New class of monoclonal antibodies against severe influenza: prophylactic and therapeutic efficacy in ferrets

Abstract

Background: The urgent medical need for innovative approaches to control influenza is emphasized by the widespread resistance of circulating subtype H1N1 viruses to the leading antiviral drug oseltamivir, the pandemic threat posed by the occurrences of human infections with highly pathogenic avian H5N1 viruses, and indeed the evolving swine-origin H1N1 influenza pandemic. A recently discovered class of human monoclonal antibodies with the ability to neutralize a broad spectrum of influenza viruses (including H1, H2, H5, H6 and H9 subtypes) has the potential to prevent and treat influenza in humans. Here we report the latest efficacy data for a representative antibody of this novel class.

Methodology/principal findings: We evaluated the prophylactic and therapeutic efficacy of the human monoclonal antibody CR6261 against lethal challenge with the highly pathogenic avian H5N1 virus in ferrets, the optimal model of human influenza infection. Survival rates, clinically relevant disease signs such as changes in body weight and temperature, virus replication in lungs and upper respiratory tract, as well as macro- and microscopic pathology were investigated. Prophylactic administration of 30 and 10 mg/kg CR6261 prior to viral challenge completely prevented mortality, weight loss and reduced the amount of infectious virus in the lungs by more than 99.9%, abolished shedding of virus in pharyngeal secretions and largely prevented H5N1-induced lung pathology. When administered therapeutically 1 day after challenge, 30 mg/kg CR6261 prevented death in all animals and blunted disease, as evidenced by decreased weight loss and temperature rise, reduced lung viral loads and shedding, and less lung damage.

Conclusions/significance: These data demonstrate the prophylactic and therapeutic efficacy of this new class of human monoclonal antibodies in a highly stringent and clinically relevant animal model of influenza and justify clinical development of this approach as intervention for both seasonal and pandemic influenza.

Figure 1. Prophylactic efficacy of CR6261 against lethal H5N1 challenge.

Groups of 6 ferrets received 30, 10, 3, or 1 mg/kg of mAb CR6261 or 30 mg/kg control mAb by intravenous injection and were challenged 24 hours later with 10⁵ TCID₅₀ of influenza A/Indonesia/5/2005 (H5N1). Ferrets were monitored for 5 days or until death. Panel A: Kaplan–Meier survival probability curves. Panel B: Change in body weight at the end of study (or at death if the event occurred earlier) expressed as percentage from baseline body weight. Panel C: Maximal body temperature observed during the day after challenge. Panel D: Viral shedding of infectious virus in the upper respiratory tract. The graph shows the proportion of ferrets alive with infectious virus detected in nasal and/or throat swabs. Panel E: Viral load in lung tissue as determined by virus titration on MDCK cells. Panel F: lung weights as determined after necropsy. Dots in panels B, C, E and F represent individual animals; group means are indicated by the horizontal lines.

Figure 2. Therapeutic efficacy of CR6261 against lethal H5N1 challenge.

Groups of 10 ferrets received 30 mg/kg mAb CR6261 by intravenous injection either 4 or 24 hours after challenge with 10⁵ TCID₅₀ of influenza A/Indonesia/5/2005 (H5N1) virus. A control group of 10 ferrets received 30 mg/kg of a control mAb 4 hours after challenge. Ferrets were monitored for 5 days or until death. Panel A: Kaplan–Meier survival probability curves. Panel B: Change in body weight at the end of study (or at death if earlier) expressed as percentage from baseline weight. Panel C: Maximal body temperature observed the day after challenge. Panel D: Viral shedding of infectious virus in the upper respiratory tract. The graph shows the proportion of ferrets alive with infectious virus detected in nasal and/or throat swabs. Panel E: Viral load in lung tissue as determined by virus titration on MDCK cells. Panel F: lung weights as determined after necropsy. Dots in panels B, C, E and F represent individual animals; group means are indicated by horizontal lines. The open circles (panel E and F) indicate one additional ferret per CR6261 group that was euthanized at day 3 for virus isolation and pathology.