[Expression of HIV-1 Reverse Transcriptase in Murine Cancer Cells Increases Mitochondrial Respiration].

Changes in metabolic pathways are often associated with the development of a wide range of pathologies. Increased glycolysis under conditions of sufficient tissue oxygen supply and its dissociation from the Krebs cycle, known as aerobic glycolysis or the Warburg effect, is a hallmark of many malignant neoplasms. Identification of specific metabolic shifts can characterize the metabolic programming of individual types of tumor cells, the stage of their transformation, and predict their metastatic potential. Viral infection can also alter the metabolism of cells to support the process of viral replication. Infection with human immunodeficiency virus type 1 (HIV-1) is associated with an increased incidence of various cancers, and for some viral proteins a direct oncogenic effect was demonstrated. In particular, we showed that the expression of HIV-1 reverse transcriptase (RT) in 4T1 breast adenocarcinoma cells increases the tumorigenic and metastatic potential of cells in vitro and in vivo by a mechanism associated with the ability of RT to induce reactive oxygen species in cells (ROS). The aim of this work was to study the molecular mechanism of this process, namely the effect of HIV-1 RT on the key metabolic pathways associated with tumor progression: glycolysis and mitochondrial respiration. Expression of HIV-1 RT had no effect on the glycolysis process. At the same time, it led to an increase in mitochondrial respiration and the level of ATP synthesis in the cell, while not affecting the availability of the substrates, carbon donors for the Krebs cycle, which excludes the effect of RT on the metabolic enzymes of cells. Increased mitochondrial respiration was associated with restoration of the mitochondrial network despite the RT-induced reduction in mitochondrial mass. Increased mitochondrial respiration may increase cell motility, which explains their increased tumorigenicity and metastatic potential. These data are important for understanding the pathogenesis of HIV-1 infection, including the stimulation of the formation and spread of HIV-1 associated malignancies.

Therapeutic Vaccines Against Human Papilloma Viruses: Achievements and Prospects.

Human papillomaviruses of high carcinogenic risk (HR HPVs) are major etiological agents of malignant diseases of the cervix, vulva, penis, anal canal, larynx, head, and neck. Prophylactic vaccination against HPV, which mainly covers girls and women under 25, does not prevent vertical and horizontal HPV transmission in infants and children and does not have a therapeutic effect. As a result, a significant proportion of the population is not protected from the HPV infection and development of HPV-associated neoplastic transformation and cancer, which indicates the need for development and introduction of therapeutic HPV vaccines. Unlike prophylactic vaccines aimed at the formation of virus-neutralizing antibodies, therapeutic vaccines elicit cellular immune response leading to the elimination of infected and malignant cells expressing viral proteins. The ideal targets for vaccine immunotherapy are highly conserved HR HPV oncoproteins E6 and E7 expressed in precancerous and tumor tissues. Here, we describe expression of these proteins during different stages of HPV infection, their antigenic and immunogenic properties, and T-cell epitopes, the response to which correlates with natural regression of HPV-induced neoplastic changes. The review describes patterns of E6 and E7 oncoproteins presentation to the immune system as components of candidate vaccines along with the results of the most promising preclinical trials and animal models used in these trials. Special attention is paid to vaccine candidates which have shown efficacy in clinical trials in patients with HPV-associated neoplastic changes.

Codon optimization and improved delivery/immunization regimen enhance the immune response against wild-type and drug-resistant HIV-1 reverse transcriptase, preserving its Th2-polarity.

DNA vaccines require a considerable enhancement of immunogenicity. Here, we optimized a prototype DNA vaccine against drug-resistant HIV-1 based on a weak Th2-immunogen, HIV-1 reverse transcriptase (RT). We designed expression-optimized genes encoding inactivated wild-type and drug-resistant RTs (RT-DNAs) and introduced them into mice by intradermal injections followed by electroporation. RT-DNAs were administered as single or double primes with or without cyclic-di-GMP, or as a prime followed by boost with RT-DNA mixed with a luciferase-encoding plasmid ("surrogate challenge"). Repeated primes improved cellular responses and broadened epitope specificity. Addition of cyclic-di-GMP induced a transient increase in IFN-γ production. The strongest anti-RT immune response was achieved in a prime-boost protocol with electroporation by short 100V pulses done using penetrating electrodes. The RT-specific response, dominated by CD4+ T-cells, targeted epitopes at aa 199-220 and aa 528-543. Drug-resistance mutations disrupted the epitope at aa 205-220, while the CTL epitope at aa 202-210 was not affected. Overall, multiparametric optimization of RT strengthened its Th2- performance. A rapid loss of RT/luciferase-expressing cells in the surrogate challenge experiment revealed a lytic potential of anti-RT response. Such lytic CD4+ response would be beneficial for an HIV vaccine due to its comparative insensitivity to immune escape.

Frequency of Interferon-Resistance Conferring Substitutions in Amino Acid Positions 70 and 91 of Core Protein of the Russian HCV 1b Isolates Analyzed in the T-Cell Epitopic Context.

Amino acid substitutions R70Q/H and L91M in HCV subtype 1b core protein can affect the response to interferon and are associated with the development of hepatocellular carcinoma. We found that the rate of R70Q/H in HCV 1b from Russia was 31.2%, similar to that in HCV strains from Asia (34.0%), higher than that in the European (18.0%, p = 0.0010), but lower than that in the US HCV 1b strains (62.8%, p < 0.0001). Substitution L91M was found in 80.4% of the Russian HCV 1b isolates, higher than in Asian isolates (43.8%, p < 0.0001). Thus, a significant proportion of Russian HCV 1b isolates carry the unfavorable R70Q/H and/or L91M substitution. In silico analysis of the epitopic structure of the regions of substitutions revealed that both harbor clusters of T-cell epitopes. Peptides encompassing these regions were predicted to bind to a panel of HLA class I molecules, with substitutions impairing peptide recognition by HLA I molecules of the alleles prevalent in Russia. This indicates that HCV 1b with R70Q/H and L91M substitutions may have evolved as the immune escape variants. Impairment of T-cell recognition may play a part in the negative effect of these substitutions on the response to IFN treatment.

Assessment of the Parameters of Adaptive Cell-Mediated Immunity in Naïve Common Marmosets (Callithrix jacchus).

Common marmosets are small New World primates that have been increasingly used in biomedical research. This report presents efficient protocols for assessment of the parameters of adaptive cell-mediated immunity in common marmosets, including the major subpopulations of lymphocytes and main markers of T- and B-cell maturation and activation using flow cytometry with a multicolor panel of fluorescently labelled antibodies. Blood samples from eight common marmosets were stained with fluorescently labeled monoclonal antibodies against their population markers (CD45, CD3, CD20, CD4, CD8) and lymphocyte maturation and activation markers (CD69, CD62L, CD45RO, CD107a and CD27) and analyzed by flow cytometry. Within the CD45+ population, 22.7±5.5% cells were CD3- CD20+ and 67.6±6.3% were CD3+CD20-. The CD3+ subpopulation included 55.7±5.5% CD3+CD4+CD8- and 34.3±3.7% CD3+CD4-CD8+ cells. Activation and maturation markers were expressed in the following lymphocyte proportions: CD62L on 54.0±10.7% of CD3+CD4+ cells and 74.4±12.1% of CD3+CD8+ cells; CD69 on 2.7±1.2% of CD3+CD4+ cells and 1.2±0.5% of CD3+CD8+ cells; CD45RO on 1.6±0.6% of CD3+CD4+ cells and 1.8±0.7% of CD3+CD8+ cells; CD107a on 0.7±0.5% of CD3+CD4+ cells and 0.5±0.3% of CD3+CD8+ cells; CD27 on 94.6±2.1% of CD3+ cells and 8.9±3.9% CD20+ cells. Female and male subjects differed in the percentage of CD3+CD4+CD45RO+ cells (1.9±0.5 in females vs 1.1±0.2 in males; p < 0.05). The percentage of CD20+CD27+ cells was found to highly correlate with animals' age (r = 0.923, p < 0.005). The basal parameters of adaptive cell-mediated immunity in naïve healthy marmosets without markers of systemic immune activation were obtained. These parameters and the described procedures are crucial in documenting the changes induced in common marmosets by prophylactic and therapeutic immune interventions.

Luciferase Expression Allows Bioluminescence Imaging But Imposes Limitations on the Orthotopic Mouse (4T1) Model of Breast Cancer.

Implantation of reporter-labeled tumor cells in an immunocompetent host involves a risk of their immune elimination. We have studied this effect in a mouse model of breast cancer after the orthotopic implantation of mammary gland adenocarcinoma 4T1 cells genetically labelled with luciferase (Luc). Mice were implanted with 4T1 cells and two derivative Luc-expressing clones 4T1luc2 and 4T1luc2D6 exhibiting equal in vitro growth rates. In vivo, the daughter 4T1luc2 clone exhibited nearly the same, and 4T1luc2D6, a lower growth rate than the parental cells. The metastatic potential of 4T1 variants was assessed by magnetic resonance, bioluminescent imaging, micro-computed tomography, and densitometry which detected 100-µm metastases in multiple organs and bones at the early stage of their development. After 3-4 weeks, 4T1 generated 11.4 ± 2.1, 4T1luc2D6, 4.5 ± 0.6; and 4T1luc2, <1 metastases per mouse, locations restricted to lungs and regional lymph nodes. Mice bearing Luc-expressing tumors developed IFN-γ response to the dominant CTL epitope of Luc. Induced by intradermal DNA-immunization, such response protected mice from the establishment of 4T1luc2-tumors. Our data show that natural or induced cellular response against the reporter restricts growth and metastatic activity of the reporter-labelled tumor cells. Such cells represent a powerful instrument for improving immunization technique for cancer vaccine applications.

Analysis of the Domains of Hepatitis C Virus Core and NS5A Proteins that Activate the Nrf2/ARE Cascade.

The hepatitis C virus (HCV) triggers a chronic disease that is often accompanied by a spectrum of liver pathologies and metabolic alterations. The oxidative stress that occurs in the infected cells is considered as one of the mechanisms of HCV pathogenesis. It is induced by the viral core and NS5A proteins. It is already known that both of these proteins activate the antioxidant defense system controlled by the Nrf2 transcription factor. Here, we show that this activation is mediated by domain 1 of the NS5A protein and two fragments of the core protein. In both cases, this activation is achieved through two mechanisms. One of them is mediated by reactive oxygen species (ROS) and protein kinase C, whereas the other is triggered through ROS-independent activation of casein kinase 2 and phosphoinositide 3-kinase. In the case of the HCV core, the ROS-dependent mechanism was assigned to the 37-191 a.a. fragment, while the ROS-independent mechanism was assigned to the 1-36 a.a. fragment. Such assignment of the mechanisms to different domains is the first evidence of their independence. In addition, our data revealed that intracellular localization of HCV proteins has no impact on the regulation of the antioxidant defense system.

Influence of Drug Resistance Mutations on the Activity of HIV-1 Subtypes A and B Integrases: a Comparative Study.

Integration of human immunodeficiency virus (HIV-1) DNA into the genome of an infected cell is one of the key steps in the viral replication cycle. The viral enzyme integrase (IN), which catalyzes the integration, is an attractive target for the development of new antiviral drugs. However, the HIV-1 therapy often results in the IN gene mutations inducing viral resistance to integration inhibitors. To assess the impact of drug resistance mutations on the activity of IN of HIV-1 subtype A strain FSU-A, which is dominant in Russia, variants of the consensus IN of this subtype containing the primary resistance mutations G118R and Q148K and secondary compensatory substitutions E138K and G140S were prepared and characterized. Comparative study of these enzymes with the corresponding mutants of IN of HIV-1 subtype B strains HXB-2 was performed. The mutation Q148K almost equally reduced the activity of integrases of both subtypes. Its negative effect was partially compensated by the secondary mutations E138K and G140S. Primary substitution G118R had different influence on the activity of proteins of the subtypes A and B, and the compensatory effect of the secondary substitution E138K also depended on the viral subtype. Comparison of the mutants resistance to the known strand transfer inhibitors raltegravir and elvitegravir, and a new inhibitor XZ-259 (a dihydro-1H-isoindol derivative), showed that integrases of both subtypes with the Q148K mutation were insensitive to raltegravir and elvitegravir but were effectively inhibited by XZ-259. The substitution G118R slightly reduced the efficiency of IN inhibition by raltegravir and elvitegravir and caused no resistance to XZ_259.

Fusion to the Lysosome Targeting Signal of the Invariant Chain Alters the Processing and Enhances the Immunogenicity of HIV-1 Reverse Transcriptase.

Intracellular processing of the antigen encoded by a DNA vaccine is one of the key steps in generating an immune response. Immunization with DNA constructs targeted to the endosomal-lysosomal compartments and to the MHC class II pathway can elicit a strong immune response. Herein, the weakly immunogenic reverse transcriptase of HIV-1 was fused to the minimal lysosomal targeting motif of the human MHC class II invariant chain. The motif fused to the N-terminus shifted the enzyme intracellular localization and accelerated its degradation. Degradation of the chimeric protein occurred predominantly in the lysosomal compartment. BALB/c mice immunized with the plasmid encoding the chimeric protein demonstrated an enhanced immune response, in the form of an increased antigen-specific production of Th1 cytokines, INF-γ and IL-2, by mouse splenocytes. Moreover, the majority of the splenocytes secreted both cytokines; i.e., were polyfunctional. These findings suggest that retargeting of the antigen to the lysosomes enhances the immune response to DNA vaccine candidates with low intrinsic immunogenicity.

Regulation of Immunogen Processing: Signal Sequences and Their Application for the New Generation of DNA-Vaccines.

Immunization with naked genes (DNA-immunization) is a perspective modern approach to prophylactic as well as therapeutic vaccination against pathogens, as well as cancer and allergy. A panel of DNA immunogens has been developed, some are already in the clinical trials. However, the immunogenicity of DNA vaccines, specifically of those applied to humans, needs a considerable improvement. There are several approaches to increase DNA vaccine immunogenicity. One approach implies the modifications of the encoded immunogen that change its processing and presentation, and thus the overall pattern of anti-immunogen response. For this, eukaryotic expression vectors are constructed that encode the chimeric proteins composed of the immunogen and specialized targeting or signal sequences. The review describes a number of signals that if fused to immunogen, target it into the predefined subcellular compartments. The review gives examples of their application for DNA-immunization.

[Acute hepatitis of unspecified etiology: etiological structure and clinical-laboratory characteristics].

The straight line nucleic acids detection method of viruses and wide spectrum of virus antigens immunodiagnostics in acute hepatitis of unknown etiology patients has allowed verifying the diagnosis at 19% cases (a viral hepatitis A, C or E). Results of research do not allow to consider hepatotropic viruses HGV, TTV, PV B19, EBV, CMV, HHV 1, 2, 6 and 8 type, NV-F as etiological agents at the majority of patients of investigated group, and the data of the anamnesis and a clinical and laboratory picture of a current of disease does not allow to exclude at 29.4% of patients a drug-induced hepatitis. Despite detailed molecular-biological and immunological inspection of patients, at 37.9% of acute hepatitis of unknown etiology patients it was not possible to establish a connection with hepatitis and defined etiological factor (the infectious agent).

[Role of host in spontaneous recovery from viral hepatitis C: the body's condition at the moment of infection].

The condition of the host at the moment of infection is that its immune competence largely determines the efficiency, kinetics, and profile (Thl/Th2) of a further specific immunity response and, accordingly, the outcome of penetration of hepatitis C virus (HCV) into the body and subsequent acute infection (if it occurs). The parameters determining immune competence may include age, traumatizing exposures (operations, burns, wounds, and fractures), immunosuppressive therapy, stresses, con-infections, and alcohol use. The highest rates of spontaneous convalescence from HCV infection are observed in children and adolescents. Other human conditions are much shorter, transient; their impact is difficult to determine in the retrospective review and therefore it has not been adequately studied. Previous operations, posttransplantation immune suppression, immune modulation after blood transfusion, alcohol-induced immune imbalance, drug and narcotic intoxication are poor predictors. Immunosuppression and immune imbalance caused by viral and parasitic infections are observed among the host's temporary conditions affecting the outcome of HCV infection. The authors have analyzed the sequels of superinfections in patients with chronic hepatitis C, other hepatotropic viruses and the common liver fluke Schistosoma mansoni. The interesting therapeutic activities against HCV and parasitic infection (contamination with Echinococcus granulosus in particular), which are shown in the treatment of co-infection patients with alpha-interferon preparations that ensure normalization of immune deficiency caused by each of the infections and their increased combination. A deeper insight into the correlation between the condition of the host and its ability to eliminate the virus may be one more step on the road to the prevention of the infection and to the designing an effective vaccine against HCV.

[Role of a host in spontaneous recovery from viral hepatitis C: genetic predetermined factors].

The impact of both congenital and specific human immune responses on the invasion of viruses is determined by a broad spectrum of genetically determined parameters. The review attempts to characterize the influence of genetic determinants on the outcome of human hepatitis C viral (HCV) infection. The increased rate of convalescence is associated with female sex and white ethnicity. Hereditary immune disorders/deficiency lead to the reduced probability of spontaneous convalescence and the complicated course of a chronic stage of the disease. The carriage of some HLA haplotypes and gene alleles, which determine the development of an immune response following the Th1 or Th2 type, is essential in predicting both the outcome of acute HCV infection and the course of chronic hepatitis C. Specifically, the higher elaboration of IFN-gamma and IL-12 which specify a Th1 immune response facilitates the good outcome of HCV infection. At the same time, the increased generation of Th2-orienting IL-6 and IL-10 predisposes to the chronic course of the disease. In recent studies, the outcome of the infection is also associated with the polymorphism of genes, encoding for low-density lipoproteins and complement type 1 receptors, with other genes determining the development of a congenital immune response and a specific one. The understanding of genetic predisposition of the outcome of HCV infection and the possibility of its prediction may make a considerable contribution to the definition of treatment policy for viral hepatic C.

[Artifitial increase of HIV-1 reverse transcriptase turnover through proteasome pathway].

Proteasome plays a key role in antigen presentation through MHC class I pathway. Thus, approaches are actively developed to increase proteasome targeting of DNA-vaccine encoded proteins. Gene of reverse transcriptase of HIV-1 is used in DNA-vaccines. It was shown, that revertase degraded in cells slowly (half-life is 18-20 h). Revertase content increased in presence of proteasome inhibitors MG132 and epoxomicin indicated that it degraded by proteasome. Level of protein was 2 fold higher after treatment with MG132 then after epoxomicin treatment. Since epoxomicin is more specific proteasome inhibitor it indicated that other cellular proteases can take part in revertase degradation. With the aim to increase affinity and degradation rate by proteasome of revertase we have to add strong degradation signal. Ornithine decarboxylase contains this kind of signals, it's unique properties are fast degradation by proteasome in ubiquitin-independent manner. As result fusion protein of revertase and ornithine decarboxylase was created. Half-life of fusion protein was 6 time less than revertase (3 h). Degradation of fusion protein was blocked by proteasome inhibitors 10 times stronger than revertase. Thus, degradation by proteasome pathway of reverse transcriptase was enhanced by fusion with ornithine decarboxylase. Performance of this fusion could improve presentation of revertase in DNA-vaccine.

Sequence-specific minor groove binding ligands as potential regulators of gene expression in Xenopus laevis oocytes.

The mouse mammary tumor virus (MMTV) promoter is induced by glucocorticoid hormone. A robust hormone- and receptor-dependent gene activation could be reproduced in Xenopus laevis oocytes. The homogeneous response in this system allowed a detailed analysis of the DNA-protein interactions following hormone activation. The strategy of artificial regulating of gene activity by sequence-specific minor groove binding ligands is very attractive. We have synthesized and studied the interaction with DNA of bis-linked netropsin derivatives in which two monomers are attached via short linkers in head-to-head and tail-to-tail manners. We have found that cis-diammine-platinum bridged bis-netropsin added to Xenopus oocytes media penetrates cellular and nuclear membrane and binds selectively to the MMTV promoter at the DNA segment that partly overlaps with the site recognized by glucocorticoid receptor. DNase I footprinting studies demonstrate that there are more stronger binding sites for cis-diammine-platinum bridged bis-netropsin on the naked MMTV DNA which are found to be inaccessible for its binding in oocytes.

[Immune status of patients with different outcomes of acute hepatitis C].

AIM: To ascertain parameters of immune response significant for prognosis of the disease outcome in patients with acute hepatitis C (AHC). MATERIAL AND METHODS: Seventy two examinees were divided into three groups: 30 patients of group 1 had AHC; 29 patients of group 2 had chronic hepatitis C (CHC) with the disease history 3-10 years; 13 AHC convalescents who had the disease 3-10 years ago. The control group consisted of 10 healthy subjects. The following parameters of immune status were studied: CD3+, CD4+, CD8+, CD16+, CD20+, HLA-DR+CD3+, CD95+, O-lymphocytes. RESULTS: By clinicobiochemical picture and the results of 12-month follow-up RT-PCR investigations of blood HCV RNA, AHC patients were divided into two groups: in 18 (72%) of 25 patients AHC became chronic, 7 (28%) patients achieved convalescence. The proportion and absolute number of subpopulations of lymphocytes CD8+, CD20+, CD16+ as well as CD4/CD8 in patients with AHC with different outcomes did not differ from the controls. AHC convalescents and patients with AHC transformation into chronic hepatitis had in the acute period of the disease much higher absolute number of subpopulations of the lymphocytes CD3+, CD4+, HLA-DR+CD3+ vs the controls. In patients with chronic hepatitis C with elevated levels of AlAT, 3-10 year follow-up registered significantly higher absolute amount of CD8+, CD3+, CD4+, HLA-DR+CD3+ vs the controls. Only patients with AHC which later became chronic had for 6 months of the disease significantly elevated absolute number of O-lymphocytes vs the controls. CONCLUSION: A high absolute count of O-lymphocytes in AHC patients may indicate probable development of chronic hepatitis C.

Immunogenic properties of reverse transcriptase of HIV type 1 assessed by DNA and protein immunization of rabbits.

Genetic immunization may be one way to prime individuals for a subsequent broad anti-HIV-1 immune response. Reverse transcriptase of HIV-1 (RT) presents a selective target for attempts to arrest replication of HIV-1. Rabbits immunized with a plasmid carrying the gene for reverse transcriptase HIV-1 (RT DNA) developed potent antibody and cellular responses to the gene product. The immunogenic properties of RT DNA and recombinant reverse transcriptase were compared in rabbits. The specific immune responses were similar to those reported previously for HIV-1 infected humans. The array of B and T cell epitopes recognized in RT DNA-immunized rabbits was broader than in rabbits immunized with the recombinant RT. We localized seven novel B and T cell epitopes and concordance between B cell and helper T cell epitopes was observed. B cell epitopes of RT induced proliferation of peripheral blood mononuclear cells and were active as helper T cell epitopes. T cell-proliferative responses to the epitopes of RT preceded or paralleled the production of antibodies of the same specificity. Subdomains of reverse transcriptase involved in the enzymatic activity of RT were highly immunogenic. Anti-RT IgG partially inhibited reverse transcription in vitro.

DNA-encoding enzymatically active HIV-1 reverse transcriptase, but not the inactive mutant, confers resistance to experimental HIV-1 challenge.

The present study was undertaken to examine the immunogenicity of a single plasmid DNA representing the reverse transcriptase (RT) of HIV-1. Plasmids containing the enzymatically active RT as well as a mutated nonenzymatically active RT with nucleotide (nt)-binding motifs of YMDD and YMLL, respectively, were used to immunize mice. Both constructs induced similar good antibody and T cell responses, with a tendency towards antibody directed to peptides representing the active and mutated sites. Immunized mice were challenged with a murine pseudotype HIV-1/MuLV infected spleen cells. Seven out of 10 mice immunized with RT had no recoverable HIV-1, while 10 individuals immunized with the RT mutant and all the 18 controls had high levels of recoverable HIV-1. This indicates that mutation of RT reduces the desired immunogenicity.

Eukaryotic expression of enzymatically active human immunodeficiency virus type 1 reverse transcriptase.

Reverse transcriptase of human immunodeficiency virus type I is a vitalenzyme in the HIV-1 replication cycle and an attractive target of attempts to arrest a primary viral infection. We designed a vector for eukaryotic expression of the 66 kDa subunit of reverse transcriptase under the control of the immediate early cytomegalovirus promoter. Efficient transient expression of the 66 kDa subunit of reverse transcriptase was achieved in a variety of cells. Immunostaining of the transfected cells revealed the cytoplasmatic localization of reverse transcriptase. Reverse transcriptase activity was detected in all transfected cell lines. Injection of this plasmid encoding the 66 kDa subunit of reverse transcriptase into mice resulted in strong reverse transcriptase-specific immune responses indicating that the 66 kDa subunit of reverse transcriptase is expressed in vivo. Sera from DNA-immunized mice inhibited reverse transcription in vitro.

Specificity of humoral and cellular immune response against recombinant particles of nucleocapsid protein of human hepatitis B virus in rabbits.

Nucleocapsid (core) protein of hepatitis B virus (HBcAg) induces potent cellular and humoral responses that have a clear protective potential. Rabbits were immunized by particles formed by recombinant molecules of HBcAg carrying N-terminally inserted heterologous sequences. Specificity of humoral and cellular immune response against HBcAg and selection of HBcAg epitopes was surveyed. Immunological properties of the recombinant particles were similar to those of the original HBcAg. Recombinant particles were not toxic to the peripheral blood mononuclear cells (PBMC) of non-immune or HBcAg-immunized animals ex vivo. Proliferative response of PBMC (T-lymphocytes) to HBcAg in immunized animals increased in a concentration-dependent manner in the broad interval of HBcAg concentrations (10-104 ng/ml). On the contrary, a narrow bell-shaped HBcAg dose-dependence curve was earlier observed for T-lymphocytes of donors immune to HBV after natural infection that was probably due to the cytotoxic effect of HBcAg on the expressing cells. Specificity of humoral and cellular immune response against HBcAg particles in the immunized animals and in natural infection with hepatitis B virus (HBV) was compared. Immunization with recombinant HBcAg particles induced potent anti-HBcAg antibody responses: high (up to 2.107) titers of anti-HBcAg antibodies were reached. Appearance of anti-HBcAg antibodies was in every case preceded by an increasing T-cell response to the whole protein and HBcAg-derived peptides, thus mimicking immune responses during acute HBV infection in humans. A predominant universal (haplotype-independent) T-helper cell epitope (amino acid residues (aa) 61-85 of HBcAg (p61-85)) was recognized by T-cells of all animals. Transient antibody response against p61-85 was recorded during the early stages of immunization in spite of the fact that a major B-cell epitope localized in this region is supposed to be purely conformational. A sequence representing another cluster of immunodominant T-cell epitopes of mice and HBV infected humans, aa 121-140 (p121-140), was not immunogenic on the T-cell level. However, it appeared to be a potent B-cell immunogen, despite a common assumption that HBcAg and p121-140 are not cross-reactive at the B-cell level. A possibility that anti-p121-140 antibodies were induced by an exposed region of the native particulate HBcAg and not by the denatured protein molecules, was confirmed by recognition of the particulate HBcAg by antibodies specific to synthetic peptides representing aa 120-140 of HBcAg. The data point to the exposition of aa 121-140 on the surface of the particles.