Improving survival from Burkholderia pseudomallei and other pathogenic intracellular bacteria

Abstract. Burkholderia pseudomallei (Bpm) is a facultative intracellular bacterium that is the causative agent of melioidosis. Bpm is a CDC Tier 1 Select agent, which a biological agent that has been determined to have the potential to pose a severe threat to public health and safety. NIAID classifies Bpm as a Category B pathogen, which is a pathogen that provides the highest risk to national security and public health due to its ease of dissemination, high mortality rate, and potential use as a bioterrorism weapon. There are no approved treatments or vaccines to protect against acute or chronic Bpm infection, and the genus is resistant to most antibiotics. Thus, there is an urgent need for new medicines to treat Bpm infection. Vaccines in general require at least 10 days for subjects to develop immunity and thus are not useful for treating newly infected patients or protecting non-vaccinated healthcare providers and first responders in an emergency outbreak situation. A concern for both vaccines and antibiotics is that resistant Bpm strains may develop through random or directed mutation such as for a bioweapon. An alternative and potentially synergistic approach for protecting against Bpm infection is to stimulate the innate arm of the host immune system to resist infection. Interferon gamma (IFN-) is a critical component of the innate immune system and has been shown to be absolutely required for protection from Bpm lethality. IFN- quickly (within hours) activates host cells to resist infection by Bpm and other deadly facultative intracellular bacteria such as Tularemia, protozoa like toxoplasma, and viruses like Ebola. Thus, IFN- has the potential to be an effective broad-spectrum treatment against several deadly bioterrorism threats. However, IFN- has a very short in vivo half-life, poor bioavailability, and requires intraperitoneal (ip) injection to reach protective plasma levels in mice, which limit the protein's utility as a Bpm therapeutic. Subcutaneous (sc) dosing of IFN- results in ~ 10-fold lower plasma levels and greatly reduced in efficacy. We created site-specific PEGylated human and mouse IFN- analogs (PEG IFN-) that have superior bioavailability and > 20-fold longer half-lives than IFN- following sc dosing. The PEG murine IFN- homolog proved significantly more efficacious than mIFN- at improving survival from Ebola virus infection following sc injection in mice. We hypothesize PEG-IFN- also will be significantly more effective than IFN- at preventing morbidity and mortality from Bpm infection when administered by sc injection and will test this hypothesis by evaluating efficacy of PEG mIFN- and mIFN- using a well characterized murine Bpm infection model. These studies will lead to a fast-acting treatment that confers protection within hours and which can be administered easily by sc injection to patients who recently contracted Bpm, as well as potentially to first responders and healthcare providers in an emergency outbreak situation. Utilizing the host innate immune system and its myriad anti-microbial pathways to combat deadly pathogens like Bpm greatly reduces the likelihood that drug resistance may develop through genetic mutational escape mechanisms, either natural or man-made.