Postexposure antibody prophylaxis protects nonhuman primates from filovirus disease

Abstract

Antibody therapies to prevent or limit filovirus infections have received modest interest in recent years, in part because of early negative experimental evidence. We have overcome the limitations of this approach, leveraging the use of antibody from nonhuman primates (NHPs) that survived challenge to filoviruses under controlled conditions. By using concentrated, polyclonal IgG antibody from these survivors, we treated filovirus-infected NHPs with multiple doses administered over the clinical phase of disease. In the first study, Marburg virus (MARV)-infected NHPs were treated 15 to 30 min postexposure with virus-specific IgG, with additional treatments on days 4 and 8 postexposure. The postexposure IgG treatment was completely protective, with no signs of disease or detectable viremia. MARV-specific IgM antibody responses were generated, and all macaques survived rechallenge with MARV, suggesting that they generated an immune response to virus replication. In the next set of studies, NHPs were infected with MARV or Ebola virus (EBOV), and treatments were delayed 48 h, with additional treatments on days 4 and 8 postexposure. The delayed treatments protected both MARV- and EBOV-challenged NHPs. In both studies, two of the three IgG-treated NHPs had no clinical signs of illness, with the third NHP developing mild and delayed signs of disease followed by full recovery. These studies clearly demonstrate that postexposure antibody treatments can protect NHPs and open avenues for filovirus therapies for human use using established Food and Drug Administration-approved polyclonal or monoclonal antibody technologies.

Fig. 1.

Filovirus-specific plaque-reduction neutralization titers of fractionated IgG. (A) MARV-specific or (B) EBOV-specific plaque-reduction neutralization titration of fractionated IgGs. Twofold serial dilutions of fractionated IgG was mixed with 100 pfu of (A) MARV or (B) EBOV at 37 °C for 1 h and used to infect Vero cells. Neutralization titers were determined, in duplicate, to be the last dilution of serum that reduced the number of plaques by 80% compared with control wells. Error bars indicate SEM in replicate experiments.

Fig. 2.

Percent survival and MARV specific antibody titers in NHPs treated 15 to 30 min after infection with MARV. (A) Percent survival following MARV challenge (**P < 0.01, Fisher exact test). MARV-specific (B) IgG and (C) IgM. Serum collected from NHPs at indicated days postinfection was analyzed by ELISA against whole irradiated MARV antigen. MARV-specific antibody end titers are reported. Dotted line indicates assay limit of detection. Arrows indicate IgG treatment days.

Fig. 3.

Percent survival and MARV-specific antibody titers in NHPs treated 48 h postinfection with MARV. (A) Percent survival following MARV challenge (**P < 0.01, Fisher exact test). MARV-specific (B) IgG and (C) IgM. Serum collected from NHPs at indicated days postinfection was analyzed by ELISA against whole irradiated MARV antigen. MARV-specific antibody end titers are reported. Dotted line indicates assay limit of detection. Arrows indicate IgG treatment days.

Fig. 4.

Percent survival and EBOV specific antibody titers in NHPs treated 48 h postinfection with EBOV. (A) Percent survival following EBOV challenge (**P < 0.01, Fisher exact test). EBOV-specific (B) IgG and (C) IgM. Serum collected from NHPs at indicated days postinfection was analyzed by ELISA against whole irradiated EBOV antigen. EBOV-specific antibody end titers are reported. Dotted line indicates assay limit of detection. Arrows indicate IgG treatment days.

Fig. 5.

Filovirus-specific IgG antibody titers. (A) EBOV- and MARV-specific IgG antibody titers of IgGs. Fractionated naive IgG and EBOV-specific IgG was analyzed by ELISA against whole irradiated EBOV (blue) or MARV (red) antigen. Antibody end titers are reported. Error bars indicate SEM in replicate experiments (***P < 0.001, two-way ANOVA). (B) EBOV- and MARV-specific serum IgG antibody titers after EBOV infection. Serum collected from NHPs at indicated days after infection was analyzed by ELISA against whole irradiated EBOV (blue) or MARV (red) antigen. Filovirus specific antibody end titers are reported. Error bars indicate SEM of three experimental NHPs. Dotted line indicates assay limit of detection. Arrows indicate IgG treatment days.