Article

Epitope Mapping of Ibalizumab, a Humanized Anti-CD4 Monoclonal Antibody with Anti-HIV-1 Activity in Infected Patients

Aaron Diamond AIDS Research Center, 455 First Avenue, New York, NY, USA.
Journal of Virology (Impact Factor: 4.65). 07/2010; 84(14):6935-42. DOI: 10.1128/JVI.00453-10
Source: PubMed

ABSTRACT Ibalizumab is a humanized monoclonal antibody that binds human CD4, the primary receptor for human immunodeficiency virus type 1 (HIV-1). With its unique specificity for domain 2 of CD4, this antibody potently and broadly blocks HIV-1 infection in vitro by inhibiting a postbinding step required for viral entry but without interfering with major histocompatibility complex class II (MHC-II)-mediated immune function. In clinical trials, ibalizumab has demonstrated anti-HIV-1 activity in patients without causing immunosuppression. Thus, a characterization of the ibalizumab epitope was conducted in an attempt to gain insight into the underlying mechanism of its antiviral activity as well as its safety profile. By studying mouse/human chimeric CD4 molecules and site-directed point mutants of CD4, amino acids L96, P121, P122, and Q163 in domain 2 were found to be important for ibalizumab binding, with E77 and S79 in domain 1 also contributing. All these residues appear to cluster on the interface between domains 1 and 2 of human CD4 on a surface opposite the site where gp120 and the MHC-II molecule bind on domain 1. Separately, the epitope of M-T441, a weakly neutralizing mouse monoclonal antibody that competes with ibalizumab, was localized entirely within domain 2 on residues 123 to 125 and 138 to 140. The results reported herein not only provide an appreciation for why ibalizumab has not had significant adverse immunological consequences in infected patients to date but also raise possible steric hindrance mechanisms by which this antibody blocks HIV-1 entry into a CD4-positive cell.

0 Followers
 · 
120 Views
  • Source
    • "Ibalizumab (5A8, TNX-355, TMB-355) is a humanized monoclonal Nab that targets the domain 2 of the CD4 receptor (Moore et al., 1992). A detailed epitope mapping study suggests that some residues within domain 1 also contribute to the binding (Song et al., 2010). Ibalizumab serves as a molecular lock on CD4, which does not interfere with the binding of virion, but it does abort its capability of inducing conformational changes in gp120 through a noncompetitive inhibition manner. "
    [Show abstract] [Hide abstract]
    ABSTRACT: The pandemic of human immunodeficiency virus type one (HIV-1), the major etiologic agent of acquired immunodeficiency disease (AIDS), has led to over 33 million people living with the virus, among which 18 million are women and children. Until now, there is neither an effective vaccine nor a therapeutic cure despite over 30 years of efforts. Although the Thai RV144 vaccine trial has demonstrated an efficacy of 31.2%, an effective vaccine will likely rely on a breakthrough discovery of immunogens to elicit broadly reactive neutralizing antibodies, which may take years to achieve. Therefore, there is an urgency of exploring other prophylactic strategies. Recently, antiretroviral treatment as prevention is an exciting area of progress in HIV-1 research. Although effective, the implementation of such strategy faces great financial, political and social challenges in heavily affected regions such as developing countries where drug resistant viruses have already been found with growing incidence. Activating latently infected cells for therapeutic cure is another area of challenge. Since it is greatly difficult to eradicate HIV-1 after the establishment of viral latency, it is necessary to investigate strategies that may close the door to HIV-1. Here, we review studies on non-vaccine strategies in targeting viral entry, which may have critical implications for HIV-1 prevention.
    Protein & Cell 02/2013; 4(2):86-102. DOI:10.1007/s13238-012-2111-9 · 2.85 Impact Factor
  • Source
    • "Two humanized mAbs targeting host receptors are in phase II clinical development: ibalizumab binds domain 2 of the CD4 receptor and PRO140 (Progenics Pharmaceuticals, Tarrytown, NY) attaches to the ligand-binding site of the CCR5 coreceptor (Huber et al., 2008). Ibalizumab binding does not inhibit HIV-1 gp120 attachment to CD4 domain 1, but rather inhibits a post-attachment step required for cell entry (Burkly et al., 1992; Freeman et al., 2010; Moore et al., 1992; Song et al., 2010). In contrast to mAbs that bind CD4 domain 1, ibalizumab does not deplete CD4+ lymphocytes or interfere with MHC Class II immune function (Boon et al., 2002; Jacobson et al., 2009; Kuritzkes et al., 2004). "
    [Show abstract] [Hide abstract]
    ABSTRACT: The availability of 24 antiretroviral (ARV) drugs within six distinct drug classes has transformed HIV-1 infection (AIDS) into a treatable chronic disease. However, the ability of HIV-1 to develop resistance to multiple classes continues to present challenges to the treatment of many ARV treatment-experienced patients. In this case report, we describe the response to ibalizumab, an investigational CD4-binding monoclonal antibody (mAb), in a patient with advanced immunodeficiency and high-level five-class antiretroviral resistance. After starting an ibalizumab-based salvage regimen, the patient had an approximately 4.0 log(10) reduction in viral load. An inadvertently missed infusion at week 32 led to the rapid loss of virologic response and decreased susceptibility to the remainder of the patient's salvage therapy regimen. Following the reinstitution of ibalizumab, phenotypic and genotypic resistance to ibalizumab was detected. Nonetheless, plasma HIV-1 RNA levels stabilized at ∼2.0 log(10) copies/ml below pre-ibalizumab levels. Continued ARV drug development may yield additional clinical and public health benefits. This report illustrates the promise of mAbs for HIV-1 therapy in highly treatment-experienced patients. Therapeutic mAbs may also have a role in pre-exposure prophylaxis in high-risk uninfected populations and may facilitate directly observed therapy (DOT) if two or more synergistic long acting agents become available.
    Antiviral research 12/2011; 92(3):484-7. DOI:10.1016/j.antiviral.2011.09.010 · 3.94 Impact Factor
  • Source
    • "The BC-loop of D2 in CD4 near the D1- D2 junction constitutes the core epitope of ibalizumab, which does not overlap with the binding site of either gp120 or MHC class II. The crystal structure provides a clear explanation, at atomic resolution, of why ibalizumab does not directly block HIV-1 attachment or interfere with immune functions mediated by CD4, in agreement with previous mutagenesis studies (Burkly et al., 1992; Song et al., 2010). Ibalizumab binding induces only a small, local movement of the FG loop in CD4, but this change does not propagate to other regions and does not lead to any significant consequences for receptor function. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Ibalizumab is a humanized, anti-CD4 monoclonal antibody. It potently blocks HIV-1 infection and targets an epitope in the second domain of CD4 without interfering with immune functions mediated by interaction of CD4 with major histocompatibility complex (MHC) class II molecules. We report here the crystal structure of ibalizumab Fab fragment in complex with the first two domains (D1-D2) of CD4 at 2.2 Å resolution. Ibalizumab grips CD4 primarily by the BC-loop (residues 121-125) of D2, sitting on the opposite side of gp120 and MHC-II binding sites. No major conformational change in CD4 accompanies binding to ibalizumab. Both monovalent and bivalent forms of ibalizumab effectively block viral infection, suggesting that it does not need to crosslink CD4 to exert antiviral activity. While gp120-induced structural rearrangements in CD4 are probably minimal, CD4 structural rigidity is dispensable for ibalizumab inhibition. These results could guide CD4-based immunogen design and lead to a better understanding of HIV-1 entry.
    Structure 12/2010; 18(12):1632-41. DOI:10.1016/j.str.2010.09.017 · 6.79 Impact Factor
Show more

Preview

Download
3 Downloads
Available from