ROBO4 and neoplasm: Importantly, while naïve OVA-specific OT-1 T cells were not activated (based on CD69 upregulation) following co-culture with endpoint tumor explants derived from day 5 MIS416 Vax + MRB-OVA treated mice (consistent with ALV), OT-1 T cells were readily activated by co-culture with endpoint tumor explants from day 12 treated tumors (MIS416 Vax + MRB-OVA), indicating continued target antigen expression/presentation (Fig. 3d).