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

ANA FARIAS; ANDRES H. ROSSI; FERNANDO A. GOLDBAUM; HERNAN RUY BONOMI; PAULA M. BERGUER

Buenos Aires

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

SAI

Brucellalumazine synthase (BLS) is a highly immunogenic decameric protein. It ispossible to insert foreign proteins at its 10 N-termini and these chimeraselicit immunity without adjuvants. BLS activates dendritic cells via TLR4,induces the cross-presentation of attached peptides and generates a stronglong-lasting humoral immune response. We have shown that BLS elicits atherapeutic effect in mice against B16 melanoma, slowing tumor growth andprolonging survival both in wt and TLR4- deficient mice. These effects areobserved when mice are inoculated with BLS at 2-3 days but not at 10 days aftertumor 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 UVspectrophotometry in B16 cells in vitro and in the growing tumor of untreatedmice. Results show that at the time of the inoculation, TLR4/MD-2 is expressedin 84% of B16 cells; in a 7-day tumor is expressed in 47.8% of the cells andthis percentage drops to 5.7% at day 10. We observed that melanin is absent incultured B16 cells and in tumors up to day 7 after inoculation. At day 10 aftertumor inoculation, melanin was evidenced and its level increased over timebetween days 10 to 14. These results suggest that melanin or melanogenesiscould contribute to the lack of efficacy of BLS treatment at day 10 andsupports our previous hypothesis that BLS therapeutic effect is due to BLSsignaling through tumor TLR4.