Brucella lumazine synthase (BLS) as immunomodulator and carrier of antigens for melanoma B16 treatment

SOTO ARIADNA; BERGUER PAULA; GOLDIN CARLA; SOSA SANTIAGO; FARIAS ANA; GOLDBAUM FERNANDO

Simposio; Advances in Cancer Immunotherapy; 2020

Keystone Symposia

Brucella lumazine synthase (BLS) is a homodecameric protein that activates dendritic cells via TLR4, inducing the upregulation of costimulatory molecules and the secretion of proinflammatory cytokines and chemokines. BLS has a therapeutic effect in B16 melanoma-bearing mice only when administered at early stages of tumor growth. Moreover, it is possible to merge peptides at BLS N-termini and elicit their immunogenicity without affecting their structure, inducing the antigen cross-presentation and a specific CD8+ T cell cytotoxicity, constituting a proven platform for vaccine development.We hypothesized that the antitumor response induced by BLS immunomodulatory effect would be increased by its properties as a carrier of peptides. Previous results shown that treatment with the BLS-OVA257-264 chimera does not increase the therapeutic effect of BLS in mice with B16-OVA melanoma. Hence, we evaluated if other chimeras with peptides that allow an improved antigenic presentation can enhance the antitumor effect. We also studied whether the combined use of checkpoint inhibitor α-PD-L1 increases this effect.We built two different BLS chimeras: BLS-OVAXL (containing OVA247-264 peptide) and BLS-gp100 (containing gp10020-39 murine peptide) to evaluate their therapeutic effect on B16-OVA melanoma.We found that BLS-OVAXL can activate BMDC and induce an increase in the expression of PD-L1; moreover, these activated BMDC can present the ovalbumin antigen to CD8+ T cells, inducing their proliferation and activation. Furthermore, the effect of each chimera was evaluated in tumor growth and survival of B16-OVA bearing-mice. Although a delay in tumor growth was detected with each quimera, there was a significant impact on the survival only in mice treated with BLS-OVAXL. Based on this, we evaluated the combined therapy of the chimeras with PD-L1 blockade treatment, without any improvement over monotherapy.In order to understand the underlying mechanisms of the antitumor response, the tumor microenvironment of mice was studied on day 14. A significant increase in the percentage of tumor infiltrating lymphocytes (TIL) and CD8+ T cells was found when BLS-OVAXL was administered. In addition, a significant increase in CD8+ T cells was found when administered with α-PD-L1, compared to the monotherapy. BLS-gp100 increased the percentage of TIL only when administered with α-PD-L1.In conclusion, these chimeras induce an antitumor effect in melanoma bearing-mice, which is not improved with a single dose of α-PD-L1.