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  1. Biologics Research Projects

Evaluation and Characterization of Neutralizing Antibodies against Viruses Relevant to Blood-derived Products

Principal Investigator: Pei Zhang, MD
Office / Division / Lab: OTAT / DPPT / PDB

General Overview

FDA establishes tests to determine the quality of products it regulates. One class of products that the Office of Blood Research and Review regulates is known as "specific immune globulins", which are concentrated solutions of antibodies directed against specific infectious microbes. Hepatitis C Immune Globulin Intravenous (HCIGIV) belongs to this class and is currently under development but not yet licensed for the treatment of hepatitis C virus infections. Like all other products in its class, HCIGIV will require a reliable potency test as part of the lot release testing that correlates with its clinical effectiveness. It is particularly important to have such a test in place during the development phase of the product. Institution of an appropriate potency assay during clinical trials allows collection of data that may demonstrate the correlation of the potency assay test results and clinical outcome in terms of efficacy. These data are then submitted for FDA review as part of a license application. The validity of these studies depends on accurate measuring and monitoring of the level of effective anti-hepatitis C virus antibodies in individuals who received this product in clinical trials.

We use a variety of techniques to characterize antibodies present in HCIGIV with different neutralizing capacities to determine where the antibody binds to the virus and how the antibody neutralizes the virus. This information will help us to develop tests that FDA can use to ensure product quality.

In addition, our work is helping us to understand why the currently manufactured HCIGIV has proven to be ineffective; specifically, some antibodies present in these HCIGIV appear to interfere with other neutralizing antibodies that would otherwise effectively inactivate the virus.

Scientific Overview

Our research program is focused on the antibody-mediated neutralization of hepatitis C virus (HCV). We continue to define the key molecular and structural determinants for generating broadly neutralizing antibodies. The information generated from our experiments will contribute to the prevention and treatment of hepatitis C, a contagious liver disease afflicting approximately 170 million people worldwide. We believe that this research program is highly relevant to FDA's mission, as it focuses on a major public health problem and an unmet need for the improvement of FDA-regulated immune globulin products.

HCV infection is hard to control. One of reasons is that the antibodies produced naturally in individuals are unable to neutralize the virus. The envelope glycoprotein E2 has been considered to be essential for virus entry into host liver cells, thus making it one of the most promising targets for improving neutralization. However, E2 protein has a very flexible structure. The flexibility of E2 protein not only affects the optimal presentation of the immunogenic sites of interest, but also offers a mechanism of immune evasion for HCV. Our central hypothesis is that E2 protein has defined conformations and the transition states of E2 protein conformations could serve as specific targets for the improvement of antibody-mediated neutralization of HCV.

Through X-ray crystallographic analysis, we have demonstrated that individual epitopes on E2 protein can be presented in different local conformations. These conformations could be recognized by site-specific antibodies of either neutralizing or non-neutralizing activity. These results indicate that the host immune cells may produce neutralizing or non-neutralizing antibodies depending on which conformation of the epitope happens to present on the HCV to the immune host system at the time of infection.

We have also found that E2 protein can exist in two different states in terms of the presentation of the epitopes: a closed state, where the epitopes are partially hidden, and an open state, where the epitopes are fully exposed. This apparent ability of HCV E2 protein to undergo structural transition between open and closed states coincides with the availability of highly conserved glycine residues (e.g., G436, G451) that serves as flexible joints for the transition. The structural heterogeneity of E2 may thus be an important factor in determining how antibodies are elicited during the natural course of HCV infection.

Antibody-mediated neutralization of HCV can thus be viewed as the outcome from either blocking access to the structurally defined E2receptor interface during the closed state of E2, when the epitope is hidden, or from locking the epitope in a particular local conformation that inhibits virus entry into the liver cell during the open state of E2, when the epitope is fully exposed. The structural insights into the dynamic transition of the E2 conformations will allow us to uncover the vulnerability of HCV that forms the structural basis of antibody-mediated neutralization.


J Immunol Res 2017;2017:7373196
Passive immunoprophylaxis for the protection of the mother and her baby: insights from in vivo models of antibody transport.
Xu Y, Mahmood I, Zhong L, Zhang P, Struble EB

Hepatology 2015 Dec;62(6):1670-82
Antibodies to an interfering epitope in hepatitis C Virus E2 can mask vaccine-induced neutralizing activity.
Kachko A, Frey SE, Sirota L, Ray R, Wells F, Zubkova I, Zhang P, Major ME

Placenta 2015 Dec;36(12):1370-7
Gestation age dependent transfer of human immunoglobulins across placenta in timed-pregnant guinea pigs.
Xu Y, Ma L, Norton MG, Stuart C, Zhao Z, Toibero D, Dahlen S, Zhong L, Zhang P, Struble EB

J Virol 2015 Jan;89(1):492-501
A view of the E2-CD81 interface at the binding site of a neutralizing antibody against hepatitis C virus.
Harman C, Zhong L, Ma L, Liu P, Deng L, Zhao Z, Yan H, Struble E, Virata-Theimer ML, Zhang P

Proc Natl Acad Sci U S A 2014 Jul 22;111(29):10690-5
Discrete conformations of epitope II on the hepatitis C virus E2 protein for antibody-mediated neutralization and nonneutralization.
Deng L, Ma L, Virata-Theimer ML, Zhong L, Yan H, Zhao Z, Struble E, Feinstone S, Alter H, Zhang P

Hepat Res Treat 2014;2014:159206
Transplacental Transfer of Hepatitis B Neutralizing Antibody during Pregnancy in an Animal Model: Implications for Newborn and Maternal Health.
Ma L, Norton MG, Mahmood I, Zhao Z, Zhong L, Zhang P, Struble EB

PLoS One 2014 Jan 6;9(1):e84346
A neutralization epitope in the hepatitis C virus e2 glycoprotein interacts with host entry factor CD81.
Zhao Z, Zhong L, Elrod E, Struble E, Ma L, Yan H, Harman C, Deng L, Virata-Theimer ML, Liu P, Alter H, Grakoui A, Zhang P

Annu Rev Biophys 2013 May 6;42:191-215
Structural insights into the evolution of the adaptive immune system.
Deng L, Luo M, Velikovsky A, Mariuzza RA

Proc Natl Acad Sci U S A 2013 Apr 30;110(18):7418-22
Structural evidence for a bifurcated mode of action in the antibody-mediated neutralization of hepatitis C virus.
Deng L, Zhong L, Struble E, Duan H, Ma L, Harman C, Yan H, Virata-Theimer ML, Zhao Z, Feinstone S, Alter H, Zhang P

J Virol 2012 Dec;86(23):12686-94
Amino Acid residue-specific neutralization and nonneutralization of hepatitis C virus by monoclonal antibodies to the e2 protein.
Duan H, Kachko A, Zhong L, Struble E, Pandey S, Yan H, Harman C, Virata-Theimer ML, Deng L, Zhao Z, Major M, Feinstone S, Zhang P

Virol J 2012 Sep 24;9:217
Epitope mapping by random peptide phage display reveals essential residues for vaccinia extracellular enveloped virion spread.
He Y, Wang Y, Struble EB, Zhang P, Chowdhury S, Reed JL, Kennedy M, Scott DE, Fisher RW

Clin Dev Immunol 2012;2012:538701
Human antibodies can cross guinea pig placenta and bind its neonatal Fc Receptor: implications for studying immune prophylaxis and therapy during pregnancy.
Struble EB, Ma L, Zhong L, Lesher A, Beren J, Zhang P

Vaccine 2010 Jun 7;28(25):4138-44
Hepatitis C virus with a naturally occurring single amino-acid substitution in the E2 envelope protein escapes neutralization by naturally-induced and vaccine-induced antibodies.
Duan H, Struble E, Zhong L, Mihalik K, Major M, Zhang P, Feinstone S, Feigelstock D

Biochem Biophys Res Commun 2009 Dec 18;390(3):1056-60
Antibody-mediated Synergy and Interference in the Neutralization of SARS-CoV at an Epitope Cluster on the Spike Protein.
Zhong L, Haynes L, Struble EB, Tamin A, Virata-Theimer ML, Zhang P

Proc Natl Acad Sci U S A 2009 May 5;106(18):7537-41
Depletion of interfering antibodies in chronic hepatitis C patients and vaccinated chimpanzees reveals broad cross-genotype neutralizing activity.
Zhang P, Zhong L, Struble EB, Watanabe H, Kachko A, Mihalik K, Virata-Theimer ML, Alter HJ, Feinstone S, Major M

Proc Natl Acad Sci U S A 2007 May 15;104(20):8449-54
Hepatitis C virus epitope-specific neutralizing antibodies in Igs prepared from human plasma.
Zhang P, Wu CG, Mihalik K, Virata-Theimer ML, Yu MY, Alter HJ, Feinstone SM

Proc Natl Acad Sci U S A 2006 Jun 13;103(24):9214-9
Neutralization epitope responsible for the hepatitis B virus subtype-specific protection in chimpanzees.
Zhang P, Yu MY, Venable R, Alter HJ, Shih JW

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