression of immunosupp ressive factors, however, tumor hif - 1 signaling subdues both the innate and adaptive immune responses, thereby shielding the tumor from immune attacks. in addition, insufficient expression of mhc class i on cancer cells is one of the important strategies employed by cancer to evade the immune system. therefore, inhibition of hif - 1 and improvement of mhc class i expression on cancer cells is important to induce effective responses of cell - mediated immunity against cancer such as lung cancer for immunotherap ies, including pd - 1 / pd - l1 inhibitor. the effect of endostar in inhibiting hif - 1 and promoting mhc class i expression on cancer cells, such as lung cancer cells, may counteract cancer immune evasion and thereby benefit cancer immunotherap y. however, this remains unclear. this study was designed to determine the effect of endostar in inhibiting hif - 1 and promoting mhc class i expression on lung cancer cells. endostar was administrated to a549 and nci - h1299 lung cancer cells and the protein of hif - 1 and mhc class i and their mrnas was detected by western blot and rt - qpcr. the lower hif - 1 and higher mhc class i were found in endostar treated a549 and nci - h1299 cells. these findings demonstrated inhibtion on hif - 1 and promotion on mhc class i by endostar, suggesting the potential of endostar to benefit lung cancer immunotherap y. endostar, an n - terminal modified recombinant human endostatin, is a human recombinant endostatin, an attractive anti - angiogenesis protein. therefore, endostar has anti - angiogenesis effects. endostar was developed as a specific drug permitted by the state food and drug administration in china in 2005 for its use in nsclc therapy. 25, 26 endostatin is a natural protein, first isolated and extracted from mouse tumors by judah folkman, with a wide antitumor spectrum and strong antiangiogenic capacity. 27, 28 angiogenesis is a physiological process of forming new blood vessels from existing blood vessels and circulating endothelial precursors. it is essential to the occurrence and development of tumors, which grow rapidly and metastasize eventually. 24 physiologically, angiogenesis is essential to physiological processes like embryogenesis, tissue growth, and regeneration. 29, 30 oncologically, it is also important for cancer cells that grow rapidly and metastasize eventually because angiogenesis supplies oxygen and nutrients which are deficient in cancer cells for their rapid growth and eventual metastasis. 31 therefore, anti - angiogenesis is one of the most important cancer therapies. 32 endostar as a recombinant human endostatin with nine added amino acids ( mggshhhhh ) 33 to maintain stability and a long half - life has effective antiangiogenic effect. besides, it was shown in this study that endostar inhibited hif - 1 with upregulation of mhc class i expression in a549 and nci - h1299 lung cancer cells, benefiting cancer cell killing by effectory lymphocytes. hif - 1, a heterodimer consisting of a constitutive β - subunit and an oxygen - sensitive α - subunit, 34 is a main transcriptional regulator responsible for metabolic adaptation to alterations in the oxygen environment. it involves in many physiological and pathological processes in the body and is closely associated with the pathogenesis of many diseases. 13 in solid tumors, uncontrolled proliferation of cancer cells vs disor ganized growth of blood vessels results in limited supply of nutrients and oxygen resulting in low oxygen tension; therefore, regions with hypoxic microenvironments are created. in these regions, the highly overexpressed hif - 1 is important to drive tumor growing, invasion, and metastasis in different human cancers. 35, 36 the association of a poor survival with the high expression of hif - 1α has been indicated by survival analysis in patients with lung cancer, and different snps in hif - 1α may have different effects on overall cancer risk in an ethnicity - and type - specific manner. 37 reduction of hif - 1α by simvastatin enhanced anti-tumor effects of bevacizumab in a549 cells. 38 targeting atm / hif - 1α signaling by solanidine induced anti - angiogenesis and anti - cancer effect in lung cancer. 39 besides its involvement in various aspects of tumor development, such as tumor growth, invasion, metastasis, and angiogenesis, hif - 1 is also involved in tumor immune evasion which facilitates cancer cells to proliferate and metastasize, and contributes to failure in immunotherap y. 40 inhibition of hif - 1 expression in cancer cells contributes to cancer control and induction of effective anti - cancer immunity in cancer immunotherap y. endostar has the effect to down-regulate hif - 1. 41 it was shown in this study that 25 μg / ml endostar inhibited hif - 1 expression in a549 and nci - h1299 lung cancer cells. hif - 1 is induced by hypoxia in cancer cells, 42 and in normoxia, it is not usually observed or only basal expression can be observed. 43, 44 in this study, experiments showed a high expression of hif - 1 in control and untreated cells. however, this did not necessarily mean that the expression of hif - 1 in control and untreated cells was really high because it was detected with the expression in endostar treated a549 cells and nci - h1299 cells as the backgroud. the expression detected by western blot and immunocytochemistry is relative quantification. the assays had been optimized for enough sensitivity to detect the reduced expression in endostar treated a549 cells and nci - h1299 cells. an effective adaptive response can be achieved through a multi - step antigen processing and pathway, namely the cellular antigen processing machinery ( apm ). antigens must be processed into antigenic peptides by apm. these peptides are loaded onto an mhc class i molecule. mhc class i molecules are glyco proteins of heterodimers with a polymorphic heavy chain ( α - chain ) and an invariable β2 microglobulin ( β2 m ) light chain ( β - chain ). the α - chain is encoded by the human leukocyte antigen - hla a, b, and c genes in humans. there is a groove in the mhc class i molecules to preferentially bind 8 - 11mer peptides. the antigenic epitope binds to the exposed surface of this groove as a part of the mhc class i complex. it is recognized by the tcr on the t cells. 45 this study showed that the expression of mhc class i α - heavy chain and β2 m light chain in a549 and nci - h1299 lung cancer cells was improved by endostar, which benefited cancer immunotherap y against the lung cancer cells. in the context of hif - 1 down - regulation by endostar, which was shown in this study, to demonstrate the role of hif - 1 on the mhc class i α - heavy chain and β2 m light chain in a549 and nci - h1299 lung cancer cells, the over - expressing hif - 1 gene was transfected into a549 and nci - h1299 cells resulting in decrease of relative levels of mhc class i α - heavy chain and β2 m light chain. this results were in line with the decrease of hif - 1 by endostar treatment accompanied with the enhancement of mhc class i α - heavy chain and β2 m light chain. in addition to the important role in metabolic adaptation to hypoxia stress caused by deficient supply of nutrients and oxygen because of uncontrolled growth of cancer cells and disor ganized neoangiogenesis, the signaling pathways of hif - 1, a heterodimer highly expressed in a variety of tumor cells, suppress innate and adaptive immune systems to escape immune attack.