A humanized mouse model of chronic COVID-19

Abstract

OVID-19, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) 1 , is a heterogenous disease with few therapeutic options. Although anti-viral immunity mediates viral clearance in mild COVID-19, robust inflammatory cytokines, decreased circulating lymphocytes and dysregulated myeloid and lymphocyte compartments characterize immunopathology in severe ). Accurate model systems are essential to evaluate promising discoveries, but most available rodent and non-human primate models do not reveal the immunopathology seen in patients and are not well suited to test therapeutics in the context of severe COVID-19 or post-acute sequelae of ).ACE2 is a SARS-CoV-2 receptor [20][21][22] . SARS-CoV-2 does not infect standard laboratory mice owing to differences between mouse and human ACE2 (hACE2) that limit viral entry 14,15,[20][21][22] . Mice with transgenic or transient hACE2 expression can be infected with SARS-CoV-2 (refs. 14,[16][17][18][19] ). Although acute viral response, transmission and vaccine efficacy can be tested in these models, they lack severe, chronic disease (Extended Data Fig. 1). We hypothesized that a functional human immune system would model innate and adaptive human immunity during SARS-CoV-2 infection and confer chronicity and pathology seen in patients. Mice with a human immune system (humanized mice), generated via transplantation of human hematopoietic stem and progenitor cells (HSPCs), are invaluable tools to study the human immune system in vivo 23,24 . MISTRG6 (ref. 25 ) mice were engineered by a human/mouse homolog gene replacement strategy to provide physiological expression with regard to quantity, location and time of M-CSF (monocytes and tissue macrophage development) 26 , GM-CSF/IL3 (lung alveolar macrophages) 27 , SIRPα (macrophage tolerance to human cells) 28 , ThPO (hematopoiesis and platelets) 29 and IL6 (improved engraftment and antibody responses) 25,30,31 in a Rag2/γ common chain deleted background. When engrafted with human HSPCs, these mice have a comprehensive immune system similar to humans 25,32 . Delivering hACE2 via an adeno-associated virus (AAV) vector to the lungs allows SARS-CoV-2 infection of HSPC-engrafted MISTRG6 mice. Thus, we created a humanized mouse model of COVID-19 that recapitulates the human innate and adaptive immune systems that is amenable to the mechanistic study of COVID-19 and its myriad of complications.

Inflammasome activation in infected macrophages drives COVID-19 pathology

“…S1K), highlighting the selective effects of combined anti-IFNAR2/Remdesivir therapy on chronic COVID-19 pathology. Consistent with the fibrosis, seen both in patients 32-36 and humanized mice 19 , alveolar self-renewal and differentiation programs were inhibited, resulting in the accumulation of pre-alveolar type 1 transitional cell state (PATS) program in pneumocytes 7,37-39 that was reversed in infected MISTRG6-hACE2 mice by anti-IFNAR2/Remdesivir combination therapy, restoring self-renewal and differentiation programs (Fig. S1L).…”

“…Two hallmarks of severe COVID-19 are a sustained interferon (IFN) response and viral RNA persisting for months 1-13,20,27,28 . This chronicity is recapitulated in SARS-CoV-2 infected MISTRG6-hACE2 humanized mice 19 . Copious Interleukin (IL)-1β, IL-18 and lactate dehydrogenase (LDH) correlates with COVID-19 severity in patients, suggesting a role for inflammasome activation and pyroptosis in pathology 5-7,14-18,29 .…”

A model of persistent post SARS-CoV-2 induced lung disease for target identification and testing of therapeutic strategies

“…Currently, our understanding of PASC and COVID-19 induced CAP/PF is poor and countermeasures are limited due to the wide spectrum of potential disease pathophysiologies. Recently, a chronic (30 dpi) SARS-CoV-2 infection model was reported in immunosuppressed, humanized mice characterized by persistent virus replication and chronic inflammation with fibrotic markers, typical of rare infections seen in immunosuppressed humans who cannot clear virus ( 65 ). We developed a model of long-term pulmonary sequelae of SARS-CoV-2 infection that persisted after virus clearance and was more characteristic of the general patient population.…”

Genetically engineered MRI-trackable extracellular vesicles as SARS-CoV-2 mimetics for mapping ACE2 bindingin vivo

“…Several studies have already shown the ability of engineered EVs to interact and bind to receptors of interest in vivo , including acetylcholine receptors in the brain 32 , tumor cells 27 , immune cell surfaces 49 , and viral receptors, including ACE2 40 . Since human ACE2 receptors are not naturally present in mice, a few transgenic mice models had been proposed 50,51 , but they are not readily accessible, and therefore, are not yet extensively used. Therefore, we established a xenograft model to study the in vivo targetability of EVs RBD to ACE2 following their systemic administration.…”