Background
HIV-1 envelope glycoproteins (Env) from primary HIV-1 isolates typically adopt a “closed” conformation resistant to the binding of non-neutralizing antibodies (nnAbs). CD4-mimetic compounds (CD4mcs) “open-up” Env, sensitizing infected cells to antibody-dependent cellular cytotoxicity (ADCC) by CD4-induced (CD4i) nnAbs. Two CD4i nnAb families, anti-cluster A and anti-coreceptor binding site (CoRBS) Abs, are necessary for ADCC with the indane CD4mc BNM-III-170. While indane CD4mcs boost recognition of infected cells by anti-CoRBS Abs, these nnAbs alone mediate ADCC poorly. The combination of anti-CoRBS Abs, indane CD4mc and anti-Cluster A Abs mediates ADCC, reducing the HIV-1 reservoir and delaying viral rebound after ART interruption in humanized mice. New indoline CD4mcs with improved potency and breath over indane CD4mcs were recently described. Here, we investigate the mechanism behind their improved ADCC activity.
Methods
The ability of nnAbs to mediate ADCC with indane or indoline CD4mcs was tested in vitro, and their impact on viral rebound was evaluated in vivo in HIV-1-infected humanized mice. The impact of indoline CD4mc on Env conformation was evaluated by smFRET, cryo-EM and cryo-ET.
Results
Unlike indane CD4mcs, the lead indoline CD4mc CJF-III-288 enables anti-CoRBS Abs to mediate ADCC across multiple HIV-1 primary strains. Strikingly, CJF-III-288 exposes the CoRBS and sensitizes infected cells to ADCC by anti-CoRBS Abs or plasma from PLWH, at concentrations where indane CD4mcs fail. Masking the CoRBS with anti-CoRBS Fabs significantly reduced ADCC mediated by plasma from PLWH in the presence of CJF-III-288. In humanized mice, CJF-III-288 with a CoRBS Ab alone delays viral rebound after ART interruption. Structural and conformational analyses reveal that CJF-III-288 stabilizes an asymmetric “open” State-3 Env conformation that alters anti-CoRBS Ab binding orientation. Our analyses also reveal a variation in the Env’s tilting and the anti-CoRBS Ab binding angle, which likely facilitates Fc receptor engagement on effector cells.
Conclusions
Overall, functional and structural data support that CJF-III-288 induces an “open” asymmetric Env conformation modifying the binding orientation of anti-CoRBS Abs, boosting their ADCC activity. This highlights CJF-III-288’s therapeutic potential to eliminate HIV-1-infected cells by ADCC.
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