Vaccination against tumour endothelial marker Robo4 inhibits tumour growth

Introduction: Targeting tumour antigens is a major challenge in cancer-immunotherapy. We use active vaccination to induce antibodies targeting self-antigen Robo4, which is selectively expressed on tumour vascular endothelium, and supports vascular development. Our previous work showed that a conjugate of Robo4 with a foreign carrier protein induced autoantibodies specific to Robo4, which inhibited angiogenesis and tumour growth. Methods: To translate the vaccine protocol to exploit a carrier protein used in routine human vaccination schedules, the well-characterized, non-toxic fragment C of tetanus toxin (TTc) was selected as the carrier protein. Recombinant protein Robo4-TTc (R4-TTc) was produced by Robo4 genetically linked to TTc. Results: Priming with the carrier TTc followed by boost with Robo4-TTc (R4-TTc) efficiently induces strong antibody responses to Robo4 and inhibits tumour growth in LLC1 and 4T1 tumour models. The growth inhibition was correlated with anti-Robo4 IgG1 titres. Furthermore, decreased vessel formation and increased immune cell infiltration in tumours from R4-TTc vaccinated mice in the absence of detectable adverse effects on health. Conclusion: The data indicate that this vaccination strategy remodels tumour vessels and probably promotes immunogenic pathway activation, therefore repressing tumour growth.