Nearly half of new GC cases annually are reported in China, and half of Chinese patients are diagnosed at an advanced stage of the disease[2]. The safety and efficacy of anti-PD-1 therapy in Chinese patients with AGC as salvage monotherapy or in combination with XELOX (oxaliplatin and capecitabine) at the first-line setting has been previously reported. The identification of reliable predictive markers for the OS of patients with GC receiving immunotherapy is the current research hotspot[23]. Somatic missense mutations strongly contribute to the generation of novel tumor epitopes[22]. The presence of more neoantigens on the tumor surface facilitates their recognition by immune cells, thus increasing the likelihood of immune response induction and potentially enhancing the efficacy of immunotherapy[24]. Furthermore, according to a clinical study, TMB-high patients responded to immunotherapy significantly better than TMB-low patients[3]. Although the development of immunotherapies has provided a new basis for the treatment of patients with GC, their potential mechanisms remain unclear. Thus, further investigations should be performed to develop the corresponding targeted therapy and immunotherapy[25–27]. Moreover, the increase in TMB, leads to more novel tumor epitopes, which may influence the TIICs. TIICs can promote and inhibit tumor growth, and studies have suggested that TIICs have great potential for the prediction of clinical outcome and therapeutic response among individual patients. The density and distribution of TIICs may play a role in predicting the survival of patients with GC[28]. Previous studies revealed that TIICs, such as mature T cells, dendritic cells, and memory T cells with increased infiltration, are associated with good prognosis, whereas immunosuppressive Treg cells are linked to poor prognosis[29, 30]. Some studies suggest that M1 macrophages can inhibit the growth of GC, while M2 macrophages play an important role in tumor progression, promoting a pro-angiogenic and immunosuppressive signal in the tumor[31]. However, most research studies applied immunohistochemical methods to evaluate TIICs and identify the TIIC subgroup with a single surface marker; these methods are ineffective in identifying closely related cell types. Furthermore, the distribution of multiple immune cells and their relative proportions are rarely studied. In addition, differences in TIICs between the TMB-high and TMB-low groups of patients with GC have been rarely reported. We propose that the differences in TIICs between the two GC groups may influence tumor immunotherapy and the OS of patients. Some meta-analyses showed that the expression levels of CD3, CD4, and CD8 were positively correlated with overall survival; however, higher FOXP3 expression was correlated with reduced overall survival[32, 33].
A combination of CIBERSOFT algorithms can overcome the shortcomings of traditional immunohistochemical methods and accurately determine the relative proportions of different TIICs[34]. In this study, we used CIBERSORT to describe the proportion of 22 immune cell subsets between the TMB-high and TMB-low groups. The results showed that the TMB-high group had a significant increase in some immune cells. With elevated TMB, more neoantigens may occur, and affect TIICs in the immune microenvironment[35]. According to the multivariate analysis, CD8 + T cells, activated memory CD4 + T cells, and neutrophils were associated with better OS. In contrast, monocytes, macrophages M2, and eosinophils were associated with worse OS[36]. Whether these complex differences in TIICs between the two groups could be potential targets for immunotherapy warrants further investigations.
In the present study, we analyzed mutations in gastric adenocarcinoma samples. The results showed that missense mutations, SNP, and C > T mutation were the most common mutations. The three most frequently mutated genes were TTN, TP53, and MUC16. TP53 is an established tumor suppressor gene reported to regulate the cell cycle, thus inhibiting the development of cancerous cells. TTN is the largest described protein and constitutes the third most abundant type of filament in both cardiac and skeletal human muscle. TTN is emerging as a major gene in human inherited disease[37]. MUC16 is frequently mutated in multiple types of human cancer, particularly GC[38]. In addition, MUC16 can play an important role in tumorigenicity and acquired resistance to therapy[39].
The potential biological functions of DEGs in gastric adenocarcinoma were analyzed. The functions of DEGs were mainly associated with extracellular structure organization, organic hydroxy compound transport, ECM, proteinaceous ECM, organic acid transmembrane transporter activity, and carboxylic acid transmembrane transporter activity. These genes were mainly involved in ‘ECM-receptor interaction’, ‘Wnt signaling pathway’, ‘protein digestion and absorption’, and the ‘PI3K-AKT signaling pathway’. The pathway of ‘ECM-receptor interaction’ has been reported in numerous types of cancer; the involved genes conferred the occurrence and progression of tumors and influenced cell phenotype[40–42]. The Wnt signaling pathway is mainly responsible for the development and homeostasis of cells and tissues via regulation of their endogenous stem cells, and could be used as a new therapeutic target to eliminate cancer stem cells[43, 44]. Activation of the PI3K/AKT pathway plays a critical role in frequent molecular alterations and the initiation and progression of cancer[45–47].
In this study, we found that 4 survival-related DEGs can influence the survival of gastric adenocarcinoma. These genes may become new targets for immunotherapy. It has been reported that DYNC1I1 could promote the proliferation and migration of GC by upregulating the expression of interleukin 6 (IL6)[48]. Matrix metalloproteinase 13 (MMP13) was highly expressed in GC tissues and related to invasion, metastasis, tumor stage, and worse survival[49]. Moreover, PD-1 ligand expression and CD3 + T cells are regulated by MMP13, which should be taken into account when using PD-1/PD-L1 blocking immunotherapies[50]. Zinc finger and BTB domain-containing 16 (ZBTB16) is a new biomarker for the primitive neuroectodermal tumor element or Ewing sarcoma[51]. Whether these genes could influence immune cell infiltration and be novel latent targets for immunotherapy warrants further investigation.