Lack of Response to Exogenous Interferon-α in the Liver of HCV Chronically
Infected Chimpanzees
Fig. 1. Lack of antiviral response to peg-IFNα in HCV infected
chimpanzees. Three chimpanzees were dosed weekly with peg-IFNα2a and monitored
for reductions in serum viral RNA levels by quantitative RT-PCR. The genotype 1a
animal was dosed for 12 weeks, while the genotype 1b animal was stopped at 8
weeks of therapy due to unrelated health issues. The genotype 3 animal was given
a single dose of peg-IFNα in order to examine ISG response and was monitored for
14 days.
Fig. 2. Heatmap of IFNα induced liver gene expression. A data
set of 822 genes were obtained by ANOVA (SLR≥1, p≤0.02) and PAM clustering
(Supplement Table 2). The heatmap compares the signal intensity between the
pretreatment baseline liver samples and the 4, 8 and 24 hr post-IFNα dosing
samples from three uninfected (each with two independent dosing studies) and
three HCV infected chimpanzees. The average value for all samples for a given
gene are assigned the color black. Red and green intensity indicate positive and
negative changes from the average values. One dimensional hierarchical
clustering analysis with gene symbols is shown to the left. In uninfected
animals, this gene set is induced at 4 and 8 hr post-IFNα dosing (green to red),
while in infected animals the genes are induced at baseline and no or minimal
increase occurs post-IFNα dosing. [View
full-size PDF of Figure 2]
The mechanism of the interferon-alpha (IFNα)-induced antiviral response is not
completely understood. We recently examined the transcriptional response to IFNα
in uninfected chimpanzees. The transcriptional response to IFNα in the liver and
peripheral blood mononuclear cells (PBMC) was rapidly induced but was also
rapidly down-regulated, with most IFNα stimulated genes (ISGs) returning to
baseline within 24 hr. We have extended these observations to include
chimpanzees chronically infected with hepatitis C virus (HCV). Remarkably, using
total genome microarray analysis, almost no induction of ISG transcripts was
observed in the liver of chronically infected animals following IFNα dosing,
while the response in PBMC was similar to that in uninfected animals. Consistent
with this finding, no decrease in viral load occurred in up to 12 weeks of
pegylated (peg)-IFNα therapy. The block in response to exogenous IFNα appeared
to be HCV specific, since the response in an HBV infected animal was similar to
that of uninfected animals. The lack of response to exogenous IFNα may be due to
an already maximally induced ISG response, since HCV chronically infected
chimpanzees already have a highly up-regulated hepatic ISG response.
Alternatively, negative regulation may block the response to exogenous IFNα, yet
does not prevent the continued response to endogenous ISG stimuli. The IFNα
response in HCV chronically infected chimpanzees may be mechanistically similar
to the null response in the human population.
Table 1. Genes up-regulated ( ≥2.0-fold; p≤0.02) by IFNα in the liver
of uninfected and HCV chronically infected chimpanzees. n = 511
A total of 71 arrays were used in the analysis, 36 of which represented
uninfected animals and 40 of which represented infected animals including liver
and PBMC from two pre-dose baseline samples (designated 0 hr), 4, 8 and 24 hr
post-IFN on each of three HCV infected animals and one HBV infected animal. All
cel files were scaled to 250 and normalized. Data analyses were facilitated
using Affymetrix GCOS and DMT 2.0 software and the GeneSifter web-based package.
Using Affymetrix software, each experimental chp file was compared to 2 baseline
chp files taken from the same animal prior to IFNα inoculation. A Wilcoxon’s
Signed Rank test was used to compare each probe set to the corresponding
baseline samples and to compute Change p-values for genes increasing or
decreasing, and genes without p-values of <0.002 or >0.998 were excluded. The
data were further filtered to omit genes not altered in expression by an SLR ≥1
(2-fold change) and not reproducibly altered against both baseline samples and
in the majority of samples from a given time point in all like animals. [Download
excel table].
