CONICET | Buscador de Institutos y Recursos Humanos

Brucella lumazine synthase (BLS) is a homodecameric protein. It is possible to insert foreign proteins at its 10 N-termini and these chimeras are very efficient to elicit immunity without adjuvants. BLS and BLS-OVA, a chimera containing ovalbumin peptide 257-264, have a similar therapeutic effect in B16-OVA-expressing tumor-bearing mice. In this work, mice were s.c. inoculated with B16-OVA cells and at day 2, 200µg of BLS or BLS-OVA were injected s.c.. After 14 days, their splenocytes were co-cultured for 4h with B16-OVA cells. IFNγ was undetectable by ELISA in the supernatants of all groups. Since B16-OVA cells express high levels of PDL-1, anti-PD-1 or anti-PDL-1 antibodies were added to the culture. Interestingly, IFNγ was detected only in co-culture of splenocytes from BLS-OVA treated mice. These results suggest that BLS-OVA induces a specific response against the tumor-associated antigen (TAA) but it is suppressed through the PD-1/PDL-1 pathway. We then evaluated if the administration of BLS-OVA and anti-PD-1 or anti-PDL-1 affected the tumor microenvironment. To that end, mice inoculated with B16-OVA cells were treated with BLS-OVA or BLS at day 2 and with anti-PD-1 or anti-PDL-1 at days 4, 7 and 10. At day 14, tumors were analysed through flow cytometry. Surprisingly, BLS-OVA does not increase the percentage of immune cells into the tumor but combination with anti-PDL-1 increases CD45+ cells (18,28%±10,24 vs 2,91%±0,61) including CD8+, CD4+, dendritic cells and regulatory cells. Tumor growth and survival with these combined strategies were evaluated. Only the combination of BLS-OVA with anti-PDL-1 delays tumor growth compared to BLS-OVA. The presence of the TAA OVA in the chimera improves the outcome of the treatment only in the presence of the checkpoint inhibitor anti-PDL-1. Therefore, BLS can be used as a carrier for a TAA generating a specific response that can be improved with immune checkpoint blockade treatment.