During this week's Fourth Conference on Human Retroviruses and Related Infections in Washington, D.C., scientists from the Laboratory of Immunoregulation (LIR) of the National Institute of Allergy and Infectious Diseases (NIAID) will present important new findings that help illuminate the HIV disease process and the complex interactions between the virus and the human immune system.
LIR investigators will make 11 poster and slide presentations during the conference, which runs from Wednesday, January 22 through Sunday, January 26.
LIR chief and NIAID director Anthony S. Fauci, M.D., comments, "At the Washington meeting, our group will discuss new data from laboratory studies and clinical trials that underscore the importance of host factors to the pathogenesis of HIV disease. Our studies of the soluble molecules which regulate HIV replication, the co-receptors on immune system cells used by the virus for fusion and entry, and other factors intrinsic to the HIV-infected individual suggest potential strategies for the treatment and prevention of HIV infection."
Below are brief summaries of the LIR presentations. Information for each is EMBARGOED UNTIL THE TIME OF PRESENTATION.
1. Critical Elements of Fusin Gene Identified
Among the most significant research findings in AIDS research to date is the discovery of co-receptors on immune system cells used by HIV for entry. The first of these HIV co-receptors to be identified was "fusin", also known as CXCR4. T-tropic strains of HIV use fusin, along with the CD4 molecule, for entry into cells.
In recent experiments, Masako Moriuchi, Ph.D., and her colleagues have cloned the promoter region of the CXCR4 gene, and identified key elements of the promotor region which begin the process in the cell of new fusin molecules being synthesized.
Because increased expression of fusin on immune system cells may facilitate HIV's replication and spread, a further understanding of the mechanisms involved in the genetic regulation of fusin expression by immune system cells may help us more precisely delineate the pathogenic processes of HIV disease," says Dr. Fauci.
Masako Moriuchi, et al. Cloning and analysis of the promoter region of CXCR4, a co-receptor for HIV-1 entry. Session 6, Abstract 20, Thursday, 11:15 a.m.
2. NK Cells Are Important Sources of Beta-Chemokines
New findings by Alessandra Oliva, M.D., and her LIR colleagues demonstrate that natural killer (NK) cells are potent producers of immune system molecules called beta-chemokines, which inhibit the replication and spread of certain strains of HIV.
Beta-chemokines include MIP-1alpha, MIP-1beta and RANTES, and inhibit infection with the strains of HIV most commonly transmitted from person-to-person, perhaps by competitively occupying or downregulating co-receptors on immune system cells used by HIV for fusion and entry.
In cell culture experiments, the researchers found that NK cells suppressed viral replication to a degree comparable to that previously observed with CD8+ T cells, another source of beta-chemokines.
"Further delineation of immune system cells and molecules involved in the regulation of HIV replication will be critical for a more comprehensive understanding of the mechanisms of HIV disease, as well as for the design of strategies for potential therapeutic manipulation of these factors," notes Dr. Fauci.
Alessandra Oliva, et al. Suppression of HIV replication by NK cell-derived beta-chemokines. Session 6, Abstract 21. Thursday, 11:30 a.m.
3. Thalidomide Ineffective in Reducing IL 2 Related Toxicities
NIAID scientists have shown that treatment with the cytokine interleukin 2 can significantly raise the CD4+ counts of HIV infected patients with baseline counts above 200 cells/mm3 of blood (see New England Journal of Medicine 1996;335:1350 56). However, IL 2 therapy also is associated with increases in serum levels of tumor necrosis factor alpha, which may account for the flu like symptoms and transient increases in viral load sometimes seen during IL 2 infusions. Blocking TNF alpha may provide a way to obviate some of the undesired effects of IL 2 therapy.
An ongoing randomized, controlled study at NIAID has assessed two TNF alpha blockers. One of them, thalidomide, proved ineffective in blocking either IL 2 related side effects or increases in TNF alpha at the maximally tolerated dose of 300 milligrams three times daily, says Robert Walker, M.D. Thalidomide is useful in other contexts, Dr. Walker notes, including as a treatment for oral aphthous ulcers frequently seen in HIV infected people.
In another arm of the study, an anti TNF monoclonal antibody has been well tolerated by IL 2 patients. Although low doses of the antibodies have had little effect on IL 2 side effects, higher doses of this treatment are now being assessed.
Robert Walker, et al. Effects of TNF alpha antagonists thalidomide and monoclonal anti TNF antibody (cA2) on reducing IL 2 associated toxicities: a randomized, controlled trial. Session 8, Abstract 36. Thursday, 10:30 a.m.
4. IL-10 Study: Transient Reduction in Viral Load Due to Altered Cytokine Environment and Co Receptor Expression
In cell culture experiments conducted over the past decade, LIR scientists have demonstrated that certain cytokines normally secreted by immune system cells, such as tumor necrosis factor alpha and interleukin 6, can boost the replication of HIV. Other cytokines such as interleukin 10 inhibit HIV replication, in part by blocking the activity of TNF alpha and IL 6.
These in vitro experiments have shown that HIV replication is regulated by a delicate balance between inductive and suppressive cytokines. Altering this balance can dramatically influence HIV replication in the test tube and perhaps, new research suggests, in the body as well.
In a phase I clinical trial at NIAID, Drew Weissman, M.D., Ph.D., and his colleagues administered a single, low dose of IL 10 to 11 HIV infected people and found that their bloodstream levels of HIV dropped by about 70 percent. Virus levels were lowest approximately 12 hours following injection, and returned to baseline about 24 hours after the IL 10 injection. The investigators noted no adverse events associated with the injection.
Two observations may help explain the transient drop in virus levels associated with IL 10 injections, the researchers suggest. First, following IL 10 injection, patients' immune system cells made considerably less of the inductive cytokines such as TNF alpha known to boost HIV replication. Second, the patients' CD4+ T cells expressed fewer of the co-receptors that are needed by HIV to bind to and enter these cells.
"Our findings fortify the concept that the body's own complex network of cytokines plays a pivotal role in determining the net rate of viral replication in an HIV infected individual," says Dr. Weissman. "It may prove possible to manipulate this network to therapeutic advantage."
Drew Weissman, et al. Interleukin-10 decreases HIV plasma viral load: results of a phase I clinical trial. Session 8, abstract 37. Thursday, 11:30 a.m.
5. IL-10, TGF-Beta Inhibit TB-Induced HIV Replication
Last year, LIR scientists demonstrated that active TB infection boosts HIV replication in HIV-infected people (see Journal of Immunology 1996;157:1271-1278). This observation helped explain why HIV-infected people with active TB have a poorer prognosis that HIV-infected people without TB. The researchers also found that the TB organism and TB-derived proteins increase HIV replication in the test tube when added to cells taken from HIV-infected patients.
New in vitro observations, to be presented by Delia Goletti, M.D., Ph.D, formerly of LIR and now working in Italy, show that TB-induced increases in HIV replication are associated with high levels of pro-inflammatory cytokines such as interleukin-1, tumor necrosis-alpha and interleukin-6.
Dr. Goletti and colleagues also have found that TB-induced increases in HIV replication can be blocked in cell culture by adding the suppressive cytokines interleukin-10 (IL-10) and transforming growth factor-beta (TGF-beta). The suppressive cytokines appear to inhibit virus replication by blocking the activity of the pro-inflammatory cytokines, as well as by diminishing proliferation and activation of HIV-infected cells. Dr. Goletti and colleagues also have found that small amounts of IL-10 and TGF-beta are induced by TB or TB-derived proteins, in addition to pro-inflammatory cytokines. When they used antibodies to block this "endogenous" IL-10 and TGF-beta in cell cultures, they observed an increase in cellular activation and consequently an elevation of HIV replication.
"The delicate balance between pro-inflammatory and anti-inflammatory cytokines plays a major role in HIV replication induced by a common pathogen such as TB," says Dr. Fauci.
Delia Goletti, et al. Exogenous and endogenous anti-inflammatory cytokines IL-10 and TGF-beta inhibit tuberculosis-induced human immunodeficiency virus (HIV) replication in CD8-depleted peripheral blood mononuclear cells from HIV-infected individuals. Session 17, Abstract 121. Thursday, 4:00 p.m.
6. Latently Infected Cells Are A Major Source of Viral Burst After Immunization
In a person infected with HIV, activation of the immune system by immunization or other stimuli results in a short-term increase in the amount of the virus in the plasma. Where does the new virus come from -- cells that are already producing virus, or cells that are latently infected?
Mario Ostrowski, M.D., and his colleagues have new data that help answer this question. They tested tissue samples from the blood and lymph nodes of an HIV-infected individual, and found that the person had two distinct "quasispecies" of HIV in his body. Although both types were found in all the samples tested, one type predominated in the plasma, the other in the peripheral blood and lymph node mononuclear cells. After the patient was given a tetanus shot, levels of virus in the plasma rose transiently 7.5-fold, reaching a peak after eight days. Now, the researchers found, the predominant virus type in the plasma was the quasispecies previously seen mostly in the blood and lymph node mononuclear cells.
"These findings, in conjunction with other work, suggest that the increase in viremia following activation of the immune system is a consequence of mobilization of latently infected CD4+ T cells in the lymphoid organs, not merely an increase in virus replication in cells that are already producing virus," says Dr. Fauci.
Mario Ostrowski, et al. Examination of HIV-1 viral quasispecies after tetanus immunization. Session 17, Abstract 118. Thursday, 4:00 p.m.
7. Compound from Dogfish Shark is Potent Inhibitor of HIV
Audrey Kinter and her LIR colleagues have found that MSI 1436, a compound isolated from the dogfish shark, can dramatically inhibit HIV replication in the test tube without disrupting CD4+ T cell proliferation and other normal cellular activities.
MSI 1436 works by blocking a process central to cellular activation the exchange of ions across the cell membrane. Previous research by LIR scientists and others has shown that cellular activation by stimuli such as opportunistic infections and immunizations boosts HIV replication. "MSI 1436 and related compounds that interfere with cellular activation events warrant further testing as possible therapies for the treatment of HIV infected individuals," says Ms. Kinter.
Audrey Kinter, et al. MSI 1436, a novel aminosterol, inhibits HIV replication in vitro and in vivo infected mononuclear cells. Session 25, Abstract 231. Thursday, 4:00 p.m.
8. Loss of CD4+ T Cell Diversity in Late-Stage Disease Not Reversed by Therapy
In a study of patients whose CD4+ T cell counts dropped from more than 500 cells/mm3 to under 50 cells/mm3, NIAID researchers found that certain types, or clones, of CD4+ T cells may be permanently lost as disease progresses.
Therapies that increase CD4+ T cell numbers, such as interleukin-2 and protease inhibitors, may boost the remaining clones, but appear to have little effect on the lost cell types.
The findings, says Dr. Fauci, "argue for early intervention before elements of the immune system are irretrievably lost. In addition, prophylaxis for opportunistic infections may remain important for patients who have rising T cell counts but may be missing part of their T-cell repertoire."
Mark Connors et al. HIV induces changes in CD4+ T cell phenotype and repertoire that are not immediately restored by antiviral or immune-based therapies. Session 39, Abstract 369. Friday, 11:00 a.m.
9. Cytokine Environment Influences HIV Phenotype
New in vitro data suggest that the presence or absence of certain cytokines influences the relative rate of replication of different strains of HIV.
Early in the course of HIV disease, the main strains of HIV found in HIV-infected people are macrophage-tropic (M-tropic) isolates. As disease progresses, T-cell line tropic (T-tropic) strains of HIV appear, coincident with the decline of the immune system. People who have mostly T-tropic strains of HIV replicating in their bodies are at considerable risk of disease progression.
M-tropic and T-tropic isolates of HIV also are known as non-syncytia-inducing (NSI) and syncytia-inducing (SI) strains, respectively, based on observed differences in their ability to cause the formation of giant cells called syncytia in cell culture. Recent studies have shown that NSI (M-tropic) strains, but not SI (T-tropic) strains are inhibited by immune system molecules called beta-chemokines.
LIR researchers JoAn Monaco, Audrey Kinter and their colleagues have developed a model system to determine whether the cytokine microenvironment of HIV-infected cell cultures can be manipulated to influence the relative replication of NSI and SI strains of HIV.
In certain individuals, they found that either an M-topic or a T-topic virus was predominant in culture regardless of the conditions of the culture. However, in certain individuals, the propagation of one or the other type of virus was dependent on the culture conditions. For example, in certain experiments they added the cytokines IL-2 and IL-4 to cells taken from HIV-infected people. They found that virus subsequently isolated from these cells could be suppressed for prolonged periods by beta-chemokines, suggesting that IL-2 and IL-4 had selected for NSI variant replication. In contrast, virus from cells treated with IL-2 and a mitogen, but not with IL-4, rapidly became insensitive to beta-chemokines, suggesting that SI variant replication had been selected.
Ongoing studies with the model system are assessing the effects of other cytokines on the relative replication of NSI and SI HIV strains.
"Understanding the conditions that regulate the replication of different strains of HIV in a person's body, including the cytokine microenvironment in lymph nodes and other organs, may provide new leads for therapeutic strategies for HIV-infected people," says Dr. Fauci.
JoAn Monaco, et al. Cytokine/chemokine-mediated regulation of in vitro predominance of SI versus NSI HIV replication in PBMC from HIV-infected subjects. Session 51, Abstract 442. Friday, 4:00 p.m.
10. Monocyte/Macrophage Resistance to T-tropic HIV Strains Due to Alterations in Fusin
Hiroyuki Moriuchi, M.D., and his colleague have provided a likely explanation for a seemingly paradoxical phenomenon: monocyte/macrophage (M/M) cells express fusin, yet generally are resistant to T-tropic strains of the virus.
Their research suggests that although M/M cells make fusin, the molecule is altered on its way to the cell surface. The modified form of fusin binds T-tropic strains of HIV poorly; hence, these viruses are unable to establish a foothold and enter the cell.
"This research confirms what made sense to us intuitively: that resistance to infection of monocyte/macrophages by T-tropic strains of HIV occurs at the level of fusion and entry," says Dr. Fauci.
Hiroyuki Moriuchi et al. Resistance to infection of promonocytic U937 subclones with T cell-tropic HIV-1 occurs at the level of fusion/entry. Session 51, Abstract 446. Friday, 4:00 p.m.
11. Dendritic Cells Have Multiple Co-Receptors for HIV Entry
Dendritic cells, the first cells infected by HIV when a person is exposed to the virus during sex, carry the virus from the site of infection to the lymph nodes and other organs, where CD4+ T cells become infected in large numbers.
Because of their importance to the initial events in HIV disease, dendritic cells have been a focus of LIR research. One important LIR project has focused on the co-receptors on dendritic cells used by HIV (in addition to the primary HIV receptor, CD4) to enter the cell.
In recent experiments, Andrea Rubbert, M.D., and her colleagues have shown that dendritic cells have multiple HIV co-receptors. Among these co-receptors are CCR3, which normally binds to an immune system molecule called eotaxin, and a previously unrecognized receptor that binds a signalling molecule called stromal cell-derived factor 1 (SDF-1). Interestingly, another known HIV co-receptor called fusin or CXCR4, which also binds SDF-1, was not found on the surface of dendritic cells.
"Further understanding of the complexity of co-receptor expression by dendritic cells will be important to understanding the pathogenesis of HIV infection, and may suggest new targets for drug and vaccine development," says Dr. Fauci.
Andrea Rubbert, et al. Dendritic cells express and use multiple co-receptors for HIV entry. Session 88, Abstract LB16. Sunday, 10:30 a.m.
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