Previously infected and recovered chimpanzees exhibit rapid responses that control hepatitis C virus replication upon rechallenge

Abstract

Responses in three chimpanzees were compared following challenge with a clonal hepatitis C virus (HCV) contained in plasma from an animal that had received infectious RNA transcripts. Two of the chimpanzees (Ch1552 and ChX0186) had recovered from a previous infection with HCV, while the third (Ch1605) was a naïve animal. All animals were challenged by reverse titration with decreasing dilutions of plasma and became serum RNA positive following challenge. Ch1605 displayed a typical disease profile for a chimpanzee. We observed increasing levels of serum RNA from week 1 postinoculation (p.i.), reaching a peak of 10(6) copies/ml at week 9 p.i., and alanine aminotransferase (ALT) elevations and seroconversion to HCV antibodies at week 10 p.i. In contrast, both Ch1552 and ChX0186 exhibited much shorter periods of viremia (4 weeks), low serum RNA levels (peak, 10(3) copies/ml), and minimal ALT elevations. A comparison of intrahepatic cytokine levels in Ch1552 and Ch1605 showed greater and earlier gamma interferon (IFN-gamma) and tumor necrosis factor alpha responses in the previously infected animal, responses that were 30-fold greater than baseline responses at week 4 p.i. for IFN-gamma in Ch1552 compared to 12-fold in Ch1605 at week 10 p.i. These data indicate (i) that clonal HCV generated from an infectious RNA transcript will lead to a typical HCV infection in naïve chimpanzees, (ii) that there are memory immune responses in recovered chimpanzees that control HCV infection upon rechallenge, and (iii) that these responses seem to be T-cell mediated, as none of the animals had detectable antibody against the HCV envelope glycoproteins. These observations have encouraging implications for the development of a vaccine for HCV.

FIG. 1.

Clinical response of Ch1605 to challenge with increasing doses of plasma from Ch1536. Arrowheads indicate the dates of challenge with increasing doses. Weeks postinoculation are counted as postchallenge with the 10⁻⁴ dilution of plasma. Results from nested PCR are indicated at the top of the graph. Vertical open bars represent negative PCR signals, and vertical filled bars represent positive PCRs. Serum positivity in Ortho EIA 3.0 is indicated by a horizontal shaded bar.

FIG. 2.

Clinical response of Ch1552 to challenge with increasing doses of plasma from Ch1536. Arrowheads indicate the dates of challenge with increasing doses. Weeks postinoculation are counted as postchallenge with the 10⁻⁴ dilution of plasma. Results from nested PCR are indicated at the top of the graph. Vertical open bars represent negative PCR signals, and vertical filled bars represent positive PCRs. Serum positivity in Ortho EIA 3.0 is indicated by a horizontal shaded bar.

FIG. 3.

Clinical response of ChX0186 to challenge with increasing doses of plasma from Ch1536. Arrowheads indicate the dates of challenge with increasing doses. Weeks postinoculation are counted as postchallenge with the 10⁻⁴ dilution of plasma. Results from nested PCR are indicated at the top of the graph. Vertical open bars represent negative PCR signals, and vertical filled bars represent positive PCRs. Serum positivity in Ortho EIA 3.0 is indicated by a horizontal shaded bar.

FIG. 4.

RIBA and NS3 ELISA results obtained for sera from Ch1605 (A), Ch1552 (B), and ChX0186 (C) following challenge with plasma from Ch1536. In the top panels, filled bars represent 5-1-1/c100 and open bars represent C33c; the filled bar at the extreme right in panel C represents C22. In the bottom panels, shaded bars represent NS3 (derived from Sindbis virus). OD, optical density.

FIG. 5.

T-cell proliferation assay with PBMCs from Ch1605, Ch1552, and ChX0186 prechallenge (top panels) and postchallenge (lower panels) with infecting plasma. The cutoff for positive responses was an SI of 3, indicated by a dashed line. pos., positive; Hel., helicase portion of NS3.

FIG. 6.

Relative cytokine levels (measured in fold increase over baseline) observed in liver biopsies from Ch1605 (A) and Ch1552 (B).

FIG. 7.

Clinical profile and intrahepatic cytokine levels of Ch1605 following rechallenge with 100 CID₅₀ of Ch1536 plasma. Relative cytokine levels are measured in fold increase over baseline. Results from nested PCR are indicated at the top of the graph. Vertical open bars represent negative PCR signals, and vertical filled bars represent positive PCRs.