Background
Glioma is the most prevalent malignant brain tumor in adult, accounting for 45 ~ 60% of all cases [
1]. According to the biological behavior, glioma can be classified into lower-grade glioma (grade II and grade III) and glioblastoma by World Health Organization. The molecular features, including IDH, MGMT, 1p/19q, and so on, were brought into the updated CNS classification in 2016 [
2]. Even though numerous studies facilitated the development of glioma, the median overall survival of glioblastoma is 14.6 months, with standard of care surgery, radiotherapy, and chemotherapy [
3]. New approaches are needed for glioma patients urgently.
Recently, immunotherapy has revolutionized the treatment of multiple tumors and has been successful for treatment of lung cancer [
4], bladder cancer [
5], and skin cancer [
6]. Tumor-specific antigens (TSAs), silenced in most somatic tissues, are specifically expressed in cancer cells and often evoke strong immune responses [
7]. The majority of TSAs were neoantigens that resulted from several genomic aberrations in tumors, such as somatic mutation, copy number aberration, and gene overexpressed [
8]. This “tumor-specific” expression pattern in TSA displayed crucial significance for targets in cancer management. Therapeutic mRNA vaccination approaches against human had some encouraging clinical data in influenza virus, Zika virus, rabies virus, and MERS-CoV and SARS‑CoV-2 viruses [
9‐
11]. mRNA vaccine technology provides a new promising era for vaccine technology and had several advantages over DNA vaccines as they induce immune response at a very low concentration, possess high efficacy and safety [
12]. Therefore, mRNA vaccines are pivotal target for cancer immunotherapy.
The goal of this study was to dig out the potential mRNA vaccines for LGG and GBM patients, respectively. Two over-expressed, amplified, and mutated genes were discovered as TSAs in LGG (PTBP1 and SLC39A1), and two TSAs were identified in GBM (MMP9 and SLC16A3). The four TSAs were relevant to poor prognosis and antigen presenting cell (APC) infiltration. LGG and GBM samples were clustered based on immune characteristics, and different immune subtypes corresponded to distinct clinical, molecular, and cellular characteristics. Our results indicated that the immune pattern in LGG was not exactly the same as GBM patients. The four candidates might provide a theoretical basis for the development of mRNA vaccines.
Discussion
Glioma are the most prevalent brain malignant tumor in adults [
21]. Current treatment for glioma is mainly donated by surgical resection followed by radiotherapy and chemotherapy. However, due to the toxicity to normal cell, resistance to temozolomide and high rate to recurrent, the treatment is limited [
22,
23]. mRNA vaccine, which could activate innate immune activation-mediated co-stimulation, is one important approach in immunotherapy [
24]. One of the challenge and bottleneck for manufacturing mRNA vaccine for glioma was to select antigens uniquely overexpressed in cancer cells.
Here, we combined the gene expressed pattern, mutation profiles, and copy number aberration to detect TSA genes as immunological and clinical targets in glioma. Tumor antigens are mainly derived from upregulated and mutated genes. In CGGA and TCGA datasets, the tumor-normal comparisons were executed to find out the over-expressed, amplified, and mutated genes in LGG and GBM, respectively. Then the Kaplan–Meier analysis was conducted to explain the clinical significance of candidate tumor-specific antigens. We found the expression of PTBP1 and SLC39A1 in LGG and MMP9 and SLC16A3 in GBM were significantly associated with worse OS in CGGA and TCGA cohorts. The results indicated that the development of mRNA vaccines targeted these four genes may prolong the survival time of glioma patients.
Antigen-presenting cells (APCs), a heterogeneous group of immune cells, mediated the cellular immune response by processing and presenting antigens for T cells, including macrophages, B cells and dendritic cells. The correlation analysis of APCs and TSA genes indicated that the expression of PTBP1 and SLC39A1 were significantly positively associated with high APC infiltration, especially macrophages and DCs. Meanwhile, the expression of MMP9 and SLC16A3 were significantly positively associated with macrophages infiltration. The macrophages, composed of bone marrow-derived macrophages (BMDMs) and brain-resident microglia (MG), constituted the most abundant immune cell population in the tumor microenvironment in glioma [
25]. The macrophages have been revealed as key role for the progression of glioma. Our results indicated that the amount and subtype of macrophage had critical effect on antigen presenting in glioma, especially GBM.
These results indicated that PTBP1, SLC39A1, MMP9, and SLC16A3 potentially played vital roles in immunity as TSAs. Numerous studies have shown that PTBP1, a protein coding gene, played essential roles in various cancers, including colorectal cancer, renal cell cancer, breast cancer, and glioma [
26]. The PTBP1 performed functions through regulating of glycolysis, apoptosis, proliferation, tumorigenesis, invasion, and migration [
27]. SLC39A proteins are ZIP metal ion transport proteins which mainly expressed on the plasma membrane in various tissues [
28]. SLC39A1 may play an important role in tumor progression [
29]. SLC39A1 could significantly decreased the level of Zn2 + in cancer tissue, thereby reducing the level of citrate, and ultimately resulting in the malignant progression of prostate cancer and glioma [
30]. MMP-9, a member of the matrix metalloproteinases (MMP) family known to confer invasive behavior to cancer cells. MMP9 is highly expressed in cancer and played crucial roles in carcinogenesis and progression [
31]. SLC16A3 is a member of the proton-linked monocarboxylate transporter (MCT) family. Previous studies have confirmed that hypoxia can induce SLC16A3 expression through HIF-1 pathway and participate in the occurrence and development of tumors [
32,
33]. These results clearly suggested that they may be potential targets for mRNA vaccines.
mRNA vaccines are a type of treatment that active the immune system to fight cancer cells and induced long-term remission only in the minority of patients. We categorized LGG and GBM into different immune subtypes based on immune gene expression profiles for selecting the population suitable for vaccination. Each immune subtype corresponded to distinct clinical, molecular and cellular characteristics. In LGG patients, LGG2 was shown to have a better prognosis. The expression level of ICD modulators and ICPs were significantly upregulated in LGG2 patients. Meanwhile, LGG2 showed significantly elevated scores in antigen-presenting cells and cytolytic T lymphocytes. In GBM patients, GBM1 was shown to have a better prognosis. The expression level of ICD modulators and ICPs were significantly upregulated in GBM1 patients. Meanwhile, GBM1 showed significantly elevated scores in antigen-presenting cells and cytolytic T lymphocytes. These results indicated that mRNA vaccine could be more effective in patients in LGG2 and GBM1.
Compared to the studies conducted by Quanwei Zhou et al. [
34], Shuai Ma et al. [
35], and Hua Zhong [
36], the approach for selecting antigen genes in this study exhibited more advantages. We used normal brain samples as control group to find out specific antigen genes in LGG and GBM patients in multi-platform. In this study, limited by the retrospective nature of our study, a large-scale prospective study is needed to evaluate the clinical significance of the four potential antigen genes.