In VitroandIn VivoStudies of Monoclonal Antibodies with Prominent Bactericidal Activity against Burkholderia pseudomallei and Burkholderia mallei

Abstract

Our laboratory has developed more than a hundred mouse monoclonal antibodies (MAbs) against Burkholderia pseudomallei and Burkholderia mallei. These antibodies have been categorized into different groups based on their specificities and the biochemical natures of their target antigens. The current study first examined the bactericidal activities of a number of these MAbs by an in vitro opsonic assay. Then, the in vivo protective efficacy of selected MAbs was evaluated using BALB/c mice challenged intranasally with a lethal dose of the bacteria. The opsonic assay using dimethyl sulfoxide-treated human HL-60 cells as phagocytes revealed that 19 out of 47 tested MAbs (40%) have prominent bactericidal activities against B. pseudomallei and/or B. mallei. Interestingly, all MAbs with strong opsonic activities are those with specificity against either the capsular polysaccharides (PS) or the lipopolysaccharides (LPS) of the bacteria. On the other hand, none of the MAbs reacting to bacterial proteins or glycoproteins showed prominent bactericidal activity. Further study revealed that the antigenic epitopes on either the capsular PS or LPS molecules were readily available for binding in intact bacteria, while the epitopes on proteins/glycoproteins were less accessible to the MAbs. Our in vivo study showed that four MAbs reactive to either the capsular PS or LPS were highly effective in protecting mice against lethal bacterial challenge. The result is compatible with that of our in vitro study. The MAbs with the highest protective efficacy are those reactive to either the capsular PS or LPS of the Burkholderia bacteria.

Burkholderia pseudomallei Capsular Polysaccharide Conjugates Provide Protection against Acute Melioidosis

“…Nevertheless, these attributes bode well from a vaccine development standpoint. Relevant to the current study, a number of studies have shown that monoclonal and polyclonal antibodies specific for OPS and CPS can be used to passively immunize mice against lethal challenges of B. pseudomallei (18,20,(23)(24)(25)(26). Such findings confirm the protective capacity of these surface-exposed antigens and support the ratio-nale for exploring the use of OPS and CPS antigens for active immunization against melioidosis.…”

“…Similarly, both polyclonal and monoclonal antibodies recognizing OPS have been shown to offer significant protection in experimental models of melioidosis when administered passively (18,20,(23)(24)(25)(26). Thus, given the magnitude of the antibody responses raised against OPS2B1, it was surprising that the construct failed to provide protection in our challenge study.…”

“…B. pseudomallei OPS and CPS antigens also represent attractive candidates to develop melioidosis vaccines, since they have both been identified as protective antigens in animal models using active (18) and passive (18,20,(23)(24)(25)(26) immunization strategies. In this report, two glycoconjugates composed of OPS or CPS linked to a common carrier protein were constructed, and their immunogenic potential and protective capacities were evaluated in a murine model of melioidosis.…”

Correlates of Immune Protection following Cutaneous Immunization with an Attenuated Burkholderia pseudomallei Vaccine

“…It is plausible to suggest that vaccination may protect from lethality mainly by blocking bacterial dissemination from the lungs to other sites (e.g., spleen and liver), rather than by neutralizing bacteria directly in the lungs. The protective antibody immune response in Burkholderia infection has been shown previously to be specific to the lipopolysaccharide (LPS) of B. pseudomallei, which promotes opsonic phagocytic killing (59,60).…”

Protection against Experimental Melioidosis following Immunization with Live Burkholderia thailandensis Expressing amanno-Heptose Capsule

“…The exact mechanism of protection observed in this study remains to be fully elucidated, and it is probable that this is multifactorial in nature, utilizing both cell-mediated and antibody responses. Antibodies are known to protect to a degree when used passively in animals (25,(37)(38)(39)(40)(41), and certain types of antibody are correlated with better clinical outcomes in humans (42). The complete protection induced by immunization with E555 precluded correlation between antibody levels and survival in this study, although it is of interest to note that the single surviving CDC2721121-immunized mouse in the group challenged with 6 ϫ 10 6 CFU B. pseudomallei also had the highest concentration of anti-B.…”