PhD student Drexel university Philadelphia, Pennsylvania, United States
Disclosure(s):
Amirali Amirfallah, PharmD: No financial relationships to disclose
Introduction/Rationale: Immune checkpoint inhibitors (ICIs) have revolutionized melanoma treatment. However, about half of patients still face disease progression. ICI efficacy depends on tumor-infiltrating lymphocytes, particularly CD8+ T cells. Understanding genes that influence CD8+ T cell infiltration is critical for improving and predicting ICI responses. Here, we investigate ST8SIA4, a sialyltransferase that synthesizes polysialic acid(polySia). Our data suggest ST8SIA4 influences the tumor microenvironment (TME) toward a hot tumor.
Methods: To better understand determinants of tumor immune infiltration, we examined TCGA-SKCM data utilizing Tumor Immune Estimation Resource, grouping samples by CD8+ T cell infiltration. SurfaceGenie was used to prioritize proteins that localize to the cell surface or contribute to surface modifications. Based on in silico data, we created a murine melanoma cell line inducibly expressing ST8SIA4. Immune infiltration was assessed in vitro using spheroid co-cultures with syngeneic CD8+ T cells and in vivo with high-dimensional flow cytometry-based immune phenotyping. Siglec binding was assessed by flow cytometry using Siglec FC chimera.
Results: In silico analysis revealed 43 genes upregulated in high CD8+ T cell tumors. Among these, ST8SIA4 had the highest correlation with survival. Further analysis shows that ST8SIA4 expression is elevated in patients responsive to ICIs, including PD-1 and CTLA-4 inhibitors. Spheroid co-cultures with syngeneic CD8+ T cells indicate more immune infiltration when melanoma spheroids are expressing ST8SIA4. Furthermore, in vivo analysis suggests that ST8SIA4-expressing melanomas recruit more CD45+CD8+ and CD45+NK1.1+ populations compared to parental tumors. Our preliminary in vitro data suggest this phenotype is Siglec-independent in murine cell lines and potentially mediated by other immune regulatory factors.
Conclusion: These findings suggest ST8SIA4-mediated polySia modulates TME immune population and can be a potential biomarker for ICI response.
