The therapeutic effect of Brucella lumazine synthase correlates with the expression of TLR4 in B16 melanoma

FARIAS ANA; ROSSI ANDRÉS; GOLDBAUM, FERNANDO; BONOMI, HERNÁN; BERGUER, PAULA

Ciudad de Buenos Aires

Congreso; First International Joint Meeting between the Latin American Society for Immunodeficiencies (LASID), the Argentinean Society for Immunology (SAI), and the French Society for Immunology (SFI); 2015

Brucella lumazine synthase (BLS) is a highly immunogenic decameric protein. It is possible to insert foreign proteins at its 10 N-termini and these chimeras elicit immunity without adjuvants. BLS activates dendritic cells via TLR4, induces the cross-presentation of attached peptides and generates a strong long-lasting humoral immune response. We have shown that BLS elicits a therapeutic effect in mice against B16 melanoma, slowing tumor growth and prolonging survival both in wt and TLR4- deficient mice. These effects are observed when mice are inoculated with BLS at 2-3 days but not at 10 days after tumor injection. To address the reason of the different outcomes of BLS treatment, we measured the levels of TLR4 by FACS and the presence of melanin by UV spectrophotometry in B16 cells in vitro and in the growing tumor of untreated mice. Results show that at the time of the inoculation, TLR4/MD-2 is expressed in 84% of B16 cells; in a 7-day tumor is expressed in 47.8% of the cells and this percentage drops to 5.7% at day 10. We observed that melanin is absent in cultured B16 cells and in tumors up to day 7 after inoculation. At day 10 after tumor inoculation, melanin was evidenced and its level increased over time between days 10 to 14. These results suggest that melanin or melanogenesis could contribute to the lack of efficacy of BLS treatment at day 10 and supports our previous hypothesis that BLS therapeutic effect is due to BLS signaling through tumor TLR4.