Relationship between event rates and treatment effects in clinical site differences within multicenter trials: an example from primary Pneumocystis carinii prophylaxis

The results of multicenter clinical trials may differ across participating clinical sites. We present a diagnostic approach for evaluating this diversity that emphasizes the relationship between the observed event rates and treatment effects. We use as an example a trial of sequential strategies of Pneumocystis prophylaxis in human immunodeficiency virus infection with 842 patients randomly allocated to start prophylaxis with trimethoprim/sulfamethoxazole, dapsone, or pentamidine. Prophylaxis failure rates varied significantly across the 30 clinical sites (0-30.3%, p = 0.002 by Fisher's exact test) with prominent variability in the pentamidine arm (0-63.6%). Starting with oral regimens was better than starting with pentamidine in sites with high rates of events, whereas the three strategies had more similar efficacy in other sites. Sites enrolling fewer patients had lower event rates and had more patients who withdrew prematurely or were lost to follow-up. In a hierarchical regression model adjusting for random measurement error in the observed event rates, starting with trimethoprim/sulfamethoxazole was predicted to be increasingly better than starting with aerosolized pentamidine as the risk of prophylaxis failure increased (p = 0.01), reducing the risk of failure by 47% when the failure rate of pentamidine was 30%, whereas the two regimens were predicted to be equivalent when the failure rate was 17%. Differences in event rates could reflect a combination of heterogeneity in diagnosis, administration of treatments, and disease risk in patients across sites. The evaluation of clinical site differences with a systematic approach focusing on event rates may give further insight in the interpretation of the results of multicenter trials beyond an average treatment effect.

Experience with a cross-study endpoint review committee for AIDS clinical trials. Terry Beirn Community Programs for Clinical Research on AIDS

OBJECTIVES

To describe the methods and results of a standardized system for clinical endpoint determination for defining and reviewing endpoints in clinical trials for HIV-infected individuals.

DESIGN

A system was developed utilizing standard definitions for the 24 diagnoses or clinical events that serve as trial endpoints and together define the combined endpoint 'progression of HIV disease. A common set of case report forms were used for all trials. Thus, an event of Pneumocystis carinii pneumonia (PCP), for example, for a subject co-enrolled in an antiretroviral trial and a PCP prophylaxis trial was only reported once.

METHODS

A central committee was established to define clinical events and review endpoints across all studies. Events were classified according to established criteria for confirmed, probable and possible levels of certainty.

RESULTS

This report describes the methods used to ascertain and review endpoints, and summarized 2299 clinical events for 8097 subjects enrolled in one or more of nine clinical trials. Data on the diagnostic certainty of events and agreement between site clinicians and the endpoint committee are presented.

CONCLUSIONS

Uniform classification of endpoints across AIDS clinical trials can be accomplished by multicenter, multitrial organizations with standardized definitions and review of endpoint documentation. Our experience suggests that nurse coordinators reviewing all submitted endpoints for every trial are warranted and the need for external review by a clinical events committee may depend on the type of trial conducted.

Zidovudine treatment in patients with primary (acute) human immunodeficiency virus type 1 infection: a randomized, double-blind, placebo-controlled trial. DATRI 002 Study Group. Division of AIDS Treatment Research Initiative

A multicenter, double-blind, placebo-controlled trial randomized 28 patients with primary (acute) human immunodeficiency virus (HIV)-1 infection (PHI) to receive zidovudine, 1000 mg daily, or placebo for 24 weeks. At week 48, compared with placebo patients, zidovudine-treated patients had significantly higher CD4 cell counts (zidovudine, 666 cells/mm3; placebo, 362; P = .004) and lower peripheral blood mononuclear cell (PBMC) culture titers (zidovudine, 0.58 log infectious units per million cells; placebo, 1.68; P = .02) but no difference in plasma RNA (zidovudine, 3.93 log copies/mL; placebo, 4.00; P = .83). Serious adverse events and minor clinical events were infrequent and comparable in both arms. There were two deaths: 1 patient died of sepsis and renal disease (zidovudine arm), and 1 patient died of sepsis and tension pneumothorax (placebo arm). Six months of high-dose zidovudine initiated during PHI results in higher CD4 cell counts and lower PBMC culture titers but no difference in plasma HIV-1 RNA. Further studies with more potent antiretroviral combination therapies are warranted.

Evolutionary pattern of human immunodeficiency virus (HIV) replication and distribution in lymph nodes following primary infection: implications for antiviral therapy

Evolutionary patterns of virus replication and distribution in lymphoid tissue during the early phases of HIV infection have not been delineated. Lymph node (LN) biopsies were excised from patients at different times after the estimated time of primary infection. Within 3 months of the acute viral syndrome, HIV was mostly present in individual virus-expressing cells in LNs; trapping of virions in the follicular dendritic cell (FDC) network was minimal or absent, but was the predominant form of HIV detected in LNs of subjects with chronic infection, either recent (4-20 months after primary infection) or long-term (>2-3 years after primary infection). Plasma viremia was significantly higher in patients during the first 3 months than in those recently infected; however, there were no significant differences in the number of virus-expressing cells per square millimeter of LN tissue in these two groups. Numbers of virus-expressing cells in lymphoid tissue were significantly lower in the subjects with long-term infection than in the other two groups. Therefore, during the transition from primary to chronic HIV infection, the level of HIV replication in lymphoid tissue remains elevated despite the fact that viremia is significantly downregulated. These findings have implications for therapeutic strategies in primary HIV infection and in recent seroconvertors.

Preliminary evidence for partial restoration of immune function in HIV type 1 infection with potent antiretroviral therapies: clues from the Fourth Conference on Retroviruses and Opportunistic Diseases

Critical advances in understanding the pathogenesis and treatment of HIV-1 infection have been made. These include the following: delineation of the replication kinetics of HIV in all stages of disease, underscoring the role of viral replication in disease pathogenesis; development of highly sensitive quantitative assays to determine viral load in infected individuals; and potent new antiretroviral drugs, the availability of which has provided a tool for the investigation of viral pathogenesis and immunopathogenesis, and has permitted the demonstration of the clinical efficacy of combination therapies. The results of studies of potent antiretroviral combination therapies presented at the Fourth Conference on Retroviruses and Opportunistic Infections (January 22-26, 1997, Washington, D.C.) demonstrate that such therapies are capable of at least partially restoring the immune system that is damaged by infection with HIV-1. This includes evidence for the ability of potent therapies to begin to reverse the abnormalities of maturation, activation, and function that are attributable directly or indirectly to the CD4+ helper T lymphocyte population.

A phase I study of interferon-alpha 2b in combination with interleukin-2 in patients with human immunodeficiency virus infection

Interferon-alpha (IFN-alpha) can inhibit human immunodeficiency virus (HIV-1) replication and is effective in treating Kaposi's sarcoma; interleukin-2 (IL-2) can increase circulating lymphocytes in HIV-1-infected patients. The safety of combination treatment with recombinant (r)IFN-alpha 2b and IL-2 was evaluated in HIV-1-infected patients with > 200 CD4+ T cells/mm3. A maximal tolerated dose of rIFN-alpha 2b was determined for 17 patients; then they received in combination 3, 6, or 12 x 10(6) IU/day rIL-2, given intravenously over 21 days. Twelve patients ultimately received the combination, 9 for the full 21 days. Significant toxicities included flu-like symptoms, anemia, transaminemia, and depression. Transient increases in CD4+ T cell percentages and spontaneous lymphocyte blast transformation were observed. Quantitative microcultures demonstrate a decline in HIV titers in patients receiving rIFN-alpha 2b (5/9) with a further decline on addition of rIL-2 (7/9). In summary, continuous rIL-2 at 6 x 10(6) IU/day in combination with rIFN-alpha 2b was reasonably tolerated and provided preliminary evidence of immunomodulatory and antiviral activity.

CD8+ cytolytic T lymphocytes become infected in vitro in the process of killing HIV-1-infected target cells

In the present study the requirements for in vitro infection of antigen-specific CD8+ cytotoxic T lymphocytes (CTL) with human immunodeficiency virus -1(HIV-1) were investigated. CD3+CD8+CD4- HIV-1 nef-specific CTL become infected with HIV-1 after short-term co-culture with HLA-matched HIV-1-infected CD20+ B lymphoblastoid cells (B-LCL) which are specifically killed. Similar results were observed with an allospecific CD8+ CTL population. In addition, co-culture experiments showed that once infected with HIV-1, these CD8+ CTL could spread the infection further to uninfected CD4+ lymphocytes. In contrast, CD8+ CTL did not become infected with HIV-1 when co-cultured with HLA-mismatched HIV-1-infected B-LCL which are not killed. These observations in vitro could have relevance in peripheral lymphoid organs contributing to the progressive decrease of HIV-specific CD8+ CTL activity that is associated with the progression to AIDS.

Primary human immunodeficiency virus type 1 infection: review of pathogenesis and early treatment intervention in humans and animal retrovirus infections

Primary human immunodeficiency virus type 1 (HIV-1) infection can present clinically as the abrupt onset of a febrile illness resembling acute mononucleosis. The symptoms coincide with high titers of culturable plasma viremia, cell-associated virus, and antigenemia, which rapidly decrease coincident with the emergence of detectable HIV-specific antibody and HIV-specific cytotoxic T lymphocytes. This article reviews the human and animal model data on the virologic and immunologic events that occur during primary HIV-1 and animal retrovirus infections, evaluates the prophylactic treatment experience of retrovirus infections in the animal model, and provides a plausible rationale for treatment intervention of primary HIV-1 infection in humans. Recent work delineating the pathogenesis of primary HIV-1 infection provides insight into the major mechanisms of viral dissemination and host immune response. The results from retrovirus-infected animal models treated with antiviral agents suggests that therapy at the time of viral dissemination may be an effective strategy that may modify disease progression. Clinical trials to evaluate this approach are in progress.

Treatment research priorities for human immunodeficiency virus infection

Viral infections such as with the human immunodeficiency virus (HIV) present difficult challenges for the development of effective antiviral therapies. These viruses depend on the host cell machinery for their existence, and interference with these processes typically interferes with other important host physiology. HIV presents other challenges as well because of its inherent pathogenic destruction of the immune system. It is the goal of HIV therapeutics to attempt to cure HIV infection, or if that is not possible, to stop HIV disease progression while preserving a high quality of life for HIV-infected individuals. This may be achieved through an effective combination of interference with the viral life cycle and the pathogenic processes, and by slowing or reversing the immunologic dysfunction that leads to the complications of HIV infection. Unprecedented progress has been made in understanding the virus and HIV disease pathogenesis. This knowledge has led to the identification of viral features that have become targets for therapeutic intervention. This article reviews the most important priorities of HIV treatment research for adult HIV-infected patients for the immediate future. These priorities include the following: development of new antiretroviral compounds and their application as both monotherapies and in combination therapy approaches; immune-based therapeutic approaches; and research and treatment for acute or primary HIV infections.

Immune-based therapeutics: scientific rationale and the promising approaches to the treatment of the human immunodeficiency virus-infected individual

The primary approach to therapy for infection with human immunodeficiency virus (HIV) continues to be centered around antiretroviral agents that have conferred significant clinical benefits. The considerable degree of immunologic dysfunction in HIV infection, however, has led to intense interest in methods of immune stimulation and reconstitution. Immunomodulatory intervention in HIV infection is highly controversial. Over the years a number of immunomodulatory agents--many with only a poor rationale for their clinical use--have been evaluated. In this review we concentrate on immunomodulatory approaches that are currently being investigated. We group these interventions, reviewing the rationale and clinical data for each category: passive immunity (administration of immunoglobulins and use of apheresis), thymic hormone treatment, cytokine treatment (administration of interleukins, tumor necrosis factor, and interferons), adoptive cellular immunity, and therapeutic vaccination. At present, the only interventions supported by data from well-controlled studies are the parenteral administration of interferon alpha to patients with HIV-associated Kaposi's sarcoma and the administration of pooled immunoglobulin (to decrease the rate of bacterial infections) to children who cannot take trimethoprim-sulfamethoxazole. However, several other approaches under development show promise in reversing some of the immune deficits of HIV infection. Clinical evaluation of these approaches should yield valuable insights into the immunopathogenesis of HIV infection, and these insights should facilitate the formulation of new modalities of treatment.

Summary of the National Institutes of Health workshop on primary human immunodeficiency virus type 1 infection

A Workshop on primary human immunodeficiency virus type 1 (HIV-1) infection sponsored by the National Institute of Allergy and Infectious Diseases (NIAID) and the Office of AIDS Research (OAR) of the National Institutes of Health (NIH) was held February 25-26, 1993 in Bethesda, Maryland. The major goals of this scientific meeting were to bring together researchers and infectious disease specialists who have expertise in primary HIV-1 infection (PHI) to review the pathogenesis of PHI, the treatment experience of PHI in humans and of early retroviral infection in animal models, and to devise theoretical and operational strategies for future clinical trials relating to therapeutic intervention of PHI. The proceedings of this workshop are timely and serve to further the development of innovative strategies for the treatment of HIV-1 infection.

CD34+ bone marrow cells are infected with HIV in a subset of seropositive individuals

Individuals infected with HIV frequently develop cytopenias and suppressed hematopoiesis. The role of direct HIV infection of hematopoietic progenitor cells in this process has not been defined. In this study, purified CD34+ bone marrow progenitor cells from 74 Zairian and American patients were studied by both coculture viral isolation and polymerase chain reaction for evidence of HIV infection. A total of 36.5% of Zairian and 14% of American patients had HIV infection of the CD34+ cell subset, with as many as 1 in 500 CD34+ cells infected. Most of the Zairian patients in this study had advanced HIV infection and markedly decreased CD4/CD8 T lymphocyte ratios (mean 0.160 +/- 0.08), and no laboratory value predicted the presence of infection in the CD34+ subset of a given Zairian individual. In contrast, American patients with CD34+ cell infection had total CD4 cells less than 20/mm3 and a greater decrease of the CD4/CD8 T lymphocyte ratio compared to seropositive Americans without CD34+ cell infection (p = 0.003). Hematopoiesis, studied by methylcellulose colony assays, was depressed in all seropositive patients studied with no significant further suppression when CD34+ cells were infected. Thus, CD34+ bone marrow progenitor cells are infected in vivo in a subset of seropositive individuals and may serve as an additional reservoir of virus in HIV-infected individuals.

CD34+ bone marrow cells are infected with HIV in a subset of seropositive individuals

Individuals infected with HIV frequently develop cytopenias and suppressed hematopoiesis. The role of direct HIV infection of hematopoietic progenitor cells in this process has not been defined. In this study, purified CD34+ bone marrow progenitor cells from 74 Zairian and American patients were studied by both coculture viral isolation and polymerase chain reaction for evidence of HIV infection. A total of 36.5% of Zairian and 14% of American patients had HIV infection of the CD34+ cell subset, with as many as 1 in 500 CD34+ cells infected. Most of the Zairian patients in this study had advanced HIV infection and markedly decreased CD4/CD8 T lymphocyte ratios (mean 0.160 +/- 0.08), and no laboratory value predicted the presence of infection in the CD34+ subset of a given Zairian individual. In contrast, American patients with CD34+ cell infection had total CD4 cells less than 20/mm3 and a greater decrease of the CD4/CD8 T lymphocyte ratio compared to seropositive Americans without CD34+ cell infection (p = 0.003). Hematopoiesis, studied by methylcellulose colony assays, was depressed in all seropositive patients studied with no significant further suppression when CD34+ cells were infected. Thus, CD34+ bone marrow progenitor cells are infected in vivo in a subset of seropositive individuals and may serve as an additional reservoir of virus in HIV-infected individuals.

Emergence of unusual opportunistic pathogens in AIDS: a review

Opportunistic infections are a major cause of morbidity and death among patients infected with the human immunodeficiency virus (HIV), particularly late in the disease, when immunosuppression is severe. Some pathogens, such as Pneumocystis carinii and Toxoplasma gondii, are extremely common in this population and are readily recognized by clinicians caring for these patients. However, many other organisms occasionally cause conditions that clinically mimic the more commonly encountered pathogens. Clinicians must be alert to the threat posed by these less frequently occurring organisms and of the broader differential diagnosis that must be considered for infections in patients with HIV infection.

Lymphoid organs function as major reservoirs for human immunodeficiency virus

The total number of human immunodeficiency virus type 1 (HIV-1)-infected circulating CD4+ T lymphocytes is considered to be a reflection of the HIV burden at any given time during the course of HIV infection. However, the low frequency of HIV-infected circulating CD4+ T lymphocytes and the low level or absence of plasma viremia in the early stages of infection do not correlate with the progressive immune dysfunction characteristic of HIV infection. In this study, we have determined whether HIV-infected circulating CD4+ T lymphocytes are a correct reflection of the total pool of HIV-infected CD4+ T cells (i.e., HIV burden). To this end, HIV burden has been comparatively analyzed in peripheral blood and lymphoid tissues (lymph nodes, adenoids, and tonsils) from the same patients. The presence of HIV-1 DNA in mononuclear cells isolated simultaneously from peripheral blood and lymphoid tissues of the same patients was determined by polymerase chain reaction amplification. We found that the frequency of HIV-1-infected cells in unfractionated or sorted CD4+ cell populations isolated from lymphoid tissues was significantly higher (0.5-1 log10 unit) than the frequency in peripheral blood. Comparable results were obtained in five HIV seropositive patients in the early stages of disease and in one patient with AIDS. These results demonstrate that a heavy viral load does reside in the lymphoid organs, indicating that they may function as major reservoirs for HIV. In addition, the finding of a heavy viral load in the lymphoid organs of patients in the early stages of disease may explain the progressive depletion of CD4+ T lymphocytes and the immune dysfunction associated with the early stages of HIV infection.

Thymic microenvironment induces HIV expression. Physiologic secretion of IL-6 by thymic epithelial cells up-regulates virus expression in chronically infected cells

The hallmark of infection with HIV-1 is progressive depletion and qualitative dysfunction of the CD4+ Th cell population in infected individuals. Clinical trials of antiretroviral agents have shown that, despite suppression of virus replication, regeneration of the T cell pool does not occur. One proposed explanation for the defective regenerative capacity of the CD4+ T cell pool is infection of early T lymphocyte progenitors or stem cells. An additional explanation could be failure of cells of the intrathymic microenvironment (thymic epithelial (TE) cells) to carry out critical nurturing functions for developing thymocytes, i.e., secretion of thymocyte-trophic cytokines and expression of adhesion molecules. This study examines the effect of HIV on cultured TE cells and determines the role of TE cells in the regulation of viral expression in chronically HIV-infected cells. We found no evidence of infection of TE cells after exposure to HIV-1. However, normal human serum induced secretion of IL-6 by TE cells; induction of TE IL-6 was partially blocked by anti-IFN-gamma antibodies. Moreover, supernatants from TE cells maintained in normal human serum up-regulated HIV replication in chronically HIV-1-infected cells. Because intrathymic T cell precursors can be infected with HIV and T cell precursors come into close contact with TE cells in the thymus, IL-6 secreted by TE cells during normal intrathymic development may induce HIV expression in infected thymocytes in vivo and promote the intrathymic spread of HIV.

Thymic microenvironment induces HIV expression. Physiologic secretion of IL-6 by thymic epithelial cells up-regulates virus expression in chronically infected cells

The hallmark of infection with HIV-1 is progressive depletion and qualitative dysfunction of the CD4+ Th cell population in infected individuals. Clinical trials of antiretroviral agents have shown that, despite suppression of virus replication, regeneration of the T cell pool does not occur. One proposed explanation for the defective regenerative capacity of the CD4+ T cell pool is infection of early T lymphocyte progenitors or stem cells. An additional explanation could be failure of cells of the intrathymic microenvironment (thymic epithelial (TE) cells) to carry out critical nurturing functions for developing thymocytes, i.e., secretion of thymocyte-trophic cytokines and expression of adhesion molecules. This study examines the effect of HIV on cultured TE cells and determines the role of TE cells in the regulation of viral expression in chronically HIV-infected cells. We found no evidence of infection of TE cells after exposure to HIV-1. However, normal human serum induced secretion of IL-6 by TE cells; induction of TE IL-6 was partially blocked by anti-IFN-gamma antibodies. Moreover, supernatants from TE cells maintained in normal human serum up-regulated HIV replication in chronically HIV-1-infected cells. Because intrathymic T cell precursors can be infected with HIV and T cell precursors come into close contact with TE cells in the thymus, IL-6 secreted by TE cells during normal intrathymic development may induce HIV expression in infected thymocytes in vivo and promote the intrathymic spread of HIV.

Epidermal Langerhans cells are not principal reservoirs of virus in HIV disease

Several reports implicate Langerhans cells of skin as susceptible targets, reservoirs, and vectors for transmission of HIV: 1) numbers of Langerhans cells in skin of HIV-infected patients were decreased about 50% of that in control skin; 2) as many as 30% of Langerhans cells in the skin of HIV-infected patients were morphologically abnormal; 3) viral particles typical for HIV were identified in or around 2 to 5% of these cells; and 4) infectious HIV was isolated from skin biopsies of infected patients. These results were consistent with similar observations of HIV-infected macrophages in such tissues as brain, lung, and lymph node. Despite these findings, other investigators find no evidence for virus infection in the epidermis of HIV-infected patients by any of several immunohistochemical or ultrastructural criteria. To address this controversy, we obtained skin from 28 HIV-seropositive subjects at various clinical stages by full thickness biopsy or suction blister. Samples were analyzed by transmission electron microscopy for presence of HIV virions, by immunofluorescent staining for viral proteins, by in situ hybridization for HIV-specific mRNA, by polymerase chain reaction amplification of virus-specific DNA, and by direct virus isolation by coculture of epidermis onto monocyte target cells. By any of these techniques, demonstration of HIV in the epidermis of infected patients was equivocal and even then, infrequent. In contrast, viral DNA was detected from the dermis of the same skin samples (26 of 28 samples). Moreover, the number and morphology of Langerhans cells in skin of infected patients were within normal limits, regardless of stage of disease. These studies in toto suggest that a role for Langerhans cells as a principal viral reservoir or vector of transmission is highly unlikely.

Epidermal Langerhans cells are not principal reservoirs of virus in HIV disease

Several reports implicate Langerhans cells of skin as susceptible targets, reservoirs, and vectors for transmission of HIV: 1) numbers of Langerhans cells in skin of HIV-infected patients were decreased about 50% of that in control skin; 2) as many as 30% of Langerhans cells in the skin of HIV-infected patients were morphologically abnormal; 3) viral particles typical for HIV were identified in or around 2 to 5% of these cells; and 4) infectious HIV was isolated from skin biopsies of infected patients. These results were consistent with similar observations of HIV-infected macrophages in such tissues as brain, lung, and lymph node. Despite these findings, other investigators find no evidence for virus infection in the epidermis of HIV-infected patients by any of several immunohistochemical or ultrastructural criteria. To address this controversy, we obtained skin from 28 HIV-seropositive subjects at various clinical stages by full thickness biopsy or suction blister. Samples were analyzed by transmission electron microscopy for presence of HIV virions, by immunofluorescent staining for viral proteins, by in situ hybridization for HIV-specific mRNA, by polymerase chain reaction amplification of virus-specific DNA, and by direct virus isolation by coculture of epidermis onto monocyte target cells. By any of these techniques, demonstration of HIV in the epidermis of infected patients was equivocal and even then, infrequent. In contrast, viral DNA was detected from the dermis of the same skin samples (26 of 28 samples). Moreover, the number and morphology of Langerhans cells in skin of infected patients were within normal limits, regardless of stage of disease. These studies in toto suggest that a role for Langerhans cells as a principal viral reservoir or vector of transmission is highly unlikely.

NIH conference. Immunopathogenic mechanisms in human immunodeficiency virus (HIV) infection

An understanding of the immunopathogenic mechanisms of infection with human immunodeficiency virus (HIV) is fundamental in developing successful approaches to designing effective therapeutic and vaccine strategies. In this regard, we have investigated the mechanisms by which HIV inserts itself into the human immune system and uses the elaborate cytokine network to its own replicative advantage. We have also shown that the burden of HIV in CD4+ T cells is directly associated with a decline in this cell population in vivo and a progression to disease. Mononuclear phagocytes may play a role in the pathogenesis of HIV infection by serving as reservoirs of the virus. Of note is the fact that monocytes in the peripheral blood of HIV-infected individuals are rarely infected in vivo, whereas infected-tissue macrophages may play a role in organ-specific HIV-related pathogenesis. The role of HIV-specific humoral and cell-mediated immunity in HIV infection is not well understood. However, fine specificity of responses against HIV have been delineated in some in-vitro systems. It is unclear why these responses, particularly HIV-specific cytolytic T-cell responses, diminish over the course of infection and are unable to contain progression of infection.

Infection of CD8+ T lymphocytes with HIV. Requirement for interaction with infected CD4+ cells and induction of infectious virus from chronically infected CD8+ cells

In this study, we have investigated the basic requirements for HIV-1 infection of CD8+ lymphocytes in vitro. Unfractionated PBL obtained from healthy HIV-1 seronegative donors were activated with PHA and infected in vitro with HIV-1LAV. Based on immunofluorescent labeling, the vast majority of cells (85 to 97%) surviving peak virus replication belonged to the CD8+ subset and only a small percentage (0.5 to 1.5%) were CD4+. Amplification of HIV-1 proviral sequences by polymerase chain reaction performed on the sorted surviving CD8+ cells demonstrated that CD8+ cells harbored HIV-1 proviral DNA. In addition, stimulation of these HIV-1-infected, CD8(+)-sorted cells either with PHA or anti-CD2 mAb resulted in induction of virus replication, as measured by reverse transcriptase activity. Electron microscopic analysis of CD8+ cells chronically infected with HIV-1 and stimulated with PHA showed typical virions budding from, and associated with, the surface of cells immunolabeled with gold beads directed toward the CD8 molecule. Infection of CD8+ cells with HIV-1 occurred only when CD4+ cells were present in the PHA-activated lymphocyte population exposed to HIV-1 at the beginning of the culture or when sorted CD8+CD4- lymphocytes were cocultured with autologous sorted CD8-CD4+ cells that had been previously infected with HIV-1. Coculture of these cells with PHA-blasts and incubation of their supernatants with a CD4+ cell line showed that these chronically infected CD8+ cells could spread HIV-1 infection to uninfected CD4+ cells after stimulation with PHA or anti-CD2 mAb. Therefore, these results suggest that the minimal requirement for in vitro infection of CD3+CD8+CD4- lymphocytes is the presence of infected CD4+ cells and that infected CD8+ T lymphocytes can further spread the infection to CD4+ cells.

Infection of CD8+ T lymphocytes with HIV. Requirement for interaction with infected CD4+ cells and induction of infectious virus from chronically infected CD8+ cells

In this study, we have investigated the basic requirements for HIV-1 infection of CD8+ lymphocytes in vitro. Unfractionated PBL obtained from healthy HIV-1 seronegative donors were activated with PHA and infected in vitro with HIV-1LAV. Based on immunofluorescent labeling, the vast majority of cells (85 to 97%) surviving peak virus replication belonged to the CD8+ subset and only a small percentage (0.5 to 1.5%) were CD4+. Amplification of HIV-1 proviral sequences by polymerase chain reaction performed on the sorted surviving CD8+ cells demonstrated that CD8+ cells harbored HIV-1 proviral DNA. In addition, stimulation of these HIV-1-infected, CD8(+)-sorted cells either with PHA or anti-CD2 mAb resulted in induction of virus replication, as measured by reverse transcriptase activity. Electron microscopic analysis of CD8+ cells chronically infected with HIV-1 and stimulated with PHA showed typical virions budding from, and associated with, the surface of cells immunolabeled with gold beads directed toward the CD8 molecule. Infection of CD8+ cells with HIV-1 occurred only when CD4+ cells were present in the PHA-activated lymphocyte population exposed to HIV-1 at the beginning of the culture or when sorted CD8+CD4- lymphocytes were cocultured with autologous sorted CD8-CD4+ cells that had been previously infected with HIV-1. Coculture of these cells with PHA-blasts and incubation of their supernatants with a CD4+ cell line showed that these chronically infected CD8+ cells could spread HIV-1 infection to uninfected CD4+ cells after stimulation with PHA or anti-CD2 mAb. Therefore, these results suggest that the minimal requirement for in vitro infection of CD3+CD8+CD4- lymphocytes is the presence of infected CD4+ cells and that infected CD8+ T lymphocytes can further spread the infection to CD4+ cells.

Frequent detection of HIV-1-specific mRNAs in infected individuals suggests ongoing active viral expression in all stages of disease

It has been shown that only a small fraction of CD4+ T cells are infected with human immunodeficiency virus type 1 (HIV-1) in vivo, particularly early in the course of infection. An even smaller proportion of cells have been shown to be expressing virus. Recent studies suggest that plasma viremia in asymptomatic HIV-infected individuals, representing active viral replication, is more common than was previously believed (range 23-100% of patients). To determine the in vivo state of HIV expression, samples of peripheral blood of 49 HIV-infected individuals at all stages of disease were examined. All subjects were positive for viral DNA by standard polymerase chain reaction (PCR), and a modified PCR was utilized to detect HIV-specific mRNAs (gag, major splice junction, env, and tat/rev). Patient's plasma was also assayed for p24 antigen and viremia. The results were as follows: (formula: see text) Overall, the findings suggest that active viral expression occurs at all stages of HIV infection. In particular, the presence of gag mRNA was determined in only 2 of 14 patients with T4% greater than 30% but in 20 of 35 patients with T4% less than or equal to 30% (p less than 0.05), demonstrating a direct association between the presence of message for a structural protein, and more advanced immunosuppression. Determination of the expression of certain HIV-specific messages from within a patient's cells adds a new dimension to understanding the pathogenesis of HIV infection. The presence of HIV-specific mRNAs, and in particular gag message, in many healthy seropositives may further argue for early initiation of antiviral therapy.

Human immunodeficiency virus (HIV) infection in CD4+ T lymphocytes genetically deficient in LFA-1: LFA-1 is required for HIV-mediated cell fusion but not for viral transmission

In the present study, we demonstrated that expression of the LFA-1 molecule is necessary for cell fusion and syncytia formation in human immunodeficiency virus (HIV)-infected CD4+ T lymphocytes. In contrast, the lack of expression of LFA-1 does not influence significantly cell-to-cell transmission of HIV. In fact, LFA-1- T lymphocytes obtained from a leukocyte adhesion deficiency patient were unable to fuse and form syncytia when infected with HIV-1 or HIV-2, despite the fact that efficiency of HIV infection (i.e., virus entry, HIV spreading, and levels of virus replication) was comparable with that observed in LFA-1+ T lymphocytes. In addition, we provide evidence that LFA-1 by mediating cell fusion contributes to the depletion of HIV-infected CD4+ T lymphocytes in vitro.

Evidence for susceptibility of intrathymic T-cell precursors and their progeny carrying T-cell antigen receptor phenotypes TCR alpha beta + and TCR gamma delta + to human immunodeficiency virus infection: a mechanism for CD4+ (T4) lymphocyte depletion

Individuals infected by the human immunodeficiency virus type 1 (HIV-1) demonstrate progressive depletion and qualitative dysfunction of the helper T4 (CD4+) cell population. Mechanisms proposed for attrition of CD4+ T cells include direct cytopathicity of these mature cells following infection as well as infection of early T-lymphocyte progenitors. The latter mechanism could lead to failure to regenerate mature functioning CD4+ T cells. The present study determines the susceptibility of thymocytes at various stages of maturity to infection with HIV-1. Various normal thymocyte populations were inoculated with HIV-1, including unfractionated (UF), CD3- CD4- CD8- ["triple negative" (TN)], CD4+ CD8+ ["double positive" (DP)] thymocytes, and thymocyte populations obtained by limited dilution cloning. Cultures were studied for the presence of HIV-1 DNA by polymerase chain reaction in addition to examination for reverse transcriptase activity. We determined that transformed T-cell and thymocyte cell lines completely lacking CD4 were not susceptible to infection by HIV-1, whereas all of the following lines were: UF thymocytes (70-90% CD4hi+); DP thymocytes (99% CD4hi+); TN thymocytes (0% CD4hi+); and TCR alpha beta +, TCR gamma delta +, or CD16+ CD3- (natural killer) thymocyte clones expressing variable levels of CD4 and representing the progeny of TN thymocytes. [TCR alpha beta + and TCR gamma delta + refer to the chains of the T-cell antigen receptor (TCR), and CD4hi refers to a strong rightward shift (greater than 30 linear channels) of the CD4 curve on flow cytometric analysis compared with control.] Monoclonal antibodies (mAbs) to CD4 (T4a epitope) but not to CD3 (T3) were capable of blocking infection of mature and immature CD4hi+ thymocytes. Moreover, anti-CD4(T4a) mAbs also inhibited infection of CD4hi- TN thymocytes, indicating that these T-cell precursors--despite their apparent "triple negativity" (CD3- CD4hi- CD8-)--expressed sufficient CD4 molecules to become infected. Cell sorter analysis with a panel of CD4 mAbs demonstrated a mean shift of the mean fluorescence channel (MFC) with CD4 mAbs on TN thymocytes of 6 +/- 4 MFC units. Thus, intrathymic T-cell precursors and their progeny representing many stages of T-cell ontogeny are susceptible to infection by HIV-1, including early TN thymocytes, which express very low levels of CD4. Infection of multiple stages and multiple subsets of the T-cell lineage in man, mediated via the CD4 molecule, may explain the inability of the T-cell pool to regenerate in the setting of progressive HIV infection.

Increasing viral burden in CD4+ T cells from patients with human immunodeficiency virus (HIV) infection reflects rapidly progressive immunosuppression and clinical disease

OBJECTIVE

To determine over time the relation between viral burden and immunologic decline in patients with asymptomatic human immunodeficiency virus (HIV) infection.

DESIGN

Blind analysis of cell samples from matched cohorts for HIV proviral DNA by polymerase chain reaction, retrospective analysis of clinical data on patients, and prospective follow-up of patients seropositive for the human immunodeficiency virus type 1 (HIV-1).

SETTING

National research clinic and academic medical centers.

PATIENTS

Cohort 1 included 12 healthy HIV-1-seropositive patients (average follow-up, 14 months): Six patients had stable disease and 6 developed rapidly progressive disease. Cohort 2 included 15 healthy HIV-1-seropositive patients from the Multi-center AIDS Cohort Study (average follow-up, 32 months): Eight patients had stable disease and 7 developed rapidly progressive disease. LABORATORY STUDIES: Quantitative polymerase chain reaction was done to determine the HIV-1 viral burden in sort-purified CD4+ T cells obtained from patients at various timepoints.

MEASUREMENTS AND MAIN RESULTS

In patients who remained asymptomatic, frequencies of HIV-infected CD4+ T cells were low (less than 1/10,000 to 1/1000) at study entry and increased only minimally (none higher than 1/1000). In contrast, among patients who developed HIV-related symptoms including the acquired immunodeficiency syndrome (AIDS) despite having similar CD4 counts, frequencies of HIV-infected CD4+ T cells were higher at entry (greater than 1/1000) and increased substantially (greater than 1/100) in most within 3 months of developing progressive disease. This increase in HIV burden coincided with a significant decline over time in the percent of T4 cells (31% to 16%), whereas the percent of T4 cells was unchanged in persons who remained asymptomatic (33% to 34%).

CONCLUSIONS

Increasing viral burden in peripheral blood CD4+ T-cells is directly associated with a progressive decline in CD4+ T cells and deteriorating clinical course in HIV-infected patients.

Preferential infection of CD4+ memory T cells by human immunodeficiency virus type 1: evidence for a role in the selective T-cell functional defects observed in infected individuals

CD4+ T cells of patients with AIDS exhibit a qualitative defect in their ability to respond to soluble antigen while their responses to mitogens remain normal. CD4+ T cells can be broadly divided phenotypically into "naive" [CD45RA+ (2H4+)] and "memory" [CD29+ (4B4+) or CD45RO+ (UCHL1+)] cell subpopulations, which represent distinct maturation stages. To determine the human immunodeficiency virus type 1 (HIV-1) infectability of memory and naive CD4+ T-cell subsets in vitro and to determine the in vivo preference of HIV-1 in these subpopulations, we obtained highly purified CD4+ T-cell subsets from normal and HIV-1-infected individuals and studied them by viral cultivation, quantitative polymerase chain reaction, and functional assays. Polymerase chain reaction studies demonstrated that the memory cell subset of CD4+ T cells is preferentially infected (4- to 10-fold more than naive T cells) by HIV-1 in vitro, and these memory cells are the principal reservoir for HIV-1 within CD4+ T cells obtained from infected individuals. Functional abnormalities attributable to CD4+ T cells in HIV-infected individuals (failure to respond in vitro to soluble antigen or to anti-CD3 monoclonal antibodies) were shown to reside primarily within these memory cells. Thus, the present study suggests that the selective functional defects present in the memory CD4+ T-cell subset of HIV-infected individuals may be a direct result of the preferential infection and consequently greater viral burden within these cells.

In vivo T lymphocyte origin of macrophage-tropic strains of HIV. Role of monocytes during in vitro isolation and in vivo infection

Previously published isolation techniques with T cell blasts and monocyte-derived macrophages (MDM) were used to recover HIV from the PBMC of a group of 23 asymptomatic seropositive individuals. Viral isolation was more readily accomplished by MDM coculture resulting in 9 isolates being obtained exclusively by this method (macrophage tropic strains). To determine the in vivo cellular source of these isolates we separated PBMC from 5 of these 9 patients into T lymphocyte and monocyte fractions by flow microfluorometry. These fractions were then analyzed by polymerase chain reaction (PCR) for the presence of HIV-1 proviral DNA. In 4 out of these 5 patients HIV-1 proviral DNA could be detected exclusively in T lymphocytes but not in monocytes, although the virus could be isolated only by MDM coculture. In the remaining patient HIV could be amplified in both T lymphocytes and monocytes. Further phenotypic analysis revealed that, among T lymphocytes, only the CD4+ subset was infected with HIV. We conclude that among PBMC the most common in vivo source of HIV strains which preferentially infect macrophages in vitro is the CD4+ T lymphocyte. These data also suggest that the macrophage tropism characteristic of some HIV strains reflects predominantly an in vitro phenomenon.

In vivo T lymphocyte origin of macrophage-tropic strains of HIV. Role of monocytes during in vitro isolation and in vivo infection

Previously published isolation techniques with T cell blasts and monocyte-derived macrophages (MDM) were used to recover HIV from the PBMC of a group of 23 asymptomatic seropositive individuals. Viral isolation was more readily accomplished by MDM coculture resulting in 9 isolates being obtained exclusively by this method (macrophage tropic strains). To determine the in vivo cellular source of these isolates we separated PBMC from 5 of these 9 patients into T lymphocyte and monocyte fractions by flow microfluorometry. These fractions were then analyzed by polymerase chain reaction (PCR) for the presence of HIV-1 proviral DNA. In 4 out of these 5 patients HIV-1 proviral DNA could be detected exclusively in T lymphocytes but not in monocytes, although the virus could be isolated only by MDM coculture. In the remaining patient HIV could be amplified in both T lymphocytes and monocytes. Further phenotypic analysis revealed that, among T lymphocytes, only the CD4+ subset was infected with HIV. We conclude that among PBMC the most common in vivo source of HIV strains which preferentially infect macrophages in vitro is the CD4+ T lymphocyte. These data also suggest that the macrophage tropism characteristic of some HIV strains reflects predominantly an in vitro phenomenon.

Integrated proviral human immunodeficiency virus type 1 is present in CD4+ peripheral blood lymphocytes in healthy seropositive individuals

Evidence of a latent human immunodeficiency virus type 1 (HIV-1) infection in healthy, seropositive individuals who do not have viral antigens in their sera and from whom virions cannot be rescued in cocultivation experiments was examined. Proviral DNA was detected by amplification by the polymerase chain reaction procedure. In each of 10 seropositive individuals, the presence of HIV-1 proviral sequences was demonstrated in their peripheral blood mononuclear cells. By using fluorescence-activated cell sorting, we obtained highly enriched subpopulations of peripheral blood mononuclear cells and found that the CD4+ T-cell subset is the cell subset that consistently harbors the HIV-1 proviral sequences. The number of HIV-1-infected CD4+ T cells was variable among the 10 healthy individuals, ranging from 1 in 100 to 1 in 40,000. While in vitro infection of CD4+ T cells causes down regulation and eventual loss of CD4 surface molecules, this is not true in vivo where it is only the CD4+ population that harbors the virus. This disparity may reflect differences between a latent infection in vivo with the lytic response of cells infected in vitro.

The reservoir for HIV-1 in human peripheral blood is a T cell that maintains expression of CD4

Human immunodeficiency virus type 1 (HIV-1) selectively infects cells expressing the CD4 molecule, resulting in substantial quantitative and qualitative defects in CD4+ T lymphocyte function in patients with acquired immunodeficiency syndrome (AIDS). However, only a very small number of cells in the peripheral blood of HIV-1-infected individuals are expressing virus at any given time. Previous studies have demonstrated that in vitro infection of CD4+ T cells with HIV-1 results in downregulation of CD4 expression such that CD4 protein is no longer detectable on the surface of the infected cells. In the present study, highly purified subpopulations of peripheral blood mononuclear cells (PBMCs) from AIDS patients were obtained and purified by fluorescence-automated cell sorting. They were examined with the methodologies of virus isolation by limiting dilution analysis, in situ hybridization, immunofluorescence, and gene amplification. Within PBMCs, HIV-1 was expressed in vivo predominantly in the T cell subpopulation which, in contrast to the in vitro observations, continued to express CD4. The precursor frequency of these HIV-1-expressing cells was about 1/1000 CD4+ T cells. The CD4+ T cell population contained HIV-1 DNA in all HIV-1-infected individuals studied and the frequency in AIDS patients was at least 1/100 cells. This high level of infection may be the primary cause for the progressive decline in number and function of CD4+ T cells in patients with AIDS.

Characterization of GP120 binding to CD4 and an assay that measures ability of sera to inhibit this binding

There is evidence that the initial interaction between HIV-1 and the host that is essential for infection is the specific binding of the viral envelope glycoprotein, gp120, to the CD4 molecule found on certain T cells and monocytes. Most individuals infected with HIV develop antibodies against the gp120 protein. Although in vitro treatment of CD4+ T cells with mAb to a specific epitope of the CD4 molecule (T4a) blocks virus binding, syncytia formation, and infectivity, it is unclear if antibodies to gp120 from an infected individual that can inhibit the binding of gp120 to CD4 is in any way related to the clinical course of disease. Our present study characterizes the binding of 125I-labeled rgp120 to CD4+ cells, and describes an assay system that measures a potentially relevant form of immunity to HIV infection, i.e., the blocking of HIV binding to CD4+ cells. Optimal binding conditions included a 2-h incubation at 22 degrees C, 4 x 10(6) CD4+ cells, and 1 nM gp120. The dissociation constant (KD) for gp120 binding to cell surface CD4 was 5 nM, and was inhibited by soluble CD4 and by mAb to T4a but not to T3 or T4. For the binding inhibition assay, negative controls included healthy seronegatives, seronegatives with connective tissue diseases, patients with HTLV-1 disease, and patients infected with HIV-2. In studying over 100 sera, the assay was highly sensitive (98%) and specific (100%). The majority of HIV+ sera could inhibit binding at dilutions of 1/100 to 1/1000. No correlation was noted between binding inhibition (BI) titer in this assay and clinical stage of HIV infection. In addition, there was no correlation between BI titer and HIV neutralizing activity. The BI titer was correlated with the titer of anti-gp160 (r = 0.63) and the titer of anti-gp120 (r = 0.52) antibodies determined by Western blot dilution. As with neutralizing antibodies and other forms of immune response to HIV, it is unclear what role antibody blocking of HIV binding to CD4+ cells may play in active immunity to HIV in infected individuals. This activity may prove to have some value in protection against initial HIV infection and, thus, the assay may be of use in monitoring vaccine trials.

Characterization of GP120 binding to CD4 and an assay that measures ability of sera to inhibit this binding

There is evidence that the initial interaction between HIV-1 and the host that is essential for infection is the specific binding of the viral envelope glycoprotein, gp120, to the CD4 molecule found on certain T cells and monocytes. Most individuals infected with HIV develop antibodies against the gp120 protein. Although in vitro treatment of CD4+ T cells with mAb to a specific epitope of the CD4 molecule (T4a) blocks virus binding, syncytia formation, and infectivity, it is unclear if antibodies to gp120 from an infected individual that can inhibit the binding of gp120 to CD4 is in any way related to the clinical course of disease. Our present study characterizes the binding of 125I-labeled rgp120 to CD4+ cells, and describes an assay system that measures a potentially relevant form of immunity to HIV infection, i.e., the blocking of HIV binding to CD4+ cells. Optimal binding conditions included a 2-h incubation at 22 degrees C, 4 x 10(6) CD4+ cells, and 1 nM gp120. The dissociation constant (KD) for gp120 binding to cell surface CD4 was 5 nM, and was inhibited by soluble CD4 and by mAb to T4a but not to T3 or T4. For the binding inhibition assay, negative controls included healthy seronegatives, seronegatives with connective tissue diseases, patients with HTLV-1 disease, and patients infected with HIV-2. In studying over 100 sera, the assay was highly sensitive (98%) and specific (100%). The majority of HIV+ sera could inhibit binding at dilutions of 1/100 to 1/1000. No correlation was noted between binding inhibition (BI) titer in this assay and clinical stage of HIV infection. In addition, there was no correlation between BI titer and HIV neutralizing activity. The BI titer was correlated with the titer of anti-gp160 (r = 0.63) and the titer of anti-gp120 (r = 0.52) antibodies determined by Western blot dilution. As with neutralizing antibodies and other forms of immune response to HIV, it is unclear what role antibody blocking of HIV binding to CD4+ cells may play in active immunity to HIV in infected individuals. This activity may prove to have some value in protection against initial HIV infection and, thus, the assay may be of use in monitoring vaccine trials.

Direct polyclonal activation of human B lymphocytes by the acquired immune deficiency syndrome virus

When B lymphocytes from normal human peripheral blood were incubated for 1 hour with the retrovirus that causes the acquired immune deficiency syndrome (AIDS), the B cells showed marked proliferation and differentiation. Proliferative responses to the virus peaked on day 4 and appeared to be independent of accessory cells. This finding was repeated with three separate viral isolates, one of which was from a patient from Zaire. The magnitude of the observed responses was comparable to that seen with standard polyclonal B-cell activators. This phenomenon may be at least partially responsible for the polyclonal B-cell activation seen in patients with AIDS.