Ebola viral dynamics in nonhuman primates: insights into virus immuno-pathogenesis and antiviral strategies
Vincent Madelain (1), Sylvain Baize (2), Frédéric Jacquot (3), Caroline Carbonnelle (3), Hervé Raoul (3), Xavier de Lamballerie (4), France Mentré (1), Jérémie Guedj (1).
(1) IAME, UMR 1137, INSERM, Université Paris Diderot, Sorbonne Paris Cité Paris, France ; (2) UBIVE, Institut Pasteur, Centre International de Recherche en Infectiologie, Lyon, France ; (3) Laboratoire P4 Inserm-Jean Mérieux, US003 Inserm, 69365 Lyon, France ; (4) UMR
Objectives:
The 2014-2016 Ebola virus outbreak in West Africa, with more than 11,000 deaths, showed that hemorrhagic fever viruses are posing an increasing threat to public health, and the need to develop effective antiviral approaches [1]. Our group and others have focused since 2015 on the assessment of polymerase inhibitor favipiravir, which has shown in vitro and in vivo efficacy against several viruses, including Ebola, Lassa and Marburg viruses [2–4]. Part of this evaluation, this work aimed to:
- Develop a mechanistic host pathogen model to characterize the role of innate, adaptive immune response and favipiravir treatment on Ebola pathogenesis in NHPs.
- Predict the effect of treatment efficacy and timing of initiation on survival in NHPs.
Methods:
1) A total of 44 cynomolgus macaques were infected with Ebola virus, including 16 that were treated with doses of favipiravir ranging from 100 to 180 mg/kg BID initiated two days before viral challenge [3,5]. Frequent measurements of viral load, cytokines levels, cytotoxic CD8 T cells and favipiravir plasma concentration were collected and integrated into mechanistic models of host pathogen interaction. Models of increasing complexity were fitted to these data to incorporate the effect of favipiravir on viral replication, the effect of innate response on controlling peak viremia and finally the adaptive immune response on viral clearance. At each stage, a systematic model selection was performed based on the value of the log likelihood of the viral load, and selected models were evaluated using VPC.
2) Next the viral dynamics model was extended to include time to death (joint model) [6]. A forward procedure was used to select the model variables included in the hazard function providing the best improvement of BIC. Model prediction was then validated externally using previously published data obtained with another potent polymerase inhibitor, GS-5734, in NHP to evaluate the model capability to capture the relationship between antiviral potency and survival times [7]. Finally, simulations studies were performed to extrapolate the impact of treatment potency and timing of treatment on viral load, immunopathogenesis and survival.
Model estimations were performed using the SAEM algorithm, implemented in Monolix software 2016R1.
Results:
1) Capture of the Ebola viral dynamics required to incorporate the effect of the innate response mediated by IFNα. The main role of IFNα was to increase the conversion of target cells into non permissive cells, and so to control the viral replication. Treatment with favipiravir, albeit modest, was sufficient to reduce viral replication and cytokine storm, while still conferring cell protection. After peak viremia, modeling identified that progressive increase in CD8 T lymphocytes expressing perforin shortened the half-life of infected cells from 3 days to 16 hours, allowing viral clearance in surviving animals. The EC50 of favipiravir was estimated to 191 µg/mL, corresponding to an inhibition of 50% of the viral replication for the highest evaluated dose.
2) A joint model assuming that hazard rate was related to IFNα provided the best description of time to death. The model could reproduce both the viral load profiles obtained during treatment with GS-5734 and well predicted the survival rate of 100% observed in the experiment [7]. Using the model to further predict the efficacy of favipiravir and GS-5734 in various settings we predicted that: i) favipiravir initiation in post exposure up to D2 post challenge would maintain similar survival rate of about 60% compared to prophylaxis initiation, ii) treatments of higher potency could maintain 100% protection if administered before D4 and iii) treatment initiation after D5 would lead to 0% protection regardless of treatment efficacy.
Conclusions:
The model showed that mortality is primarily driven by the inflammatory reaction rather than by the virus replication per se. The early administration of a potent direct antiviral drug impairs viral replication, reduce the number of infected cells and consecutively the release of inflammatory cytokines. As the potency of the drug increases, the time window to initiate treatment after infection and save animals extends, but not over 6 days, when the cytokine storm can no longer be reversed. These results support the design of prophylaxis or post exposure trials for the evaluation of direct antiviral in future outbreaks.
References:
[1] World Health Organization. WHO | Ebola situation reports [Internet]. [cited 2016 Jun 14]. Available from: http://apps.who.int/iris/bitstream/10665/208883/1/ebolasitrep_10Jun2016_eng.pdf?ua=1;
[2] Bixler SL, Bocan TM, Wells J, Wetzel K, Van Tongeren S, Dong L, et al. Efficacy of favipiravir (T-705) in nonhuman primates infected with Ebola virus or Marburg virus. Antiviral Res. 2017;
[3] Guedj J, Piorkowski G, Jacquot F, Madelain V, Nguyen THT, Rodallec A, et al. Antiviral efficacy of favipiravir against Ebola virus in cynomolgus macaques. 2018 Accept Plos Med;
[4] Furuta Y, Komeno T, Nakamura T. Favipiravir (T-705), a broad spectrum inhibitor of viral RNA polymerase. Proc Jpn Acad Ser B Phys Biol Sci. 2017;93:449–63;
[5] Piorkowski G, Jacquot F, Quérat G, Carbonnelle C, Pannetier D, Mentré F, et al. Implementation of a non-human primate model of Ebola disease: Infection of Mauritian cynomolgus macaques and analysis of virus populations. Antiviral Res. 2017;140:95–105;
[6] Desmée S, Mentré F, Veyrat-Follet C, Guedj J. Nonlinear Mixed-effect Models for Prostate-specific Antigen Kinetics and Link with Survival in the Context of Metastatic Prostate Cancer: A Comparison by Simulation of Two-stage and Joint Approaches. AAPS J. 2015;17:691–9;
[7] Warren TK, Jordan R, Lo MK, Ray AS, Mackman RL, Soloveva V, et al. Therapeutic efficacy of the small molecule GS-5734 against Ebola virus in rhesus monkeys. Nature. 2016;531:381–5.
