Molecular Profile and Dynamics of Commensal Viruses in Brazilian Patients Who Underwent Allogeneic Hematopoietic Stem Cell Transplantation

Background: Commensal viruses are typically well-tolerated by healthy individuals, but their behavior in immunocompromised patients is not fully understood. Methods: This study investigated the prevalence, molecular dynamics, and circulating genotypes of human pegivirus-1 (HPgV-1) and three types of torque teno viruses (TTV-3, -16, and -22) in Brazilian patients undergoing allogeneic hematopoietic stem cell transplantation (HSCT). Plasma samples from 20 patients were collected at three time points: pretransplantation (D+0), 30 days post-transplantation (D+30), and 100 days post-transplantation (D+100). We conducted longitudinal screening for HPgV-1 and three TTV variants using real-time PCR, comparing cycle threshold values across these intervals. Results: The overall HPgV-1 RNA prevalence at all collection points was 45% (n = 9/20), with all infected individuals carrying genotype 2. HPgV-1 infections exhibited stable, closely related strains over time, though virus evolution was highly individualized. The overall prevalence of TTV types was 5% for TTV-3, 30% for TTV-16, and 60% for TTV-22. Notably, all commensal viruses showed a decrease in cycle threshold at D+100, indicating a possible increase in viral load. Conclusion: These findings underscore the importance of commensal viruses in the context of HSCT and suggest their potential role as biomarkers for immune suppression and transplantation outcomes. Further research is warranted to elucidate their implications. (Figure presented.).