Summary
Salmonella infections in humans are the cause of enteric fevers (Typhoid (TF) and Paratyphoid (PT)) and Non-Typhoidal Salmonellosis (NTS), which are major causes of morbidity and mortality in developing countries. There are no commercially available vaccines for PT and NTS and current vaccines for TF have not been practical to eradicate the disease. Previously, we have developed experimental vaccines for TF and NTS using purified porins from Salmonella enterica serovars Typhi and Typhimurium. TF vaccine is safe and well tolerated in humans inducing high titres of bactericidal antibodies, which last for more than 10 years. Recently, we have developed a novel experimental multivalent vaccine using a combination of porins from different Salmonella enterica that induce long lasting bactericidal antibody responses to clinical strains and protection against the challenge with Typhi, and serovars Typhimurium, Enteritidis and Paratyphi in mice. This represents a novel vaccine candidate against both enteric fevers and NTS. As part of the formulation, we use porins from a Typhi strain that requires level 3 biosafety conditions for handling making multivalent vaccine production more complicated and expensive. In order to reduce costs and to aid scaling up the production of the vaccine it is important to produce it under biosafety 1 conditions. Prokarium has developed a typhoid vaccine based on an attenuated Typhi strain ZH9 that can be handed under level 1 biosafety conditions. Here, we propose to test if ZH9 strain can be used to produce Typhi porins in level 1-biosafety conditions and if these porins could be used to formulate the multivalent experimental vaccine. We will assess, in mice, the immunogenicity and protective capacity (against Typhi, Paratyphi, Enteritidis and Typhimurium challenge) of ZH9 porins and the multivalent vaccine prepared with these porins. Furthermore, we will study their capacity to induce bactericidal antibodies to clinical isolates of different Salmonella serovars. The results of this project will be important for scaling up the multivalent vaccine production, to produce batches for toxicological tests and clinical trials and finally to obtain a commercially viable product.
Project outcomes
A method to purify porins from an attenuated S. Typhi strain (ATT) was successfully developed under biosafety level 1 conditions. 14 batches (167 mg) of highly purified porins from this strain (ATTP) were obtained (<0.2 endotoxin units per microgram), electrophoretic analysis showed the classic porins profile. Mouse anti-WTP serum reacts better with ATTP native protein forms than denatured ones. WTP and ATTP induced similar IgM, IgG and IgG subclasses antibody responses, although slightly lower IgM, IgG2a and IgG2b titres were induced by ATTP. ATTP induce less specific CD4+, IFN-g+ T cells than WTP, but similar numbers of CD8+, IFN-g+ T cells. WTP and ATTP, prime and boost immunized in mice, induced similar level of protection against live WT S. Typhi bacteria challenge. Both multivalent vaccines prepared with WTP or ATTP induced similar reduction in S. Typhi numbers.
Taken together, our results suggest that attenuated S. Typhi strain could be a suitable source of porins generated in biosafety 1 conditions, to be used in the formulation of a multivalent experimental vaccine against the diseases produced by Salmonella enterica.