Background: Although broadly neutralizing monoclonal antibodies (bNAbs) have always been considered to be a potential therapeutic option for the prophylaxis and treatment of HIV infection, their lack of breadth against all HIV variants has been one of the limiting factors. To provide sufficient neutralization breadth and potency against diverse viruses, including neutralization escape mutants, strategies to combine different bNAbs have been explored recently.
Methods: We rationally designed and engineered a novel bispecific HIV-1–neutralizing antibody (bibNAb), iMabm36. The potency and breadth of iMabm36 against HIV were extensively characterized in vitro.
Results: iMabm36 comprises the anti-CD4 Ab ibalizumab (iMab) linked to 2 copies of the single-domain Ab m36, which targets a highly conserved CD4-induced epitope. iMabm36 neutralizes a majority of a large, multiclade panel of pseudoviruses (96%, n = 118) at an IC50 concentration of less than 10 µg/mL, with 83% neutralized at an IC50 concentration of less than 0.1 µg/mL. In addition, iMabm36 neutralizes a small panel of replication-competent transmitted-founder viruses to 100% inhibition at a concentration of less than 0.1 µg/mL in a peripheral blood mononuclear cell–based neutralizing assay. Mechanistically, the improved antiviral activity of iMabm36 is dependent on both the CD4-binding activity of the iMab component and the CD4i-binding activity of the m36 component. After characterizing that viral resistance to iMabm36 neutralization was due to mutations residing in the bridging sheet of gp120, an optimized m36 variant was engineered that, when fused to iMab, improved antiviral activity significantly.
Conclusions: The interdependency of this dual mechanism of action enables iMabm36 to potently inhibit HIV-1 entry. These results demonstrate that mechanistic-based design of bibNAbs can generate potential preventive and therapeutic candidates for HIV/AIDS.
*Aaron Diamond AIDS Research Center, The Rockefeller University, New York, NY;
†Institute of Medical Biology, Chinese Academy of Medical Science and Peking Union Medical College, Kunming, China; and
‡Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA.
Correspondence to: David D. Ho, MD, The Aaron Diamond AIDS Research Center, New York, NY (e-mail: firstname.lastname@example.org and Qihan Li, MD, Institute of Medical Biology, Chinese Academy of Medical Science and Peking Union Medical College, Kunming, China (e-mail: email@example.com).
D.D.H. was supported by the Bill and Melinda Gates Foundation's Collaboration for AIDS Vaccine Discovery (CAVD), grant numbers OPP50714 and OPP1040731, and by the National Institutes of Health (NIH) grant number 1DP1DA033263-01. M.S. was supported by the Bill and Melinda Gates Foundation's Comprehensive Antibody Vaccine Immune Monitoring Consortium (CA-VIMC), grant number 1032144.
The authors have no conflicts of interest to disclose.
Received April 16, 2014
Accepted May 07, 2014