Therapeutic cancer vaccine targeting cancer glycans

All living cells are covered with a dense sugar-coat. Aberrant glycosylation, a hallmark of cancer, results in tumor-associated carbohydrate antigens on the cell surface. AcSTn is an incomplete O-linked sialic acid containing-glycan expressed in various types of carcinomas, correlating with poor prognosis and reduced patient survival. The two most common sialic acids in mammals are N-Glycolylneuraminic acid (Neu5Gc) and N-Acetylneuraminic acid (Neu5Ac). Humans cannot synthesize Neu5Gc, thus it is immunogenic in humans. Nevertheless, Neu5Gc incorporates into human cells through the diet from red meat and dairy, thereby Neu5Gc could replace Neu5Ac on cell surface glycans. We hypothesize that GcSTn would be a more potent immunogen compared to AcSTn, thus more effective in a cancer vaccine formulation. To examine antibody responses, Neu5Gc-deficient Cmah-/- mice were immunized with Keyhole limpet hemocyanin (KLH) glycan conjugates, either GcSTn-KLH, AcSTn-KLH, or KLH. The vaccines were emulsified with Freund’s Complete Adjuvant and injected intraperitoneally. This was followed by three booster injections with Freund’s Incomplete Adjuvant at weeks 1, 2, and 6, then blood sampled weekly. Serum glycan microarray analysis revealed a more potent and robust IgG response against STn and related glycans in the GcSTn-KLH group compared to the AcSTn-KLH group. To examine the efficacy as a cancer vaccine, Cmah-/- mice were immunized as above, then on week 7 inoculated with B16-F10 cancer (0.5×10⁶), and tumor volume measured every two days, revealing that the GcSTn-KLH vaccine significantly inhibited tumor growth compared to the control group. Immunization with a higher antigen dose (30g instead of 20g) and cancer cells inoculation on week 6.5 resulted in even greater tumor inhibition in the treated group compared to the control group. Furthermore, immunization with a saponin-based adjuvant using the same regimen and dose resulted in a similar anti-glycan IgG profile. This water-soluble adjuvant is better tolerated by human patients, and could support use of GcSTn-KLH as a therapeutic cancer vaccine. The commercial AcSTn-KLH vaccine failed to show efficacy in a phase-3 clinical trials, but not adverse effects were reported. Our findings support the GcSTn-KLH as a potentialy improved therapeutic cancer vaccine for active immunotherapy of various carcinomas.