Development of human monoclonal antibodies against diseases caused by emerging and biodefense-related viruses.

Polyclonal antibodies have a century-old history of being effective against some viruses; recently, monoclonal antibodies (mAbs) have also shown success. The humanized mAb Synagis (palivizumab), which is still the only mAb against a viral disease approved by the US FDA, has been widely used as a prophylactic measure against respiratory syncytial virus infections in neonates and immunocompromised individuals. The first fully human mAbs against two other paramyxoviruses, Hendra and Nipah virus, which can cause high (up to 75%) mortality, were recently developed; one of them, m101, showed exceptional potency against infectious virus. In an amazing pace of research, several potent human mAbs targeting the severe acute respiratory syndrome coronavirus S glycoprotein that can affect infections in animal models have been developed months after the virus was identified in 2003. A potent humanized mAb with therapeutic potential was recently developed against the West Nile virus. The progress in developing neutralizing human mAbs against Ebola, Crimean-Congo hemorrhagic fever, vaccinia and other emerging and biodefense-related viruses is slow. A major problem in the development of effective therapeutic agents against viruses, including therapeutic antibodies, is the viruses' heterogeneity and mutability. A related problem is the low binding affinity of crossreactive antibodies able to neutralize a variety of primary isolates. Combinations of mAbs or mAbs with other drugs, and/or the identification of potent new mAbs and their derivatives that target highly conserved viral structures, which are critical for virus entry into cells, are some of the possible solutions to these problems, and will continue to be a major focus of antiviral research.