Human anelloviruses produced by recombinant expression of synthetic genomes.
Human anelloviruses are acquired universally in infancy, highly prevalent, abundant in blood, and extremely diverse. Their apparent lack of pathogenicity indicates that they are a major component of the commensal human virome. Despite their being extensively intertwined with human biology, these viruses are poorly understood. A major impediment in studying anelloviruses is the lack of an in vitro system for their production and/ or propagation. Here we show that the T cell-derived human cell line MOLT-4 can be transfected with plasmids comprising tandem anellovirus genomes to produce viral particles visualized by electron microscopy. We found that a previously described human anellovirus of the Betatorquevirus genus (LY2), as well as a second Betatorquevirus detected by sequencing DNA extracted from a human retinal pigmental epithelium (nrVL4619), can be synthesized and produced by these means, enabling further molecular virology studies. Southern blot was used to demonstrate replication, and site-directed mutagenesis of the viral genome was performed to show that the production of anellovirus in this cell line is dependent on the expression of certain viral proteins. Finally, experiments performed in mice using purified nrVL4619 particles produced in MOLT-4 cells demonstrated infectivity in vivo in the tissue of origin. These results indicate that anelloviruses can be produced in vitro and manipulated to improve our understanding of this viral family which is ubiquitous in humans and many other mammals. Applications of this work to gene therapy and other therapeutic modalities are currently under investigation. IMPORTANCEAnelloviruses are a major component of the human virome. However, their biology is not well understood mainly due to the lack of an in vitro system for anellovirus production and/or propagation. In this study, we used multiple orthogonal measures to show that two different anelloviruses belonging to the Betatorquevirus genus can be produced in a T-cell-derived human cell line, MOLT-4, via recombinant expression of synthetic genomes. Additionally, we show that anellovirus particles generated in this in vitro system demonstrate infectivity in vivo. Our findings enable new molecular virology studies of this highly prevalent, non-pathogenic, and weakly immunogenic family of viruses, potentially leading to therapeutic applications.