CD276 suppresses CAR-T cell function by promoting tumor cell glycolysis in esophageal squamous cell carcinoma

Background

As an immune checkpoint that suppresses antitumor immunity, CD276 is a potential therapeutic target for cancer immunotherapy. However, the role of CD276 in esophageal squamous cell carcinoma (ESCC) has not been thoroughly examined. A greater understanding of the regulatory mechanism of CD276 may improve the clinical response and efficacy of cancer immunotherapy.

Methods

The expression of CD276 was measured by qRT-PCR, IHC and flow cytometry analysis. T cell infiltration in ESCC was measured by qRT-PCR and immunofluorescence analysis. The regulation function of CD276 in glucose metabolism was examined by metabolism assays, western blotting and small molecule inhibitors. Transfection was used for gene editing. The oncogenic function of CD276 was examined in vivo by CAR-T cell therapy model.

Results

Based on our findings, CD276 regulated the expression of the PKM2 gene in ESCC. Overexpression of CD276 induced the phosphorylation of PKM2 by the STAT3 signalling pathway to promote glucose metabolism in tumors. The accumulation of lactic acid in the tumor microenvironment has been reported to regulate the immune cells, particularly CD8+ T cells. We further analyzed the effect of CD276 on the function of T cells. Chimeric antigen receptor T cells (CAR-T) targeting human epidermal growth factor receptor 2 (HER2) were used as effector cells to detect the effect of CD276 on immunotherapy. The therapeutic effects of CAR-T cells were markedly limited by CD276 overexpression.

Conclusions

Our results are the first to show that tumor-derived CD276 supports disease progression. Overexpression of CD276 promoted glucose metabolism in tumor and inhibited the function of CD8+ T cells. Therefore, strategies targeting CD276 might improve the response to cancer immunotherapy of ESCC patients.

Development of a novel mammalian display system for selection of antibodies against membrane proteins

Reliable, specific polyclonal and monoclonal antibodies are important tools in research and medicine. However, the discovery of antibodies against their targets in their native forms is difficult. Here, we present a novel method for discovery of antibodies against membrane proteins in their native configuration in mammalian cells. The method involves the co-expression of an antibody library in a population of mammalian cells that express the target polypeptide within a natural membrane environment on the cell surface. Cells that secrete a single-chain fragment variable (scFv) that binds to the target membrane protein thereby become self-labeled, enabling enrichment and isolation by magnetic sorting and FRET-based flow sorting. Library sizes of up to 109 variants can be screened, thus allowing campaigns of naïve scFv libraries to be selected against membrane protein antigens in a Chinese hamster ovary cell system. We validate this method by screening a synthetic naïve human scFv library against Chinese hamster ovary cells expressing the oncogenic target epithelial cell adhesion molecule and identify a panel of three novel binders to this membrane protein, one with a dissociation constant (KD ) as low as 0.8 nm We further demonstrate that the identified antibodies have utility for killing epithelial cell adhesion molecule-positive cells when used as a targeting domain on chimeric antigen receptor T cells. Thus, we provide a new tool for identifying novel antibodies that act against membrane proteins, which could catalyze the discovery of new candidates for antibody-based therapies.