Switch to once-weekly, single-tablet islatravir–lenacapavir from daily standard of care for HIV-1 (ISLEND-2): a multicentre, randomised, open-label, active-controlled, phase 3 non-inferiority trial
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Switching virologically suppressed adults with HIV-1 to a once-weekly oral single-tablet regimen of islatravir and lenacapavir is non-inferior to continuing daily standard-of-care antiretroviral therapy at 48 weeks.
Key Findings
Study Design
Study Limitations
Clinical Significance
The ISLEND-2 trial demonstrates that a once-weekly oral combination of a nucleoside reverse transcriptase translocation inhibitor (islatravir) and a capsid inhibitor (lenacapavir) is a highly effective, well-tolerated alternative to daily pills. This validates the first complete once-weekly oral antiretroviral regimen for HIV-1, offering a simpler dosing strategy that bypasses the logistical burden and injection-site reactions associated with long-acting injectables. This advancement stands to meaningfully reduce "pill fatigue" and the daily psychological reminder of HIV status, potentially revolutionizing long-term maintenance therapy.
Historical Context
The evolution of HIV antiretroviral therapy (ART) has been driven by the dual goals of maximizing viral suppression while minimizing pill burden and toxicity. Therapy progressed from multi-class regimens requiring dozens of pills per day to the modern standard of highly potent, daily single-tablet regimens. Recognizing the challenge of lifelong daily adherence, the field recently pivoted toward long-acting therapies, yielding intramuscular injectables like cabotegravir/rilpivirine. However, injectables require frequent clinic visits and carry risks of injection-site reactions. The ISLEND trials evaluated a novel synergy between two ultra-long-acting agents: lenacapavir (a first-in-class capsid inhibitor) and islatravir (a first-in-class nucleoside reverse transcriptase translocation inhibitor). Following early setbacks related to islatravir dosing and lymphopenia, the optimized 2 mg islatravir/300 mg lenacapavir weekly oral dose emerged as a breakthrough, bridging the gap between daily oral pills and long-acting parenterals.
Guided Discussion
High-yield insights from every perspective
How do the mechanisms of action of islatravir and lenacapavir differ from traditional NRTIs and integrase inhibitors, and why do their pharmacokinetic profiles allow for once-weekly oral dosing?
Key Response
Islatravir is a nucleoside reverse transcriptase translocation inhibitor (NRTTI) that inhibits viral replication through multiple mechanisms and has a high barrier to resistance with a long intracellular half-life. Lenacapavir is a first-in-class capsid inhibitor that disrupts multiple stages of the viral life cycle (nuclear entry, virion assembly). Both possess exceptionally long half-lives compared to traditional daily NRTIs or INSTIs, allowing them to maintain therapeutic concentrations with just once-weekly oral administration.
When evaluating a virologically suppressed patient currently on a daily single-tablet regimen, what clinical factors, adherence patterns, or social determinants would make them an ideal candidate for switching to a once-weekly islatravir-lenacapavir regimen?
Key Response
Ideal candidates include those experiencing 'pill fatigue,' those with variable daily schedules (e.g., shift workers), or those who travel frequently. It serves as an excellent alternative for patients who desire less frequent dosing but have a phobia of needles or cannot commit to the clinic visits required for long-acting injectable ART (like cabotegravir-rilpivirine). Clinicians must also ensure the patient has no history of virologic failure or resistance to these classes.
Given the historical clinical holds on earlier islatravir trials due to dose-dependent lymphopenia, how should clinicians monitor immunologic parameters in patients on this weekly regimen, and what are the implications for cross-resistance if virologic failure occurs?
Key Response
Fellows must be aware of islatravir's history; previous higher doses led to declines in total lymphocytes and CD4+ T-cells. While the dose in ISLEND-2 is lower and designed to mitigate this risk, ongoing monitoring of CD4 counts remains crucial. Furthermore, failing on a two-drug regimen containing a novel capsid inhibitor (lenacapavir) risks developing resistance to a highly potent, first-in-class agent, which could severely complicate future salvage therapy options.
How does the demonstration of non-inferiority for a once-weekly oral regimen shift the paradigm of chronic HIV management compared to long-acting injectables, and what unique adherence challenges does weekly dosing present?
Key Response
Weekly oral ART bridges the gap between the high patient burden of daily pills and the high clinic/logistical burden of bi-monthly injectables. It empowers patients with a low-burden, self-administered option. However, attending physicians must counsel patients heavily on the weekly schedule, as the 'forgiveness' window for a missed weekly dose may be narrower than missing a single daily dose, potentially increasing the risk of viral rebound if patients are late by several days.
Scholarly Review
Critical appraisal through the lens of expert reviewers and guideline development
In the context of an open-label, active-controlled trial for HIV ART, how might the open-label design influence dropout rates (attrition bias), and how does the choice of the non-inferiority margin affect the statistical power and clinical validity of the ISLEND-2 findings?
Key Response
Open-label designs risk attrition bias, as patients randomized to the standard-of-care control arm might withdraw out of disappointment at not receiving the novel weekly therapy. PhD researchers must evaluate whether the per-protocol and intention-to-treat analyses align and whether the non-inferiority margin (typically strictly regulated at 4% by the FDA for HIV trials) appropriately excludes clinically meaningful differences in virologic failure without being compromised by asymmetric missing data.
When scrutinizing the primary endpoint of virologic suppression at 48 weeks using the FDA Snapshot algorithm, what specific missing data assumptions or protocol deviations would you flag to ensure the non-inferiority claim of weekly islatravir-lenacapavir is robust?
Key Response
The FDA Snapshot algorithm strictly treats missing data (due to dropouts, loss to follow-up, or protocol deviations) as virologic failure. A seasoned editor would heavily scrutinize whether missingness was asymmetric between the two arms (e.g., more missing data in the active arm due to novel drug tolerability, or in the control arm due to lack of the novel treatment). Unequal dropout rates can artificially skew non-inferiority results, threatening the trial's internal validity.
Based on the 48-week non-inferiority data from ISLEND-2, should once-weekly oral islatravir-lenacapavir be incorporated into the DHHS/EACS guidelines as a recommended 'Optimize/Switch' option for virologically suppressed adults, and what additional data are required for a Level AI recommendation?
Key Response
Current guidelines recommend long-acting injectable cabotegravir/rilpivirine as a primary optimization strategy for suppressed patients wanting non-daily ART. To integrate a weekly oral option at a Level AI (strong recommendation, high-quality evidence), the committee would require longer-term safety data (at least 96-144 weeks) to definitively rule out late-onset islatravir-induced lymphopenia, as well as real-world data confirming that patients can reliably adhere to a strict once-weekly oral schedule without elevated rates of virologic failure.
Clinical Landscape
Noteworthy Related Trials
TANGO Trial
Tested
Switch to once-daily dolutegravir/lamivudine
Population
Virologically suppressed HIV-1 adults
Comparator
Continuation of TAF-based 3- or 4-drug regimen
Endpoint
Proportion of participants with HIV-1 RNA >= 50 copies/mL at week 48
ATLAS Trial
Tested
Once-monthly intramuscular cabotegravir and rilpivirine
Population
Virologically suppressed HIV-1 patients
Comparator
Continuation of daily oral antiretroviral therapy
Endpoint
Proportion of participants with HIV-1 RNA >= 50 copies/mL at week 48
CAPELLA Trial
Tested
Subcutaneous lenacapavir plus optimized background regimen
Population
Heavily treatment-experienced patients with multidrug-resistant HIV-1
Comparator
Placebo plus failing regimen
Endpoint
Proportion of patients with >= 0.5 log10 copies/mL decrease in HIV-1 RNA by day 15
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