Inclusion Criteria:

1. age >21 and <80 years 2. ability to provided informed consent 3. diagnosis of probable or definite IPF according to American Thoracic Society (ATS) criteria 4. tolerance of full-dose (2403 mg/day) pirfenidone 5. Positive serology for EBV or CMV

Exclusion Criteria:

1. FVC < 40% predicted 2. Diffusing capacity for carbon monoxide (DLCO) < 35% predicted (Crapo) 3. Forced expiratory volume (FEV)1/FVC <0.7 4. Significant centrilobular emphysema (>40% by HRCT) 5. Active tobacco use (cigarette or cigar smoking) 6. Resting oxygen saturation (SpO2) on room air <89% 7. Listed for lung transplantation defined as being assigned a lung allocation score 8. environmental exposure (occupational, environmental, drug, etc.) felt by the principal investigator (PI) to be the etiology of the interstitial disease 9. diagnosis of collagen-vascular conditions (according to the published American College of Rheumatology criteria) 10. history of unstable or deteriorating cardiac disease 11. acute coronary syndrome, coronary artery bypass, or angioplasty within 3 months of screening 12. uncontrolled arrhythmia 13. uncontrolled hypertension 14. known HIV or hepatitis C 15. known cirrhosis or chronic active hepatitis 16. active substance or alcohol abuse 17. pregnancy or lactation 18. Women of childbearing potential who are not using a medically approved means of contraception. Subjects will be considered of childbearing potential if they are not surgically sterile or have not been postmenopausal for at least 2 years [any subject who is postmenopausal for < 2 years will be required to have a follicle-stimulating hormone (FSH) level to assess her potential to become pregnant 19. clinically relevant lab abnormalities (obtained within 30 days before enrollment), including: 1. creatinine > 2 x upper limit of normal (ULN) 2. hematology outside of specified limits: white blood cells (WBCs) < 3,500/mm3; hematocrit < 25% or > 59%; platelets < 100,000/mm3; 3. total bilirubin > 2 x ULN 4. Aspartate (AST) or alanine aminotransferases (ALT)/ serum glutamic-oxaloacetic; transaminase (SGOT), or serum glutamic pyruvic transaminase (SGPT) > 2.0 x ULN 5. alkaline phosphatase > 3 x ULN 6. albumin < 3.0 mg/dL at screening 20. known hypersensitivity to study medication 21. any condition that, in the judgment of the PI, might cause participation in this study to be detrimental to the subject or that the PI deems makes the subject a poor candidate 22. any therapy with immunosuppressants such as prednisone, azathioprine, or mycophenolate currently or anticipated to be needed during the study period (subjects on these drugs prior to the study will require a 30-day washout period before randomization) 23. participation in another IPF clinical treatment trial during the study period (if completing another IPF clinical treatment trial, then a 30-day washout period is required before randomization) 24. requirement for chronic suppressive therapy with valacyclovir for recurrent herpes virus infection 25. History of myelodysplasia, aplastic anemia, refractory anemia, or multiple myeloma.