Paired chimpanzee hepatitis B virus (ChHBV) and mtDNA sequences suggest different ChHBV genetic variants are found in geographically distinct chimpanzee subspecies

The surface antigen gene region from five chronic hepatitis B virus (HBV) infected chimpanzees was amplified by PCR and the sequence determined. Sequence comparison confirmed that all of the sequences were chimpanzee hepatitis B virus (chHBV) and they appeared to represent three distinct clusters or branches. To address the question of whether the three branches represented recently identified subspecies of chimpanzees, we determined the sequence of the mitochondrial DNA hypervariable D loop from hair samples obtained from these five chimpanzees. The results indicated that the three chHBV branches reflected three distinct subspecies of chimpanzees that are from different geographic regions in West Africa. The complete HBV sequence from members of the Pan troglodytes troglodytes cluster and the Pan troglodytes verus cluster are in the published literature; we determined the complete genome sequence for the third branch of HBV present in Pan troglodytes vellerosus.

Distribution and quantification of human immunodeficiency virus type 1, strain JC499, proviral DNA in tissues from an infected chimpanzee

Data are accumulating to show that the natural history of human immunodeficiency virus type 1 (HIV-1) in chimpanzees closely reproduces that in humans and is influenced by biologic properties of the infecting HIV-1 strain. To determine the distribution and relative amounts of HIV-1, proviral DNA in multiple tissues from a chimpanzee euthanized because of an abdominal tumor and kidney failure was quantified by nested PCR limiting-dilution assays. At death, 21 months after infection with HIV-1(JC499), this animal had a CD4(+) T-cell count of 268 and 1.7 x 10(5) copies of virion RNA/ml of plasma. The highest proviral burdens were in peripheral lymph nodes and blood, followed by lung, colon, and spleen; values ranged from 130 to 3350 proviral copies/microg DNA (equivalent to DNA in 150,000 cells). The lowest levels of virus were in the spinal cord, brain, and cecum (0.3 to 2.5 copies/microg DNA), with all other tissues harboring intermediate levels (6.8 to 114 copies/microg DNA). Viral burdens in all tissues were comparable to or greater than those reported for HIV-1-infected humans in all stages of disease. Immunohistochemistry for HIV-1 p24 Gag antigen revealed (i) trapping of HIV-1 on follicular dendritic cells in lymph node germinal centers and (ii) virus in the brain, where it was localized primarily to capillary endothelial cells in the cerebral cortex. Analysis of the genetic diversity of the Env V3 loop in tissues indicated that there was no apparent compartmentalization of HIV-1 variants. Of interest, in 83 of 94 (88.3%) clones sequenced, the unique GYGR motif at the tip of the V3 loop of HIV-1(JC499) had reverted to the more common GPGR. The results support the conclusion that HIV-1 has the potential to maintain high viral burdens in chimpanzees and to disseminate to most organs, including the central nervous system. The use of the chimpanzee model with HIV-1(JC499) (or related strains) in vaccine efficacy studies should prove valuable, especially when assessing protection against disease. Furthermore, comparison of both replicative properties of HIV-1(JC499) with SIVcpz strains and immune responses of chimpanzees infected with these viruses might provide new information about HIV pathogenesis.

Therapeutic immunization of HIV-infected chimpanzees using HIV-1 plasmid antigens and interleukin-12 expressing plasmids

OBJECTIVE

To assess HIV-1 DNA vaccination and co-immunization with interleukin (IL)-12 and IL-10 as immunotherapy in the HIV-1 infected chimpanzee model system.

METHODS

Four chimpanzees that were infected with HIV-1-IIIB for longer than 4 years and remained symptom free were immunized with HIV-1 plasmid vaccines. Two chimpanzees were immunized with DNA plasmids that encoded env/rev, gag/pol along with a plasmid that encoded both chains of human IL-12. A third animal was immunized with HIV-1 DNA vaccine constructs and co-immunized with an IL-10 expressing plasmid. Finally a control animal received the HIV-1 DNA vaccine constructs alone.

RESULTS

There was no evidence of systemic toxicity associated with the administration of the DNA vaccines or the cytokine-expressing plasmids. We observed that the IL-12/HIV-1 DNA vaccinated animals had enhanced proliferative responses to multiple HIV-1 antigens at multiple time points. The animal that was co-immunized with HIV-1 and IL-10 did not have any changes in the proliferative responses. Finally, the control chimpanzee demonstrated moderate increases in the proliferative responses to HIV-1 antigens. The animal that received HIV-1 vaccines alone and the animals co-immunized with IL-12 all had declines in viral load over the course of the study, however, the decrease in viral loads were transient in all animals.

CONCLUSION

Immunization of HIV-1 infected chimpanzees with DNA based vaccines containing the env, gag and pol genes can transiently boost the env specific proliferative responses. Co-administration of IL-12 expressing plasmids further leads to transient boosting of the proliferative response to the core protein, p24 as well. However, at these doses the impact on viral load is minimal.

HIV-1 DNA vaccines and chemokines

DNA vaccines have a demonstrated ability to induce humoral and cellular immune responses in animal models and humans. The technology, although it dates back to the 1950's, has had an insurgence of interest within the past few years following concurrent research papers. The basic technology is being applied broadly to viral, bacterial and parasitic infections. It has also been demonstrated that genes delivered via plasmid expression vectors result in expression of functional proteins in the inoculated host. Further, injection of plasmids encoding cytokine, chemokine or co-stimulatory molecules, also referred to as immunomodulatory plasmids can lead to the further expansion of this technology to include directed immunology. We have been developing DNA technology specifically with a focus as a vaccine against HIV-1 infection. We report that such vaccines can stimulate immune responses in a variety of relevant animal systems including humoral and cellular responses as well as the production of beta-chemokines. We describe that the beta-chemokines can both modulate the immune response induced by DNA vaccines and be modulated by the DNA vaccines in the murine and chimpanzee models as well as in humans.

Engineering DNA vaccines via co-delivery of co-stimulatory molecule genes

DNA immunization has been investigated as a potential immunization strategy against infectious diseases and cancer. To enhance a DNA vaccine's ability to induce CTL response in vivo, we co-administered CD80 and CD86 expression cassettes along with HIV-1 immunogens. This manipulation resulted in a dramatic increase in MHC class I-restricted and CD8+ T-cell-dependent CTL responses in both mice and chimpanzees. This strategy of engineering vaccine producing cells to be more efficient T-cell activators could be an important tool for optimizing antigen-specific T-cell-mediated immune responses in the pursuit of more rationally designed vaccines and immune therapies.

Genetic immunization of chimpanzees chronically infected with the hepatitis B virus, using a recombinant retroviral vector encoding the hepatitis B virus core antigen

Cytotoxic T lymphocyte (CTL) activity and CD4+ helper T cell responses to the hepatitis B virus (HBV) core antigen (HBcAg) have been implicated in clearance of acute and chronic HBV infections. We showed that intramuscular injections of a novel recombinant retroviral vector expressing an HBcAg-neomycin phosphotransferase II (HBc-NEO) fusion protein induces HBc/eAg-specific antibodies and CD4+ and CD8+ T cell responses in mice and rhesus monkeys. We have now immunized three chronically infected chimpanzees, each with 10(10) CFU of nonreplicating retroviral vector particles expressing the HBc-NEO fusion protein. Of two immunized chimpanzees examined for CTL responses, one developed HBcAg-specific CTLs and showed marginal, transient elevations of alanine aminotransferase (ALT) levels following injection. However, both chimpanzees remained positive for serum HBeAg, negative for anti-HBe antibody by conventional assays, and displayed no change in HBV viral load throughout the study. In contrast, the third chimpanzee exhibited a traditional seroconversion evidenced by a loss of serum HBeAg and the subsequent emergence of anti-HBe antibodies within 24 weeks after the first injection. Simultaneously, two transient ALT flares and a significant decrease in the serum HBV DNA levels were noted. Despite its limitations, the present study demonstrates (1) the safety of treatment with high titers of retroviral vector in chimpanzees, (2) the capability of a retroviral vector expressing HBcAg to stimulate immune responses in HBV chronic carrier chimpanzees, and (3) that retroviral vector immunization may be therapeutically beneficial in the treatment of chronic HBV infection.

DNA vaccination as anti-human immunodeficiency virus immunotherapy in infected chimpanzees

The role of the immune response in controlling human immunodeficiency virus type 1 (HIV-1) replication is controversial. Immunotherapeutic strategies that have the ability to broaden immune responses might play a role in slowing disease progression. DNA immunization was studied as immunotherapy in infected chimpanzees. Two HIV-1-infected chimpanzees were vaccinated with DNA plasmid vaccines, one with plasmid pCMN160, which expresses the envelope glycoprotein of HIV-1MN and rev, and the other with a control plasmid. The chimpanzee immunized with pCMN160 demonstrated enhanced humoral responses. Virus load was monitored. Virus load in the chimpanzee receiving pCMN160 decreased at week 20 and has remained at background levels. The control chimpanzee was subsequently vaccinated with pCMN160. After immunization, the antibody responses increased and, as in the first animal, the virus load decreased. These results indicate the potential of the immune response to have a direct impact on HIV-1 replication in chimpanzees.

Nucleic acid immunization of chimpanzees as a prophylactic/immunotherapeutic vaccination model for HIV-1: prelude to a clinical trial

Vaccine development strategies have often utilized recombinant envelope glycoproteins which usually generate strong humoral immune responses but which do not generate strong cytotoxic T lymphocytes (CTL). A recent novel experimental vaccination approach involves the technology known as nucleic acid immunization in which DNA plasmids expressing a gene of interest is injected intramuscularly in experimental animals. These expressed proteins then are presented to the immune system with the subsequent development of strong antibody and cellular (particularly CTL) immune responses. These types of immune responses have been elicited in rodents as well as nonhuman primates including chimpanzees. Results from studies on nucleic acid immunization of HIV-1 infected chimpanzees with envelope glycoprotein expressing constructs indicated that this method was able to decrease substantially HIV-1 viral load in these chimpanzees. These data are useful for the development and implementation of human phase I clinical trials with HIV constructs expressing various genes from the HIV-1 genome.

Protection of chimpanzees from high-dose heterologous HIV-1 challenge by DNA vaccination

Novel approaches for the generation of more effective vaccines for HIV-1 are of significant importance. In this report we analyze the immunogenicity and efficacy of an HIV-1 DNA vaccine encoding env, rev and gag/pol in a chimpanzee model system. The immunized animals developed specific cellular and humoral immune responses. Animals were challenged with a heterologous chimpanzee titered stock of HIV-1 SF2 virus and followed for 48 weeks after challenge. Polymerase chain reaction coupled with reverse transcription (RT-PCR) results indicated infection in the control animal, whereas those animals vaccinated with the DNA constructs were protected from the establishment of infection. These studies serve as an important benchmark for the use of DNA vaccine technology for the production of protective immune responses.

Resistance of previously infected chimpanzees to successive challenges with a heterologous intraclade B strain of human immunodeficiency virus type 1

To test whether the protective effects of attenuated simian immunodeficiency virus vaccines in macaques were applicable to the human immunodeficiency virus type 1 (HIV-1)-chimpanzee system, two groups of animals, previously infected with HIV-1(IIIB) or HIV-1(SF2) were each challenged with a heterologous clade B virus, HIV-1(DH12). Following challenge, the parameters measured included virus isolation (from plasma, peripheral blood mononuclear cells, and lymph node tissue); quantitative DNA PCR using primers capable of distinguishing HIV-1(IIIB), HIV-1(SF2), and HIV-1(DH12) from one another; and serologic assays to monitor changes in binding and neutralizing antibodies. In contrast to an HIV-1-naive chimpanzee that rapidly became infected following the inoculation of HIV-1(DH12), the two chimpanzees previously infected with HIV-1(IIIB) resisted repeated and escalating inoculations of HIV-1(DH12), as monitored by virus isolation and PCR. The two animals previously infected with HIV-1(SF2) became infected with HIV-1(DH12) but in contrast to the case with the HIV-1-naive chimpanzee, no cell-free viral RNA was detected in the plasma by the branched DNA procedure and levels of peripheral blood mononuclear cell-associated viral DNA were reduced 35- to 50-fold.

In vivo protective anti-HIV immune responses in non-human primates through DNA immunization

An effective immune response involves the specific recognition of and elimination of an infectious organism at multiple levels. In this context DNA immunization can present functional antigenic proteins to the host for recognition by all arms of the immune system, yet provides the opportunity to delete any genes of the infectious organism which code for antigens or pieces of antigens that may have deleterious effects. Our group has developed the use of nucleic acid immunization as a possible method of vaccination against Human immunodeficiency virus type 1 (HIV-1) [1,2,3,10,11,12]. Sera from non-human primates immunized with DNA vectors that express the envelope proteins from HIV-1 contain antibodies specific to the HIV-1 envelope. These sera also neutralize HIV-1 infection in vitro and inhibit cell to cell infection in tissue culture. Analysis of cellular responses is equally encouraging. T cell proliferation as well as cytotoxic T cell lysis of relevant env expressing target cells were observed. In addition, evidence that DNA vaccines are capable of inducing a protective response against live virus was demonstrated using a chimeric SIV/HIV (SHIV) challenge in vaccinated cynomologous macaques. We found that nucleic acid vaccination induced protection from challenge in one out of four immunized cynomolgus macaques and viral load was lower in the vaccinated group of animals versus the control group of animals. These data encouraged us to analyze this vaccination technique in chimpanzees, the most closely related animal species to man. We observed the induction of both cellular and humoral immune responses with a DNA vaccine in chimpanzees. These studies demonstrate the utility of this technology to induce relevant immune responses in primates which may ultimately lead to effective vaccines.