Resolving the initiating changes in the immunomodulatory glycome during early tumorigenesis of head and neck squamous cell carcinoma in living animals

Cancer cells exploit the intricate network of stimulatory and inhibitory pathways to prevent immune-mediated clearance and thrive in an immunocompetent biological system. While targeting immune checkpoints (ICs) to reactivate the immune response has proven to enhance tumor-immune infiltration and patient prognosis, efficacy is limited only to a subset of patients. Hence, identifying alternative approaches to enable anti-tumor immune response is crucial. Aberrant protein glycosylation is a hallmark of cancer; in particular, increased cell-surface sialylation has been shown to inhibit immune-mediated clearance of tumor cells. This is mediated by the sialic-acid-binding immunoglobulin-like lectins (Siglecs), a family of surface receptors that mediate inhibitory signals by binding to sialic acid. Several factors complicate targeting the Sialic acid-Siglec axis in cancer therapy, including (1) the systemic adverse effects of broad abrogation of sialylation or Siglecs binding, (2) the diverse binding affinities of Siglecs based on sialic acid linkage, scaffold glycan and carrying protein. To enable the full use of this regulatory pathway, we set out to determine how the sialoglycome is dysregulated during early tumorigenesis. To this end, we used longitudinal intravital microscopy to record premalignant growth within the same animal at cellular resolution over 24 weeks in a carcinogen-induced model of head and neck squamous cell carcinoma (HNSCC). This allowed us to stratify lesions into progressing, regressing and stable growth signatures. We employ spatially resolved glycomics, transcriptomics and multiplex staining to generate a longitudinal signature of premalignant lesions. We observe an increased abundance of glycans decorated with alpha2,3-linked sialic acid (alpha2,3Sia). The elevated levels of alpha2,3Sia reflected a significant upregulation of alpha2,3-Sialyltransferases expression, indicating control mechanisms at the transcriptional levels. In the epithelial compartment, alpha2,3Sia was particularly enriched in CD44+ de-differentiated tumor cells. Using Siglec-Fc Chimeric constructs, we observed a binding preference of the CD44+ tumor-cells to Siglec-E. alpha2,3Sia was also elevated in the lesion stroma, strikingly in ly6G+ CD11b+ neutrophils recruited to progressing lesions. Our findings suggest a potential engagement of the Siglec-E - alpha2,3Sia axis in premalignant HNSCC lesions. Ongoing analysis is dissecting the tumor-immune interactions implicated in this axis as a potential regulator of the immune spatio-temporal landscape during early tumorigenesis. This study offers a groundwork to delineate glycomic and transcriptomic signatures in premalignant lesions with the opportunity to identify potential preventative measures in harnessing the immune response in patients.