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Dose-response curve slope helps predict therapeutic potency and breadth of HIV broadly neutralizing antibodies.

ABSTRACT: A new generation of HIV broadly neutralizing antibodies (bnAbs) with remarkable potency, breadth and epitope diversity has rejuvenated interest in immunotherapeutic strategies. Potencies defined by in vitro IC50 and IC80 values (50 and 80% inhibitory concentrations) figure prominently into the selection of clinical candidates; however, much higher therapeutic levels will be required to reduce multiple logs of virus and impede escape. Here we predict bnAb potency at therapeutic levels by analysing dose-response curve slopes, and show that slope is independent of IC50/IC80 and specifically relates to bnAb epitope class. With few exceptions, CD4-binding site and V3-glycan bnAbs exhibit slopes >1, indicative of higher expected therapeutic effectiveness, whereas V2-glycan, gp41 membrane-proximal external region (MPER) and gp120-gp41 bnAbs exhibit less favourable slopes <1. Our results indicate that slope is one major predictor of both potency and breadth for bnAbs at clinically relevant concentrations, and may better coordinate the relationship between bnAb epitope structure and therapeutic expectations.

SUBMITTER: Webb NE

PROVIDER: S-EPMC4588098 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Broadly neutralizing antibodies (bNAbs) are currently being assessed in clinical trials for their ability to prevent HIV infection. Single chain variable fragments (scFv) of bNAbs have advantages over full antibodies as their smaller size permits improved diffusion into mucosal tissues and facilitates vector-driven gene expression. We have previously shown that scFv of bNAbs individually retain significant breadth and potency. Here we tested combinations of five scFv derived from bNAbs CAP256-VRC26.25 (V2-apex), PGT121 (N332-supersite), 3BNC117 (CD4bs), 8ANC195 (gp120-gp41 interface) and 10E8v4 (MPER). Either two or three scFv were combined in equimolar amounts and tested in the TZM-bl neutralization assay against a multiclade panel of 17 viruses. Experimental IC50 and IC80 data were compared to predicted neutralization titers based on single scFv titers using the Loewe additive and the Bliss-Hill model. Like full-sized antibodies, combinations of scFv showed significantly improved potency and breadth compared to single scFv. Combinations of two or three scFv generally followed an independent action model for breadth and potency with no significant synergy or antagonism observed overall although some exceptions were noted. The Loewe model underestimated potency for some dual and triple combinations while the Bliss-Hill model was better at predicting IC80 titers of triple combinations. Given this, we used the Bliss-Hill model to predict the coverage of scFv against a 45-virus panel at concentrations that correlated with protection in the AMP trials. Using IC80 titers and concentrations of 1μg/mL, there was 93% coverage for one dual scFv combination (3BNC117+10E8v4), and 96% coverage for two of the triple combinations (CAP256.25+3BNC117+10E8v4 and PGT121+3BNC117+10E8v4). Combinations of scFv, therefore, show significantly improved breadth and potency over individual scFv and given their size advantage, have potential for use in passive immunization.

Project description:Passive administration of HIV-directed broadly neutralizing antibodies (bNAbs) can prevent infection in animal models, and human efficacy trials are under way. Single-chain variable fragments (scFv), comprised of only the variable regions of antibody heavy and light chains, are smaller molecules that may offer advantages over full-length IgG. We designed and expressed scFv of HIV bNAbs prioritized for clinical testing that target the V2-apex (CAP256-VRC26.25), V3-glycan supersite (PGT121), CD4 binding site (3BNC117), and MPER (10E8v4). The use of either a 15- or 18-amino-acid glycine-serine linker between the heavy- and light-chain fragments provided adequate levels of scFv expression. When tested against a 45-multisubtype virus panel, all four scFv retained good neutralizing activity, although there was variable loss of function compared to the parental IgG antibodies. For CAP256-VRC26.25, there was a significant 138-fold loss of potency that was in part related to differential interaction with charged amino acids at positions 169 and 170 in the V2 epitope. Potency was reduced for the 3BNC117 (13-fold) and PGT121 (4-fold) scFv among viruses lacking the N276 and N332 glycans, respectively, and in viruses with a longer V1 loop for PGT121. This suggested that scFv interacted with their epitopes in subtly different ways, with variation at key residues affecting scFv neutralization more than the matched IgGs. Remarkably, the scFv of 10E8v4 maintained breadth of 100% with only a minor reduction in potency. Overall, scFv of clinically relevant bNAbs had significant neutralizing activity, indicating that they are suitable for passive immunization to prevent HIV-1 infection.IMPORTANCE Monoclonal antibodies have been isolated against conserved epitopes on the HIV trimer and are being investigated for passive immunization. Some of the challenges associated with full-sized antibody proteins may be overcome by using single-chain variable fragments (scFv). These smaller forms of antibodies can be produced more efficiently, may show fewer off-target effects with increased tissue penetration, and are more adaptable to vectored-mediated expression than IgG. Here, we demonstrate that scFv of four HIV-directed bNAbs (CAP256-VRC26.25, PGT121, 3BNC117, and 10E8v4) had significant neutralizing activity against diverse global strains of HIV. Loss of potency and/or breadth was shown to be due to increased dependence of the scFv on key residues within the epitope. These smaller antibody molecules with functional activity in the therapeutic range may be suitable for further development as passive immunity for HIV prevention.

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Dose-response curve slope helps predict therapeutic potency and breadth of HIV broadly neutralizing antibodies.

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