Four-dimensional computed tomography-based respiratory-gated whole-abdominal intensity-modulated radiation therapy for ovarian cancer: a feasibility study

This study assesses the feasibility and implementation of respiratory-gated whole-abdominal intensity-modulated radiation therapy (RG-WAIMRT). Three patients were treated with RG-WAIMRT. The planning target volume (PTV1) included the entire peritoneal cavity and a pelvic boost field was created (PTV2). The dose prescribed was 30 Gy to PTV1 and 14.4 Gy to PTV2. For comparison, a conventional three-dimensional (3D) plan was generated for each patient. In the WAIMRT plan, an average of 90% of PTV1 received 30 Gy compared to 70% for the conventional 3D plan. The percent volume receiving 30 Gy (V30) for liver averaged 54% (WAIMRT) vs 43% (3D). The percent volume receiving 20 Gy (V20) for kidneys averaged 19% vs 0%, and the mean V20 for bone marrow was 74% vs 83%, respectively. Major acute toxicities were anemia (grade 2: 1/3), leukopenia (grade 3: 2/3 patients), and thrombocytopenia (grade 2: 1/3 patients, grade 3: 1/3 patients). One patient could not complete the whole-abdomen field after 19.5 Gy because of persistent nausea. No major subacute toxicity has been reported. WAIMRT demonstrated superior target coverage and reduced dose to bone marrow, with a slightly increased dose to liver and kidneys. WAIMRT is a novel and feasible technique for ovarian cancer treatment.

Intrahepatic genetic inoculation of hepatitis C virus RNA confers cross-protective immunity

Naturally occurring hepatitis C virus (HCV) infection has long been thought to induce a weak immunity which is insufficient to protect an individual from subsequent infections and has cast doubt on the ability to develop effective vaccines. A series of intrahepatic genetic inoculations (IHGI) with type 1a HCV RNA were performed in a chimpanzee to determine whether a form of genetic immunization might stimulate protective immunity. We demonstrate that the chimpanzee not only developed protective immunity to the homologous type 1a RNA after rechallenge by IHGI but was also protected from chronic HCV infection after sequential rechallenge with 100 50% chimpanzee infectious doses of a heterologous type 1a (H77) and 1b (HC-J4) whole-virus inoculum. These results offer encouragement to pursue the development of HCV vaccines.

Hepatitis B virus e antigen specific epitopes and limitations of commercial anti-HBe immunoassays

Current commercial hepatitis B virus (HBV) anti-HBe immunoassays are designed so that anti-HBe is detectable only in the absence of excess HBeAg. Recently, with the use of direct anti-HBe assays, anti-HBe was detected in individuals who had been seropositive for several years for HBeAg [Maruyama et al. (1993) J. Clin. Invest. 91:2586-2595]. Although anti-HBe seroconversion does not necessarily indicate subsequent HBeAg clearance, the ability to detect earlier anti-HBe seroconversion could have clinical significance for monitoring patients undergoing HBV immunotherapy (e.g., alpha interferon therapy). Because the HBeAg and the HBcAg share 149 amino acids, an anti-HBe assay must distinguish anti-HBe from anti-HBc antibodies. Although the HBV HBeAg and HBcAg display distinct immunogenic determinants, much remains unknown regarding the complete epitope spectrum specific to each antigen. The goal of this study was 3-fold. The first objective was to identify HBeAg specific linear epitopes. The second objective was to design an anti-HBe immunoassay capable of detecting anti-HBe specific antibody in the presence of excess HBeAg. The third objective was to characterize early anti-HBe seroconversion antibodies. The major linear epitope residing in the HBeAg amino acid sequence was mapped and 2 novel minor epitopes (delta, gamma) which appear to be HBeAg specific have been identified. An anti-HBe immunoassay capable of detecting anti-HBe specific antibody in the presence of excess HBeAg was designed. Finally, it was found that early anti-HBe seroconversion antibodies appear to be conformational, whereas later seroconversion, more typically associated with the clearance of HBeAg, is characterized by the presence of antibodies to the linear HBeAg epitopes.

Use of a novel hepatitis C virus (HCV) major-epitope chimeric polypeptide for diagnosis of HCV infection

The genome of hepatitis C virus (HCV) consists of seven functional regions: the core, E1, E2/NS1, NS2, NS3, NS4, and NS5 regions. The U. S. Food and Drug Administration-licensed 2.0G immunoassay for the detection of anti-HCV uses proteins from the core, NS3, and NS4 regions (McHutchinson et al., Hepatology 15:19-25, 1992). The 3.0G enzyme-linked immunosorbent assay includes the protein from the NS5 region (Uyttendaele et al., Vox Sang. 66:122-129, 1994). The necessity of detecting antibodies to viral envelope proteins (E1 and E2) and to different genotype samples has been demonstrated previously (Chien et al., Lancet 342:933, 1993; Lok et al., Hepatology 18:497-502, 1993). In this study we have attempted to improve the sensitivity of the anti-HCV assay by developing a single multiple-epitope fusion antigen (MEFA; MEFA-6) which incorporates all of the major immunodominant epitopes from the seven functional regions of the HCV genome. A nucleic acid sequence consisting of proteins from the viral core, E1, E2, NS3, NS4, and NS5 regions and different subtype-specific regions of the NS4 region was constructed, cloned, and expressed in yeast. The epitopes present on this antigen can be detected by epitope-specific monoclonal and polyclonal antibodies. In a competition assay, the MEFA-6 protein competed with 83 to 96% of genotype-specific antibodies from HCV genotype-specific peptides. This recombinant antigen was subsequently used to design an anti-HCV chemiluminescent immunoassay. We designed our assay using a monoclonal anti-human immunoglobulin G antibody bound to the solid phase. Because MEFA-6 is fused with human superoxide dismutase (h-SOD), we used an anti-human superoxide dismutase, dimethyl acridinium ester-labeled monoclonal antibody for detection. Our results indicate that MEFA-6 exposes all of the major immunogenic epitopes. Its excellent sensitivity and specificity for the detection of clinical seroconversion are demonstrated by this assay.

Evaluation of hepatitis B and C viral markers: clinical significance in Asian and Caucasian patients with hepatocellular carcinoma in the United States of America

In order to evaluate the roles of hepatitis B virus (HBV) and hepatitis C virus (HCV) and their clinical significance in Asian-American and Caucasian patients with hepatocellular carcinoma (HCC) in the USA, 110 HCC patients, seen in a community-based teaching hospital in the Los Angeles area over a 10 year period, were enrolled. Seventy-nine (72%) patients were Asian-American and 31 (28%) were Caucasians. Of the 110 HCC patients, 69 (63%) were positive for serum hepatitis B surface antigen (HBsAg), 26 (24%) were positive for serum antibody to hepatitis C virus (anti-HCV), five (all Asian-Americans) were positive for both markers; 11 (10%) patients had a history of alcoholism. HBsAg was detected in 63 (80%) Asian-American patients, significantly higher than in the six (19%) Caucasian HCC patients (P < 0.01). Anti-HCV was detected in 10 (32%) Caucasian and in 16 (20%) Asian-American HCC patients (P > 0.05). Among Asian-American HCC patients, anti-HCV was more prevalent in those who were HBsAg-negative than in the HBsAg-positive patients (69 vs 8%; P < 0.01). A history of alcoholism was obtained in nine (29%) Caucasian HCC patients, significantly higher than in the two (3%) Asian-American HCC patients (P < 0.05). Comparing HCC patients with positive HBsAg and with anti-HCV, HBsAg-positive HCC patients were younger, Asian-Americans and predominantly male; 38% had a family history of liver disease. In contrast, anti-HCV-positive HCC patients were older by nearly a decade and 46% had a history of blood transfusion. Using a stepwise logistic regression analysis, Asian race and patient age < 50 years were found to be independent predictors for HBsAg-positivity, while a history of blood transfusion was the only predictor for anti-HCV-positivity in HCC patients. There was no significant difference in the rate of cirrhosis, serum levels of alpha-fetoprotein and survival between HBsAg-positive and anti-HCV-positive HCC patients. In conclusion, chronic HBV infection was the major aetiological factor in Asian-American HCC patients, while chronic HCV infection and alcoholism were major aetiological factors in Caucasian HCC patients in the USA.

Effect of immune globulin on the prevention of experimental hepatitis C virus infection

The efficacy of postexposure prophylaxis for the prevention of hepatitis C virus (HCV) infection was studied in experimentally infected chimpanzees. Three chimpanzees were inoculated with HCV: Two were treated 1 h later with anti-HCV--negative intravenous immune globulin (IGIV) or hepatitis C immune globulin (HCIG), and a third animal was not treated. HCV infection was detected in all 3 animals within a few days of inoculation. Once passively transferred anti-HCV declined in the HCIG-treated animal, there was an increase of HCV antigen (Ag)--positive hepatocytes followed by reappearance of anti-HCV; HCV Ag disappeared concordant with the development of acute hepatitis. Acute hepatitis C developed in both the IGIV-treated and untreated chimpanzees, with peak liver enzyme activity on day 59, but was delayed in the HCIG-treated animal until day 146. Postexposure HCIG treatment markedly prolonged the incubation period of acute hepatitis C but did not prevent or delay HCV infection. IGIV had no effect on the course of HCV infection.

Cardiopulmonary effects of tumor necrosis factor-alpha in the piglet: influence of cyclooxygenase inhibition

Tumor necrosis factor-alpha (TNF) is believed to play an important role in mediating many of the pathophysiologic changes accompanying bacterial sepsis. In order to characterize the cardiopulmonary responses to TNF in a young animal model and to determine to what extent these changes were secondary to cyclooxygenase byproducts, three groups of mechanically ventilated piglets received an infusion of either TNF, indomethacin followed by TNF (Indo+TNF) or neither (control). Compared to controls at 120 min, TNF resulted in the following changes beginning 30-60 min after the infusion began: mean pulmonary artery pressure (Ppa) increased from 1.7 +/- 0.3 to 4.4 +/- 0.7 kPa (13 +/- 2 to 33 +/- 5 mm Hg) (p < 0.001); cardiac output (CO) fell from 0.28 +/- 0.05 to 0.20 +/- 0.07 liters/kg/min (p < 0.01); mean arterial blood pressure (Psa) decreased from 9.5 +/- 1.2 to 7.9 +/- 1.9 kPa (71 +/- 9 to 59 +/- 14 mm Hg) as did pH from 7.49 +/- 0.04 to 7.13 +/- 0.17 (p < 0.001). Dynamic lung compliance (Cdyn) also decreased; however, pulmonary resistance (RI) remained unchanged. Thromboxane B2 (TxB2) rose in all animals at 60 min coincident with Psa elevation and was significantly blocked by Indo (p < 0.03). In the Indo+TNF group the early TNF-induced rise in Psa was blunted compared to the TNF group [2.9 +/- 1.2 vs. 3.6 +/- 0.8 kPa (22 +/- 3 vs. 27 +/- 6 mm Hg; p < 0.04)] as were the late decreases in pH and Psa (p < 0.04). There were no significant changes in Cdyn secondary to Indo. Although delayed, the hemodynamic changes observed with TNF infusion are similar to those reported for piglets receiving group B streptococci; however, in contrast to the latter the early changes secondary to TNF are only mildly effected by indomethacin. The significant improvement in the late occurring hypotension and acidosis suggests that TNF may act in part via the cyclooxygenase pathway as a mediator of the late hypotension associated with sepsis.

Evaluation of sexual transmission in patients with chronic hepatitis C infection

BACKGROUND

The transmission of hepatitis C virus (HCV) by parenteral exposure is well documented. However, a proportion of patients with acute or chronic HCV infection have an unknown source of infection.

OBJECTIVES

The purpose of this study is to evaluate the role of sexual transmission in HCV infection.

STUDY DESIGN

68 patients (median age, 50 years) with chronic hepatitis C and their spouses were tested for the presence of antibody to HCV (anti-HCV) by multi-antigen and chimeric C25 antigen enzyme immunoassays and for HCV RNA by the polymerase chain reaction. Information on sexual activity and risk factors for HCV infection were obtained from all couples via a questionnaire.

RESULTS

All index patients were positive for both anti-HCV and HCV RNA. Antibody to HCV was detected in four (5.9%) of their spouses. One anti-HCV-positive spouse had a history of blood transfusion while the other three (4.4%, 95% CI = 1.5-12.2%) had no known risk factors for HCV infection and thus may have been exposed to HCV via sexual transmission. Two of these 3 spouses had positive serum HCV RNA and had identical HCV genotype to the index patients. The length of sexual exposure was significantly longer in the couples who both were anti-HCV-positive than in patients whose spouses were anti-HCV negative (median: 25 vs. 10 years, P = 0.02, Mann-Whitney test). In our 68 index patients, 96% had antibodies to the recombinant proteins from the C22 (core) and C33C (NS3) regions, and 82% and 76% had antibodies to the proteins from the NS5 and C100-3 (NS4) regions. Identical anti-HCV profiles were noted in two of the four anti-HCV-positive couples.

CONCLUSIONS

Our results indicate that sexual transmission, although uncommon, should be considered as a risk factor for HCV infection, especially in spouses who have had long-term intimate relationships with a chronic hepatitis C patient.

Hepatitis C virus markers in patients with long-term biochemical and histological remission of chronic hepatitis

We measured hepatitis C virus (HCV) RNA and antibodies against HCV recombinant proteins (C22/S1, E1/S2, E2/NS1, C33/NS3, C100/NS4, NS5) in serial serum samples from 22 interferon-treated patients with a long-term follow up (range: 36-44 months). Eleven of them showed persistently normal liver function tests and a significant histological amelioration or a complete resolution of chronic hepatitis (long-term responders, LTRs). In the remaining 11 patients (non-responders (NRs)) liver function tests normalized temporarily during therapy or remained unchanged. At the end of the follow up (3 years), viraemia was undetectable in six of 11 LTRs (54.6%). HCV-RNA was always detectable in the serum of NRs (p = 0.017). At admission, anti-C22/S1, anti-E1/S2, anti-E2/NS1, anti-C33/NS3, anti-C100/NS4 and anti-NS5 were detected in 95.4%, 40.9%, 77.3%, 95.4%, 72.7% and 77.3% of the patients, respectively. Three years after suspension of therapy, anti-C100/NS4 was undetectable in five of six (83.3%) LTRs who cleared HCV-RNA and in only one with ongoing viraemia (20%). Anti-E2/NS1 was undetectable in 54.5% of LTRs and in no NRs (p = 0.067). Anti-E1/S2 was detected more frequently in LTRs than in NRs (81.8% vs 45.5%). Serum levels of anti-C22/S1, C33/NS3 and NS5 did not change during therapy and the follow up in either group of patients. The clearance of viraemia in LTRs was associated with that of anti-C100/NS4 (p = 0.017). Serum HCV-RNA and anti-C100/NS4 appear suitable tools for monitoring patients who respond to therapy.(ABSTRACT TRUNCATED AT 250 WORDS)

Vaccination of chimpanzees against infection by the hepatitis C virus

A high incidence of community-acquired hepatitis C virus infection that can lead to the progressive development of chronic active hepatitis, liver cirrhosis, and primary hepatocellular carcinoma occurs throughout the world. A vaccine to control the spread of this agent that represents a major cause of chronic liver disease is therefore needed. Seven chimpanzees (Pan troglodytes) have been immunized with both putative envelope glycoproteins [E1 (gp33) and E2 (gp72)] that were copurified from HeLa cells infected with a recombinant vaccinia virus expression vector. Despite the induction of a weak humoral immune response to these viral glycoproteins in experimentally infected chimpanzees, a strong humoral immune response was obtained in all vaccines. The five highest responders showed complete protection against an i.v. challenge with homologous hepatitis C virus 1. The remaining two vaccines became infected, but both infection and disease may have been ameliorated in comparison with four similarly challenged control chimpanzees, all of which developed acute hepatitis and chronic infections. These results provide considerable encouragement for the eventual control of hepatitis C virus infection by vaccination.

Evidence for hepatitis C viral infection in patients with primary hepatocellular carcinoma

In testing for antibodies to the hepatitis C virus (anti-HCV) in 112 patients with primary hepatocellular carcinoma, 10 of 33 white patients (30%) and 15 of 79 Asian patients (19%) had a positive response to the antibody. The antibody profile to individual hepatitis C viral antigens and the presence of circulating hepatitis C viral RNA were determined in the 25 patients. The anti-HCV antibodies most frequently detected were toward the antigens from the core (C22) and NS3 regions. Serum hepatitis C viral RNA was present in 17 of the 25 patients (68%), and these patients tended to have serum levels of alanine and aspartate aminotransferases higher than those patients without viremia (136 +/- 22 U per liter versus 64 +/- 11 U per liter and 161 +/- 26 U per liter versus 79 +/- 14 U per liter, respectively, both P < .05). Of the 15 Asian patients with hepatocellular carcinoma and anti-HCV, 4 (27%) had coexisting hepatitis B surface antigen (HBsAg) and 13 (87%) had antibodies to either hepatitis B core or surface antigen. Of the 10 white patients with anti-HCV, however, only 1 (10%) had hepatitis B virus antibodies (P < .01). Among 4 Asian patients with coexisting anti-HCV and HBsAg, 1 was found to have serum hepatitis B viral DNA and the other 3 had hepatitis C viral RNA. A history of blood transfusion was obtained from 12 of the 25 patients with anti-HCV (48%); 20 (80%) had coexisting cirrhosis. Our findings support the hypothesis that hepatitis C virus is an important etiologic agent in the development of primary hepatocellular carcinoma in both white and Asian patients in the United States.

Characterization of hepatitis C virus envelope glycoprotein complexes expressed by recombinant vaccinia viruses

We constructed recombinant vaccinia virus vectors for expression of the structural region of hepatitis C virus (HCV). Infection of mammalian cells with a vector (vv/HCV1-906) encoding C-E1-E2-NS2 generated major protein species of 22 kDa (C), 33 to 35 kDa (E1), and 70 to 72 kDa (E2), as observed previously with other mammalian expression systems. The bulk of the E1 and E2 expressed by vv/HCV1-906 was found integrated into endoplasmic reticulum membranes as core-glycosylated species, suggesting that these E1 and E2 species represent intracellular forms of the HCV envelope proteins. HCV E1 and E2 formed E1-E2 complexes which were precipitated by either anti-E1 or anti-E2 serum and which sedimented at approximately 15 S on glycerol density gradients. No evidence of intermolecular disulfide bonding between E1 and E2 was detected. E1 and E2 were copurified to approximately 90% purity by mild detergent extraction followed by chromatography on Galanthus nivalus lectin-agarose and DEAE-Fractogel. Immunization of chimpanzees with purified E1-E2 generated high titers of anti-E1 and anti-E2 antibodies. Further studies, to be reported separately, demonstrated that purified E1-E2 complexes were recognized at high frequency by HCV+ human sera (D. Y. Chien, Q.-L. Choo, R. Ralston, R. Spaete, M. Tong, M. Houghton, and G. Kuo, Lancet, in press) and generated protective immunity in chimpanzees (Q.-L. Choo, G. Kuo, R. Ralston, A. Weiner, D. Chien, G. Van Nest, J. Han, K. Berger, K. Thudium, J. Kansopon, J. McFarland, A. Tabrizi, K. Ching, B. Mass, L. B. Cummins, E. Muchmore, and M. Houghton, submitted for publication), suggesting that these purified HCV envelope proteins display native HCV epitopes.

Antibody response to core, envelope and nonstructural hepatitis C virus antigens: comparison of immunocompetent and immunosuppressed patients

Some immunosuppressed patients with hepatitis C virus infection do not have detectable levels of antibody to hepatitis C virus on second-generation enzyme immunoassay. Antibodies to the envelope and nonstructural region 5 proteins have not been examined. Four groups of patients with hepatitis C virus infection were studied: (a) 20 immunocompetent patients, (b) 15 hemodialysis patients, (c) 17 kidney transplant recipients and (d) 3 acute leukemia patients who underwent bone marrow transplantation. Serum samples were tested for antibody to hepatitis C virus with a second-generation enzyme immunoassay and multi-antigen enzyme immunoassays and for hepatitis C virus RNA with a nested polymerase chain reaction assay. All the immunocompetent patients reacted to C25, C22 and C33C; 90% reacted to nonstructural region 5 antigen and 80% reacted to C100-3. Only 55% reacted against yeast-derived e1 and e2 antigens, but all reacted against vaccinia virus--expressed N e1 and e2 antigens, indicating that the envelope epitopes are conformational and glycosylated. Sixty-five percent to 90% of dialysis and kidney transplant patients reacted to C25, C22 and N e1 and e2, but only 12% to 60% reacted to C100-3, C33C and nonstructural region 5 antigen. Diminution or loss of reactivity to hepatitis C virus antigens was observed after kidney and bone marrow transplantation, with C25 and N e1 and e2 less affected. Our data suggest that incorporation of C25 and N e1 and e2 antigens in the assay for antibody to hepatitis C virus would improve the detection of hepatitis C virus infection in immunosuppressed patients.

Antibody response to core, envelope and nonstructural hepatitis C virus antigens: comparison of immunocompetent and immunosuppressed patients

Some immunosuppressed patients with hepatitis C virus infection do not have detectable levels of antibody to hepatitis C virus on second-generation enzyme immunoassay. Antibodies to the envelope and nonstructural region 5 proteins have not been examined. Four groups of patients with hepatitis C virus infection were studied: (a) 20 immunocompetent patients, (b) 15 hemodialysis patients, (c) 17 kidney transplant recipients and (d) 3 acute leukemia patients who underwent bone marrow transplantation. Serum samples were tested for antibody to hepatitis C virus with a second-generation enzyme immunoassay and multi-antigen enzyme immunoassays and for hepatitis C virus RNA with a nested polymerase chain reaction assay. All the immunocompetent patients reacted to C25, C22 and C33C; 90% reacted to nonstructural region 5 antigen and 80% reacted to C100-3. Only 55% reacted against yeast-derived e1 and e2 antigens, but all reacted against vaccinia virus--expressed N e1 and e2 antigens, indicating that the envelope epitopes are conformational and glycosylated. Sixty-five percent to 90% of dialysis and kidney transplant patients reacted to C25, C22 and N e1 and e2, but only 12% to 60% reacted to C100-3, C33C and nonstructural region 5 antigen. Diminution or loss of reactivity to hepatitis C virus antigens was observed after kidney and bone marrow transplantation, with C25 and N e1 and e2 less affected. Our data suggest that incorporation of C25 and N e1 and e2 antigens in the assay for antibody to hepatitis C virus would improve the detection of hepatitis C virus infection in immunosuppressed patients.

Compartmentalization of T lymphocytes to the site of disease: intrahepatic CD4+ T cells specific for the protein NS4 of hepatitis C virus in patients with chronic hepatitis C

The adult liver is an organ without constitutive lymphoid components. Therefore, any intrahepatic T cell found in chronic hepatitis should have migrated to the liver after infection and inflammation. Because of the little information available on the differences between intrahepatic and peripheral T cells, we used recombinant proteins of the hepatitis C virus (HCV) to establish specific T cell lines and clones from liver biopsies of patients with chronic hepatitis C and compared them with those present in peripheral blood mononuclear cells (PBMC). We found that the protein nonstructural 4 (NS4) was able to stimulate CD4+ T cells isolated from liver biopsies, whereas with all the other HCV proteins we consistently failed to establish liver-derived T cell lines from 16 biopsies. We then compared NS4-specific T cell clones obtained on the same day from PBMC and liver of the same patient. We found that the 22 PBMC-derived T cell clones represent, at least, six distinct clonal populations that differ in major histocompatibility complex restriction and response to superantigens, whereas the 27 liver-derived T cell clones appear all identical, as further confirmed by cloning and sequencing of the T cell receptor (TCR) variable and hypervariable regions. Remarkably, none of the PBMC-derived clones has a TCR identical to the liver-derived clone, and even with polymerase chain reaction oligotyping we did not find the liver-derived clonotypic TCR transcript in the PBMC, indicating a preferential intrahepatic localization of these T cells. Functionally, the liver-derived T cells provided help for polyclonal immunoglobulin (Ig)A production by B cells in vitro that is 10-fold more effective than that provided by the PBMC-derived clones, whereas there is no difference in the help provided for IgM and IgG production. Altogether these results demonstrate that the protein NS4 is highly immunogenic for intrahepatic CD4+ T cells primed by HCV in vivo, and that there can be compartmentalization of some NS4-specific CD4+ T cells to the liver of patients with chronic hepatitis C.

Expression, identification and subcellular localization of the proteins encoded by the hepatitis C viral genome

We have expressed the full-length coding region and selected domains of the hepatitis C virus (HCV) cDNA in mammalian cells by transfection. Using HCV antibody-positive human sera and monospecific antibodies the proteins encoded by the putative structural and non-structural regions of the open reading frame of HCV were identified as core (p22), E1 (gp32-35), E2 (gp68-72), NS2 (p23), NS3 (p72), NS4a and b (p10 and p27) and NS5a and b (p56 and p70). We have also defined the subcellular localizations of the HCV proteins using indirect immunofluorescence assays.

The hepatitis C virus encodes a serine protease involved in processing of the putative nonstructural proteins from the viral polyprotein precursor

The hepatitis C virus (HCV) nonstructural protein 3 (NS3) domain has been predicted from sequence comparisons to represent a trypsin-like serine protease. By expressing wild-type and mutant HCV-1 cDNAs in transfected mammalian cells, we have identified putative nonstructural proteins 3 (72 kDa), 4 (10 kDa and 27 kDa) and 5 (58 kDa) and have shown that their processing from the viral polyprotein precursor is dependent on Ser1165 located in the proposed protease catalytic site. Data obtained from in vitro RNA translations indicate that unlike the processing of the NS2/NS3 junction, NS3/NS4 processing is dependent on Ser1165. In contrast to the situation for the related flaviviral NS3 proteases, the HCV NS3-mediated cleavage of the NS3/NS4 junction does not require the upstream NS2 domain and may not occur at dibasic sites.

T-lymphocyte response to hepatitis C virus in different clinical courses of infection

BACKGROUND

To assess the role played by the immune response in the outcome of hepatitis C virus infection, the CD4+ T-lymphocyte response to viral antigens was studied in infected individuals with different clinical courses.

METHODS

Using six recombinant proteins of hepatitis C virus, the study assessed the proliferative responses of peripheral blood mononuclear cells from 41 patients with chronic hepatitis C, 11 patients whose chronic hepatitis was successfully treated with interferon alfa and 11 healthy HCV seropositive individuals.

RESULTS

(1) Sixty-five percent of hepatitis C virus-seropositive individuals had CD4+ T-cell responses to viral proteins. (2) All viral proteins were immunogenic for T cells, although NS4 was the most immunogenic. (3) There was a significant correlation between the presence of CD4+ T cell responses to Core and a benign course of infection in healthy seropositives, most of whom were viremic.

CONCLUSIONS

CD4+ T-cell responses to Core, although they do not coincide with virus clearance, are associated with a benign course of infection and may be required to maintain humoral and cellular responses protective against the disease.

Hepatitis C--its prevalence in end-stage renal failure patients and clinical course after kidney transplantation

There is a high incidence of chronic liver disease in end-stage renal failure patients on dialysis. Hepatitis C virus appears responsible for 80% of posttransfusion hepatitis, and up to 80% of sporadic hepatitis and cryptogenic cirrhosis. Anti-HCV antibodies correlate highly with the presence of active infection. The clinical implications of HCV infection in patients undergoing renal transplantation is unknown. Part I: We undertook a descriptive cross-sectional study of all renal failure patients admitted for kidney transplant between 1/84 and 12/88. Pretransplant sera were assayed for anti-HCV using an ELISA. Patients were divided into anti-HCV-positive (study group) and anti-HCV-negative (controls). Part II: A cohort study was performed with both groups followed from the time of transplantation to the present. Comparisons were made by t tests, chi-square analysis with Yates correction, Mann Whitney test for nonparametric results and multiple regression analysis. Part I: Anti-HCV was present in 76 of 716 sera assayed. There were no differences in sex, age, number of previous transplants, and underlying renal disease. Four variables predicted the presence of anti-HCV: number of blood transfusions; duration on dialysis; i.v. drug abuse, and nonwhite race. Part II: A group of 596 patients was further analyzed. The mean duration of follow-up was not different between the two groups. There were no differences in graft survival, overall mortality, or mortality secondary to liver disease or sepsis. Based on these results, the presence of anti-HCV should not be a contraindication for kidney transplantation.

[Chronic hepatitis C. Experience with 50 patients]

We studied 50 patients (36 males and 14 females) with chronic hepatitis C who were admitted consecutively to our medical department during the period 1987-91. Eight patients (16%) had had a blood transfusion, 17 (34%) had used intravenous drugs and 25 (50%) were "sporadic cases" with no identifiable risk factor except that at least five had been tattooed. Most of the patients had moderate symptoms, including tiredness and asthenia. Few were jaundiced. A percutaneous liver biopsy was performed in 27 patients and showed chronic persistent hepatitis in 12 of them, chronic active hepatitis in six and cirrhosis in nine. Three patients with cirrhosis died; one from hepatoma, one from an endstage cirrhosis with bleeding and coma hepaticum, and one from septicaemia.

At least five related, but distinct, hepatitis C viral genotypes exist

Hepatitis C virus, the major causative agent of blood-borne non-A, non-B hepatitis in the world, has been the subject of considerable nucleic acid sequence analysis. Although all reported hepatitis C sequences from the United States have been represented by the prototype hepatitis C virus type 1 sequence, two groups of variant sequences have been reported in Japan. However, we have noted five distinct, but related, genotypes (I-V) throughout the world, based on detailed sequence determination and analysis of the first 1700 nucleotides and part of the nonstructural region 5 at the C terminus of the open reading frame. The nucleotide sequence for a large number of hepatitis C virus isolates spanning six continents was obtained by direct sequence analysis of PCR products after reverse transcription. Genotype was classified by using several distinct sequence motifs. We observed that most genotypes coexist in several geographic regions, including the United States, Japan, Germany, and Italy. So far, genotype V has been found only in South Africa. Interestingly, each distinct genotype seems to be maintained throughout the genome in the segments studied. These genotype distinctions should be considered when designing specific diagnostic tests, developing potential vaccines, and studying viral transmission.

Hepatitis C virus antigen in hepatocytes: immunomorphologic detection and identification

Hepatitis C virus (HCV) antigen was detected immunohistochemically using fluorescein isothiocyanate-labeled immunoglobulin G fractions from chimpanzee and human sera strongly reactive with recombinant hepatitis C virus structural and non-structural proteins. The antigen was localized in the cytoplasm of hepatocytes in all 9 chimpanzees with acute hepatitis C, in 5 of 10 chimpanzees with chronic HCV infection, and in 11 of 12 patients with chronic hepatitis C. The specificity of the hepatocellular HCV and FITC-labeled probes for HCV was ascertained by blocking studies with paired serum samples obtained from 8 infected and uninfected chimpanzees or from 14 patients during the acute and chronic phases of HCV infection. Absorption experiments on FITC-labeled probes with selected host proteins (normal liver homogenate, plasma proteins, red blood cells) did not indicate cross reactivity of the probes with these antigens. Direct immunomorphologic evidence for the HCV specificity of hepatocellular HCV antigen deposits and the FITC-labeled polyclonal anti-HCVAg probe was established in absorption experiments using recombinant HCV nonstructural proteins. The putative HCV NS3 protein was the most prominent component of hepatocellular HCV antigen.

Comparative evaluation of supplemental hepatitis C virus antibody test systems

Implementation of routine blood donor screening using anti-hepatitis C virus (HCV) enzyme immunoassay (EIA) has resulted in an urgent need for well-characterized supplemental assays to confirm the presence of HCV antibodies. A comparative study of four commercially available supplemental assays is reported here: first- and second-generation versions of a strip recombinant immunoblot assay (RIBA-1 and RIBA-2), an HCV neutralization EIA, and HCV neutralization plus synthetic peptide EIA. Three hundred sixty-seven blood donor specimens that were repeatedly reactive on HCV EIA were studied. Most specimens (93%) were also evaluated by radioimmunoassay (RIA) with a six-antigen panel, and 60 selected specimens were tested for HCV RNA by the polymerase chain reaction (PCR). RIBA-1 and RIBA-2 gave concordant results with 86 percent of specimens, while an additional 13 percent were correctly classified by RIBA-2 but not RIBA-1. Neutralization EIA alone correctly identified 94 percent of the study group, while the remaining 6 percent required the peptide EIA or the combined neutralization-peptide assay system for correct classification. The RIBA-2 and neutralization-peptide assay system for correct classification. The RIBA-2 and neutralization-peptide assay systems yielded identical results for 86 percent of specimens, and these results were supported by RIA and selected PCR testing. Only 2 specimens (0.5%) were frankly discrepant, while 51 specimens were indeterminate on either (47) or both (4) assays. When either the RIBA-2 or neutralization-peptide assay yielded an indeterminate interpretation, the other system correctly classified the specimen (based on concordance with RIA and PCR data) in a high proportion (92%) of cases.(ABSTRACT TRUNCATED AT 250 WORDS)

Enhanced sensitivity of a second generation ELISA for antibody to hepatitis C virus

A second generation ELISA for combined detection of antibodies to three hepatitis C virus (HCV) recombinant proteins, i.e. C100, C33c and core, was compared with a first generation anti-HCV ELISA in which only antibodies to C100 are detected. The results of the ELISAs were evaluated in 225 haemophilia patients (panel A) and 44 patients with non-A, non-B (NANB) hepatitis (panel B). HCV infection was established by cDNA-polymerase chain reaction (PCR) (in panel B only) and by studying the anti-HCV reaction patterns in 4 separate ELISAs for detection of antibodies to the recombinant proteins C100, C33c, core and a combination of two synthetic peptides sp67/65 derived from the C100 region. The sensitivity for the detection of HCV infection had increased from 0.92[95% confidence interval (CI): 0.87-0.95] to 1.00 (95% CI: 0.89-1.00) in haemophiliacs and from 0.84 (95% CI: 0.66-0.95) to 1.00 (95% CI: 0.89-1.00) in NANB hepatitis patients when the second generation ELISA was used instead of the first generation ELISA. Concurrently the chance of a false negative result was reduced in panel A and B from 0.37 to 0 and from 0.28 to 0, respectively. Analysis of anti-HCV reaction patterns revealed that 172 of 206 (83.5%) anti-HCV ELISA-reactive haemophilia patients had antibodies to all 4 antigens tested. In the NANB hepatitis patients 18 of 31 (58.1%) anti-HCV ELISA-reactive subjects reacted with 4 antigens. In the PCR tested panel of NANB hepatitis patients 2 subjects who showed antibody reactivity to only one antigen and 5 patients with reactivity to 2 antigens were PCR-positive.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of hepatitis C virus markers in patients with NANB hepatitis

10 different HCV-specific assays and RT-PCR of the 5' untranslated region of HCV RNA were used to analyze sixty-four patients with chronic NANB liver disease. Po, CP-9 and C22 antigens are located in the putative core; C33c in the putative NS3; C100-3 in the putative NS3/4; KCL in the putative NS4/5 and C825 is located in the putative NS5. GOR protein is not part of the HCV genome, but antibodies to it appear to be present in response to a hepatitis C infection. Positive rates were 91% for Po, 89% for CP-9, 94% for C22, 97% for C33c, 88% for C100-3 (Ortho, EIA), 86% for C100-3 (Abbott, EIA), 84% for C100-3 (Ohtsuka, RIA), 88% for KCL, 59% for C825, 58% for GOR, and 83% for RT-PCR. There were 8 cases which were negative by all anti-C100 tests. 7 of these cases were positive by other anti-HCV markers and/or PCR suggesting the need for improved blood screening assays. There is a variation in the relative reactivity for different markers with different samples. Of the tests employed, anti C33c shows the highest positivity rate.

Use of a signature nucleotide sequence of hepatitis C virus for detection of viral RNA in human serum and plasma

The nucleic acid sequence of the putative 5'-untranslated (5PUT) region of hepatitis C virus (HCV), determined for samples obtained from a variety of geographic origins, was found to be over 98% conserved among all isolates. On the basis of this signature sequence for HCV, a viral RNA assay was developed by using cDNA synthesis with reverse transcriptase, followed by polymerase chain reaction (PCR). The new assay was compared with the Ortho-Chiron C100-3 HCV enzyme-linked immunosorbent assay to research radioimmunoassays for antibodies to the C33c and C22 HCV antigens and to the first reported set of HCV PCR primers designed from the NS3 domain. Plasma samples from 16 Japanese patients with non-A, non-B hepatitis (NANBH) and 16 immunoassay-positive blood donors from the United States were investigated. The 5PUT PCR primers were found to be superior to the NS3 primers in sensitivity and specificity (15 of 25 versus 3 of 25 of the C100 enzyme-linked immunosorbent assay-positive samples, respectively). Samples from two C100-negative patients with acute NANBH were found to react with the 5PUT primers but not with the NS3 primers. Also, two of three patients with chronic NANBH converted from reverse transcriptase PCR positive to negative after interferon treatment. Although the clinical significance of the presence or absence of HCV RNA in samples from patients is not fully understood, the use of probes and primers from the 5PUT region (as opposed to primers from other segments) should not lead to false-negative results due to nucleic acid sequence variations in viral isolates.

Hepatitis C virus antibodies in acute icteric and chronic non-A, non-B hepatitis

Hepatitis C virus antibodies were measured in 213 patients who had acute (n = 122) and chronic (n = 91) non-A, non-B hepatitis. In acute infection, anti-hepatitis C virus was detected in 61% of IV drug abusers, in 33% of patients with transfusion-associated hepatitis, and in 22% of patients with sporadic infections (P less than 0.0005, drug abusers vs. sporadic). Mean time to seroconversion was 11.6 weeks (range, 1-80 weeks). Anti-hepatitis C virus was more common in chronic infection (P less than 0.001) and was more often detected in IV drug users (89%; P less than 0.0001) and after transfusion (71%; P less than 0.005) compared with chronic sporadic infection (27%). Antibody persisted for up to 8 years. Six chronic case patients (8.3%) later lost antibody (mean, 24 months; range, 12-48 months).

Risk factors in hepatitis C virus-infected blood donors

Risk factors of parenteral and nonparenteral exposure to hepatitis C virus (HCV) infection were studied in 125 blood donors in The Netherlands who were positive for anti-HCV on enzyme-linked immunosorbent assay (ELISA). Risk factors were related to confirmatory test results of four-antigen recombinant immunoblot assay (4-RIBA) and polymerase chain reaction (PCR) of the HCV 5' untranslated region. Twelve (10%) of the 125 anti-HCV C100 ELISA-positive blood donors were 4-RIBA positive. Eleven (92%) of 12 4-RIBA-positive blood donors were PCR positive, and all 113 remaining 4-RIBA-negative or -indeterminate donors were PCR negative. Eleven (92%) of 12 4-RIBA-positive blood donors had a risk factor of parenteral exposure, as compared to 17 (15%) of 113 4-RIBA-negative or -indeterminate donors. The prevalence of confirmed HCV infection among Amsterdam blood donors is calculated at 0.04 percent; parenteral exposure appears to be the major risk factor for HCV infection.

Hepatitis C antibody in patients with chronic liver disease and hepatocellular carcinoma

Hepatitis C virus (HCV) is the major etiologic agent of parenterally transmitted non-A, non-B hepatitis. To determine whether there is a relationship between this virus agent and hepatocellular carcinoma (HCC), the sera of patients with HCC and chronic hepatitis were assessed using a sensitive immunoassay for HCV antibody. Anti-HCV was detected in 65% of 132 patients with HCC, without any relationship with the presence of the hepatitis B surface antigen (HBsAg). The prevalence (74%) of anti-HCV was high, as expected in patients with putative non-A, non-B cirrhosis also. The prevalence of anti-HCV was less in patients with HBsAg-positive cirrhosis (28%) and in patients with disease not related to viral hepatitis and healthy controls (8%). These data suggest, but do not prove, that HCV is an important factor associated with HCC.

Role of hepatitis C virus in non-B chronic liver disease

To assess the contribution of the recently identified hepatitis C virus to chronic liver diseases of unknown cause and chronic hepatitis attributed by exclusion to non-A, non-B hepatitis, we tested for antibody to hepatitis C in hepatitis B surface antigen-negative patients with a spectrum of chronic liver diseases. Antibody to hepatitis C virus, a marker of hepatitis C infection, was detected with a first-generation radioimmunoassay at the following frequencies in the following patient groups: 69% of transfusion-associated non-A, non-B hepatitis; 53% of non-transfusion-associated non-A, non-B hepatitis; 26% of hepatitis B surface antigen-negative hepatocellular carcinoma; 8% of cryptogenic cirrhosis; 5% to 7% of autoimmune chronic liver diseases; 19% of patients with miscellaneous types of chronic liver disease; and 0.67% of healthy controls. Among non-transfusion-associated cases, 81% with a history of intravenous drug use but only 18% with occupational exposure as health workers had antibody to hepatitis C virus. Among cases of hepatocellular carcinoma, 63% of Japanese patients but only 11% of American patients had evidence of hepatitis C infection. Comparison in a subgroup of 79 serum samples of a second-generation radioimmunoassay with the first-generation assay demonstrated a 12% increase in antibody frequency from 30% to 42%. We conclude that hepatitis C plays a substantial role in transfusion-associated and non-transfusion-associated non-A, non-B hepatitis as well as in hepatocellular carcinoma, especially in Japan, a limited role in cryptogenic cirrhosis, and essentially no role in autoimmune chronic liver diseases. Application of more sensitive immunoassays will increase the frequency of antibody seropositivity in all subgroups, but relative distinctions among risk groups are likely to remain.

Antibody to the hepatitis C virus in acute hepatitis and chronic liver diseases in Japan

In a 6-month follow-up study of acute hepatitis in Japan, 31 out of 41 (75.6%) cases of post-transfusion non-A and non-B hepatitis (NANB-PTH) and 14 out of 40 (35.0%) cases of sporadic non-A non-B hepatitis (NANB-SPO) were found to be positive for antibody to the hepatitis C virus (HCVAb). After 12 months of follow-up, 30 cases (81.1%) became chronic among 37 HCVAb positive acute NANB hepatitis cases. This figure shows a significantly higher rate of chronicity as compared with HCVAb negative acute NANB hepatitis. The prevalences of HCVAb in hepatitis B surface antigen (HBsAg) negative cases of chronic hepatitis and liver cirrhosis were 76.3% (200/262) and 66.7% (106/159), respectively, which were significantly different from the values of 5.1% (13/255) and 10.6% (13/123) observed in HBsAg positive cases. Of chronic liver disease cases positive for HCVAb, 45.8% (152/332) had a history of blood transfusion, in contrast to the value of 3.7% (13/352) observed in HBsAg positive cases of chronic liver disease that were negative for HCVAb.

Characterization of the terminal regions of hepatitis C viral RNA: identification of conserved sequences in the 5' untranslated region and poly(A) tails at the 3' end

We have determined the nucleotide sequence at the extreme 5' and 3' termini of the hepatitis C virus (HCV) genome. Our analyses of these sequences show (i) the nucleotide sequence in the 5' untranslated region is highly conserved among HCV isolates of widely varying geographical origin, (ii) within this region, there are blocks of nucleotide sequence homology with pestiviruses but not with other viruses, (iii) the relative position of short open reading frames present in the same region of the HCV genome is similar to that of the pestiviral genome, (iv) RNAs truncated at the 5' and 3' ends are found, but the origin and functions of these RNAs are unknown, and (v) poly(A) tails appear to be present on 3' subgenomic RNAs. These data differentiate HCV from the flaviviruses and indicate a closer evolutionary relationship of HCV with the pestiviruses. However, HCV also appears to be substantially different from other known pestiviruses. These data are consistent with the assignment of HCV to a separate viral genus.

The role of chronic viral hepatitis in hepatocellular carcinoma in the United States

Although hepatocellular carcinoma is a relatively uncommon tumor in the United States, it is quite common in sub-Saharan Africa and the Far East, where most cases are associated with infection with the hepatitis B virus. We have studied 99 American patients with hepatocellular carcinoma for evidence of hepatitis B or hepatitis C viral infection and compared these findings to those in a group of matched controls with other cancers. The two groups differed in proportion, with hepatitis B surface antigen in serum being significantly higher in patients with hepatocellular carcinoma (7% vs. 0%, p = 0.009). Antibody to hepatitis C virus was also found more frequently in patients with hepatocellular carcinoma (13% vs. 2%, p = 0.002). The relative risk for hepatocellular carcinoma in hepatitis B surface antigen-positive patients was calculated to be 17.3 and for antibody to hepatitis C virus to be 7.3. The attributable fraction of cases related to the hepatitis B surface antigen carrier state was 6.7% and for patients infected with the hepatitis C virus was 11.4%. Approximately three quarters of cases of hepatocellular carcinoma did not have evidence of either hepatitis C or hepatitis B virus infection. These findings provide strong evidence that hepatitis C virus infection is associated with the development of hepatocellular carcinoma, and in the United States may even play a more important role than the hepatitis B virus.

A high prevalence of antibody to the hepatitis C virus in patients with hepatocellular carcinoma in Japan

In Japan, hepatocellular carcinoma (HCC) is one of the most prevalent cancers, with a reported fatality rate showing a consistent and significant increase in the last decade. At most, only 25% of HCC cases are positive for the hepatitis B surface antigen (HBsAg). To investigate a potential role for hepatitis C virus (HCV) in the development of HCC, sera from 105 HBsAg-negative HCC patients were collected from five districts of Japan and assayed for antibody to HCV antigen (HCVAb). A large number of these patients (76.2%) were found to be positive for the HCVAb in comparison with the reported prevalence in sera from blood donors (1.1%). A history of blood transfusion was found in 39.6% of the cases positive for HCVAb, which was significantly different to the lower rate (4.7%) observed in HCC patients who were both positive for HBsAg and negative for HCVAb (P less than 0.001).

A high prevalence of antibody to the hepatitis C virus in patients with hepatocellular carcinoma in Japan

In Japan, hepatocellular carcinoma (HCC) is one of the most prevalent cancers, with a reported fatality rate showing a consistent and significant increase in the last decade. At most, only 25% of HCC cases are positive for the hepatitis B surface antigen (HBsAg). To investigate a potential role for hepatitis C virus (HCV) in the development of HCC, sera from 105 HBsAg-negative HCC patients were collected from five districts of Japan and assayed for antibody to HCV antigen (HCVAb). A large number of these patients (76.2%) were found to be positive for the HCVAb in comparison with the reported prevalence in sera from blood donors (1.1%). A history of blood transfusion was found in 39.6% of the cases positive for HCVAb, which was significantly different to the lower rate (4.7%) observed in HCC patients who were both positive for HBsAg and negative for HCVAb (P less than 0.001).

A high prevalence of antibody to the hepatitis C virus in patients with hepatocellular carcinoma in Japan

In Japan, hepatocellular carcinoma (HCC) is one of the most prevalent cancers, with a reported fatality rate showing a consistent and significant increase in the last decade. At most, only 25% of HCC cases are positive for the hepatitis B surface antigen (HBsAg). To investigate a potential role for hepatitis C virus (HCV) in the development of HCC, sera from 105 HBsAg-negative HCC patients were collected from five districts of Japan and assayed for antibody to HCV antigen (HCVAb). A large number of these patients (76.2%) were found to be positive for the HCVAb in comparison with the reported prevalence in sera from blood donors (1.1%). A history of blood transfusion was found in 39.6% of the cases positive for HCVAb, which was significantly different to the lower rate (4.7%) observed in HCC patients who were both positive for HBsAg and negative for HCVAb (P less than 0.001).

The putative nucleocapsid and envelope protein genes of hepatitis C virus determined by comparison of the nucleotide sequences of two isolates derived from an experimentally infected chimpanzee and healthy human carriers

cDNA fragments of a 5'-terminal region of the hepatitis C virus (HCV) genome were isolated by the reverse polymerase chain reaction from RNA extracted from plasma samples of healthy Japanese carriers. Their nucleotide sequence was compared with that of the original isolate which had been passaged twice in chimpanzees. No deletions or insertions were observed between the two sequences in the regions examined. Both the 5' untranslated and putative nucleocapsid (core) protein regions were highly conserved (99% and 91% nucleotide identities, respectively). In contrast, the region immediately downstream which encodes a putative envelope glycoprotein(s) showed only 74% nucleotide identity between the two isolates. At the polypeptide level, the core and envelope domains showed 97% and 75% amino acid identities, respectively. This envelope variation may reflect the adaptation of HCV to the different hosts and/or the result of immunological selection. The highly conserved nucleotide sequence of the 5' untranslated and core regions may play an important regulatory role in the life cycle of HCV.

Parenterally transmitted non-A, non-B hepatitis: virus-specific antibody response patterns in hepatitis C virus-infected chimpanzees

An established chimpanzee model of parenterally-transmitted non-A, non-B hepatitis was used to define virus-specific immune response patterns in acutely and persistently infected animals. Serial bleedings were obtained from 23 chimpanzees that had been experimentally infected with an isolate of hepatitis C virus, originally recovered from contaminated lots of factor VIII (antihemophilic) materials. Sera were assayed for the presence of antihepatitis C virus by a newly developed radioimmunoassay procedure that incorporated recombinant DNA-expressed viral antigen as a reagent. Twenty-one of 23 hepatitis C virus infected animals were shown to acquire antihepatitis C virus, most within 2-8 weeks after the major peak of alanine aminotransferase activity. All chimpanzees with biochemical, electron microscopic, and histological evidence of chronic disease clearly acquired antibody; 14 of 16 animals observed through the acute phase of disease were also shown to acquire antibody. A booster effect or anamnestic response was noted in two chimpanzees (one of which was negative for antihepatitis C virus following the acute phase of disease) after challenge with hepatitis C virus. Antihepatitis C virus was not neutralizing, because some animals with high levels of antibody were also shown to have high titers of circulating hepatitis C virus. The development and maintenance of anti-hepatitis C virus appears to reflect concomitant virus replication and high potential for infectivity.