In silico identification and in vivo analysis of a novel T-cell antigen from Chlamydia, NrdB

Chlamydial infections are a serious economic burden and health threat to developed and developing countries. Development of an efficacious vaccine is thought to be the most convenient, potentially reliable and cost effective option to control chlamydial infection and disease complications. Currently there are very few efficacious vaccine candidates that have been identified and characterized. In this study we have identified a number of unique vaccine candidates using a novel in silico approach. The chlamydial genome was screened for proteins containing epitopes predicted to bind multiple HLA class II molecules (i.e. 'promiscuous' epitopes). A selection of target proteins were cloned, expressed, and purified. Recombinant proteins were screened against sera samples from patients with Chlamydia trachomatis genital tract infections. Two proteins, hypothetical protein CT425 and ribonucleotide reductase small chain protein (NrdB) were identified as being immunoreactive. Using a mouse model, we found that intranasal immunization with NrdB conferred a CD4+ T-cell driven degree of protection similar to that seen with CD4+ T-cells primed from a whole organism, live challenge. In addition, serum from immunized mice was found to neutralize chlamydial infection of a cell monolayer in vitro. NrdB is a highly conserved chlamydial protein with an essential role in the replication of chlamydiae and could be a useful component of a multi-subunit vaccine against chlamydial genital tract infections.