title: HIV-1 Env C2-V4 diversification in a slow-progressor infant reveals a flat but rugged fitness landscape.
abstract: Human immunodeficiency virus type-1 (HIV-1) fitness has been associated with virus entry, a process mediated by the envelope glycoprotein (Env). We previously described Env genetic diversification in a Zambian, subtype C infected, slow-progressor child (1157i) in parallel with an evolving neutralizing antibody response. Because of the role the Variable-3 loop (V3) plays in transmission, cell tropism, neutralization sensitivity, and fitness, longitudinally isolated 1157i C2-V4 alleles were cloned into HIV-1NL4-3-eGFP and -DsRed2 infectious molecular clones. The fluorescent reporters allowed for dual-infection competitions between all patient-derived C2-V4 chimeras to quantify the effect of V3 diversification and selection on fitness. 'Winners' and 'losers' were readily discriminated among the C2-V4 alleles. Exceptional sensitivity for detection of subtle fitness differences was revealed through analysis of two alleles differing in a single synonymous amino acid. However, when the outcomes of N = 33 competitions were averaged for each chimera, the aggregate analysis showed that despite increasing diversification and divergence with time, natural selection of C2-V4 sequences in this individual did not appear to be producing a 'survival of the fittest' evolutionary pattern. Rather, we detected a relatively flat fitness landscape consistent with mutational robustness. Fitness outcomes were then correlated with individual components of the entry process. Env incorporation into particles correlated best with fitness, suggesting a role for Env avidity, as opposed to receptor/coreceptor affinity, in defining fitness. Nevertheless, biochemical analyses did not identify any step in HIV-1 entry as a dominant determinant of fitness. Our results lead us to conclude that multiple aspects of entry contribute to maintaining adequate HIV-1 fitness, and there is no surrogate analysis for determining fitness. The capacity for subtle polymorphisms in Env to nevertheless significantly impact viral fitness suggests fitness is best defined by head-to-head competition.
authors: Department of Microbiology and Immunology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, United States of America.
authors: S Abigail
authors: SA
authors: Smith
authors: Charles
authors: C
authors: Wood
authors: John T
authors: JT
authors: West
mesh_terms: D000483:Alleles; D015496:CD4-Positive T-Lymphocytes / Q000821:virology; D003001:Cloning, Molecular; D014644:Genetic Variation; D048788:Growth and Development; D057809:HEK293 Cells; D015497:HIV-1 / Q000235:genetics* / Q000502:physiology*; D006801:Humans; D006824:Hybridization, Genetic; D007223:Infant; D009154:Mutation; D011991:Receptors, Virus / Q000378:metabolism; D014759:Viral Envelope Proteins / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D014771:Virion / Q000235:genetics / Q000502:physiology; D053586:Virus Internalization; D014779:Virus Replication / Q000235:genetics
chemical_list: D011991:Receptors, Virus; D014759:Viral Envelope Proteins
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