Persistent infection of normal mice with human immunodeficiency virus

Links between progressive HIV-1 infection of humanized mice and viral neuropathogenesis

Few rodent models of human immunodeficiency virus type one (HIV-1) infection can reflect the course of viral infection in humans. To this end, we investigated the relationships between progressive HIV-1 infection, immune compromise, and neuroinflammatory responses in NOD/scid-IL-2Rγ(c)(null) mice reconstituted with human hematopoietic CD34(+) stem cells. Human blood-borne macrophages repopulated the meninges and perivascular spaces of chimeric animals. Viral infection in lymphoid tissue led to the accelerated entry of human cells into the brain, marked neuroinflammation, and HIV-1 replication in human mononuclear phagocytes. A meningitis and less commonly an encephalitis followed cM-T807 antibody-mediated CD8(+) cell depletion. We conclude that HIV-1-infected NOD/scid-IL-2Rγ(c)(null) humanized mice can, at least in part, recapitulate lentiviral neuropathobiology. This model of neuroAIDS reflects the virological, immunological, and early disease-associated neuropathological components of human disease.

Potential relationships between the presence of HIV, macrophages, and astrogliosis in SCID mice with HIV encephalitis

The pathogenesis of HIV encephalitis (HIVE) has not been determined although increased numbers of mononuclear phagocytes (macrophages and microglia), some of which are HIV-infected, and reactive astrogliosis are important pathological findings in this condition. For this experiment, fifty-one SCID mice were inoculated intracerebrally either with human cells and HIV-1, human cells only or HIV only and then sacrificed at various time points. HIV gag mRNA was detected by reverse transcriptase polymerase chain reaction (PCR) distant from the site of inoculation in 73% of mouse brains inoculated with HIV and human cells attesting to the pervasiveness of HIV infection in SCID brain. HIV mRNA was detected as long as 91 days after inoculation of human cells and virus and the presence of HIV gag, nef, and tat/rev mRNA in HIV-infected SCID brains indicates ongoing HIV mRNA synthesis. Brain tissue sections were immunostained for HIV, human macrophages, and astrocytes from a subset of mice (n = 29) from the above groups and qualitatively assessed. PCR data for HIV mRNA was correlated with staining results and these data suggested that the greatest astrogliosis was present in mice inoculated with HIV and human cells, consistent with previously reported data. The data further suggest that astrogliosis is greater when HIV is detected. Taken together the data are consistent with a synergistic effect between macrophages and HIV in the development of astrogliosis.

Transgenic mice, carrying an expressed anti-HIV ribozyme in their genome, show no sign of phenotypic alterations

Transgenic mice are suitable model animals for testing the in vivo functionality of custom-tailored ribozymes. Transgenic experiments can demonstrate whether a ribozyme is able to cleave any RNA transcript of the host animal or not. Most probably, this kind of cleavage activity gives rise to phenotypic alterations in mice. In the present paper we demonstrate that an anti-HIV ribozyme does not cause any detectable phenotypic effect in mice carrying and expressing it. Our transgenic mice developed well and were indistinguishable from their wild type counterparts.

Use of the transgenic mouse in models of AIDS cardiomyopathy

Heart disease in AIDS, particularly cardiomyopathy (CM), is an increasingly recognized clinical problem with as yet undefined pathogenetic mechanisms. Among the potential etiologies of AIDS CM are HIV-1 infection of cardiac myocytes and subsequent cardiac dysfunction, opportunistic infection, inflammatory reactions, cytokine effects, and cardiotoxicity of prescribed or illicit drugs. It seems probable that multiple factors may impact on the development of CM in AIDS. Transgenic mice (TG) are useful biological tools to explore mechanisms of cardiac function and disease. In AIDS models, TG offer novel ways to elucidate mechanisms of AIDS CM through combined in vivo and in vitro studies. With targeted and non-targeted TG, structural and functional effects of specific HIV-1 gene products on heart tissue may be addressed. The impact of environmental agents including therapeutics or cardiotoxins may also be defined. To address the complexity of AIDS CM using TG, an experimental approach has been employed in our laboratories to model the clinical condition. We utilize AIDS TG with generalized expression of HIV-1 gene products in CM models with combined antiretroviral regimens to define the cardiovascular effects of AIDS and its therapy on the structure and function of the murine heart. We are developing a series of cardiac specific TG bearing selected HIV-1 genes. These TG target the selected HIV-1 genes expressed in cardiac ventricular myocytes. Tissue-specific targeting of this type enables us to define structural and functional effects of specific HIV-1 gene products on the cardiac myocyte.

Acute ethanol administration downregulates human immunodeficiency virus-1 glycoprotein 120-induced KC and RANTES production by murine Kupffer cells and splenocytes

Glycoprotein 120 from HIV-1, HIV-2 and SIV is known to stimulate secretion of chemokines by mononuclear cells. Thus, this work tests the hypothesis that acute ethanol intoxication suppresses HIV-1 gp120-induced chemokine production by murine Kupffer cells and splenocytes. Male Balb/c mice were given ethanol (1.70 g/Kg) by intragastric gavage in 0.1 ml volume of saline. Five minutes after ethanol administration, mice received an intravenous injection of HIV-1 gp120 (5 microg/Kg). After 24 hr, serum samples, splenocytes and Kupffer cells were obtained. Isolated cells were cultured in DMEM for 24 hr to determine production of chemokines and cytokines in vitro. Chemokines (MIP-2, KC, RANTES, MIP-1 alpha and MCP-1) and cytokines (IL-1 beta, TNF alpha, IL-10, gamma-IFN) were measured by ELISA. M-RNA abundance of these mediators was determined by RT-PCR. Results show that HIV-1 gp120 treatment was associated with significant elevations in serum KC and RANTES. No changes were observed with regard to other chemokines and cytokines. Oral administration of ethanol significantly suppressed HIV-1gp120-induced KC and RANTES release. KC and RANTES-mRNA expression and protein release by splenocytes and Kupffer cells were up-regulated by HIV-1 gp120. Such up-regulation was attenuated by ethanol treatment. These data show that acute ethanol administration attenuates HIV-1 gp120-induced chemokine release in vivo by isolated splenocytes and Kupffer cells. Through this mechanism, previous in vivo ethanol use may compromise the ability of HIV-1 gp120 to induce chemokine-mediated inhibition of HIV-1 entry into target cells.

Vaginal transmission of HIV-1 in hu-SCID mice: a new model for the evaluation of vaginal microbicides

OBJECTIVE

To develop an animal model of vaginal transmission of HIV-1 for the evaluation of vaginal microbicides.

DESIGN

Vaginal infection was performed in SCID mice reconstituted with 4 x 107 human peripheral blood lymphocytes (hu-PBL) by non-invasive vaginal administration. The hu-PBL were previously infected in vitro with a non-syncytium (NSI) strain of HIV-1 (SF162) (hu-PBL-SCID). Lymphocyte migration in vivo was examined using fluorescently labelled human lymphocytes.

METHODS

The percentage of CD4 T cells, plasma viral load and p24 antigen were evaluated using fluorescent activated cell sorting (FACS), the Amplicor HIV-1 monitor kit and enzyme-linked immunosorbent assay, respectively. Polymerase chain reaction (PCR) analysis was performed on DNA extracted from spleen and lymph nodes. For in vivo migration of labelled lymphocytes, the mice were sacrificed after 4, 24 and 48 h; vaginae and local lymph nodes were removed, snap frozen with OCT, sectioned and examined by fluorescent microscopy and FACS.

RESULTS

HIV transmission was established using virus-infected cells inoculated vaginally, as shown by FACS, HIV viral load, p24 and PCR results. Labelled cells were easily located within the vaginal tissues after 4 h. However, few or no cells could be identified after 24 or 48 h at the vaginal level, whereas labelled cells could be detected at the level of regional lymph nodes.

CONCLUSIONS

Because of its simplicity and practical features compared with other animal models, the vaginal HIV-infected hu-SCID mouse model may prove useful to test the activity of compounds against cell-associated HIV and, possibly, other sexually transmitted diseases.

U937-SCID mouse xenografts: a new model for acute in vivo HIV-1 infection suitable to test antiviral strategies

In this study we attempted to develop a new xenochimeric model for HIV infection in SCID mice, characterized by an easy engraftment of target cells, high levels of viremia and long-lasting HIV-1 infection. SCID mice were injected subcutaneously with uninfected human U937 cells and cell-free HIV-1 (IIIB strain) or HIV-1-infected human peripheral blood lymphocytes (PBL). Mice were evaluated for tumor growth, viral infection at the tumor level (DNA-polymerase chain reaction (PCR), RNA-PCR) and immunostaining for the p55/p18 HIV protein) and p24 antigenemia or serum HIV-1 RNA copies. Pretreatment of mice with antibodies to either mouse-IFN alpha/beta or granulocytes resulted in a tumor take and levels of p24 antigenemia higher than in control mice. In mice treated with these antibody preparations, there was a long-lasting HIV infection with the presence of high levels of circulating infectious virus (serum p24 values up to 4000 pg/ml and serum RNA copies up to 5 x 10(7)/ml over 3 months, with the majority of the cells expressing HIV-antigens at the tumor site). Intraperitoneal treatment of SCID mice with AZT (480 mg/kg per day) resulted in a complete inhibition of both p24 and RNA HIV-1 copies in the serum, together with a marked reduction in the number of infected cells and the levels of virus expression at the tumor site. We conclude that some specific features of this model (i.e. easy establishment, high reproducibility, well defined kinetics of virus infection, massive and long persistent viremia) underline the special advantages of its use for testing new antiviral therapies.

Long-term persistent infection of domestic rabbits by the human foamy virus

Human foamy virus (HFV) belongs to the spumaretrovirus group of the Retroviridae taxonomic family. Attempts to associate HFV or other foamy viruses to a specific pathology still remain unsuccessful. However, viral gene expression as well as tissue-specific tropism in an in vivo context remain poorly analyzed. To address this issue, we have infected domestic rabbits with a single dose of HFV and followed them at the biological and molecular levels for 5 years. No apparent pathology was detectable in the infected animals which have developed a strong immunological response against major viral proteins. We found that HFV provirus in blood cells and several organs persisted predominantly in its defective form, delta HFV, suggesting that in vivo viral persistence could be related to homologous interference as was recently shown in vitro. This animal model might be useful for studying the in vivo targets of HFV and should also be convenient for testing therapeutic effects of antiretroviral drugs.

T-cell dysfunctions in hu-PBL-SCID mice infected with human immunodeficiency virus (HIV) shortly after reconstitution: in vivo effects of HIV on highly activated human immune cells

The state of activation of the immune system may be an important factor which renders a host more receptive to human immunodeficiency virus (HIV) and more vulnerable to its effects. To explore this issue with a practical in vivo model, we developed a modified protocol of HIV infection in hu-PBL-SCID mice. First, we assessed the time course of activation of human peripheral blood lymphocytes (hu-PBL) in the peritoneal cavity of SCID mice. At 2 to 24 h after the intraperitoneal injection into SCID mice, there was a clear-cut increase in the percentage of hu-PBL expressing early activation markers (CD69), concomitant with the release of soluble intercellular adhesion molecule-1 (sICAM-1) and the soluble interleukin-2 receptor (sIL-2R) and with the accumulation of mRNAs for a number of human cytokines. At 2 weeks, virtually all of the hu-PBL expressed the memory phenotype (CD45RO) and HLA-DR antigens as well. Cells collected from the SCID mouse peritoneum at 2 and 24 h after transplantation were fully susceptible to in vitro infection with HIV type 1 (HIV-1) in the absence of either IL-2 or mitogens. The injection of HIV into hu-PBL-SCID mice at 2 h after reconstitution resulted in a generalized and productive HIV infection of the xenochimeras. This early HIV-1 infection resulted in a dramatic depletion of human CD4+ cells and in decreased levels of sICAM-1 (in the peritoneal lavage fluid) as well as of sIL-2R and immunoglobulins M and A (in the serum). Enzyme-linked immunosorbent assay and/or reverse transcriptase PCR analysis showed higher levels of IL-4, IL-5, and IL-10 in the HIV-infected animals than in control hu-PBL-SCID mice, while gamma interferon levels in the two groups were comparable. When we compared the current model of HIV-1 infection at 2 weeks after the intraperitoneal injection of the hu-PBL in the SCID mice with the model described here, we found that the majority of immune dysfunctions induced in the 2-h infection of the xenochimeras are not inducible in the 2-week infection. This supports the concept that the state of activation of human cells at the moment of the in vivo infection with HIV-1 is a crucial factor in determining the immune derangement observed in AIDS patients. These results show that some immunological dysfunctions induced by HIV infection in AIDS patients can be mimicked in this xenochimeric model. Thus, the hu-PBL-SCID mouse model may be useful in exploring, in vivo, the relevance of hu-PBL activation and differentiation in HIV-1 infection and for testing therapeutic intervention directed towards either the virus or the immune system.

Human immunodeficiency virus type 1 entry into murine cell lines and lymphocytes from transgenic mice expressing a glycoprotein 120-binding mutant mouse CD4

Human CD4, the receptor for the gp120 envelope glycoprotein of HIV-1, is the route for viral entry into CD4+ cells; other cellular factors may cooperate with CD4 to facilitate HIV-1 entry into human cells. Human CD4 expressed on murine cells does not readily mediate HIV-1 entry, which may reflect a functional incompatibility of human CD4 with murine cellular components. We postulated that a HIV-1 gp120-binding mutant murine CD4 (L3T4) possessing a minimal number of human amino acid residues could facilitate HIV-1 entry into rodent cells, unlike human CD4. This hypothesis led us to develop a series of murine L3T4 mutants that bear human CD4 gp120-binding region amino acid residues while retaining most L3T4 epitopes. HeLa cell transfectants expressing gp120-binding mutant L3T4 proteins could be infected with HIV-1. Three mouse cell lines expressing these L3T4 mutant proteins could also be infected with HIV-1 as determined by PCR techniques that detect viral DNA and spliced RNAs. Lectin-stimulated polymorphonuclear leukocytes from transgenic mice (SBL mouse) expressing a gp120-binding L3T4 mutant protein were infected with HIV-1 at the same frequency as lectin-stimulated human peripheral blood lymphocytes as determined by in situ PCR analyses. Supernatant p24gag and reverse transcriptase levels in HIV-infected mouse cell cultures, however, were routinely at background levels, unlike HIV-infected human cell cultures. Thus, gp120-binding mutant L3T4 proteins mediate viral entry in all mouse cells that were tested, but high-level viral replication is absent in these cells.

HIV type 1 intraperitoneal infection of rabbits permits early detection of serum antibodies to Gag, Pol, and Env proteins, neutralizing antibodies, and proviral DNA from peripheral blood mononuclear cells

The aim of this study is the development of an animal model useful for studying HIV-1 pathogenesis, candidate vaccines, and antiviral drugs. Aseptic thioglycolate peritonitis was induced in six rabbits. After 4 days, four rabbits were infected with 1 ml of HIV-1 stock containing 100 times the MID50. Blood samples were collected every 2 weeks for 8 months. Serum antibodies were tested by ELISA, using as antigen the recombinant protein p24; synthetic peptides of highly conserved regions of p31, gp41, and gp120; and a synthetic peptide of gp120 at the V3 loop region of HIV-1 strains IIIB and MN. Furthermore, neutralizing antibodies were tested by a microscale neutralization assay. Proviral DNA was detected by PCR, and virus isolation was performed by a cocultivation technique using primary rabbit peripheral blood mononuclear cells (PBMCs). All infected rabbits produced antibodies to HIV-1 proteins within 2 weeks and up to 8 months after virus infection. Serum antibodies were directed against the Env (gp120 and gp41), Gag (p24), and Pol (p31) proteins and against two synthetic peptides whose sequence corresponds to gp120 at the V3 loop region of HIV-1 strains IIIB and MN. Neutralizing antibodies were also detected in the sera of infected animals. Proviral DNA was detected in PBMCs by PCR within 4 weeks and up to 8 months after HIV-1 infection. HIV-1 was also isolated from PBMCs of infected animals at 30, 60, and 120 days after infection. Results obtained indicate that HIV-1 intraperitoneal infection of the rabbit permits the early detection of serum antibodies to Gag, Pol, and Env proteins, neutralizing antibodies, and proviral DNA sequences from PBMCs.

Humoral and cell-mediated immunity in rabbits immunized with live non-replicating avipox recombinants expressing the HIV-1SF2 env gene

The canarypox (CP) and fowlpox (FP) viruses, which are unable to replicate productively in non-avian species, have been utilized as live vectors carrying the HIV-1SF2 env gene with the putative immunosuppressive (IS) region complete (CPIS+ and FPIS+) or deleted (CPIS- and FPIS-). To determine if these avipox-env recombinants could be utilized to elicit a specific immune response against HIV-1, six groups of rabbits were immunized with CPIS+, CPIS-, FPIS+, FPIS- constructs or their non-engineered wild-type CPwt or FPwt counterparts. After a primary inoculation and successive boosters, env-specific humoral and cell-mediated immunity were demonstrated by ELISA, immunoblots and lymphoproliferation assays. Antibody titres and neutralization activities were higher in CP- than FP-inoculated rabbits, the CPIS+ always showing a similar immunogenic capacity to CPIS-. Evidence is also presented indicating that rabbit sera possess group-specific antibodies, which were, however, unable to cross-neutralize divergent HIV-1 strains. Although the protective capacity against HIV-1 experimental infection has not yet been determined in these animals, our results suggest that these recombinants might represent promising and safer candidate vaccines against HIV-1.

Persistent infection with SIVmac chimeric virus having tat, rev, vpu, env and nef of HIV type 1 in macaque monkeys

A chimeric human and simian immunodeficiency virus carrying the tat, rev, vpu, env, and nef genes of human immunodeficiency virus type 1 was generated. The chimeric virus, NM-3n, grew competently in peripheral blood mononuclear cells from cynomolgus monkeys like the parental SIVmac. Two cynomolgus monkeys and one rhesus monkey inoculated with NM-3n raised antibodies to SIVmac Gag and HIV-1 Env. The antibodies raised in the cynomolgus monkeys persisted for at least 1.7 years. The antibodies contained virus neutralizing activity not only to the original chimeric virus but also to the parental HIV-1. Infectious viruses were isolated from one of the cynomolgus monkeys 37 and 63 weeks after inoculation and from the rhesus monkey continuously from 6 weeks after infection onward. The recovered virus maintained its chimeric structure but included several clones with mutations in the env V3 region. When the recovered virus was inoculated to another rhesus monkey, no difference in the frequency of virus recovery was seen from the originally infected monkeys. These carrier monkeys have so far shown no sign of the disease.

Serological, biological, and molecular characterization of New Zealand white rabbits infected by intraperitoneal inoculation with cell-free human immunodeficiency virus

The availability of a small laboratory animal model suitable for the evaluation of methods for prevention and treatment of human immunodeficiency virus type 1 infection would be a valuable resource for AIDS research. Here we describe the infection of a strain of domestic rabbits by intraperitoneal inoculation with cell-free human immunodeficiency virus type 1. Evidence of infection includes the presence of an immune response that has persisted for almost 3 years and the detection of an reisolation of infectious virus from peripheral blood mononuclear cells (PBMCs) and other tissues during the first 2 years. Typical viral proteins, DNA and RNA patterns, were observed in rabbit PBMCs and in cells infected by cocultivation with rabbit PBMCs. While a number of possible pathological changes were evaluated in infected rabbits, the presence of changes in lymph node structure similar to those reported in infected humans merits further investigation.

Tissue-specific expression of human CD4 in transgenic mice

The gene for the human CD4 glycoprotein, which serves as the receptor for human immunodeficiency virus type 1, along with approximately 23 kb of sequence upstream of the translational start site, was cloned. The ability of 5' flanking sequences to direct tissue-specific expression was tested in cell culture and in transgenic mice. A 5' flanking region of 6 kb was able to direct transcription of the CD4 gene in NIH 3T3 cells but did not result in detectable expression in the murine T-cell line EL4 or in four lines of transgenic mice. A larger 5' flanking region of approximately 23 kb directed high-level CD4 transcription in the murine T-cell line EL4 and in three independent lines of transgenic mice. Human CD4 expression in all tissues analyzed was tightly correlated with murine CD4 expression; the highest levels of human CD4 RNA expression were found in the thymus and spleen, with relatively low levels detected in other tissues. Expression of human CD4 protein in peripheral blood mononuclear cells was examined by flow cytometry in these transgenic animals and found to be restricted to the murine CD4+ subset of lymphocytes. Human CD4 protein, detected with an anti-human CD4 monoclonal antibody, was present on the surface of 45 to 50% of the peripheral blood mononuclear cells from all transgenic lines.

Tissue-specific expression of human CD4 in transgenic mice

The gene for the human CD4 glycoprotein, which serves as the receptor for human immunodeficiency virus type 1, along with approximately 23 kb of sequence upstream of the translational start site, was cloned. The ability of 5' flanking sequences to direct tissue-specific expression was tested in cell culture and in transgenic mice. A 5' flanking region of 6 kb was able to direct transcription of the CD4 gene in NIH 3T3 cells but did not result in detectable expression in the murine T-cell line EL4 or in four lines of transgenic mice. A larger 5' flanking region of approximately 23 kb directed high-level CD4 transcription in the murine T-cell line EL4 and in three independent lines of transgenic mice. Human CD4 expression in all tissues analyzed was tightly correlated with murine CD4 expression; the highest levels of human CD4 RNA expression were found in the thymus and spleen, with relatively low levels detected in other tissues. Expression of human CD4 protein in peripheral blood mononuclear cells was examined by flow cytometry in these transgenic animals and found to be restricted to the murine CD4+ subset of lymphocytes. Human CD4 protein, detected with an anti-human CD4 monoclonal antibody, was present on the surface of 45 to 50% of the peripheral blood mononuclear cells from all transgenic lines.

Expression of human CD4 in transgenic mice does not confer sensitivity to human immunodeficiency virus infection

Transfection of the human CD4 molecule into mouse cells does not confer susceptibility to human immunodeficiency virus type 1 (HIV-1) infection. Expression of the human CD4 molecule in transgenic mice was seen to offer some new possibilities. However, transgenic mouse T cells expressing either the human CD4 receptor, or a hybrid human/mouse CD4 receptor alone or in conjunction with human major histocompatibility complex class I molecules, were refractory to in vitro HIV-1 infection. In addition, no infection was observed after in vivo HIV inoculation to mice of these various transgenic lines. Injection of recombinant gp160 viral protein to the transgenic mice did not alter their T and B cell populations. The existence of a dominant block in mouse cells that prevents HIV entry is discussed.

Animal models for anti-AIDS therapy

Primate and non-primate species have been used to study the pathobiology of the simian immunodeficiency virus (SIV) and of the human immunodeficiency virus type 1 (HIV-1), respectively, and to develop new therapeutic regimes. Transgenic mice which express either the entire HIV-1 provirus or subgenomic fragments have been used to analyze viral gene products in vivo and may serve as models for the development of agents targeted to select viral functions. Chimeric mice which were created by transplanting human hematolymphoid cells into mice suffering from congenital severe combined immunodeficiency (scid/scid or so called SCID mice), can be infected with HIV-1 and allow one to study the entire HIV-1 replicative cycle. Type C murine leukemia virus models have been used to develop new prophylactic and therapeutic strategies but their use is restricted to the evaluation of select antiviral drug inhibition, targeted to retroviral genes common to both Lentivirinae and Oncovirinae. The role of various animal model systems in the development of anti-HIV-1 and anti-AIDS therapies is summarized.