Temperature-dependent replication and sensitivity to innate immunity of human coronavirus HKU1.

The human coronavirus HKU1, causing common colds and occasionally severe illness, remains largely uncharacterized because it has not been successfully grown on immortalized cells. Here, we identify Caco2 cells overexpressing TMPRSS2, the HKU1 receptor, as being highly permissive to infection. HKU1 replicates efficiently, forms syncytia and releases infectious progeny in these cells at 33 °C, the temperature of the nasal cavity, but is attenuated at 37 °C. Viral entry occurs similarly at both temperatures, but subsequent viral RNA synthesis is enhanced at 33 °C. Released virions display higher stability at 33 °C. In Caco2 and primary epithelial nasal cells, HKU1 is sensitive to interferons (IFN), but induction of IFN stimulated genes, such as IFN-Induced Transmembrane Proteins (IFITMs), is delayed at 33 °C. Once expressed, IFITMs comparably inhibit HKU1 fusion at both temperatures. In contrast, SARS-CoV-2 robustly replicates at 37 °C. Thus, cellular permissiveness, innate immunity and viral properties collectively explain why HKU1 replicates more efficiently at nasal temperature. Our results highlight temperature-sensitivity disparities between coronaviruses, likely associated to different pathogenic outcomes.