Ledipasvir/Sofosbuvir Treatment for Hepatitis C in HCT Recipients.

Inclusion Criteria: 1. Participant must be male or female at least 18 years of age at time of screening 2. Participant must be able to provide written Informed Consent 3. Participant must be able to adhere to study visit/procedure schedule and protocol requirements 4. Time available (at least 12 weeks) for treatment of hepatitis C prior to autologous or allogeneic transplantation 5. First autologous or allogeneic HCT and hematologic disease in remission on initiation of antiviral therapy for hepatitis C infection 6. Patients with myelodysplastic syndrome, aplastic anemia or hemoglobinopathies will be eligible to participate regardless of disease status if plan is to proceed to HCT 7. Female participant without childbearing potential must meet at least one of the following: * Postmenopausal defined as women \>54 years of age with amenorrhea for ≥ 2 years prior to screening * Surgically sterile defined as bilateral tubal ligation or bilateral oophorectomy or hysterectomy * Has male sexual partner with vasectomy 8. Female participant of childbearing potential must meet at least one of the following: * Must be using at least 1 effective contraceptive method at screening and agree to practice 2 effective contraceptive methods1 for study duration, starting Screening through 30 days after stopping study drug * Practice total abstinence from sexual intercourse (minimum 1 complete menstrual cycle) * Sexually active with female partner only 9. Male participant who is not surgically sterile and is sexually active with female partner of childbearing potential must agree to practice 2 effective contraceptive methods1 for study duration, starting at Screening through 30 days after stopping study drug 10. Participant must have the following indicator- of chronic hepatitis C virus infection prior to study enrollment: • Positive for HCV RNA at the time of screening 11. Participant screening laboratory result must indicate HCV genotype 1, 4, 5 or 6-infection if historical result is not available. Exclusion Criteria: 1. Participant unwilling to provide written informed consent 2. Participant unwilling to adhere to study visit/procedure schedule and protocol requirements 3. Participant is pregnant or is a breastfeeding female 4. Positive test result for hepatitis B surface antigen (HBsAG), hepatitis B core antibody (HBcAb), or confirmed positive anti-HIV antibody test 5. Received study contraindicated medications prior to study drug administration including but not limited to those listed in the Full Prescribing Information Sheet for ledipasvir/sofosbuvir (Harvoni®). 6. Clinically significant abnormalities or co-morbidities, other than HCV infection that in opinion of the investigator makes subject unsuitable for this study or drug regimen 7. Prior or current use of any investigational or commercially available anti-HCV agents other than interferon or ribavirin or receipt of any investigational product within 6 weeks prior to study drug administration 8. Prior treatment of chronic HCV infection with a direct acting antiviral agent(s): telaprevir, boceprevir, sofosbuvir, simeprevir, or other direct acting antiviral 9. History of solid organ transplant 10. Screening laboratory analyses shows any of the following abnormal laboratory results: Estimated Glomerular filtration (eGFR) rate \< 30 mL/min 11. Evidence of cirrhosis, documented by one of the following: Liver biopsy histologic diagnosis: Metavir Score greater than 3 (includes 3 - 4 or ¾) or Ishak score greater than 4 In the absence of liver biopsy: a FibroScan score greater than or equal to 12.5 kPa or Fibrotest score of \>0.75 AND an APRI score greater than 1.5 12. History of liver decompensation: ascites noted on a physical exam, imaging or other test; variceal bleeding; hepatic encephalopathy 13. Confirmed presence of hepatocellular carcinoma indicated on computed tomography, magnetic resonance, or other imaging techniques within 3 months prior to screening 14. HCV genotype performed during screening indicates infection with genotype 2 or 3 15. Recent history of drug or alcohol abuse that could, in the opinion of the investigator, affect adherence to the study protocol