The immunopathogenesis of human immunodeficiency virus infection

Plasma viremia as a sensitive indicator of the antiretroviral activity of L-697,661

L-697,661 is a non-nucleoside analogue with potent, selective inhibitory activity against the reverse transcriptase of human immunodeficiency virus type 1 (HIV-1). The present study evaluated the potential role of this compound in the treatment of HIV-1-infected patients in a double-blinded, placebo- and zidovudine-controlled trial using plasma viremia as a marker of antiviral activity and real-time phenotypic evaluation of viral isolates for the emergence of resistance. Participants received 12 weeks of either placebo, 25 mg twice a day, 100 mg three times a day, or 500 mg twice a day of L-697,661, or zidovudine, 100 mg five times a day. Mean logarithmic reciprocal titers of plasma virus in patients taking either L-697,661 or zidovudine decreased by week 4 of therapy; for L-697,661 recipients these changes were dose-dependent and, at the highest dose tested, were comparable in magnitude to those seen with zidovudine. Viral suppression induced by L-697,661 persisted through 8 weeks of treatment but decreased by week 12. This rebound paralleled emergence of viral isolates showing resistance to L-697,661. We conclude that although L-697,661 has potent antiretroviral activity in vivo, its utility may be compromised by rapid emergence of L-697,661-resistant virus. Plasma viremia is a highly sensitive technique affording considerable utility in the early testing of such agents.

Challenges in the therapy of HIV infection

Drugs that inhibit HIV replication have been shown to have clinical utility in patients with HIV infection. However, the immunological improvement induced by available anti-HIV therapies in patients with AIDS is incomplete and transient. Explanations for this may include immunological barriers to complete reconstitution, low therapeutic indices of the available drugs, and the development of viral resistance. An understanding of these processes may provide important leads for the development of improved therapy for AIDS.

Present status and future prospects for HIV therapies

Since the discovery of human immunodeficiency virus (HIV) in 1983, significant progress has been made toward the discovery, development, and licensing of anti-HIV drugs. In vitro screens against whole virus are now being complemented by screens against specific viral targets, resulting in the development of clinical candidates acting at several critical stages of the viral life cycle. Despite these advances, clinical therapy remains largely palliative. In addition, it has recently been recognized that HIV resistance to most drugs may pose even greater obstacles. Moreover, emerging data on immunopathogenesis raise the possibility that even if virus was eliminated from an infected individual, the patient's immune system might not be capable of restoration to normal function. In the face of such obstacles, deeper insights into the pathogenic mechanisms of disease, aggressive exploitation of those mechanisms for therapeutic gain, and continued commitment of both public and private sectors to support and collaborate in this research are needed.

Scientific and social issues of human immunodeficiency virus vaccine development

Development of a preventive immunogen for human immunodeficiency virus (HIV) infection is a national priority. The complexities associated with HIV host-virus interactions, coupled with the rapid progression of the HIV epidemic worldwide, have necessitated lowering expectations for an HIV vaccine that is 100 percent effective and have raised important scientific and nonscientific issues regarding development and use of preventive and therapeutic HIV vaccines.

Apoptosis and disease

The intercellular connections that characterise advanced forms of life would not be possible without a mechanism to remove individual cells that are no longer needed, or that function abnormally. Such physiological cell death, in the absence of inflammation, is achieved by apoptosis, a structurally distinct programmed cell death pathway. Defective regulation of programmed cell death may play a part in the aetiology of cancer, AIDS, autoimmune diseases, and degenerative diseases of the central nervous system. The pharmacological manipulation of apoptosis offers new possibilities for the prevention and treatment of these illnesses.

Detection of HIV-1 DNA and messenger RNA in individual cells by PCR-driven in situ hybridization and flow cytometry

Human immunodeficiency virus type-1 (HIV-1) DNA and messenger RNA sequences in both cell lines and blood obtained directly from HIV-1-infected patients were amplified by polymerase chain reaction and hybridized to fluorescein-labeled probes in situ, and the individually labeled cells were analyzed by flow cytometry. After flow cytometric analysis, heterogeneous cell populations were reproducibly resolved into HIV-1-positive and -negative distributions. Fluorescence microscopy showed that the cellular morphology was preserved and intracellular localization of amplified product DNA was maintained. Retention of nonspecific probe was not observed. Analysis of proviral DNA and viral messenger RNA in cells in the blood of HIV-1-infected patients showed that the HIV-1 genome persists in a large reservoir of latently infected cells. With the use of this technique it is now possible to detect single-copy DNA or low-abundance messenger RNA rapidly and reproducibly in a minor subpopulation of cells in suspension at single-cell resolution and to sort those cells for further characterization.

Challenges in the therapy of HIV infection

Drugs that inhibit human immunodeficiency virus (HIV) replication have been shown to have clinical utility in patients with HIV infection. However, the immunological improvement induced by available anti-HIV therapies in patients with acquired immune deficiency syndrome (AIDS) is incomplete and transient. Explanations for this may include immunological barriers to complete reconstitution, low therapeutic indices of the available drugs, and the development of viral resistance. An understanding of these processes, as discussed here by Robert Yarchoan and colleagues, may provide important leads for the development of improved therapy for AIDS.

High levels of HIV-1 in plasma during all stages of infection determined by competitive PCR

Quantitative competitive polymerase chain reaction (QC-PCR) methods were used to quantify virion-associated human immunodeficiency virus type-1 (HIV-1) RNA in plasma from 66 patients with Centers for Disease Control stage I to IVC1 infection. HIV-1 RNA, ranging from 100 to nearly 22,000,000 copies per milliliter of plasma (corresponding to 50 to 11,000,000 virions per milliliter), was readily quantified in all subjects, was significantly associated with disease stage and CD4+ T cell counts, and decreased by as much as 235-fold with resolution of primary infection or institution of antiretroviral therapy. Plasma virus levels determined by QC-PCR correlated with, but exceeded by an average of 60,000-fold, virus titers measured by endpoint dilution culture. Quantitation of HIV-1 in plasma by QC-PCR may be useful in assessing the efficacy of antiretroviral agents, especially in early stage disease when conventional viral markers are often negative.

Elevated levels of soluble CD54 (ICAM-1) in human immunodeficiency virus infection

Soluble CD54 levels in sera were quantitated in asymptomatic intravenous drug users, homosexuals, and patients with lymphadenopathy, AIDS-related complex, or acquired immunodeficiency syndrome. Soluble CD54 levels were elevated in human immunodeficiency virus (HIV)-seronegative asymptomatic intravenous drug users, reflecting infections like cytomegalovirus, Epstein-Barr virus, and hepatitis B virus. The sera of human immunodeficiency virus-seropositive groups of patients also had elevated levels of soluble CD54, reflecting infections like cytomegalovirus and human immunodeficiency virus infection.

Viruses, chemotherapy and immunity

An increasing number of antiviral agents are presently in various stages of development and testing, and an increasing number have recently been licensed for use in humans. These drugs have been used extensively to treat viral infections in immunocompromised individuals, and these studies indicate that for many antiviral agents the response to therapy is highly dependent on the integrity of the underlying host immune response. In particular, the response to zidovudine, acyclovir and ganciclovir in persons with HIV-1 infection is highly dependent upon CD4 number, which can be considered a surrogate marker for the state of host immune function in these subjects. Responses to interferons likewise can be shown to depend on the host immune response, with responses due to both direct antiviral effects of this agent as well as immunomodulatory effects mediated through interferon-induced upregulation of HLA molecule expression. The interdependence of host immunity with antiviral efficacy is underscored by the increased antiviral drug resistance in persons with advanced degrees of chronic immunosuppression, related to the higher level of viral replication and viraemia which occurs in the absence of an effective host immune response. Further definition of the precise mechanisms of these interactions should facilitate the rational design of antiviral agents and immunomodulatory therapies to improve treatment of viral infections.