Multi-step pathogenesis of AIDS--role of cytomegalovirus

The Knife's Edge of Tolerance: Inducing Stable Multilineage Mixed Chimerism but With a Significant Risk of CMV Reactivation and Disease in Rhesus Macaques

Although stable mixed-hematopoietic chimerism induces robust immune tolerance to solid organ allografts in mice, the translation of this strategy to large animal models and to patients has been challenging. We have previously shown that in MHC-matched nonhuman primates (NHPs), a busulfan plus combined belatacept and anti-CD154-based regimen could induce long-lived myeloid chimerism, but without T cell chimerism. In that setting, donor chimerism was eventually rejected, and tolerance to skin allografts was not achieved. Here, we describe an adaptation of this strategy, with the addition of low-dose total body irradiation to our conditioning regimen. This strategy has successfully induced multilineage hematopoietic chimerism in MHC-matched transplants that was stable for as long as 24 months posttransplant, the entire length of analysis. High-level T cell chimerism was achieved and associated with significant donor-specific prolongation of skin graft acceptance. However, we also observed significant infectious toxicities, prominently including cytomegalovirus (CMV) reactivation and end-organ disease in the setting of functional defects in anti-CMV T cell immunity. These results underscore the significant benefits that multilineage chimerism-induction approaches may represent to transplant patients as well as the inherent risks, and they emphasize the precision with which a clinically successful regimen will need to be formulated and then validated in NHP models.

Neuropathogenesis of chimeric simian/human immunodeficiency virus infection in pig-tailed and rhesus macaques

We recently reported that a chimeric simian/human immunodeficiency virus (SHIVKU-1) developed in our laboratory caused progressive depletion of CD4+ T lymphocytes and AIDS within 6 months of inoculation into pig-tailed macaques (M. nemestrina). None of the pig-tailed macaques showed productive SHIV infection in the central nervous system (CNS). In this report, we show that by further passage of the pathogenic virus in rhesus macaques [M. mulatta], we have derived a new strain of SHIV (SHIVKU-2) that has caused AIDS and productive CNS infection in 3 of 5 rhesus macaques infected with the virus. Productive replication of SHIV in the CNS was clearly shown by high infectivity titers and p27 protein levels in brain homogenates, and in 2 of the 3 rhesus macaques this was associated with disseminated, nodular, demyelinating lesions, including focal multinucleated giant cell reaction, largely confined to the white matter. These findings were reminiscent of HIV-1 associated neurological disease, and our immunohistochemical and in situ hybridization data indicated that the neuropathological lesions were associated with the presence of SHIV-specific viral antigens and nucleic acid respectively. However, the concomitant reactivation of opportunistic infections in these macaques suggested that such pathogens may have influenced the replication of SHIV in the CNS, or modified the neuropathological sequelae of SHIV infection in the rhesus species, but not in pig-tailed macaques. Our findings in the two species of macaques highlight the complexities of lentiviral neuropathogenesis, the precise mechanisms of which are still elusive.

Murine cytomegalovirus infection-induced polyclonal B cell activation is independent of CD4+ T cells and CD40

The results of this study demonstrate that murine cytomegalovirus (MCMV) induces polyclonal B cell activation in mice during the acute phase of primary infection. First flow cytometric analysis revealed that surface expression of CD45R, IgM, and IgK by splenocytes from MCMV-infected mice was significantly reduced with a concomitant increase in the frequency of surface IgG-expressing cells. Second, ELIspot assays demonstrated that the changes revealed by flow cytometry were paralleled by increases in the numbers of IgG-producing cells, especially those secreting IgG2a. Third, the IgG antibodies from MCMV-infected animals reacted against a variety of self and foreign antigens. MCMV-induced B cell activation was independent of CD4+ T-cell-mediated help and CD40, since activation was observed in two models of mice deficient for this T cell subset and in mice deficient for CD40. Reverse transcription-polymerase chain reaction analysis showed that mRNA transcripts for the cytokines IL-6, IL-10, and IFN-gamma were rapidly induced following infection with MCMV, but only IL-6 and IFN-gamma proteins were detectable by ELISA. In addition, the numbers of cells producing IL-6 and IFN-gamma were significantly increased in the spleen. The magnitude of the polyclonal B cell activation response was diminished by 50% in IL-6-deficient mice but not in mice lacking IFN-gamma. In the absence of IFN-gamma, surface expression and serum levels of IgG2a were reduced while IgG1 expression was increased.

Effective treatment of experimental cytomegalovirus-induced encephalo-meningitis in immunocompromised rats with HPMPC

Cytomegalovirus (CMV)-induced encephalomeningitis is a dramatic complication in patients with the acquired immunodeficiency syndrome (AIDS) and treatment of this infection remains a major clinical problem. In order to study the pathogenesis and treatment of CMV-induced encephalomeningitis, we experimentally induced intracranial rat CMV (RCMV) infection in rats that were immunosuppressed by total body X-irradiation. CMV infection was monitored by viral plaque assay for estimation of the viral load. CMV-induced pathology, the presence of CMV-infected cells, as well as the presence of T-lymphocytes and monocytes/macrophages were studied by histopathologic and immunohistochemical staining techniques. The meninges showed CMV infection in mononuclear infiltrative cells and in endothelium of small blood vessels 8 days after intracerebral inoculation. This was accompagnied by multiple haemorraghes and inflammatory cell infiltration. The infection and inflammatory response persisted for at least 21 days p.i. Animals were treated with (S)-1-(3-hydroxy-2-phosphonylmethoxypropyl)cytosine (HPMPC), 9-(1,3-dihydroxy-2-propoxymethyl)guanine (DHPG), hyperimmune serum (HIS) and both DHPG and HIS combined. Treatment with one dosage of HPMPC at 20 mg/kg effectively reduced virus titers. However, all other treatment modalities were not effective. In conclusion, the pathology of RCMV-induced encephalomeningitis in immunocompromised rats closely resembles that of AIDS patients. The infection is effectively treated by HPMPC.

Cytomegalovirus and simian immunodeficiency virus coinfection: longitudinal study of antibody responses and disease progression

Antibody titers to rhesus cytomegalovirus (RhCMV) were prospectively analyzed over a period of 68 weeks in a longitudinal serosurvey of 17 RhCMV-seropositive rhesus macaques (Macaca mulatta) experimentally coinfected with simian immunodeficiency virus (SIV). These were compared with anti-RhCMV titers in 18 animals that were also naturally infected with RhCMV but not infected with SIV. Fluctuations in anti-RhCMV antibody titers were observed within 5 weeks of SIV inoculation, and two distinct patterns of RhCMV antibody response were observed in SIV-infected animals. Animals showing a progressive decline in anti-RhCMV immunoglobulin G (IgG) exhibited the most rapid disease progression, coincident with low anti-SIV and anti-tetanus toxoid IgG responses, high levels of p27 antigen in the plasma, and short survival. Animals exhibiting a more stable CMV-specific response after SIV inoculation had the least rapid disease course. Anti-RhCMV antibody titers in SIV-uninfected animals remained relatively stable during the period of study. Evidence that preinoculation immunologic measures predicted postinoculation outcome was equivocal.

Cytotoxic T-lymphocyte responses to cytomegalovirus in normal and simian immunodeficiency virus-infected rhesus macaques

Disseminated cytomegalovirus (CMV) infection is a frequent occurrence in human immunodeficiency virus-infected humans and in simian immunodeficiency virus (SIV)-infected rhesus macaques. Rhesus macaques are a suitable animal model with which to study in vivo interactions between CMV and AIDS-associated retroviruses. Since cytotoxic T lymphocytes (CTL) play a major role in control of viral infections, we have characterized CMV-specific CTL responses in SIV-infected and uninfected rhesus macaques. Autologous fibroblasts infected with rhesus CMV were used to stimulate freshly isolated peripheral blood mononuclear cells from CMV-seropositive animals. Following in vitro stimulation, specific CTL activity against CMV-infected autologous fibroblasts was detected in CMV-seropositive but not in CMV-seronegative normal macaques. CMV-specific CTL activity comparable to that in normal animals was also detected in two CMV-seropositive macaques infected with a live attenuated SIV strain (SIVdelta3) and in two of three macaques infected with pathogenic SIV strains. The CMV-specific CTL response was class I major histocompatibility complex restricted and mediated by CD8+ cells. An early CMV protein(s) was the dominant target recognized by bulk CTL, although the pattern of CTL recognition of CMV proteins varied among animals. Analysis of CMV-specific CTL responses in macaques should serve as a valuable model for CMV immunopathogenesis and will facilitate prospective in vivo studies of immune interactions between CMV and SIV in AIDS.

Characterization of an epitope of the human cytomegalovirus protein IE1 recognized by a CD4+ T cell clone

CD4+ T cells specific for human cytomegalovirus (HCMV) IE1 protein are potential effectors of the control of HCMV infection through cytokine production. Better knowledge of major histocompatibility complex (MHC)-peptide-T cell receptor (TcR) interactions in the CD4+ T cell response should result in a better design of immunizing peptides and is a prerequisite for the development of vaccines or anti-cytomegalovirus therapy. In this study, the recombinant protein comprising residues 86-491 encoded by exon 4 of IE1 (GST-e4) was cleaved by enzymatic digestion and analyzed by high pressure liquid chromatography-mass spectroscopy (HPLC-MS). We identified the 14-residue epitope 162-DKREMWMACIKELH-175 recognized by an HLA-DR8-restricted clone, BeA3. Synthetic elongated, truncated and di-Ala-substituted peptides of the 18-mer IE1 158-IVPEDKREMWMACIKELH-175 sequence were used to analyze the amino acid motifs involved in binding to HLA-DR8 and recognition by the BeA3 clone. Substitutions which abolished (MW --> AA), or decreased (RE --> AA and MA --> AA) T cell clone proliferation, cytokine production and cytotoxicity were identified. Loss of T cell function induced by the MW --> AA substitution was associated with poor HLA-DR8 binding. Decreased T cell function (RE --> AA and MA --> AA) was associated with good HLA-DR8 binding, which suggested that these motifs were involved in TcR binding. Other substitutions induced potentiation of the T cell clone response: the IV --> AA substitution induced stronger proliferation, but equivalent cytokine production, when compared with the reference peptide IE1 (158-175). CI --> AA substitution induced strong potentiation of HLA-DR8 binding, proliferation and interferon-gamma and interleukin-4 production, possibly due to the removal of negative effects of Cys, Ile, or both side chains. Cytotoxicity was not improved by any substitution. Our results show modulation of the CD4+ T cell response according to the peptide residues involved in the HLA-DR8-peptide-TcR interaction.

Cytomegalovirus infection in human immunodeficiency virus type 1-infected children

BACKGROUND

Cytomegalovirus (CMV) is a frequent opportunistic infection in human immunodeficiency virus type 1 (HIV-1)-infected children. The interactions of CMV and HIV-1 in coinfected children are not well-characterized.

OBJECTIVE

To evaluate the prevalence of asymptomatic CMV infection and symptomatic CMV disease and to assess the influence of CMV on clinical and laboratory markers of HIV disease progression in CMV-coinfected children.

METHODS

Serial urine CMV cultures were performed on 500 children (131 HIV-1-infected (HIV+), 129 seroreverters born to HIV-infected mothers, and 240 HIV-uninfected (HIV-)). The clinical, immunologic and virologic data of 131 HIV+ children were analyzed.

RESULTS

CMV was recovered in 40 of 131 HIV+ (31%), 22 of 129 seroreverters (17%) and 30 of 240 HIV- (13%) children. Of the 40 HIV+ children with CMV coinfection, 7 developed symptomatic CMV disease (17.5%) including chorioretinitis (3), colitis (2) and pneumonitis (2). The HIV+ children with symptomatic CMV disease had significantly lower mean CD4+ T lymphocyte proportions (17% vs. 26%; age-adjusted P = 0.013) and greater HIV p24 antigen concentrations (329 pg/ml vs. 57 pg/ml; age-adjusted P = 0.13) than HIV+ children with asymptomatic CMV infection. In a subset of children coinfected with CMV before 6 months of age (n = 11), 5 (45%) developed symptomatic CMV disease, and 4 of these 5 children died within 10 months of diagnosis of CMV disease. At the time of the first positive CMV culture in these children, mean CD4+ T lymphocyte proportions did not differ according to the presence or absence of CMV-related symptoms (symptomatic CMV+, 21% vs. asymptomatic CMV = 38%; P = 0.14). In HIV+ children with symptomatic CMV disease, p24 antigen concentrations were greater than in those with asymptomatic CMV infection (461 vs. 190 pg/ml, P = 0.06).

CONCLUSIONS

Symptomatic CMV disease occurred in young CMV-coinfected children with low CD4+ lymphocytes and elevated HIV p24 antigen concentrations. Whether progressive immunodeficiency allows the emergence of CMV disease or CMV infection causes more rapidly progressive HIV-1 disease or whether there is a more complex relationship remains to be determined.

Murine cytomegalovirus with a deletion of genes spanning HindIII-J and -I displays altered cell and tissue tropism

Murine cytomegalovirus (MCMV) gene products dispensable for growth in cell culture are likely to have important functions within the infected host, influencing tissue tropism, dissemination, or immunological responses against the virus. To identify such genes, our strategy was to delete large regions of the MCMV genome likely to contain genes nonessential for virus replication in NIH 3T3 cells. Mutant virus RV7 contained a deletion of 7.7 kb spanning portions of MCMV HindIII-J and -I. This virus grew comparably to wild-type (WT) virus in NIH 3T3 fibroblasts, primary embryo fibroblasts, and bone marrow macrophages. However, RV7 failed to replicate in target organs of immunocompetent BALB/c mice and severe combined immunodeficient mice, which are exquisitely sensitive to MCMV infection. This defect in vivo growth may be related to the observation that RV7 grew poorly in the peritoneal macrophage cell line IC-21, which is highly permissive for growth of WT MCMV. Two other mutant viruses with an insertion or smaller deletion in the region common to the RV7 deletion grew comparably to WT virus in the macrophage cell line and replicated in salivary gland tissue. The poor growth of RV7 in IC-21 cells was due to a block in immediate-early gene expression, as levels of RNA from immediate-early gene IE1 were reduced eightfold compared with levels for WT virus in macrophages infected with RV7. Consequently, levels of RNA from early and late genes were also reduced. The lower expression of IE1 in RV7-infected IC-21 macrophages was not due to defective entry of virus into the cells, as equal amounts of viral DNA were present in cells 3 h after infection with RV7 or WT MCMV. These studies demonstrate that deletion of sequences in HindIII-J and -I confer altered cell and tissue tropism.

Anticytomegaloviral activity of methotrexate associated with preferential accumulation of drug by cytomegalovirus-infected cells

We extend the observation that inhibitors of pyrimidine biosynthesis are active against human cytomegalovirus by demonstrating that methotrexate (MTX) has preferential activity against cytomegalovirus replication. The 50% and 90% inhibitory concentrations of MTX for inhibition of cytomegaloviral DNA replication at 3 days postinfection in MRC-5 cells were 0.05 and 0.2 microM, respectively. No cell toxicity was observed in uninfected confluent cells at the highest concentration tested (1 microM). Under similar conditions (3 days of treatment with 0.2 microM MTX), intracellular dTTP pools were diminished in cytomegalovirus-infected cells (87% decrease relative to untreated infected cells, P < 0.001) but were not reduced in uninfected cells. A potential explanation for the preferential antiviral effect of MTX was that human cytomegalovirus-infected cells preferentially accumulated MTX. Increased intracellular accumulation and increased polyglutamation of MTX were observed in cytomegalovirus-infected cells compared with uninfected cells. Increased uptake of [3H]MTX by cytomegalovirus-infected cells was first observed at 48 h postinfection, with threefold-higher accumulation within infected cells. By 96 h, accumulation had increased to approximately fourfold in comparison with uninfected cells. The uptake of [3H]MTX was saturable and was blocked by addition of unlabelled MTX. Intracellular MTX in infected cells was almost entirely in the polyglutamated form, as demonstrated by thin-layer chromatography, whereas intracellular MTX was almost exclusively in the parent form in uninfected cells.

Modulation of cellular gene expression of HIV type 1 infection as determined by subtractive hybridization cloning: downregulation of thymosin beta 4 in vitro and in vivo

Chronic infection with HIV-1 has profound effects on host cell growth and function. We used subtractive hybridization cloning to identify genes whose expression is modulated by HIV-1 infection in the T leukemia cell line CEM. The gene encoding thymosin beta 4, a ubiquitous polypeptide associated with hematopoietic differentiation, showed two- to threefold reduced transcription in HIV-1-infected CEM cells and other HIV-1-infected T cells and macrophages in vitro. Solid-phase radioimmunoassay revealed about a threefold decrease in the level of thymosin beta 4 protein in lysates of infected cells. Northern blot analysis of RNA samples from lymphocytes of five AIDS patients reveals an up to fivefold reduction in the level of thymosin beta 4 mRNA. These results indicate that HIV-1 infection may directly influence the expression of certain physiologically important proteins.

Human immunodeficiency virus type 1 infection of the brain

Direct infection of the central nervous system by human immunodeficiency virus type 1 (HIV-1), the causative agent of AIDS, was not appreciated in the early years of the AIDS epidemic. Neurological complications associated with AIDS were largely attributed to opportunistic infections that arose as a result of the immunocompromised state of the patient and to depression. In 1985, several groups succeeded in isolating HIV-1 directly from brain tissue. Also that year, the viral genome was completely sequenced, and HIV-1 was found to belong to a neurotropic subfamily of retrovirus known as the Lentivirinae. These findings clearly indicated that direct HIV-1 infection of the central nervous system played a role in the development of AIDS-related neurological disease. This review summarizes the clinical manifestations of HIV-1 infection of the central nervous system and the related neuropathology, the tropism of HIV-1 for specific cell types both within and outside of the nervous system, the possible mechanisms by which HIV-1 damages the nervous system, and the current strategies for diagnosis and treatment of HIV-1-associated neuropathology.

Adult mouse kidneys become permissive to acute polyomavirus infection and reactivate persistent infections in response to cellular damage and regeneration

Kidneys of newborn (but not adult) mice are normally high permissive for polyomavirus (Py) infection and readily establish persistent infections. We have proposed that ongoing cellular differentiation, which occurs in newborn mice, may be necessary for a high level of in vivo Py replication (R. Rochford, J. P. Moreno, M. L. Peake, and L. P. Villarreal, J. Virol. 66:3287-3297, 1992). This cellular differentiation requirement may also be necessary for the reactivation of a persistent Py kidney infection and could provide an alternative to the accepted view that reactivation results from immunosuppression. To examine this proposal, the ability of adult BALB/c mouse kidneys to support primary acute Py infection or to reactivate previously established persistent Py infections after kidney-specific damage was investigated. Kidney damage was induced by both chemical (glycerol, cisplatin, or methotrexate) and mechanical (through renal artery clamping to produce unilateral renal ischemia) treatments. We also examined the effects of epidermal growth factor (EGF), which enhances the rate of kidney regeneration, on Py replication. Using histopathologic techniques, in situ hybridization for Py DNA, and immunofluorescence for Py VP1 production, we established that both chemical damage and damage through renal artery clamping of adult kidneys promoted high levels of primary Py replication in these normally nonpermissive cells. This damage also promoted the efficient reactivation of Py replication from persistently infected kidneys, in the absence of immunosuppression. EGF treatment significantly increased acute Py replication and also reactivation in damaged kidneys. These results support the view that ongoing cellular division and differentiation may be needed both for high levels of acute Py replication and for reactivation of persistent infections in vivo.

Role of CD8+ in late opportunistic infections of patients with AIDS

We studied the relationship of CD4+ and CD8+ depletion to initial and late opportunistic infections in 62 patients with AIDS. The mean interval between initial and late infections was 12.2 months. Geometric mean (and 95% confidence intervals) of T-cell counts at the diagnosis of each infection were: (Pneumocystis carinii pneumonia) CD4+ 0.051 (0.044-0.058) x 10(9)/l, CD8+ 0.561 (0.476-0.646) x 10(9)/l; (cytomegalovirus retinitis) CD4+ 0.025 (0.019-0.031) x 10(9)/l, CD8+ 0.333 (0.183-0.483) x 10(9)/l. Mycobacterium avium-intracellulare bacteraemia closely followed cytomegalovirus dissemination. Most patients were free from late opportunistic infections caused by disseminated cytomegalovirus and M. avium-intracellulare until CD8+ declined below 0.500 x 10(9)/l. Zidovudine improved CD4+, but less so CD8+, and similarly enhanced the survival of patients treated in 1985-1990 and 1991.

Human immunodeficiency virus type 1 antigenaemia is enhanced in patients with disseminated cytomegalovirus infection and deficient T lymphocytes

We have studied 61 patients with the acquired immunodeficiency syndrome (AIDS) regarding the relationships between disseminated cytomegalovirus (CMV) infection with CMV retinitis, HIV1 antigenaemia and CD4+ and CD8+ T-cell deficiency. HIV1 p24 antigenaemia was present in all patients with CMV retinitis (at a high concentration), but in only 28% of patients without retinitis (at a low concentration). Compared to patients without retinitis, those patients who developed retinitis had lower CD4+ and CD8+ prior to and during AIDS. CMV may contribute to deficiencies of T lymphocytes in patients with AIDS.