Identification of a novel HKU4-related coronavirus in single-cell datasets and clade viral host analysis

HKU4-related coronaviruses (CoVs) are merbecoviruses related to Middle Eastern Respiratory Syndrome coronavirus (MERS-CoV). In 2022 and 2023, two HKU4-related CoV strains were discovered in Manis javanica (Malayan pangolin) metagenomic datasets derived from organ samples: HKU4-P251T and MjHKU4r-CoV-1. Together with the Tylonycteris robustula bat CoV 162275, which was discovered in 2022, pangolin CoVs HKU4-P251T and MjHKU4r-CoV-1 form a novel phylogenetic clade distinct from all previously documented HKU4-related CoVs. In this study, we identified a novel HKU4-related CoV in a pangolin single-cell sequencing dataset generated by BGI-Shenzhen in Shenzhen, Guangdong, China in 2020. The CoV phylogenetically belongs to the same newly identified clade. The single cell datasets were reported as generated from organ samples of a single pangolin that died of natural causes. 98% of the HKU4-related CoV reads were found in only one of the seven single cell datasets -- a large intestine cell dataset, cells of which exhibit low expression of DPP4. Bacterial contamination was found to be moderately correlated with HKU4-related CoV presence. We further identified with high confidence that the RNA-Seq dataset supporting one of four near identical variants of MjHKU4r-CoV-1 is a Sus scrofa (wild pig) metagenomic dataset, with only a trace level of Manis javanica genomic content. The presence of HKU4-related CoV reads in the dataset are almost certainly laboratory research-related and not from a premortal pangolin or pig infection. Our findings raise concerns about the provenance of the novel HKU4-related CoV we identify here, MjHKU4r-CoV-1 and its four near-identical variants.