Circular forms of viral genomic DNA are generated during infection of cells with retroviruses like HIV-1. Such circles are unable to replicate and are eventually lost as a result of cell division, lending support to the prevalent notion that episomal retroviral DNA forms are dead-end products of reverse transcription.
Moldt, B., Staunstrup, N. H., Jakobsen, M., Yáñez-Muñoz, R. J., & Mikkelsen, J. G. (2008). Genomic insertion of lentiviral DNA circles directed by the yeast Flp recombinase. BMC Biotechnology, 8. https://doi.org/10.1186/1472-6750-8-60