Viral load surrogate endpoints transformed development of HIV and hepatitis C therapeutics. Surrogate endpoints for cytomegalovirus (CMV)-related morbidity and mortality could advance development of antiviral treatments. While observational data support using CMV viral load (VL) as a trial endpoint, randomized controlled trials (RCT) demonstrating direct associations between virologic markers and clinical endpoints are lacking.
We performed CMV DNA polymerase chain reaction (PCR) on frozen serum samples from the only placebo-controlled RCT of ganciclovir for early treatment of CMV after hematopoietic cell transplantation (HCT). We used established criteria to assess VL kinetics as surrogates for CMV disease or death by weeks 8, 24, and 48 after randomization and quantified antiviral effects captured by each marker. We used ensemble-based machine learning to assess the predictive ability of VL kinetics and performed this analysis on a ganciclovir prophylaxis RCT for validation.
VL suppression with ganciclovir reduced cumulative incidence of CMV disease and death for 20 years after HCT. Mean VL, peak VL, and change in VL during the first five weeks of treatment fulfilled the Prentice definition for surrogacy, capturing > 95% of ganciclovir’s effect, and yielded highly sensitive and specific predictions by week 48. In the prophylaxis trial, viral shedding rate satisfied the Prentice definition for CMV disease by week 24.
Our results support using CMV VL kinetics as surrogates for CMV disease, provide a framework for developing CMV preventative and therapeutic agents, and support reductions in viral load as the mechanism through which antivirals reduce CMV disease.