Therapeutic antibodies for infectious diseases

Passive immunization is the transfer of antibodies and occurs naturally during pregnancy. The transplacental transfer of maternal antibodies to the fetus can protect the infant from many infectious diseases for the first vulnerable months of its life. Passive immunization has been used in the global effort to eliminate maternal and neonatal tetanus. Researchers have estimated that vaccinating pregnant women with two or more doses of tetanus-containing vaccine has reduced neonatal mortality from tetanus by 94%. 1 In addition, clinicians have used passive immunization, to prevent or to treat various infections for over a century for diseases such as rabies, diphtheria, tetanus, hepatitis B, respiratory syncytial virus and botulism. Passive immunization is also used in immunocompromised individuals and to manage complications after vaccination. Most of the antibody preparations administered to patients, containing polyclonal antibodies, have been derived from sera of immunized animals, immunized humans, and for some rarer diseases, from sera of convalescent patients.2–4 Box 1 presents blood-derived polyclonal antibodies currently in use.5–7 The production and use of polyclonal antibodies have revealed several challenges, including standardization, patient safety, supply and access. These challenges have led researchers to explore the possibility of replacing polyclonal antibodies with monoclonal antibodies (mAbs), which can be produced through recombinant deoxyribonucleic acid technologies. In the past, producing mAbs was difficult and expensive. However, the increasing use of mAbs as therapeutics for cancer, autoimmune diseases and other chronic diseases has led to increased production capacities and improved manufacturing processes.8 These advancements have made mAbs potentially cost-competitive with blood-derived polyclonal antibodies, while at the same time contributing towards an improved supply at a global level. Over 40 therapeutic mAbs are currently in use, targeting a range of noncommunicable diseases. In addition to potentially addressing the patient safety and supply limitations of polyclonal antibodies, antiinfective mAbs may offer prophylactic or therapeutic interventions for infectious diseases where drugs or vaccines are not available or are poorly efficacious. For example, the use of broadly crossreactive mAbs to prevent influenza or neutralizing mAbs against Ebola and Middle East respiratory syndrome coronavirus (MERS-CoV). Furthermore, anti-infective mAbs could be used to target multidrug resistant pathogens, such as Staphylococcus aureus, to reduce the incidence of hospital-acquired infections and may help to prevent the emergence of antimicrobial resistance. Although passive immunization produces a short-lived protection against infections, mAbs have some advantages over vaccines for active immunization. First, protection from vaccination takes longer and often requires several doses to elicit a protective immune response, whereas passive immunization provides a much quicker protection. Second, passive immunization can provide protection in immunosuppressed individuals, who are often at a high risk of acquiring infections. Third, since the mAb manufacturing process is generic, a manufacturer can start production of mAbs with minimal lead-time. Therefore, mAbs could become available faster than vaccines during an emergency. The 2013–2016 Ebola virus disease outbreak in West Africa demonstrated the need for mAb research and development. In August 2014, two American health-care workers infected with Ebola were treated with ZmappTM, an experimental drug containing three mAbs against Ebola.9 Unfortunately, the drug supply was only sufficient to treat seven patients and efforts had to be made to increase production before clinical evaluation could take place.10 Efficacy trials in Ebola infected patients in West Africa were completed in January 2016. However, due to the waning epidemic, the trial could only enroll 72 patients out of the planned 200. The outcomes showed that out of the 36 patients who received ZmappTM, eight died, which was less than in the group receiving only standard care (13 of 35 patients died). However, the trial sample size was too low to draw any conclusions.11 Despite this setback, anti-Ebola mAb development – which has been ongoing for several years and the first neutralizing mAb reported in 199912 – continues towards the goal of licensure under alternative pathways to standard randomized controlled clinical trials. While there are numerous mAb products under development for a range of infectious diseases, currently only three have been licensed: palivizumab for prevention of respiratory syncytial virus in high-risk infants; and raxibacumab and obiltoxaximab for prophylaxis and treatment of anthrax. Numerous mAbs have shown the potential to treat infectious diseases in preclinical evaluation, both in vitro and in animal models. However, not many of these mAbs have reached clinical trials.13–16 A review of the WHO International Clinical Trials Registry Platform17 and ClinicalTrials.gov, found that as of November 2016, there were at least 38 mAb products in active clinical development for 14 infectious diseases: Anthrax, Clostridium botulinum (botulinum neurotoxin A), C difficile, Ebola virus disease, hepatitis B, hepatitis C, Hendra virus, herpes simplex virus, human immunodeficiency virus, influenza, rabies, respiratory syncytial virus, S aureus and S epidermidis. While mAbs have great potential to address health threats, their developTherapeutic antibodies for infectious diseases Erin Sparrow, Martin Friede, Mohamud Sheikh & Siranda Torvaldsen