(538) Monoclonal Antibodies Targeting Psl and PcrV Potentiate Bacterial Clearance of Pseudomonas aeruginosa from Cystic Fibrosis Children that Failed Eradication Therapy

Background: Antibiotics such as inhaled tobramycin (TOB) are routinely used to treat new-onset Pseudomonas aeruginosa (PA) infections in Cystic Fibrosis (CF) patients in order to prevent progression to chronic infection, but unfortunately, up to 40% of patients fail eradication therapy. Our group previously showed that PA isolates from patients who failed TOB demonstrated resistance to neutrophil (Nφ)-mediated opsonophagocytosis and intracellular bacterial killing (OPK), and formed biofilms with high Psl. Monoclonal antibodies (mAb) targeting the exopolysaccharide Psl and the type III secretion system protein PcrV have been shown to potentiate Nφ-mediated OPK against the laboratory PA strain PAO1 and non-CF clinical isolates. The goal of this study was to determine the effect of mAb targeting Psl and PcrV on Nφ-mediated OPK in vitro, and bacterial clearance in vivo using PA clinical isolates from new-onset CF infections.

Methods: We tested a collection of PA clinical isolates from CF children (SickKids,Toronto) who underwent TOB eradication therapy for new-onset PA infections, with Persistent (N=7 isolates from 7 patients that failed eradication therapy) and Eradicated (N=8 isolates from 8 patients that eradicated their infection) isolates collected prior to TOB eradication therapy. All isolates were tested for the effect of an anti-Psl mAb (Psl0096), a bispecific anti-Psl anti-PcrV mAb (MEDI3902) or an IgG isotype control on in vitro Nφ OPK using immortalized human dHL-60 cells. PcrV expression was measured by immunoblotting. A murine PA lung infection model was used to determine the effect of MEDI3902 on bacterial clearance in Persistent PA isolates.

Results: Psl0096 or MEDI3902 were equally effective in enhancing in vitro Nφ OPK. Specifically, both Psl0096 and MEDI3902 elicited
≥2-fold increase in OPK in 85% Persistent isolates and 65% Eradicated isolates (P= NS). Interestingly, potentiation of Nφ-mediated intracellular bacterial killing of these clinical isolates by MEDI3902 was correlated with PcrV expression (P=.001). Moreover, treatment with MEDI3902 prior to infection with a representative Persistent isolate resulted in overall reduced bacterial burden (1.4x10^4 vs 2.6x10^5 CFU/g lung tissue, P=.002), with a greater proportion of mice with complete bacterial clearance at 24h post-infection (46% vs 0%, P=.01) compared to treatment with IgG control.

Conclusions: Targeting Psl and PcrV with mAb potentiates Nφ-mediated OPK of Persistent PA isolates. Preliminary results suggest that MEDI3902 treatment may also enhance in vivo bacterial clearance of Persistent isolates, raising the possibility that such therapies may improve the outcome of PA eradication in CF patients.

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