Potent Neutralization of Hendra and Nipah Viruses by Human Monoclonal Antibodies - Monoclonal Antibodies

Potent Neutralization of Hendra and Nipah Viruses by Human Monoclonal Antibodies
January 2006
Zhongyu Zhu, Antony S. Dimitrov, Katharine N. Bossart, Gary Crameri,Kimberly A. Bishop, Vidita Choudhry,Bruce A. Mungall,Yan-Ru Feng, Anil Choudhary, Mei-Yun Zhang, Yang Feng, Lin-Fa Wang, Xiaodong Xiao, Bryan T. Eaton,Christopher C. Broder, and Dimiter S. Dimitrov
Journal of Virology; PubMed
Abstract
Hendra virus (HeV) and Nipah virus (NiV) are closely related emerging viruses comprising the Henipavirus genus of the Paramyxovirinae. Each has a broad species tropism and can cause disease with high mortality in both animal and human hosts. These viruses infect cells by a pH-independent membrane fusion event mediated by their attachment (G) and fusion (F) envelope glycoproteins (Envs). Seven Fabs, m101 to -7, were selected for their significant binding to a soluble form of Hendra G (sG) which was used as the antigen for panning of a large na?ve human antibody library. The selected Fabs inhibited, to various degrees, cell fusion mediated by the HeV or NiV Envs and virus infection. The conversion of the most potent neutralizer of infectious HeV, Fab m101, to immunoglobulin G1 (IgG1) significantly increased its cell fusion inhibitory activity: the 50% inhibitory concentration was decreased more than 10-fold to approximately 1 ?g/ml. The IgG1 m101 was also exceptionally potent in neutralizing infectious HeV; complete (100%) neutralization was achieved with 12.5 ?g/ml, and 98% neutralization required only 1.6 ?g/ml. The inhibition of fusion and infection correlated with binding of the Fabs to full-length G as measured by immunoprecipitation and less with binding to sG as measured by enzyme-linked immunosorbent assay and Biacore. m101 and m102 competed with the ephrin-B2, which we recently identified as a functional receptor for both HeV and NiV, indicating a possible mechanism of neutralization by these antibodies. The m101, m102, and m103 antibodies competed with each other, suggesting that they bind to overlapping epitopes which are distinct from the epitopes of m106 and m107. In an initial attempt to localize the epitopes of m101 and m102, we measured their binding to a panel of 11 G alanine-scanning mutants and identified two mutants, P185A and Q191 K192A, which significantly decreased binding to m101 and one, G183, which decreased binding of m102 to G. These results suggest that m101 to -7 are specific for HeV or NiV or both and exhibit various neutralizing activities; they are the first human monoclonal antibodies identified against these viruses and could be used for treatment, prophylaxis, and diagnosis and as research reagents and could aid in the development of vaccines.
Nipah virus (NiV) and Hendra virus (HeV) are closely related emerging paramyxoviruses that comprise the Henipavirus genus (1, 12-15, 18, 21, 27, 28, 30). Paramyxoviruses are negative-sense RNA-containing enveloped viruses and contain two major membrane-anchored envelope glycoproteins that are required for infection of a receptive host cell. All members contain an F glycoprotein which mediates pH-independent membrane fusion between the virus and its host cell, while the second attachment glycoprotein can be either a hemagglutinin-neuraminidase protein (HN), a hemagglutinin protein (H), or a G glycoprotein, depending on the particular virus (reviewed in reference 26). As with all paramyxoviruses, the fusion and attachment glycoproteins are also the principal antigens to which virtually all neutralizing antibodies are directed.
The broad species tropisms and the ability to cause fatal disease in both animals and humans distinguish HeV and NiV from all other known paramyxoviruses (reviewed in reference 17). They are biological safety level 4 (BSL-4) pathogens and are on the National Institute of Allergy and Infectious Diseases biodefense research agenda as zoonotic emerging category C priority pathogens that could be used as bioterror agents. The henipaviruses can be amplified and cause disease in large animals and be transmitted to humans, where disease can be a severe respiratory illness and febrile encephalitis. They can be readily grown in cell culture or embryonated chicken eggs, produce high unconcentrated titers (~108) 50% tissue culture infective doses (TCID50)/ml (16), and are highly infectious (20, 23).
NiV has reemerged on several occasions in Bangladesh. Two recent outbreaks of NiV in 2004 have been confirmed, and yet another one occurred in January of 2005 (4). Several important observations in these most recent outbreaks have been made, including a higher incidence of acute respiratory distress syndrome, person-to-person transmission, and significantly higher case fatality rates (60 to 75%), in contrast to the Malaysian outbreak (about 40%), where the virus was discovered or suspected to have originated (2, 3, 11, 19, 24). There are currently no therapeutic modalities for treating NiV or HeV infections, and a vaccine for prevention of disease in human or livestock populations does not exist. Although antibody responses were detected in infections caused by these viruses, human monoclonal antibodies (hMAbs) have not been identified against either virus. A number of studies have shown the importance of neutralizing antibodies in recovery and protection from viral infections (17). Therefore, the development of neutralizing hMAbs against NiV and HeV could have important implications for prophylaxis and passive immunotherapy. In addition, the characterization of the epitopes of the neutralizing antibodies could provide helpful information for development of candidate vaccines and drugs. Finally, such antibodies could be used for diagnosis and as research reagents.
Here, we report the identification of potent neutralizing hMAbs targeting the viral envelope glycoprotein G by using a highly purified, oligomeric, soluble HeV G (sG) glycoprotein as the antigen for screening of a large na?ve human phage display library. One of these antibodies exhibited exceptional potency against infectious HeV, and another one neutralized both HeV and NiV. Because these antibodies are fully human antibodies, they could be directly used for prophylaxis and treatment of humans infected with HeV or NiV.
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