P0128 Ubiquitinated proteins collected from tumour cells as a potent cancer vaccine

Abstract

Introduction We have previously shown that the autophagosome-enriched vaccine DRibble (DRiPs-containing blebs), derived from tumour cells after inhibition of protein degradation, is an efficient antigen carrier for cross-priming of tumour-reactive CD8+ T cells. The anti-tumour efficacy induced by DRibbles is mainly dependent on its contents of ubiquitinated proteins. We sought to detect whether ubiquitinated proteins enriched from tumour cells could be used as a novel cancer vaccine. Methods We used two ubiquitin binding proteins (TUBES and Vx3[A7]) to isolate the ubiquitinated proteins from EL4 and B16-F10 tumour cells after blocking their proteasomal degradation pathway. C57BL/6 mice were vaccinated (intraperitoneal or subcutaneous injection) with different doses of ubiquitin-enriched proteins, DRibbles, ubiquitin-depleted proteins, and whole-cell lysate, separately. The lymphocytes from the vaccinated mice were restimulated with inactivated tumour cells and the levels of IFN- γ in the supernatant were measured by ELISA. Anti-tumour efficacy of vaccination with ubiquitin-enriched proteins was evaluated by monitoring tumour growth in established tumour mice models. Findings Vx3(A7) protein was more effective than TUBEs at purifying ubiquinated proteins from tumour whole-cell lysates. After stimulation with inactivated tumour cells, the lymphocytes from the mice vaccinated with ubiquitin-enriched proteins secreted high levels of IFN- γ in a dose-dependent manner in which intraperitoneal injection induced higher IFN- γ levels than subcutaneous injection. Furthermore, the level of secreted IFN- γ following vaccination with ubiquitin-enriched proteins was markedly higher than that after vaccination with whole-cell lysate and ubiquitin-depleted proteins. We also found that the ubiquitin-enriched proteins vaccine showed an inhibitory effect on tumour growth that regressed after vaccination with ubiquitin-enriched proteins, by contrast with other groups. Interpretation Ubiquitin-enriched proteins could be used in immunotherapy as a potent cancer vaccine.