In Vitro and In Vivo Fitness of Respiratory Syncytial Virus Monoclonal Antibody Escape Mutants

Abstract

Respiratory syncytial virus (RSV) is the only infectious disease for which a monoclonal antibody (MAb) is used in humans. Palivizumab (PZ) is a humanized murine MAb to the F protein of RSV. PZ-resistant viruses appear after in vitro and in vivo growth of RSV in the presence of PZ. Fitness for replication could be a determinant of the likelihood of dissemination of resistant viruses. We assessed the fitness of two PZ-resistant viruses (F212 and MP4). F212 grew less well in cell culture than the parent A2 virus and was predicted to be less fit than A2. Equal amounts of F212 and A2 were mixed and passaged in cell culture. F212 disappeared from the viral population, indicating it was less fit than the A2 virus. The MP4 virus grew as well as A2 in culture and in cotton rats. A2/MP4 virus input ratios of 1:1, 10:1, 100:1, and 1,000:1 were compared in competitive replication. For all input ratios except 1,000:1, the MP4 virus became dominant, supplanting the A2 virus. The MP4 virus also dominated the A2 virus during growth in cotton rats. Thus, the mutant MP4 virus was more fit than A2 virus in both in vitro and in vivo competitive replication. Whether this fitness difference was due to the identified nucleotide substitutions in the F gene or to mutations elsewhere in the genome is unknown. Understanding the mechanisms by which mutant virus fitness increased or decreased could prove useful for consideration in attenuated vaccine design efforts.

The Role of Virulence in In Vivo Superinfection Fitness of the Vertebrate RNA Virus Infectious Hematopoietic Necrosis Virus

“…These experiments are useful to directly compare two variants and can demonstrate subtle fitness differences between two variants that may not have been evident by comparing single-infection kinetics. Recently, there have been a number of coinfection fitness studies using in vivo models for vertebrate viruses (2,(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21). For example, competition experiments have been performed using many species of arbovirus in their mosquito vectors and have determined correlations between viral fitness and epidemiologic observations or recorded disease severity in humans (11,14).…”

Trivalency of a Nanobody Specific for the Human Respiratory Syncytial Virus Fusion Glycoprotein Drastically Enhances Virus Neutralization and Impacts Escape Mutant Selection

“…In the case of hRSV, escape mutants which resist Pz prophylaxis in cotton rats could readily be isolated in vitro (54), although some of these mutants showed reduced fitness in comparison with wild-type virus (23). Furthermore, mutations associated with Pz resistance were only found in about 5% of clinical samples from infants that were diagnosed with lower respiratory tract RSV disease and that had received prophylactic treatment with that MAb in a clinical trial (24).…”

“…Monthly prophylactic administration of RespiGam to children at high risk of having a severe hRSV infection reduced the frequency of hospitalization by about 55% and intensive care days by 97% (20,21). However, since RespiGam had the disadvantage of requiring intravenous infusion, besides the theoretical risk of adventitious agents and possible interference with pediatric vaccines, it was soon superseded by palivizumab (Pz; Synagis), a humanized monoclonal antibody (MAb) that binds to the hRSV F protein (22)(23)(24). Pz is the only existing medicinal product specific for hRSV which, as done before with RespiGam, is used prophylactically in children at high risk of having severe hRSV disease (21,25,26).…”

Ausência de escapes mutantes para o medicamento palivizumab® do Vírus Respiratório Sincicial Humano (hRSV) circulante, na cidade de São Paulo durante o ano de 2004.

“…Outros trabalhos colaboram com a hipótese da existência de escapes mutantes por conseguir produzir em cotton rats vírus resistentes ou parcialmente resistentes ao Palivizumab (Zhao et al, 2004(Zhao et al, , 2005(Zhao et al, , 2006.…”

“…Escapes mutantes do tratamento foram selecionados em células cultivadas com anticorpos anti-F e anti-G do hRSV (Zhao et al, 2006 …”