A Phase 2b, Randomized, Double-Blind, Placebo-Controlled Multi-Center Study Evaluating Antiviral Effects, Pharmacokinetics, Safety, and Tolerability of GS-5806 in Hematopoietic Cell Transplant (HCT) Recipients with Respiratory Syncytial Virus (RSV) Infection of the Lower Respiratory Tract

Males and females 18 to 75 years of age

Received an autologous or allogeneic HCT using any conditioning regimen

Evidence of new abnormalities on chest X-ray obtained < 48 hours prior to Screening, determined to be consistent with LRTI by the local radiologist, relative to the most recent chest X-ray. If chest X-ray is not available, a chest X-ray must be obtained for Screening.

Documented RSV in both the upper (eg, nasal swab, nasopharyngeal swab, nasal wash) and lower (eg, induced sputum, BAL, lung biopsy, but not spontaneous sputum) respiratory tract as determined by local testing (eg, PCR, DFA, RVP assay, or culture). All samples must have been collected = 6 days prior to Day 1 or as determined at Screening as per Section 6.1.1.

An informed consent document signed and dated by the subject or a legal guardian of the subject and investigator or his/her designee. In Sweden ICFs signed by a legal guardian must also be signed by a close relative of the subject.

A negative urine or serum pregnancy test is required for female subjects (unless surgically sterile or greater than two years post-menopausal)

Male and female subjects of childbearing potential must agree to contraceptive requirements as described in Appendix 5

Willingness to complete necessary study procedures and have available a working telephone or email

Are the trial subjects under 18? no

Number of subjects for this age range:

F.1.2 Adults (18-64 years) yes

F.1.2.1 Number of subjects for this age range 15

F.1.3 Elderly (>=65 years) yes

F.1.3.1 Number of subjects for this age range 45

Related to concomitant or previous medication use:

Use of non-marketed (according to region) investigational agents within 30 days, OR use of any investigational monoclonal anti-RSV antibodies within 4 months or 5 half-lives of screening, whichever is longer, OR use of any investigational RSV vaccines after HCT

Use of a moderate or strong cytochrome P450 enzyme (CYP) inducer including but not limited to rifampin, St. John’s Wort, carbamazepine, and phenytoin, efavirenz, bosentan, etravirine, modafinil, and nafcillin, within 2 weeks prior to the first dose of IMP

Related to medical history:

Pregnant, breastfeeding, or lactating females

Unable to tolerate nasal sampling required for this study, as determined by the investigator

Known history of HIV/AIDS with a CD4 count <200 cells/µL within the last month

History of drug and/or alcohol abuse that, in the opinion of the investigator, may prevent adherence to study activities

Related to medical conditions:

Requiring invasive mechanical ventilation at the time of randomization

Documented to be positive for other respiratory viruses (limited to influenza, parainfluenza, human rhinovirus, adenovirus, human metapneumovirus, or coronavirus), from the lower respiratory tract sample as determined by local testing

Clinically significant bacteremia or fungemia within 7 days prior to Screening that has not been adequately treated, as determined by the investigator

Clinically significant bacterial, fungal, or viral pneumonia within 2 weeks prior to Screening that has not been adequately treated, as determined by the investigator

Excessive nausea/vomiting at screening, as determined by the investigator, or an inability to swallow pills that precludes oral administration of the IMP (for subjects without an NG tube in place)

Any condition which, in the opinion of the investigator, would prevent full participation in this trial or would interfere with the evaluation of the trial endpoints

Related to allergies:

Known hypersensitivity or allergy to the IMP, its metabolites, or formulation excipients (microcrystalline cellulose, mannitol, croscarmellose sodium, magnesium stearate, polyvinyl alcohol, titanium dioxide, polyethylene glycol and talc)

History of hypersensitivity, anaphylactic reaction, Stevens-Johnson Syndrome, or toxic epidermal necrolysis response to sulfa drugs

Related to laboratory results:

Creatinine clearance < 30 mL/min (calculated using the Cockcroft-Gault method)

Clinically significant AST/ALT, as determined by the investigator

Clinically significant TB, as determined by the investigator