The goal of this observational study is to establish an operational framework for home self-collections of blood samples to be used for antiviral drug concentration measurements.

Participants will continue on their prescribed antiviral(s) for HIV treatment or prevention and followed for up to approximately 1 year. The investigators will compare drug concentrations of antivirals and relevant metabolites/anabolites in clinic-collected and self-collected blood samples.

Up to 150 people receiving care at the UCH-IDGP will be enrolled in the study at a routine clinic visit where a standard of care (SOC) blood collection and/or SOC dose of LA antivirals (e.g., LA IM CAB±RPV) is planned. Once consented, demographic and clinical data will be obtained. Clinical data that will be collected from participant and medical records may include: age, sex at birth and gender identity, race, ethnicity, medication history, duration of current antiviral therapy, hematocrit, CD4+ T-cell count, HIV VL, and self-reported adherence.

The investigators will collect an extra ~5 mL of blood in EDTA by venipuncture for DBS, plasma, whole blood, and blood cells at each clinic-collection visit. At the first clinic-collection visit, participants will be given home self-collection kits and instructed to self-collect samples at various timepoints prior to their next injection (if on LA antivirals), monitored by live video-streaming or time-stamped video. The investigators will go through how to self-collect, handle, and mail the blood samples by self-collecting together in the clinic (in-person training), and participants will be asked about their medical history and medications.

Participants on PO antivirals (e.g., TFV/FTC) may only complete one clinic-collection visit (and one at-home self-collection). At home self-collections and clinic-collections may continue for participants on LA antivirals (e.g., LA IM CAB±RPV) for up to approximately 1 year. All study visits will be linked to SOC visits; there will be no additional visits to the clinic beyond what is already required for SOC:

• If continuing prescribed Q8W injections, up to 7 SOC clinic visits at (approximately) weeks 0, 8, 16, 24, 32, 40, and 48
• If initiating prescribed Q8W injections, up to 7 SOC clinic visits at (approximately) weeks 0, 4, 12, 20, 28, 36, and 44
• If continuing or initiating prescribed Q4W injections, up to 13 SOC clinic visits at (approximately) weeks 0, 4, 8, 12, 16, 20, 24, 28, 32, 36, 40, 44, and 48
• If continuing or initiating prescribed Q26W injections, up to 3 SOC clinic visits at (approximately) weeks 0, 26, and 52

Participants will be asked to self-collect samples at home by two or more methods (self-collection kits): fingerstick and spotting onto Whatman 903 protein saver card, and/or use of one or more self-collection devices (e.g., Tasso-M20/Tasso+, Mitra, others). After sample collection, samples/devices will be shipped back to our laboratory in their provided box(es). All samples obtained by self-collection methods/devices are approved for shipping via mail or other carriers in the US. Participants may complete up to 25 at home self-collections (approximately once biweekly for the participants followed longitudinally).

Inclusion criteria:

• ≥18 years old
• Receiving one or more antivirals for HIV treatment or prevention. This may include TFV (as TDF or TAF) and FTC (or 3TC)-based, LA (e.g., LA IM CAB±RPV Q4W or Q8W), or other antivirals (those who are transitioning to LA antivirals [e.g., LA IM CAB±RPV Q4W or Q8W] will also be eligible)
• Current patient at the UCH-IDGP clinic
• Able to comply with study procedures, including directly observed self-collection of DBS by fingerstick, Tasso-M20/Tasso+, Mitra, and/or other self-collection methods/devices, and completion of survey

Exclusion criteria:

• Inability to provide informed consent
• Unable or unwilling to comply with directly observed self-collection of DBS (e.g., unavailable or unable to use live video-streaming or time-stamped video recording technology)
• Any uncontrolled medical, social, or mental health issue(s) that, in the opinion of the investigators, could interfere with the study participation or study outcomes (e.g., current incarceration)
• Any medical condition that, in the opinion of the study team, acutely and/or transiently influences the PK of CAB±RPV, including acute kidney injury, hepatic insufficiency, significant drug-drug interactions, active hemolysis or symptomatic hemoglobinopathies, etc. (Note: Given the need for PK data in pregnancy, women who become pregnant while on LA IM CAB±RPV Q4W or Q8W will be allowed to participate in this study, if their clinical provider decides to continue this regimen.)

Study subjects will be invited to participate in the HOME-1 study by enrolling a convenience sample of people receiving TFV (as TDF or TAF) and FTC (or 3TC)-based, LA (e.g., LA IM CAB±RPV Q4W or Q8W), or other antivirals for HIV treatment or prevention at the UCH-IDGP. Study visits will only be conducted when blood is to be collected for routine SOC clinical laboratory tests and/or a SOC dose of LA antivirals is to be given.