The effect of a therapeutic dendritic cell-based cancer vaccination depends on the blockage of CTLA-4 signaling

Dendritic eel Is (DCs) Were pulsed with the H-2K(h) binding OVA(257-264)-peptide (SIINFEKL), and used its one single-injection vaccine in combination with anti-CTLA-4 monoclonal antibody (mAb) to treat mice inoculated 3 days previously with 3 x 10(5) E.G7-OVA lymphoma cells. Neither DC vaccination nor CTLA-4 blockage alone prevented tumor growth in tumor challenged mice. In contrast, the combination of one vaccination and injection of anti-CTLA-4 mAb lead to rejection or retarded tumor growth in more than 60% of the mice. The OVA-transgene or the SIINFEKL-epitope was not lost in the progressing tumors of vaccinated mice, however, the highest degree of anti-SIINFEKL reactivity of host CTLs in an IFN-gamma ELISPOT assay was found only in mice showing complete tumor rejection. Vaccinated mice having rejected E.G7-OVA tumors were capable of rejecting subsequent challenges with 1 x 10(6) E.G7-OVA tumor cells, and later on these mice even rejected wild-type EL-4 tumor cells indicating that tumor epitope spreading takes Place during the process of vaccination-induced E.G7-OVA rejection. In agreement with these observations, mice having rejected E.G7-OVA tumors showed long lasting CTL memory in spleen and bone marrow towards both file SIINFEKL-peptide and other EL-4-derived tumor rejecting epitopes. (c) 2005 Elsevier Ireland Ltd. All rights reserved.