Efficacy of brincidofovir as prophylaxis against HSV and VZV in hematopoietic cell transplant recipients

Allogeneic hematopoietic cell transplant (HCT) recipients are at risk for herpes simplex virus (HSV) and varicella-zoster virus (VZV) infections. Routine prophylaxis with acyclovir is recommended during periods of immunosuppression. Brincidofovir (BCV, CMX001), a lipid conjugate of cidofovir, has shown in vitro activity against HSV/VZV, but has not been formally studied for HSV/VZV prophylaxis. We report our clinical experience of BCV for HSV/VZV prophylaxis in HCT recipients. This was a retrospective review of 30 hematopoietic cell transplant (HCT) recipients between 8/2010 and 8/2015 who received BCV doses not exceeding 200 mg/week for adults/adolescents and 4 mg/kg/week for pediatric (<12 years) patients, for ≥14 days BCV without concomitant acyclovir under clinical trials or single patient use. HSV/VZV cases during BCV treatment were confirmed by viral culture or PCR and clinical symptoms. Of 30 patients who met the inclusion criteria, 27 (90%) patients were adults and 22 (73%) patients received T-cell depleted HCT. The most common indications for BCV were cytomegalovirus in 12 patients (40%) and adenovirus in 11 patients (37%). One patient was treated for acyclovir-resistant HSV and one for disseminated VZV. There were two breakthrough cases of HSV infection during 2170 patient-days. There were no cases of breakthrough VZV infection. The overall rate of breakthrough HSV infection was 1.0 per 1000 patient-days, without any breakthrough VZV infections. Our study provides the only available-albeit limited-evidence on the potential efficacy of BCV for HSV/VZV prophylaxis in HCT patients. Additional studies are needed to further assess the efficacy and safety of BCV in the setting