Xenograft-like destruction of tumors and their conversion into vaccines by intratumoral injection of α-gal glycolipids

Abstract

3074 Background: We describe a novel immunotherapy exploiting the natural anti-Gal antibody to destroy tumors and convert them into endogenous vaccines. Anti-Gal constitutes 1% of immunoglobulins in humans and interacts specifically with a-gal epitopes (Gala1- 3Galβ1–4GlcNAc-R) on glycolipids and glycoproteins. a-Gal epitopes are abundant in nonprimate mammals. Binding of anti-Gal to a-gal epitopes on pig cells mediates xenograft rejection. We inject glycolipids carrying a-gal epitopes (a-gal glycolipids) into solid tumors. Methods: a-Gal glycolipids extracted from rabbit RBC have carbohydrate chains capped with a-gal epitopes. Efficacy of treatment was studied in a1,3galactosyltransferase knockout mice bearing B16 melanoma. These mice are unique since they lack a-gal epitopes and can produce anti- Gal, like humans. Also B16 cells lack a-gal epitopes. B16 lesions (∼5 mm) were injected with 1mg a-gal glycolipids. Results: Intratumoral injection of a-gal glycolipids results in local inflammation mediated by anti-Gal binding to the ∼2x1016 a-gal epitopes on these glycolipids, activation of complement and generation of chemotactic factors. a-Gal glycolipids insert spontaneously into tumor cell membranes. Binding of anti-Gal to a-gal epitopes on such tumor cells induces lesion destruction, similar to xenograft rejection. Anti-Gal further opsonizes tumor cells for effective uptake by inflammation recruited dendritic cells (DC), via Fcγ receptors of these APC. The DC transport internalized tumor Ags to draining lymph nodes and present tumor Ag peptides, thus activating tumor specific T cells and eliciting an immune response against micrometastases. Conclusions: Injected a-gal glycolipids effectively destroy lesions and convert them into vaccines. This treatment may be even more effective in humans, since complement activity is much higher than in mice. This treatment may also be considered as neo-adjuvant immunotherapy for converting primary tumor into autologous tumor vaccine that elicits a protective immune response against micrometastases, during the period preceding resection of the tumor. No significant financial relationships to disclose.