Pseudomonas aeruginosa is an opportunistic pathogen that can lead to mortality in immunocompromised patients and it is the second most common cause of nosocomial pneumonia from mechanical ventilation. The main bacterial virulence factor associated with higher morbidity and mortality is the type three secretion system (T3SS) which is used to deliver exotoxins into host cells. One critical structure of the T3SS is PcrV and has been a target of murine derived monoclonal antibodies (MAbs). Recent insight into structural differences of camelid antibodies has led to the generation of llama derived anti-PcrV monoclonal antibodies. In order to identify highly effective anti-PcrV Mabs, a pool of llama derived antibodies were characterized for their ability to block hemolysis and epithelial cell damage. Further investigation of antibodies that confer medium protection in vitro led to the development of a new format of MAbs which combine multiple epitopes. The tandembiepitopic antibodies PcrV18-15 and PcrV18-20 were the most efficient disablers of the T3SS. To determine if the tandem-biepitopic antibodies confer better protection than the leading murine derived anti-PcrV antibody, V2L2MD, which has been previously shown to mediate significant in vivo protection. Pneumonia mouse models were performed and results show that the tandem-biepitopic antibodies have significant (P<0.0001) prophylactic protection compared to V2L2MD, thus demonstrating the potential for anti-PcrV immunotherapy improvement.
