ABSTRACT
The spread of multidrug antibiotic resistance (MDR) is a widely recognized crisis in the treatment of bacterial infections, including those occurring in military communities. Recently, the World Health Organization published its first ever list of antibiotic-resistant "priority pathogens" - a catalog of 12 families of bacteria that pose the greatest threat to human health with A. baumannii listed in the "Priority 1: Critical" category of pathogens. With the increasing prevalence of antibiotic resistance and limited development of new classes of antibiotics, alternative antimicrobial therapies are needed, with lytic bacteriophage (phage) specifically targeted against each of the high priority bacterial infections as a potential approach currently in development toward regulatory approval for clinical use. Balb/c mice were prophylactically administered PBS or phage selected against A. baumannii strain AB5075. After 3 weeks, mice were anesthetized, wounded (dorsal), and challenged topically with AB5075. Following infection, mice were subsequently treated with PBS or phage for three consecutive days, and evaluated for 3 weeks to assess the safety and efficacy of the phage treatment relative to the control. We assessed mortality, bacterial burden, time to wound closure, systemic and local cytokine profiles, alterations in host cellular immunity, and finally presence of neutralizing antibodies to the phage mixture. In our study, we found that prophylactic phage administration led to a significant reduction in monocyte-related cytokines in serum compared to mice given PBS. However, we detected no significant changes to circulating blood populations or immune cell populations of secondary lymphoid organs compared to PBS-treated mice. Following prophylactic phage administration, we detected a marked increase in total immunoglobulins in serum, particularly IgG2a and IgG2b. Furthermore, we determined that these antibodies were able to specifically target phage and effectively neutralize their ability to lyse their respective target. In regards to their therapeutic efficacy, administration of phage treatment effectively decreased wound size of mice infected with AB5075 without adverse effects. In conclusion, our data demonstrate that phage can serve as a safe and effective novel therapeutic agent against A. baumannii without adverse reactions to the host and pre-exposure to phage does not seem to adversely affect therapeutic efficacy. This study is an important proof of concept to support the efforts to develop phage as a novel therapeutic product for treatment of complex bacterial wound infections.
ABSTRACT
This study describes an antibody-dependent NK cell degranulation assay, as a biomarker to assess antibody-dependent cellular cytotoxicity (ADCC) response in influenza plasma and for antibody therapies against influenza infection. The concentration of neutralizing antibodies (NAbs) against the hemagglutinin receptor of influenza viruses is a current determinant in protection against infection, particularly following receipt of the seasonal influenza vaccine. However, this is a limited assessment of protection, because: (i) NAb titers that incur full protection vary; and (ii) NAb titers do not account for the entire breadth of antibody responses against viral infection. Previous reports have indicated that antibodies that prime ADCC play a vital role in controlling influenza infections, and thus should be quantified for assessing protection against influenza. This report demonstrates a non-radioactive assay that assesses NK cell activation as a marker of ADCC, in which NK cells interact with opsonized viral antigen expressed on the surface of infected Raji target cells resulting in effector cell degranulation (surrogate CD107a expression). A positive correlation was determined between HAI titers and sustained NK cell activation, although NK cell activation was seen in plasma samples with HAI titers below 40 and varied amongst samples with high HAI titers. Furthermore, sustained NK cell degranulation was determined for influenza-vaccinated transchromosomic bovine intravenous immunoglobulin, indicating the potential utility of this therapy for influenza treatment. We conclude that this assay is reproducible and relevant.
