Improving the efficacy of anti-SSEA4 antibody in pancreatic cancer immunotherapy with glyco-optimization and immune checkpoint blockade

Pancreatic cancer remains one of the most lethal malignancies with limited therapeutic options. Among the alternative targets explored for pancreatic cancer, the glycolipid stage-specific embryonic antigen-4 (SSEA4) has been extensively studied. We have previously demonstrated that the chimeric anti-SSEA4 antibody with alpha-2,6-sialylated complex type biantennary glycan (SCT) or its 3-fluorosialyl derivative (FSCT) attached to the Fc-Asn297 residue exhibited enhanced binding to the Fc-receptors FcγRIIIA and FcγRIIA which are responsible for antibody-dependent cellular cytotoxicity and phagocytosis as well as vaccinal effect. Here, we found that high-SSEA4 expression correlates with increasing tumor proliferation and sensitivity to the glyco-optimized antibodies (anti-SSEA4-SCT and anti-SSEA4-FSCT) which preferentially recruit NKG2D-expressing natural killer cells and FcγRIIA-bearing macrophages with enhanced target killing activity. We also uncovered an immune evasion mechanism involving the interaction of sialoglycans on the cancer cell with Siglec-9 on NK cells or Siglec-10 on macrophages to block the antibody-mediated effector functions, and this immune checkpoint inhibition can be suppressed with the removal of sialic acid on cancer cells or blockade of Siglec recognition. In xenograft models, the glyco-optimized antibodies exhibited superior inhibition of tumor growth with high-SSEA4 expression compared to the wild-type antibody and persistent antitumor activity without additional antibody administration. These findings support anti-SSEA4 antibodies with enhanced effector functions and blockade of Siglec-mediated immune checkpoint as a promising therapeutic strategy for pancreatic cancer.