Inclusion Criteria:  Provision of signed and dated informed consent form Stated willingness and ability to comply with all study procedures and availability for the duration of the study Aged 18+ years Diagnosis of MS using revised 2010 McDonald criteria of clinically definite MS. Receiving treatment with either ocrelizumab or rituximab on a regular twice-yearly schedule. The first infusion must have been received at least 6 months before enrollment. Must report significant fatigue during the past 3 months not due to a cause other than MS. For females of reproductive potential: use of highly effective contraception for at least 1 month prior to screening and agreement to use such a method during study participation. For males of reproductive potential: use of condoms or other methods to ensure effective contraception with partner.  Exclusion Criteria:  Pregnancy or lactation Known allergic reactions to components of TAF Treatment with another investigational drug or other MS-directed intervention such as glatiramer acetate, or dimethyl fumarate within 3 months Positive HIV antibody test, active or latent hepatitis B Relapse and/or steroid treatment within the previous 30 days Baseline EDSS > 7 Current symptoms of severe, progressive, or uncontrolled renal, hematologic, gastrointestinal, pulmonary, cardiac, or neurologic disease, or other medical conditions that, in the opinion of the Investigator, might place the subject at unacceptable risk for participation in this study Known history of sleep apnea, narcolepsy, or other significant sleep disorders Recent changes to medications affecting sleep or fatigue or changes in dosage of those medications within 90 days Creatinine clearance (CrCl) <55mL/min, as calculated by the Cockcroft-Gault equation Taking medication with known interactions with tenofovir alafenamide including: Acyclovir, valacyclovir, adefovir, cabozantinib, carbamazepine, cidofovir, cladribine, cobicistat, diclofenac, multiple NSAIDs or chronic high dose NSAIDs, fosphenytoin or phenytoin, ganciclovir, valganciclovir, oxcarbazepine, phenobarbital, primidone, rifabutin, rifampin, rifapentine, sofosbuvir, tipranavir