Brucella spp. protease inhibitor is a useful adjuvant in oral vaccine formulations against infectious diseases

MARIANELA V. CARABAJAL; ANDRÉS E. IBAÑEZ; GABRIELA S. RISSO; LORENA M. CORIA; PAULA L. GONZALEZ COBIELLO; LAURA BRUNO; FERNANDA M. FRANK; GABRIEL BRIONES; KARINA A. PASQUEVICH; JULIANA CASSATARO

Congreso; Congreso; Brucellosis 2014 International Research Conference; 2014; 2014

Previous studies showed that a Brucella protein (BP) administered by the oral route and without adjuvants induced protection against oral Brucella challenge. BP is a broad spectrum protease inhibitor with a strong activity against serine proteases secreted by the pancreas to the intestine (elastase, trypsine and alpha chymotrypsin). These results prompted us to study its potential application as oral adjuvant for other antigens.As BP is able to inhibit in vitro the activity of many proteases present in the gastrointestinal tract we directed all our efforts to study its potential application in oral vaccine delivery. We showed that in BALB/c or C57BL/6 mice oral delivery of OVA in the presence of BP resulted in a significantly increased OVA-specific T cell response (DTH assay; p<0.05, n=6) and OVA-specific IFN-γ producing CD4+ and CD8+ T cells determined by flow cytometry at the mucosal (mesenteric lymph nodes (MLNs) or Peyer´s patches; p<0.05, n=6) and systemic level (spleen; p<0.05, n=6). Salmonella (S.) Typhimurium in combination with the novel adjuvantBP is a strong candidate for an oral vaccine because it mimics the natural route of Salmonella infections and provokes a Th1-biased response. Therefore, we fed BALB/c mice (n=7) with i) heat-killed Salmonella (HKS), ii) HKS+BP or iii) HKS+CT and challenged them later with virulent S. Typhimurium by the oral route. HKS+BP-immunized mice induced an increased Th1 immune response in the spleen and MLNs (p<0.01) and an increase in HKS-specific IL-17 production. There was an increase in HKS-specific DTH response (p<0.05) and of IgA in faeces (p<0.05) as well as a slight increase of specific IgG in the serum of HKS+BP immunized mice compared to the control groups HKS and HKS+CT. Considering that Toxoplasma gondii infects the host through the gut mucosa, the efficacy of oral immunization with a recombinant protein from Toxoplasma gondii GRA4 plus BP was analyzed.C3H/HeN mice were orally immunized with i) PBS, ii) GRA4, iii) GRA4+BP or iv) GRA4+CT. Three weeks after the last boost, mice were challenged orally with Me49 tissue cysts and individual parasite levels were assessed 1 month later. A significant decrease in the brain cyst burden (p<0.05)together with a reduction of liver damage associated enzymes (AST, LDH and ALT) in serum and an increase (p<0.05) in GRA4-specific DTH and of IgA in faeces were observed in GRA4+BP immunized mice when compared to the control groups.In summary, our results suggest that BP could be an ideal mucosal adjuvant. When codelivered orally a vaccine can bypass the harsh environment of the gastrointestinal tract. Besides, it can enhance antibody production, Th1 and CD8+T Ag-specific immune response and thus, it would be a useful adjuvant in oral vaccine formulations against infectious diseases.