Antibody-mediated control of anellovirus infection: evidence from people who inject drugs

Infections with viruses belonging to the family <i>Anelloviridae</i> are widespread among humans. Although generally considered a commensal, there is evidence to suggest that these infections may be controlled by host immune responses. However, the mechanism of immune control remains unclear. Previous research has also suggested a possible role of anellovirus capsid spikes in immune evasion. To investigate the role of antibodies in controlling infection, we used AnelloScan to profile plasma collected every 6 months over 2 years from 10 persons who inject drugs (PWID). Participants were selected based on viremia patterns: persistent (<i>n</i> = 6) versus intermittent (<i>n</i> = 4). Long-read metagenomic sequencing revealed a higher median number of alphatorquevirus (TTV) species in participants with persistent viremia compared to those with intermittent viremia (<i>P</i> < 0.0001). AnelloScan detected TTV-specific antibodies among all study participants. No significant differences were observed between the two groups when all antibody-reactive peptides located in the capsid were included. However, among participants with intermittent viremia, antibodies were more frequently reactive to peptides located in the amino acid variable region of the capsid spike domain (<i>P</i> = 0.0429). These findings suggest that among PWID, antibodies targeting the sequence variable region of the spike domain appear to be associated with control of anellovirus infection. Additionally, anelloviruses might be susceptible to pre-existing immunity, and the amino acid variable region of the spike protein may play a role in viral infectivity.IMPORTANCEAnelloviruses are highly diverse and are recognized as the major component of the blood virome in healthy humans. Despite this, little is known about their interactions with their hosts. In this study, we found that anelloviruses can elicit antibody responses. Notably, antibodies that targeted a sequence variable region on spikes present on viral capsids were associated with truncation of plasma viremia. These data suggest a possible mechanism of immune control of anellovirus infections while also indicating a role of the capsid spikes in viral infectivity.