Open Label Study of IV Brincidofovir in Adult Transplant Recipients With Adenovirus Viremia

Inclusion Criteria: * Be ≥ 18-years-old (or per local law or regulations on legal age of consent). * Have received an allogeneic hematopoietic cell transplant (HCT) within the previous 100 days. * Have plasma AdV DNA viremia ≥ 1,000 copies/mL (via quantitative polymerase chain reaction assay; local results must be confirmed by the designated central virology laboratory). Exclusion Criteria: * Diarrhea meeting the US National Institutes of Health (NIH)/National Cancer Institute (NCI) Common Terminology Criteria for Adverse Events (CTCAE) Grade 2 or greater * Acute graft versus host disease (GVHD) 1. NIH Stage 2 or higher acute GVHD of the gut (i.e., diarrhea \> 1,000 mL/day, or severe abdominal pain with or without ileus) or liver (i.e., bilirubin \> 3 mg/dL : \> 51 μmol/L) within 7 days prior to Day 1 2. Any NIH Stage 3 or Stage 4 acute GVHD within 7 days prior to Day 1 * Concurrent human immunodeficiency virus or active hepatitis B or C infection * An estimated creatinine clearance of \< 30 mL/min, and/or use of renal replacement therapy within 7 days prior to Day 1. * Poor clinical prognosis, including active malignancy, irreversible organ failure, use of vasopressors, requirement for mechanical ventilation, resting oxygen saturation \< 88%, or Pulmonary Arterial oxygen (PaO2) ≤ 55 mm Hg without supplemental oxygen at any time within 7 days prior to Day 1. * Receiving or anticipated to start systemic cyclosporine immunosuppressant treatment during study participation. * Received treatment with CDV within 14 days prior to Day 1. * Previous receipt of cell-based anti-AdV therapy within 6 weeks prior to Day 1 or prior receipt of an anti-AdV vaccine at any time. * Consumed food products containing sesame seeds, sesame oil, or dietary supplements containing sesamin within 3 days prior to Day 1. * Received any investigational drug within 28 days prior to Day 1 or currently participating in another interventional study. * Pregnant or breastfeeding.