Human Adenovirus Type 4 Comprises Two Major Phylogroups with Distinct Replicative Fitness and Virulence Phenotypes

Abstract

Human adenovirus type 4 (HAdV-E4) is the only type (and serotype) classified within species Human mastadenovirus E that has been isolated from a human host to the present. Recent phylogenetic analysis of whole genome sequences of strains representing the spectrum of intratypic genetic diversity described to date identified two major evolutionary lineages designated phylogroups (PG) I, and II, and validated the early clustering of HAdV-E4 genomic variants into two major groups by low resolution restriction fragment length polymorphism analysis. In this study we expanded our original analysis of intra- and inter-PG genetic variability, and used a panel of viruses representative of the spectrum of genetic diversity described for HAdV-E4 to examine the magnitude of inter- and intra-PG phenotypic diversity using an array of cell-based assays and a cotton rat model of HAdV respiratory infection. Our proteotyping of HAdV-E strains using concatenated protein sequences in selected coding regions including E1A, E1B-19K and -55K, DNA polymerase, L4-100K, various E3 proteins, and E4-34K confirmed that the two clades encode distinct variants/proteotypes at most of these loci. Our in vitro and in vivo studies demonstrated that PG I and PG II differ in their growth, spread, and cell killing phenotypes in cell culture and in their pulmonary pathogenic phenotypes. Surprisingly, the differences in replicative fitness documented in vitro between PGs did not correlate with the differences in virulence observed in the cotton rat model. This body of work is the first reporting phenotypic correlates of naturally occurring intratypic genetic variability for HAdV-E4. IMPORTANCE Human adenovirus type 4 (HAdV-E4) is a prevalent causative agent of acute respiratory illness of variable severity and of conjunctivitis and comprises two major phylogroups that carry distinct coding variations in proteins involved in viral replication and modulation of host responses to infection. Our data show that PG I and PG II are intrinsically different regarding their ability to grow and spread in culture and to cause pulmonary disease in cotton rats. This is the first report of phenotypic divergence among naturally occurring known genetic variants of a HAdV type of medical importance. This research reveals readily detectable phenotypic differences between strains representing phylogroups I and II, and it introduces a unique experimental system for the elucidation of the genetic basis of adenovirus fitness and virulence and thus for increasing our understanding of the implications of intratypic genetic diversity in the presentation and course of HAdV-E4-associated disease.

Characterization of Human Adenoviruses of Medical Importance: Isolation of Infectious Virus from Clinical Specimens and Molecular Typing

“…Eagle Kajon et al, 2015;Li et al, 1991;Li & Wadell, 1986van der Avoort et al, 1986) and, more recently, fitness and pathogenic phenotypes (Bair et al, 2022). The availability of WGS has enabled the analysis to be conducted in silico (Kajon et al, 2018;Kajon et al, 2020;Otto et al, 2021b).…”

“…The occurrence of intratypic genetic variability has been demonstrated for all HAdV types examined for this feature to date. The use of restriction enzyme analysis (REA)/RFLP analysis has been shown for decades to be a powerful tool to reveal the existence of genomic variants for molecular epidemiology investigations of correlations between genetic variability and geographic distribution (Adhikary et al., 2003; Adrian, Becker et al., 1989; Adrian, Best et al., 1989; Adrian et al., 1990; Adrian et al., 1986; de Jong et al., 1988; Kajon et al., 2015; Li et al., 1991; Li & Wadell, 1986, 1988; van der Avoort et al., 1986) and, more recently, fitness and pathogenic phenotypes (Bair et al., 2022). The availability of WGS has enabled the analysis to be conducted in silico (Kajon et al., 2018; Kajon et al., 2020; Otto et al., 2021b).…”