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.

High prevalence of G1 and G2 TT-virus infection in subjects with high and low blood exposure risk: identification of G4 isolates in Italy.

BACKGROUND/AIMS: A non-enveloped single-stranded DNA virus (TTV) was detected in Japanese patients with fulminant hepatitis (47%) and chronic liver disease of unknown etiology (46%) more frequently than in blood donors (12%). Subsequent studies, however, questioned the association of TTV with liver disease. We further investigated the role of this novel virus in liver diseases. METHODS: We tested 106 patients and 102 blood donors for TTV by polymerase chain reaction using conserved region primers. RESULTS: TTV DNA was found in 19 of 102 volunteer blood donors (18.6%) and in 27 of 106 patients with liver disease (25.5%): 10 of 28 chronic hepatitis B (35.7%), 9 of 28 chronic hepatitis C (32.1%) and 8 of 50 (16%) cryptogenic liver disease patients. Previous interferon treatment was not associated with a significantly lower prevalence of TTV infection. TTV prevalence was higher in patients with blood exposure (42.8%, 6/14) than in patients without risk factors (21.4%, 18/84). Four of five patients (80%) with HBV familial infection and without blood exposure were also TTV positive. Partial nucleotide sequences from 3 Italian isolates diverged more than 30% from the 2 prototype genotypes G1 and G2 and were 88% homologous to the recently described genotype G4. CONCLUSIONS: G1 and G2 TTV are common in Italy and in the USA in liver disease patients and in blood donors. The prevalence is high in patients with blood exposure but also in subjects without risk factors; other routes of transmission should therefore be considered.

Analysis of a successful immune response against hepatitis C virus.

To investigate the type of immunity responsible for resolution of hepatitis C virus (HCV) infection, we monitored antibody and intrahepatic cytotoxic T lymphocyte (CTL) responses during acute (<20 weeks) infection in chimpanzees. Two animals who terminated infection made strong CTL but poor antibody responses. In both resolvers, CTL targeted at least six viral regions. In contrast, animals developing chronic hepatitis generated weaker acute CTL responses. Extensive analysis of the fine specificity of the CTL in one resolver revealed nine peptide epitopes and restriction by all six MHC class I allotypes. Every specificity shown during acute hepatitis persisted in normal liver tissue more than 1 yr after resolution. These results suggest that CD8+CTL are better correlated with protection against HCV infection than antibodies.

Hepatitis C virus heteroduplex tracking assay : application to genotype determination, quasispecies analysis, and molecular evolution studies.

The heteroduplex tracking assay (HTA) is a tool that can be used for determining genotype, quasispecies analysis, molecular evolution, and epidemiological studies (1-7). By hybridizing a labeled, single-stranded DNA probe to colinear, reverse transcriptase (RT) PCR products from a sample of interest, the probe will either form a homoduplex with identical molecules or a heteroduplex with nonidentical sequences. The hybridization products are separated on MDE or polyacrylamide gels and visualized. Delwart et al., the developers of the HTA technique (1,2,7), have previously shown that the migration of heteroduplexes relative to the homoduplex on gels are approximately proportional to the percent nucleotide divergence between two species, and therefore, the genetic distance between two species can be determined. Genetic rearrangements, deletions, and/or insertions can alter the migration of heteroduplexes in a manner that disturbs the direct relationship between relative migration and genetic distance. Typically, heteroduplexes of 0.176-1.8 kb containing >1.4-3% to ~30% nucleotide substitutions, which lack genetic alterations, can be identified as unique species on MDE gels (1,4,6). The number and distribution of unique bands indicates the genetic complexity of viral species in each sample.

Hepatitis C virus heteroduplex tracking assay for genotype determination reveals diverging genotype 2 isolates in Italian hemodialysis patients.

A heteroduplex tracking assay (HTA) was developed for genetic analyses of the hepatitis C virus (HCV) using single-stranded probes from the core (C)/E1 region. Nucleotide sequencing of reverse transcriptase (RT)-PCR products from 15 Italian dialysis patients confirmed the specificity and accuracy of the HTA genotyping method, which identified 5 of 15 (33.3%) 1b, 7 of 15 (46.7%) 3a, and 3 of 15 (20%) type 2 infections. The genotypes of an additional 12 HCV antibody-positive blood donors from different geographical locations were also in agreement with the genotypes determined by the Inno-LiPA HCV II kit (Innogenetics) and/or restriction fragment length polymorphism (RFLP). Isolates which had between 35 to 40% nucleotide divergence from control subtype 1a, 1b, 2a, 2b, or 3a standards could be typed. Surprisingly, HTA detected one 1b-2 coinfection which was missed by DNA sequencing. Three samples that were designated non-2a or 2b type 2 by HTA were found to be type 2a by both RFLP and direct nucleotide sequencing of the 5' untranslated region. The genetic distance between patient type 2 and control 2a, 2b, and 2c isolates indicated that a new subtype was present in the population being studied. Serotyping (RIBA serotyping strip immunoblot assay kit) of 23 dialysis patients showed that the genotype could be determined in 6 of 8 (75%) C/E1 RT-PCR-negative and 15 of 23 (65.2%) RT-PCR-positive samples, indicating that the two tests complement each other.

Persistent hepatitis C virus infection in a chimpanzee is associated with emergence of a cytotoxic T lymphocyte escape variant.

Hepatitis C virus (HCV) establishes a persistent infection in humans and chimpanzees despite the presence of virus-specific, class I major histocompatibility complex-restricted CD8+ cytotoxic T lymphocytes (CTLs) in the liver. The data presented here demonstrate that CTLs directed against a conserved epitope in the HCV nonstructural 3 protein persist in the liver of a chronically infected chimpanzee for at least 2 years after infection. However, these CTLs did not recognize the HCV quasi-species present in the plasma of this animal at week 16 postinfection or at later time points. Escape from the CTL response was facilitated by an aspartic acid to glutamic acid (D-->E) substitution at amino acid position 1449 in all HCV genomes that were sequenced. The results of this study strongly support the concept that CTL responses can select for variant viruses with an enhanced ability to persist in a host and have important implications for the design of vaccines against HCV.

Association of cytotoxic T lymphocyte (CTL) escape mutations with persistent hepatitis C virus (HCV) infection.

Mechanisms by which HCV evades the cellular immune response in persistently infected humans and chimpanzees are poorly defined, but could involve mutations in epitopes recognized by class I MHC restricted CTLs. To investigate this possibility, we identified an epitope in the NS3 protein of HCV that was recognized by intrahepatic CTLs from a chimpanzee that developed persistent HCV infection after experimental challenge with the virus. Fine mapping studies with truncated synthetic peptides revealed that the epitope was 9 amino acids in length, encompassing residues 1445 to 1454 (GDFDSVIDC) of NS3. This sequence was completely conserved in all full-length NS3 genomes described to date. In view of the fact that the major genotypes of HCV may differ by up to -30% in overall amino acid homology, it appears in contrast that this epitope is highly conserved. The role of CTL escape mutations in HCV persistence was assessed in the virus inoculum used to infect this chimpanzee and in post-inoculation plasma samples. Sequencing of 6-10 M13 clones containing a 232-nucleotide fragment amplified with NS3-specific primers revealed that the epitope in the challenge inoculum and a post-inoculum plasma sample obtained at week 4 were identical to the published sequence of HCV-I. In contrast, all molecular clones sequenced from week 16, 25 and 28 plasma samples contained a single Asp--> Glu (D-->E) amino acid substitution at residue 1449. Significantly, four independently derived CTL clones established from the liver of this chimpanzee at various times up to two years after infection recognized target cells pulsed with a nonameric peptide representing the wild-type HCV-I sequence, but not those pulsed with a peptide containing the D-->E mutation. These data suggest that CTL escape mutations may play a role in viral persistence.

A unique, predominant hepatitis C virus variant found in an infant born to a mother with multiple variants.

To demonstrate vertical transmission of hepatitis C virus (HCV) from an HCV-infected, non-human immunodeficiency virus type 1-infected mother to her infant and to assess the distribution of viral species in the mother and infant, the hypervariable region of the gene encoding the putative envelope glycoprotein E2 (E2HV) was sequenced in three mothers and one mother-infant pair. The data indicate that (i) quasi-species distributions of HCV E2HV variants were found in all four mothers, (ii) a single predominant HCV E2HV variant was found in the infant of a mother shown to have nine predominant E2HV variants, and (iii) the infant's E2HV variant was highly related to, but not identical with, the nine variants identified in the mother at the time of birth. These findings indicate that HCV is transmitted from mother to infant and raise the possibility that the transmission occurs in utero.

Protective immunity induced in Aotus monkeys by a recombinant SERA protein of Plasmodium falciparum: adjuvant effects on induction of protective immunity.

We report the results of vaccination trial 2 of Panamanian Aotus monkeys with a recombinant blood-stage antigen, SERA 1, of the malaria parasite Plasmodium falciparum. Monkeys were immunized with SERA 1, a 262-amino-acid fragment (amino acids 24 to 285) of the 989-amino-acid SERA protein produced by the Honduras 1 strain of the parasite. Immunization mixtures contained 100 micrograms of recombinant SERA 1 protein per dose mixed with one of five different adjuvants. The protein mixed with either Freund's adjuvant or MF75.2 adjuvant stimulated protective immunity. When other P. falciparum antigens were included in the SERA 1-Freund's adjuvant mixture, no protective immunity was observed, although high anti-SERA 1 antibody titers were produced. Three other adjuvants mixed with SERA 1 failed to induce a protective immune response. These results, their relationship to those reported previously in the first vaccination trial (trial 1), and their relationships to the quantitative measurement of anti-SERA 1 antibodies in enzyme-linked immunosorbent assays provided insights into the induction of a protective immune response in vaccinated monkeys.

Protective immunity induced in Aotus monkeys by a recombinant SERA protein of Plasmodium falciparum: further studies using SERA 1 and MF75.2 adjuvant.

We describe the third of three vaccination trials of Panamanian Aotus monkeys with a recombinant blood-stage antigen derived from the malaria parasite Plasmodium falciparum. Immunization was performed with an N-terminal region of the SERA antigen (serine repeat antigen protein), SERA 1, that contains a 262-amino-acid fragment including amino acids 24 to 285 of the 989-amino-acid SERA protein. Vaccinations were carried out with the recombinant protein mixed with either Freund's, MF75.2, or MF59.2 adjuvant. A control group that did not receive SERA 1 but only MF75.2 adjuvant was included. Monkeys vaccinated with the antigen MF59.2 mixture produced low anti-SERA 1 titers and were not protected. Monkeys vaccinated with antigen and Freund's adjuvant had, in general, a higher average anti-SERA 1 titer (107,278) than did monkeys immunized with SERA 1 and MF75.2 (40, 143), yet monkeys in both groups were well protected. Monkeys that received only MF75.2 developed neither detectable anti-SERA 1 nor anti-P. falciparum antibodies prior to or 10 days after parasite challenge, yet were apparently protected against infection. Monkeys vaccinated with either SERA 1 and Freund's, SERA 1 and MF75.2, or MF75.2 alone and that had been challenged but did not develop a countable parasitemia were treated with a curative dose of mefloquine 100 days after parasite challenge and then rechallenged 40 days later. None of the five rechallenged monkeys that had originally received SERA 1 and Freund's developed a countable parasitemia. Only one of five rechallenged monkeys that originally received SERA 1 and MF75.2 developed a high countable parasitemia, while two animals developed a barely countable parasitemia. Four of the rechallenged monkeys that had originally received only MF75.2 developed a moderate to high countable parasitemia. The results indicate that vaccination with SERA 1 and either Freund's or MF75.2 adjuvant provides protection and vaccination with MF75.2 alone can provide a temporary protection unrelated to the induction of anti-SERA 1 or antimalarial antibodies.

An experimental vaccine cocktail for Plasmodium falciparum malaria.

Surface proteins from several different life-cycle stages of the malaria parasite Plasmodium falciparum were expressed at high levels in the yeast Saccharomyces cerevisiae. Purified proteins, both individually and in cocktails, were used to immunize mice and goats in conjunction with either Freund's adjuvant or a muramyl tripeptide-based adjuvant. Immune responses were measured by enzyme-linked immunosorbent assays and by the ability of antisera to inhibit (1) the invasion of hepatocytes by live sporozoites, (2) in vitro invasion of human erythrocytes by live merozoites, and (3) the development of oocytes in the mosquito vector. These results suggest that cocktails of different stage-specific antigens can provide the components necessary to block the development of the malaria parasite at multiple stages of its life cycle.

Muramyl peptide adjuvants for Plasmodium falciparum and Plasmodium vivax circumsporozoite vaccines in rodent model systems.

Circumsporozoite proteins from the malaria parasites Plasmodium falciparum and Plasmodium vivax were expressed at high levels in the yeast Saccharomyces cerevisiae. Recombinant proteins varied both in length and in number of the natural amino acid repeat motifs. The proteins were purified and used to immunize mice, guinea pigs, and rabbits. Novel muramyl peptide adjuvants were used that increased the immune response as measured by ELISA assays, indirect immunofluorescence of fixed sporozoites, and the invasion of cultured liver cells by live sporozoites. These results suggest that an improved humoral response to recombinant circumsporozoite vaccines might be achieved by varying the design of the recombinant protein and by the use of novel adjuvant systems.

Protective immunity induced in Aotus monkeys by recombinant SERA proteins of Plasmodium falciparum.

We describe the vaccination of Panamanian monkeys (Aotus sp.) with two recombinant blood stage antigens that each contain a portion of the N-terminal region of the SERA (serine repeat antigen) protein of the malaria parasite Plasmodium falciparum. We immunized with either a 262-amino-acid SERA fragment (SERA I) that contains amino acids 24 to 285 of the 989-amino-acid protein or a 483-amino-acid SERA fragment (SERA N) that contains amino acids 24 to 506 as part of a fusion protein with human gamma interferon. The recombinant proteins were shown to stimulate protective immunity when administered with complete and incomplete Freund adjuvant. Four of six immunized monkeys challenged by intravenous inoculation with blood stage P. falciparum developed parasitemias that were reduced by at least 1,000-fold. Two of six immunized monkeys developed parasitemias which were comparable to the lowest parasitemia in one of four controls and were 50- to 1,000-fold lower than in the other three controls.

Immunogenicity of recombinant Plasmodium falciparum SERA proteins in rodents.

We have expressed defined regions of the serine-repeat antigen (SERA) of the Honduras-1 strain of Plasmodium falciparum in the yeast Saccharomyces cerevisiae. Amino-terminal domains of the natural SERA protein have been shown previously to be targets for parasite-inhibitory murine monoclonal antibodies. Two recombinant SERA antigens were selected for purification and immunological analysis. The first (SERA 1), corresponding to amino acids 24-285 of the natural SERA precursor, was expressed by the ubiquitin fusion method. This allowed for in vivo cleavage by endogenous yeast ubiquitin hydrolase, and subsequent isolation of the mature polypeptide. The second, larger protein (SERA N), encompassing amino acids 24-506, was expressed at only low levels using this system, but could be isolated in high yields when fused to human gamma-interferon (gamma-IFN). Each purified protein was used to immunize mice with either Freund's adjuvant or a muramyl tripeptide adjuvant that has been used in humans. Sera from immunized mice were shown to be capable of in vitro inhibition of invasion of erythrocytes by the Honduras-1 strain of P. falciparum. The results suggest that a recombinant SERA antigen may be an effective component of a candidate malaria vaccine.