Expression of α-gal epitopes on ovarian carcinoma membranes to be used as a novel autologous tumor vaccine

Objective. Poor presentation of tumor-associated antigens (TAA) to the immune system remains a major obstacle to effective anti-tumor vaccine therapy. The aim of this study is to demonstrate the feasibility of producing a novel autologous tumor vaccine from ovarian carcinoma that is expected to have increased immunogenicity. The strategy is based on the ability of the anti-Gal IgG antibody (a natural antibody comprising 1% of IgG in humans) to target tumor membranes expressing α-gal epitopes (Galα1-3Galβ1- 4GlcNAc-R) to antigen-presenting cells (APC). Study design. Freshly obtained ovarian carcinoma tumors are homogenized, washed, and incubated with a mixture of neuraminidase, recombinant α1,3galactosyltransferase (rα1,3GT) and uridine diphosphate galactose (UDP-Gal) to synthesize α-gal epitopes on carbohydrate chains of glycoproteins of these membranes. Subsequently, the processed membranes are analyzed for expression of α-gal epitopes and for the binding of anti-Gal. Results. Incubation of 3 g of ovarian carcinoma membranes, from five different patients, at 100 mg/ml, mixed together with rα1,3GT (50 μg/ml), neuraminidase (1 mU/ml), and UDP-Gal (2 mM), resulted in the effective synthesis of α-gal epitopes to the extent of ∼2 × 10¹¹ epitopes/mg of tumor membranes. As a result of this de novo expression of α-gal epitopes, the tumor membranes readily bound purified anti-Gal antibody, as well as anti-Gal in autologous serum. Conclusions. The method described in this study is very effective in the synthesis of many α-gal epitopes on tumor membranes obtained from ovarian carcinoma. These novel epitopes readily bind the naturally occurring anti-Gal antibody. This technique of opsonization of α-gal-modified autologous tumor membranes carrying TAA is expected to increase effective uptake of the vaccine by APC, which is key to successful anti-tumor vaccination.