Immunopathogenesis of SARS-CoV-2 infection

National Institute Of Allergy And Infectious Diseases

Investigators

Linked publications, trials & patents

Abstract

We have written an Animal Study Proposal that has been approved by the NIAID Animal Care and Use Committee and the SVC. We began research in fall, 2020 after the BSL3 and ABSL3 facilities opened for this purpose. To date, WT and huACE2 transgenic mice on a C57BL/6 background have been infected with clinical isolates of SARS-CoV-2. The huACE2 mice are highly susceptible to fatal infection whereas the WT mice survive. We are crossing mouse strains to test chemokine receptor knockout mice on the huACE2 background prioritizing receptors encoded by genes in the CCR cluster since human GWAS studies of Covid disease have reported a strong signal in this region most proximal to CCR9. Our goal is to test a WT LD100 dose first, screening for receptor knockouts that increase survival, since any positive results will have translational potential. Receptors that screen negative will be rescreened at an LDzero looking for protective chemokine receptors in the model. To date we have identified Ccr6 knockouts as having increased susceptibility to weight loss and fatal outcome. We are also attempting to develop a AAV-huACE2 transient expression system to accelerate screening by obviating the huACE2 transgenic/chemokine receptor ko crosses. We are also pursuing a strain of SARS-CoV-2 that has been adapted to mouse infection towards accelerating discovery. For each type of experiment four virus doses will be tested to determine if models for asymptomatic, mild virulence or higher virulence can be developed for each virus. Both females and males will be tested and are expected to have differences in clinical progression of coronaviral disease and histopathology, based on other infectious disease models in mice, and differences between the sexes observed in humans infected with SARS-CoV and SARS-CoV-2. In all subsequent experiments, clinical disease progression will be assessed by virus recovery from throat swabs, blood and stool; serum antibody titers, hemograms, blood chemistries and serum cytokines before and at multiple intervals after infection; as well as physical appearance, weight loss, and progression to moribundity and survival for a month after infection. Animals will be euthanized by CO2 and cervical dislocation at the latest one-month post-infection. In our experience, to observe significant differences in survival we will need 20 mice/cohort in each experiment and repeat the experiment 3 times due to the variance in survival between experiments. These numbers should be sufficient to observe significant differences in the other clinical data as well. Fewer non-infected mice will be needed since there is expected to be less variance among these controls. A secondary goal is to characterize the local immune response in cultured human lung explants infected with SARS-CoV-2. We have succeeded in collaboration with L Margolis from NICHD in establishing this system and demonstrating productive infection.