SUMMARY Effector T cell differentiation requires the simultaneous integration of multiple, and sometimes opposing, cytokine signals. We demonstrate that mTOR plays a role in dictating the outcome of T cell fate. mTOR deficient T cells display normal activation and IL-2 production upon initial stimulation. However, such cells fail to differentiate into Th1, Th2 or Th17 effector T cells under skewing conditions. The inability to differentiate is associated with a decrease in STAT activation and failure to upregulate lineage specific transcription factors. Under all normally activating conditions, T cells lacking mTOR differentiate into Foxp3+ regulatory cells. This differentiation is associated with hyperactive Smad3 activation in the absence of exogenous TGF-β. Surprisingly, T cells in which TORC1 activity has been selectively deleted do not divert to a regulatory T cell pathway, revealing an unappreciated role for TORC2 signaling in preventing the generation of regulatory T cells. Overall our studies suggest that differential TORC1 and TORC2 signaling regulate decisions between effector and regulatory T cell lineage commitment.

Traditional approaches to antimicrobial drug development are poorly suited to combatting the emergence of novel pathogens. Additionally, the lack of small animal models for these infections hinders the in vivo testing of potential therapeutics. Here we demonstrate the use of the VelocImmune technology (a mouse that expresses human antibody-variable heavy chains and κ light chains) alongside the VelociGene technology (which allows for rapid engineering of the mouse genome) to quickly develop and evaluate antibodies against an emerging viral disease. Specifically, we show the rapid generation of fully human neutralizing antibodies against the recently emerged Middle East Respiratory Syndrome coronavirus (MERS-CoV) and development of a humanized mouse model for MERS-CoV infection, which was used to demonstrate the therapeutic efficacy of the isolated antibodies. The VelocImmune and VelociGene technologies are powerful platforms that can be used to rapidly respond to emerging epidemics.

SARS-CoV-2 emerged in China at the end of 2019 and has rapidly become a pandemic with over 20 million recorded COVID-19 cases in August 2020 (www.WHO.org). There are no FDA approved antivirals or vaccines for any coronavirus, including SARS-CoV-2. Current treatments for COVID-19 are limited to supportive therapies and off-label use of FDA approved drugs. Rapid development and human testing of potential antivirals is greatly needed. Numerous drugs are already approved for human use and subsequently there is a good understanding of their safety profiles and potential side effects, making them easier to fast-track to clinical studies in COVID-19 patients. Here, we present data on the antiviral activity of 20 FDA approved drugs against SARS-CoV-2 that also inhibit SARS-CoV and MERS-CoV. We found that 17 of these inhibit SARS-CoV-2 at non-cytotoxic concentrations. We directly follow up with seven of these to demonstrate all are capable of inhibiting infectious SARS-CoV-2 production. Moreover, we have evaluated two of these, chloroquine and chlorpromazine, in vivo using a mouse-adapted SARS-CoV model and found both drugs protect mice from clinical disease. IMPORTANCE There are no FDA approved antivirals for any coronavirus, including SARS-CoV-2. Numerous drugs are already approved for human use that may have antiviral activity and therefore could potentially be rapidly re-purposed as antivirals. Here, we present data assessing the antiviral activity of 20 FDA approved drugs against SARS-CoV-2 that also inhibit SARS-CoV and MERS-CoV in vitro. We find 17 of these inhibit SARS-CoV-2, suggesting these may have pan-anti-coronaviral activity. We directly follow-up with seven of these and find they all inhibit infectious SARS-CoV-2 production. Moreover, we have evaluated chloroquine and chlorpromazine in vivo using mouse-adapted SARS-CoV. We find neither drug inhibited viral replication in the lungs, but both protected against clinical disease.

The recently emerged Middle East respiratory syndrome coronavirus (MERS-CoV), a betacoronavirus, is associated with severe pneumonia and renal failure. The environmental origin of MERS-CoV is as yet unknown; however, its genome sequence is closely related to those of two bat coronaviruses, named BtCoV-HKU4 and BtCoV-HKU5, which were derived from Chinese bat samples. A hallmark of highly pathogenic respiratory viruses is their ability to evade the innate immune response of the host. CoV accessory proteins, for example those from severe acute respiratory syndrome CoV (SARS-CoV), have been shown to block innate antiviral signalling pathways. MERS-CoV, similar to SARS-CoV, has been shown to inhibit type I IFN induction in a variety of cell types in vitro. We therefore hypothesized that MERS-CoV and the phylogenetically related BtCoV-HKU4 and BtCoV-HKU5 may encode proteins with similar capabilities. In this study, we have demonstrated that the ORF4b-encoded accessory protein (p4b) of MERS-CoV, BtCoV-HKU4 and BtCoV-HKU5 may indeed facilitate innate immune evasion by inhibiting the type I IFN and NF-kB signalling pathways. We also analysed the subcellular localization of p4b from MERSCoV, BtCoV-HKU4 and BtCoV-HKU5 and demonstrated that all are localized to the nucleus.