Triple HIV Antibody Combo Proves Safe With Long Half-Lives in Phase 1 Trial
A three-antibody broadly neutralising combo showed strong safety, 44–65 day half-lives, and preserved neutralisation across IV and subcutaneous routes.
Summary
The HVTN 140/HPTN 101 phase 1 trial enrolled 80 HIV-negative adults across the USA, Kenya, South Africa, and Zimbabwe to test a triple broadly neutralising antibody (bNAb) combination — PGDM1400LS, VRC07-523LS, and PGT121.414.LS — delivered intravenously or subcutaneously at two doses four months apart. The regimen was safe and well tolerated, with no serious adverse events. Estimated elimination half-lives ranged from 44 days (VRC07-523LS) to 65 days (PGT121.414.LS). Subcutaneous bioavailability was 73–80% relative to intravenous dosing. No antibody interactions reduced pharmacokinetic performance, and neutralisation activity matched in vitro predictions, supporting progression to efficacy trials.
Detailed Summary
HIV prevention remains a critical global challenge, with 1.3 million new infections in 2023 alone. Broadly neutralising monoclonal antibodies (bNAbs) targeting distinct sites on the HIV-1 envelope represent a promising passive immunisation strategy, particularly following the AMP trials that showed 75% efficacy of VRC01 against sensitive viral strains — establishing proof-of-concept but underscoring the need for multi-antibody approaches.
This phase 1 trial (HVTN 140/HPTN 101 part B) evaluated a first-in-human triple bNAb combination: PGDM1400LS (targeting the V2 apex), VRC07-523LS (targeting the CD4 binding site), and PGT121.414.LS (targeting the V3-glycan supersite). All three antibodies carry the LS modification (M428L/N434S) designed to extend half-life by enhancing neonatal Fc receptor binding. Eighty healthy HIV-negative adults aged 18–50 were randomised across 13 clinical sites into five groups receiving two infusions (months 0 and 4) at varying doses and routes: 20 mg/kg IV, 20 mg/kg SC, 1.4 g fixed-dose IV, 1.4 g fixed-dose SC, or 40 mg/kg IV.
Safety results were reassuring: most adverse events were mild-to-moderate solicited local or systemic reactions, and no serious adverse events were recorded. No treatment-induced anti-drug antibody responses were detected, suggesting immune tolerance to the combination. These findings are consistent with prior single- and dual-agent trials of these antibodies.
Pharmacokinetic analysis using two-compartment population models and anti-idiotype binding assays revealed estimated elimination half-lives of 53 days for PGDM1400LS, 65 days for PGT121.414.LS, and 44 days for VRC07-523LS — substantially longer than their non-LS predecessors. Subcutaneous bioavailability was 73.0% for PGDM1400LS, 77.7% for PGT121.414.LS, and 80.1% for VRC07-523LS. Critically, weight-based and fixed-dose regimens produced comparable pharmacokinetic profiles, a finding that has significant practical implications for simplified dosing in low-resource settings. No antagonistic pharmacokinetic interactions were observed between the three antibodies when co-administered.
Neutralisation activity measured via the validated TZM-bl assay was consistent with predictions derived from serum concentrations and in vitro potency data, confirming that the antibodies retained functional activity in vivo across both routes and dose levels. Together, these results support advancing this triple bNAb combination into larger HIV prevention efficacy trials.
Key Findings
- No serious adverse events reported across all 80 participants receiving the triple bNAb combination.
- Elimination half-lives: VRC07-523LS 44 days, PGDM1400LS 53 days, PGT121.414.LS 65 days.
- Subcutaneous bioavailability ranged 73–80% relative to IV, supporting non-IV delivery.
- Fixed-dose (1.4 g) and weight-based (mg/kg) dosing produced equivalent pharmacokinetic profiles.
- No anti-drug antibodies detected and no antagonistic PK interactions between the three mAbs.
Methodology
Phase 1, open-label, randomised trial across 13 sites in the USA, Kenya, South Africa, and Zimbabwe enrolling 80 HIV-negative adults into five dosing groups (IV and SC, weight-based and fixed-dose). Two infusion visits (months 0 and 4); pharmacokinetics modelled with two-compartment population models using anti-idiotype binding assays; neutralisation assessed via validated TZM-bl assay.
Study Limitations
The study was open-label without a placebo arm, limiting blinded safety assessment. The 10-month follow-up period may be insufficient to detect delayed adverse events. The relatively small group sizes (n=16 per arm) limit statistical power for subgroup comparisons.
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