Molecular basis and protective efficacy of cross-neutralizing antibodies against four major respiratory viruses - PROJECT SUMMARY/ABSTRACT Tens of thousands of otherwise deadly cancers are cured worldwide each year by hematopoietic stem cell transplantation (HCT), but unfortunately over one in ten patients will develop a viral lower respiratory tract infection, with almost half of these patients succumbing to the infection. Without an intact immune system in the first few months after transplant, these life-threatening infections offset the benefit derived from potentially life- saving transplant. Over half of these infections are caused by four viruses: RSV, HMPV, HPIV3, and HPIV1, none of which currently have any pharmacologic interventions for treatment or prevention after HCT. Although adults are universally infected with these viruses in childhood, HCT recipients lose their immunity, making them vulnerable to severe complications. Passive immunization with monoclonal antibodies (mAbs) represents a strategy to reduce the risk of these infections. While several anti-RSV mAb candidates have progressed through clinical trials, their use is limited to infants in whom RSV is responsible for virtually all cases of lung infection. However, the clinical efficacy of these mAbs is expected to be substantially lower in HCT patients because other important viruses like HMPV, HPIV3, and HPIV1 contribute significantly to disease. To fill this clinical gap for HCT patients, we have discovered two cross-neutralizing mAbs: one that targets both RSV and HMPV and another that targets both HPIV3 and HPIV1. Together, these mAbs could be combined to simultaneously protect against the four viruses that cause most lung infections after HCT. To test efficacy, we will administer these mAbs prophylactically and therapeutically to immunocompetent and immunocompromised animals. We will also test the pharmacokinetics of these mAbs with modifications designed for increased half-life and lung bioavailability, such that a single dose could bridge the entire period of vulnerability after transplant. Another often neglected pitfall in bringing novel antibody therapies to the bedside is the potential for resistance. Recent failed clinical trials of anti-RSV mAbs have shown that the emergence of escape variants can cripple clinical development. How to predict success or failure during the preclinical phase before candidates progress into clinical trials is an important question, and the answers could save massive amounts of resources, effort, and time. To fill this knowledge gap, we have developed an innovative approach called deep mutational scanning that provides a comprehensive picture of the viral mutational landscape, allowing an unprecedented preclinical evaluation of resistance. Since the two cross-neutralizing mAbs described in this proposal bind to conserved epitopes, these and similar mAbs may have a high barrier of resistance. To prepare for and counter resistance by future viral variants, we will leverage predictions from our complete mutational maps to identify next- generation mAbs, allowing us to stay a few steps ahead of viral evolution. These novel cross-neutralizing mAbs and the innovative and rigorous approaches we have developed to vet them could provide a new standard of care for HCT patients and inform the design and testing of other candidates with the greatest chance for success.
