Nonclassically secreted proteins as possible antigens for vaccine development: a reverse vaccinology approach

Identification of potential antigens from non-classically secreted proteins and designing novel multitope peptide vaccine candidate against Brucella melitensis through reverse vaccinology and immunoinformatics approach

Brucella melitensis is an intracellular pathogen resides in the professional and non-professional phagocytes of the host, causing zoonotic disease brucellosis. The stealthy nature of the Brucella makes it's highly pathogenic, and it is hard to eliminate the bacteria completely from the infected host. Hitherto, no licensed vaccines are available for human brucellosis. In this study, we identified potential antigens for vaccine development from non-classically secreted proteins through reverse vaccinology approach. Based on the systemic screening of non-classically secreted proteins of B. melitensis 16M, we identified nine proteins as potential vaccine candidates. Among these, Omp31 and Omp22 are known immunogens, and its role in the virulence of Brucella is known. Roles of other proteins in the pathogenesis are yet to be studied. From the nine proteins, we identified six novel antigenic epitopes that can elicit both B-cell and T-cell immune responses. Among the nine proteins, the epitopes were predicted from Omp31 immunogenic protein precursor, Omp22 protein precursor, extracellular serine protease, hypothetical membrane-associated protein, iron-regulated outer membrane protein FrpB. Further, we designed a multitope vaccine using Omp31 immunogenic protein precursor, Omp22 protein precursor, extra cellular serine protease, iron-regulated outer membrane protein FrpB, hypothetical membrane-associated protein, and LPS-assembly protein LptD and polysaccharide export protein identified in the previous study. Epitopes were joined using amino acid linkers such as EAAAK and GPGPG. Cholera toxin subunit B, the nontoxic part of cholera toxin, was used as an adjuvant and it was linked to the N-terminal of the multitope vaccine candidate. The designed vaccine candidate was modeled, validated and the physicochemical properties were analyzed. Results revealed that the vaccine candidate is soluble, stable, non-allergenic, antigenic and 87% of residues of the designed vaccine candidate is located in the favored region. In conclusion, the computational analysis showed that the newly designed multitope protein could be used to develop a promising vaccine for human brucellosis.

Pneumococcal Predictive Proteins Selected by Microbial Genomic Approach Are Serotype Cross-Reactive and Bind to Host Extracellular Matrix Proteins

Streptococcus pneumoniae is a colonizer of the human nasopharynx, which accounts for most of the community-acquired pneumonia cases and can cause non-invasive and invasive diseases. Current available vaccines are serotype-specific and the use of recombinant proteins associated with virulence is an alternative to compose vaccines and to overcome these problems. In a previous work, we describe the identification of proteins in S. pneumoniae by reverse vaccinology and the genetic diversity of these proteins in clinical isolates. It was possible to purify a half of 20 selected proteins in soluble form. The expression of these proteins on the pneumococcal cells surface was confirmed by flow cytometry. We demonstrated that some of these proteins were able to bind to extracellular matrix proteins and were recognized by sera from patients with pneumococcal meningitis infection caused by several pneumococcal serotypes. In this context, our results suggest that these proteins may play a role in pneumococcal pathogenesis and might be considered as potential vaccine candidates.

Reverse Vaccinology: An Approach for Identifying Leptospiral Vaccine Candidates

Leptospirosis is a major public health problem with an incidence of over one million human cases each year. It is a globally distributed, zoonotic disease and is associated with significant economic losses in farm animals. Leptospirosis is caused by pathogenic Leptospira spp. that can infect a wide range of domestic and wild animals. Given the inability to control the cycle of transmission among animals and humans, there is an urgent demand for a new vaccine. Inactivated whole-cell vaccines (bacterins) are routinely used in livestock and domestic animals, however, protection is serovar-restricted and short-term only. To overcome these limitations, efforts have focused on the development of recombinant vaccines, with partial success. Reverse vaccinology (RV) has been successfully applied to many infectious diseases. A growing number of leptospiral genome sequences are now available in public databases, providing an opportunity to search for prospective vaccine antigens using RV. Several promising leptospiral antigens were identified using this approach, although only a few have been characterized and evaluated in animal models. In this review, we summarize the use of RV for leptospirosis and discuss the need for potential improvements for the successful development of a new vaccine towards reducing the burden of human and animal leptospirosis.