Development of an immunoPET probe to study SARS-CoV-2 pathogenesis in Rhesus Macaques

Madden, Patrick

doi:https://doi.org/10.21985/n2-8vqf-dr62

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Development of an immunoPET probe to study SARS-CoV-2 pathogenesis in Rhesus Macaques

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Infection with the novel coronavirus, SARS-CoV-2, results in pneumonia and other respiratory symptoms as well as pathologies at diverse anatomical sites. An outstanding question is whether these diverse pathologies are due to replication of the virus in these anatomical compartments and how and when the virus reaches those sites. To answer these outstanding questions and study the spatiotemporal dynamics of SARS-CoV-2 infection a method for tracking viral spread in vivo is needed. Here we report the development of the first immunoPET probe system to study SARS-CoV-2 pathogenesis in rhesus macaques. Our antibody-based in vivo probe system is based on the anti-spike monoclonal antibody CR3022. We initially demonstrated that it could successfully identify sites of SARS-CoV-2 infection in a rhesus macaque model of COVID-19 when detected using fluorescent whole-organ imaging. Our results showed that the fluorescent signal from our antibody-based probe could differentiate whole lungs of macaques infected for 9 days from those infected for 2 or 3 days. Additionally, the probe signal corroborated the frequency and density of infected cells in individual tissue blocks from infected macaques. These results provide proof of concept for the use of in vivo antibody-based probes to study SARS-CoV-2 infection dynamics in rhesus macaques. Next, we tested the probe in the context of immunoPET. Using PET/CT imaging of macaques at different times post-SARS-CoV-2 infection, we demonstrate that the 64Cu-labelled CR3022-F(ab’)2 probe targeting the spike protein of SARS-CoV-2 can be used to study the dynamics of infection within the respiratory tract and uncover novel sites of infection. Differences in lung pathology between infection with the WA1 isolate and the delta variant were readily observed using immunoPET and corroborated CT lung pathology. The ability of the probe to illuminate lung-associated pathology demonstrates its specificity and function to detect infection in PET scan. The probe also demonstrated dynamic changes occurring between 1- and 2-weeks post-infection. Remarkably, a robust signal was seen in the male genital tract (MGT) of all three animals studied. Infection of the MGT was validated by immunofluorescence imaging of infected cells in the testicular and penile tissue and severe pathology was observed in the testes of one animal at 2-weeks post-infection. The results presented here underscore the utility of using immunoPET to study the dynamics of SARS-CoV-2 infection to understand its pathogenicity and discover novel anatomical sites of viral replication. In addition, we provide direct evidence for SARS-CoV-2 infection of the MGT in rhesus macaques revealing the possible pathologic outcomes of viral replication at these sites.

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