VIROMARKERS GA n.101194735 - CMV and TTV Biomarkers Study Protocol

The study is one of the researches carried out in the VIROMARKERS Project. The project VIROMARKERS is supported by the Innovative Health Initiative Joint Undertaking (IHI JU) under grant agreement No 101194735. The JU receives support from the European Union's Horizon Europe research and innovation programme and COCIR, EFPIA, Europa Bio, MedTech Europe, Vaccines Europe, and Roboscreen. To date, the virological surveillance for CMV replication relies basically on the quantification of CMV-DNA in blood or plasma by using Real-Time PCR assays, and CMV-DNAemia is known to correlate with both CMV-related disease and non-relapse mortality \[Ljungman, 2025\]. However, the detection of CMV-DNAemia is not always associated with an active CMV replication, particularly in patients exposed to letermovir. Therefore, the identification of new virological markers to accurately monitor CMV activity in the early and late post-HSCT phases, remains a crucial issue especially in individuals receiving letermovir as prophylaxis to ensure a proper diagnosis of CMV infection/disease and to guide prophylactic and pre-emptive antiviral treatment. In this setting, the quantification of CMV-RNA represents a potential candidate marker capable of better reflecting the presence of complete, infectious CMV virions than CMV-DNAemia. Despite several data support a correlation of CMV UL21.5-mRNA with viral activity \[Nicastro, 2025\], studies investigating the kinetics of this viral mRNA among immune-suppressed patients at risk of CMV re-uptake are largely missing, especially in the setting of patients receiving antiviral prophylaxis with letermovir after HSCT. TTV-DNA load was mostly investigated in solid organ transplant patients (SOT), where it showed a good correlation of high viral load and degree of immunosuppression. In HSCT patients the interaction of the immune system, which is under reconstitution, and clinically relevant CMV infection is more complex. First data have been reported by o