Abstract A009: Development of monoclonal antibodies targeting truncated O-glycans expressed specifically by cancer cells offers a novel strategy to enhance cancer immunotherapy efficacy

Abstract Glycosylation is a vital post-translational modification of proteins and lipids in mammalian cells involved in cell–matrix interactions, cell recognition, and intracellular signaling. One glycosylation pattern often disrupted during the process of carcinogenesis is O-glycosylation. This phenomenon leads to the expression of incomplete or truncated O-glycans on proteins of cancer cells, particularly in cancers of epithelial origin, including breast, ovarian, gastric, pancreatic, and colon cancers. This alteration supports tumor progression and is often linked to poor prognosis. Developing monoclonal antibodies (mAbs) targeting truncated Oglycans expressed specifically by cancer cells could be a promising strategy to enhance cancer immunotherapy efficacy, although it could be challenging. We developed two mAbs that recognize truncated O-glycans expressed specifically on tumor tissues, sparing healthy tissues. Both mAbs were generated from the Hollinshead allogeneic colorectal cancer vaccine platform containing two immunogenic synergistic tumor associated antigens (TAAs) derived from pooled specimens from 79 patients with colon cancer. This cancer vaccine platform was used as immunogen to generate these two mAbs in mice. NEO-201 is a humanized IgG1 mAb that binds to Core 1 and/or extended Core 1 O-glycans expressed by several human solid and blood tumors, as well as neutrophils, and mediates killing of cancer cells, neutrophils, regulatory T cells (Tregs) and granulocytic myeloid-derived suppressor cells (gMDSCs) via ADCC and CDC. In the ongoing phase II clinical trial (NCT03476681), combining NEO-201 with pembrolizumab in subjects with tumor resistant to checkpoint inhibitors, it has been observed that the reduction of both circulating Tregs and gMDSCs mediated by NEO-201 was associated with durable stable disease. These findings suggest that employing a mAb able to mediate the killing of both tumor cells and immunosuppressive cells expressing core 1 O-glycans can restore the efficacy of checkpoint inhibitors and enhance overall the efficacy of cancer immunotherapy. NEO-102 was a chimeric human IgG1 mAb targeting a glycosylated variant of MUC5AC expressed specifically by colorectal and pancreatic cancer. In a phase 2 study, NEO-102 showed promising results in patients with advanced, refractory colorectal cancer. However, given its low binding affinity for its target antigen, we decided to enhance the binding affinity of NEO-102. The new clone was named PB-223. PB-223 demonstrates a higher affinity for the target antigen compared to NEO-102. PB-223 binds specifically to core-2 O-glycans expressed on cancer cell lines positive for PB-223 binding in flow cytometry. IHC analysis also showed that PB-233 binds to additional tumor tissues not reactive with NEO-102, but not healthy tissues. PB-223 can also internalize into human cancer cell lines expressing core 2 O-glycans, suggesting that PB-223 may be a potential candidate for the development of safe and effective antibody-drug conjugates (ADC) for the treatment of various human carcinomas. Citation Format: Massimo Fantini, Anjum Zaki, Sharon A Mavroukakis, Philip M Arlen, Kwong Y Tsang. Development of monoclonal antibodies targeting truncated O-glycans expressed specifically by cancer cells offers a novel strategy to enhance cancer immunotherapy efficacy [abstract]. In: Proceedings of the AACR IO Conference: Discovery and Innovation in Cancer Immunology: Revolutionizing Treatment through Immunotherapy; 2025 Feb 23-26; Los Angeles, CA. Philadelphia (PA): AACR; Cancer Immunol Res 2025;13(2 Suppl):Abstract nr A009.