Kinetics of human immunodeficiency virus type 1 reverse transcription in blood mononuclear phagocytes are slowed by limitations of nucleotide precursors

Human immunodeficiency virus type 1 infection of mononuclear phagocytes has been implicated in disease manifestations, but postentry viral replication events in these cells have not been well characterized. Productive infection of activated T cells is associated with cell proliferation and accumulation of full-length viral DNA within 6 h. In infected, nondividing quiescent peripheral blood lymphocytes, reverse transcription is aborted prior to full-length viral DNA formation. For nondividing, cultured mononuclear phagocytes, we now report a third pattern of reverse transcription with relatively slow kinetics, in which full-length viral DNA did not accumulate until 36 to 48 h. The reverse transcription rate in mononuclear phagocytes could be accelerated by addition of exogenous nucleotide precursors, but still not to the rate seen in activated T cells. These results indicate that substrate limitations in mononuclear phagocytes slow but do not arrest human immunodeficiency virus type 1 reverse transcription.

Effects of cytokines on HIV-1 production by thymocytes

The thymus is essential for normal T cell development and is particularly active during fetal and postnatal life. Here we describe in vitro studies of HIV-infected thymocytes cultured with cytokines normally produced in the thymus. Virus expression was determined by measuring p24 antigen levels in the culture supernatants. Addition of IL-2+IL-4 and IL-4+IL-7 to the HIV-infected cultures of both fetal and postnatal thymocytes resulted in various levels of synergistic expression of p24 antigen. When differences in phenotype between HIV-infected and non-infected (sham-treated) cultures from the same specimen were evaluated, there was a decrease in the percentages and absolute numbers of CD4-bearing cells in HIV-infected thymocytes cultured with IL-2+IL-4. Studies were done to determine if synergy in HIV expression was mediated by activation, proliferation or induction or suppression of other cytokines. We found a higher percentage of activated CD4+CD8+/high cells in thymocytes cultured with IL-2+IL-4 and IL-4+IL-7 than in thymocytes cultured with IL-2+IL-7. Proliferation was higher in thymocytes cultured with cytokine combinations but did not correlate with those conditions showing synergy. IL-4 reduced IFN-gamma production by thymocytes cultured with IL-2 in both HIV-infected and non-infected thymocytes. In addition, exogenous IFN-gamma decreased p24 expression by HIV-infected thymocytes when cultured with IL-4 alone, with IL-2+IL-4 or IL-4+IL-7. These results suggest that suppression of IFN-gamma by IL-4 may combine with cell activation and proliferation to produce synergy of virus expression observed with IL-2+IL-4 and IL-4+IL-7.

Establishment of human T-cell leukemia virus type I T-cell lymphomas in severe combined immunodeficient mice

Human T-cell leukemia virus type I (HTLV-I) is recognized as the etiologic agent of adult T-cell leukemia (ATL), a disease endemic in certain regions of southeastern Japan, Africa, and the Caribbean basin. Although HTLV-I can immortalize T lymphocytes in culture, factors leading to tumor progression after HTLV-I infection remain elusive. Previous attempts to propagate the ATL tumor cells in animals have been unsuccessful. Severe combined immunodeficient (SCID) mice have previously been used to support the survival of human lymphoid cell populations when inoculated with human peripheral blood lymphocytes (PBL). SCID mice were injected intraperitoneally with PBL from patients diagnosed with ATL, HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP), or from asymptomatic HTLV-I-seropositive patients. Many of these mice become persistently infected with HTLV-I. Furthermore, after human reconstitution was established in these mice, HTLV-I-infected cells displayed a proliferative advantage over uninfected human cells. Lymphoblastic lymphomas of human origin developed in animals injected with PBL from two ATL patients. The tumor cells represented outgrowth of the original ATL leukemic clone in that they had monoclonal or oligoclonal integrations of the HTLV-I provirus identical to the leukemic clone and predominantly expressed the cell surface markers, CD4 and CD25. In contrast, cell lines derived by HTLV immortalization of T cells in vitro did not persist or form tumors when inoculated into SCID mice, indicating differences between in vitro immortalized cells and ATL leukemic cells. This system represents the first small animal model to study HTLV-I tumorigenesis in vivo.

Partial inhibition of the human immunodeficiency virus type 1 protease results in aberrant virus assembly and the formation of noninfectious particles

The production of infectious particles by human immunodeficiency virus type 1 is dependent on the accurate cleavage of its Gag and Gag/Pol precursors by a virally encoded protease. In the absence of protease activity, morphologically abnormal particles which are noninfectious are formed. Recently, inhibitors of the protease of human immunodeficiency virus type 1 have been developed as potential therapeutic agents. We have examined the basis for the loss of infectivity at the limiting inhibitor concentrations that are likely to be achieved in clinical settings. We found that subtle defects in processing are correlated with profound deficits in infectivity. Further, we correlated this partially disrupted processing with an altered virion morphology. These data suggest that accurate and complete processing is essential to the formation of infectious, morphologically normal virions and that the pathway by which these precursors are processed and assembled is sensitive to partial inhibition of the protease by an inhibitor disproportionate to the effect of the inhibitor on the viral protease itself.

The SCID-hu mouse as a model for HIV-1 infection

During normal fetal ontogeny, one of the first organs to harbour CD4-positive cells is the thymus. This organ could therefore be one of the earliest targets infected by human immunodeficiency virus type 1 (HIV-1) in utero. HIV-1-infected cells and pathological abnormalities of the thymus have been seen in HIV-1-infected adults and children, and in some fetuses aborted from infected women. Studies of HIV-1 pathogenesis have been hampered by lack of a suitable animal model system. Here we use the SCID-hu mouse as a model to investigate the effect of virus infection on human tissue. The mouse is homozygous for the severe combined immunodeficiency (SCID) defect. The model is constructed by implanting human fetal liver and thymus under the mouse kidney capsule. A conjoint human organ develops, which allows normal maturation of human thymocytes. After direct inoculation of HIV-1 into these implants, we observed severe depletion of human CD4-bearing cells within a few weeks of infection. This correlated with increasing virus load in the implants. Thus the SCID-hu mouse may be a useful in vivo system for the study of HIV-1-induced pathology.

Rapid enzymatic analysis for human immunodeficiency virus type 1 DNA in clinical specimens

A clinical procedure for rapid detection of human immunodeficiency virus type 1 (HIV-1) by DNA amplification is demonstrated. The rapid procedure reduces handling requirements and amplification time and eliminates use of radioactivity for the detection of the amplification product. Total leukocyte lysates are the amplification substrates. Two conserved regions in the HIV-1 genome are amplified by 45 cycles of a two-temperature thermal cycle and the amplification products are detected by ultraviolet light after electrophoresis on agarose gels. Twenty-four specimens clinically diagnosed by detection of antibody (IgG) to HIV-1 were confirmed by the rapid DNA amplification procedure. In a blind study, 56 samples positive for HIV-1 DNA were detected in 503 individuals by the current classical polymerase chain reaction method; the same 56 positive samples were also detected by the rapid amplification protocol. No false-positive or false-negative results were obtained. The turnaround time for analysis has been reduced to < 24 h without compromising test results.

Rapid enzymatic analysis for human immunodeficiency virus type 1 DNA in clinical specimens

A clinical procedure for rapid detection of human immunodeficiency virus type 1 (HIV-1) by DNA amplification is demonstrated. The rapid procedure reduces handling requirements and amplification time and eliminates use of radioactivity for the detection of the amplification product. Total leukocyte lysates are the amplification substrates. Two conserved regions in the HIV-1 genome are amplified by 45 cycles of a two-temperature thermal cycle and the amplification products are detected by ultraviolet light after electrophoresis on agarose gels. Twenty-four specimens clinically diagnosed by detection of antibody (IgG) to HIV-1 were confirmed by the rapid DNA amplification procedure. In a blind study, 56 samples positive for HIV-1 DNA were detected in 503 individuals by the current classical polymerase chain reaction method; the same 56 positive samples were also detected by the rapid amplification protocol. No false-positive or false-negative results were obtained. The turnaround time for analysis has been reduced to < 24 h without compromising test results.

Cell-mediated immune response to human immunodeficiency virus (HIV) type 1 in seronegative homosexual men with recent sexual exposure to HIV-1

Although human immunodeficiency virus (HIV) type 1 infection is efficiently transmitted by sexual intercourse, some individuals whose sexual behavior places them at extremely high risk for infection have nevertheless remained HIV-1-seronegative. An investigation was undertaken to determine whether such individuals have circulating T helper cells that are sensitized to HIV-1. Five very high risk men who had recent sexual exposure to HIV-1 were studied. Peripheral blood mononuclear cells from all 5 produced interleukin (IL)-2 in culture in response to synthetic amphipathic HIV-1 envelope peptides. One of the 5 high-risk men has subsequently seroconverted, while 4 have remained seronegative. All were initially culture-negative, and those who have remained seronegative were also virus-negative by polymerase chain reaction (PCR) testing 10 months after they were first studied. These results demonstrate that a cell-mediated immune response to HIV-1 can be detected in the absence of a humoral immune response in individuals recently exposed to HIV-1. Furthermore, IL-2 production by T cells in response to synthetic peptides may be a more sensitive test for exposure to HIV-1 than antibody, lymphoproliferation, or PCR tests.

Incompletely reverse-transcribed human immunodeficiency virus type 1 genomes in quiescent cells can function as intermediates in the retroviral life cycle

Using a quantitative polymerase chain reaction (PCR) method, we have previously shown that a molecularly cloned isolate of human immunodeficiency virus type 1 (HIV-1) can efficiently enter quiescent primary lymphocytes; however, the reverse transcription process is not completed in these cells. In this study, we further characterized the reverse transcription of HIV-1 in quiescent cells, and our results indicate that while initiation of reverse transcription occurs simultaneously in both activated and quiescent lymphocytes, it not only ends prematurely but also proceeds more slowly in quiescent cells. We also performed experiments to address the role of partial reverse transcripts as intermediates in the viral life cycle. We used azidothymidine either before or after infection with HIV-1 to prevent formation of and further DNA synthesis by partial reverse transcripts, respectively. Decreases in virus production from these cells following mitogenic stimulation indicated that partial reverse transcripts can contribute significantly to virus rescue from infected quiescent cells stimulated subsequent to infection. Furthermore, we established that mitogenic stimulation of infected quiescent cells induces reinitiation of DNA synthesis from partial reverse transcripts. However, the virus rescue is inefficient relative to the initial multiplicity of infection, and this is explained by inefficient completion of DNA synthesis from the partial reverse transcript. Thus, the arrest of reverse transcription in quiescent cells may play an important role in HIV-1 pathogenesis by contributing to the inefficient infection of potential target cells in the peripheral blood of HIV-1-infected individuals.

In vitro studies of HIV-1 expression in thymocytes from infants and children

OBJECTIVE

To determine whether thymocytes from infants and young children can be infected with and their maturation capability altered by HIV-1, and to examine the effects of interleukin (IL)-2 and IL-4 on this process.

DESIGN

Serum-free culture medium was used so that cytokine effects could be studied under defined conditions. The primary virus isolates HIV-1JR-CSF and HIV-1JR-FL were used because their effects should most closely resemble those of viruses which might be found in an infected child.

METHODS

Thymocytes from infants and young children were infected with virus and cultured in serum-free medium with the cytokines IL-2 and IL-4 alone or in combination. HIV-1 expression was measured after 12 days by p24 levels in culture supernatants. Thymocyte maturation was determined by changes in surface phenotype, as measured by flow cytometry.

RESULTS

HIV-1 expression by thymocytes, which increased with time of culture, occurred when thymocytes were cultured with each cytokine. p24 levels were slightly increased when cultured with IL-2, compared with IL-4. Virus expression was remarkably increased when the cytokines were combined in culture. This expression was synergistic rather than additive. The synergy, evident in mature, but not immature thymocytes, was demonstrated with both pharmacologic and physiologic concentrations of cytokines. T-cells from peripheral blood cultured under the same conditions demonstrated lower virus expression in the presence of cytokines and synergy was not shown. Cytokine-induced thymocyte maturation and thymocyte survival in vitro was unimpaired by infection with HIV-1.

CONCLUSIONS

These findings indicate that the cytokines IL-2 and IL-4, which are normally present in the thymic environment, can synergize to promote HIV-1 expression by thymocytes infected in vitro. This occurs without impairing the maturation induced by these cytokines. Thus, the mature thymocyte may provide a continuous supply of virus-expressing T-cells to the peripheral blood and lymphoid tissues of the infected child.

Increased susceptibility of differentiated mononuclear phagocytes to productive infection with human immunodeficiency virus-1 (HIV-1)

Differences in susceptibility to infection of most mononuclear phagocytes with HIV-1 are not known. We investigated the relative susceptibility of autologous freshly isolated blood monocytes (MN), MN cultured in vitro to allow differentiation (CM), and alveolar macrophages (AM) from healthy subjects to productive infection with HIV-1. Cells were infected with the macrophage tropic strain HIV-1JR-FL and p24 gag antigen levels measured in supernatants by ELISA. Freshly isolated MN had negligible levels of p24 in supernatants. In contrast AM had peak p24 levels of 4145 +/- 1456 pg/ml, mean +/- SE, and CM 9216 +/- 3118. As a measure of entry and extent of reverse transcription, levels of viral DNA in infected mononuclear phagocytes were analyzed by quantitative polymerase chain reaction (PCR). The data using primers that amplify all transcripts including incompletely formed reverse transcripts indicated that differences in entry of the virus may contribute to differences in virus production observed with MN, AM, and CM. Other primer pairs that detect intermediate and full-length double-stranded DNA showed that the ability to complete reverse transcription was similar among these mononuclear phagocytes. Since the lung is a major site of opportunistic infection and noninfectious complications in HIV-1-infected individuals, this increase in productive infection with HIV-1 in AM compared with MN could contribute to the immunopathogenesis of the lung disorders seen in the acquired immunodeficiency syndrome.

HIV-1 tropism for mononuclear phagocytes can be determined by regions of gp120 outside the CD4-binding domain

Cells of the mononuclear phagocyte system are the predominant cell producing HIV-1 in most tissues including the central nervous system (CNS), spinal cord, lung and skin; infection is associated with dementia, neuropathy, pneumonitis, and dermatitis respectively. Different HIV-1 isolates vary markedly in their ability to infect mononuclear phagocytes productively. Here we describe molecular clones of a CNS-derived isolate, HIV-1(JR-FL), which can replicate efficiently in mononuclear phagocytes. Analysis by polymerase chain reaction of early events after infection indicates that the early phase of viral replication before reverse transcription determines tropism. Genetic mapping of the macrophage-tropic phenotype by construction of recombinant viruses indicates that mononuclear phagocyte infectivity can be determined by a 157-amino-acid region of the gp 120 glycoprotein of HIV-1(JR-FL). Significantly, this region is upstream from the previously defined CD4-binding domain. We propose that at least one determinant for mononuclear phagocyte tropism involves target cell interactions with regions of gp120 distinct from the CD4-binding domain.

Characterization and expression of novel singly spliced RNA species of human immunodeficiency virus type 1

Human immunodeficiency virus type 1 (HIV-1) expresses the Vif, Vpr, Vpu, and Env proteins through complex differential splicing of a single full-length RNA precursor. We used HIV-1-specific oligonucleotide primer pairs in a quantitative polymerase chain reaction procedure on RNA from fresh peripheral blood lymphocytes infected with HIV-1JR-CSF to detect and characterize the singly spliced RNA species which might encode these proteins. The nucleotide sequences at the junctions of splice donor and acceptor sites of these RNAs were determined. One of these RNAs, which has not been previously described, appears to be a novel HIV-1 RNA encoding Env and/or Vpu proteins.

HIV-1 entry into quiescent primary lymphocytes: molecular analysis reveals a labile, latent viral structure

Productive infection of human T lymphocytes by HIV-1 is dependent upon proliferation of the infected cell. Nonproliferating quiescent T cells can be infected by HIV-1 and harbor the virus in an inactive state until subsequent mitogenic stimulation. We use a modification of the polymerase chain reaction method, which is both sensitive and quantitative, to demonstrate that HIV-1 DNA synthesis is initiated in infected quiescent T cells at levels comparable with those of activated T cells. However, unlike that of activated T cells, the viral genome is not completely reverse transcribed in quiescent cells. Although this viral DNA structure can persist in quiescent cells as a latent form, it is labile. We discuss the lability of this HIV-1 DNA structure in relation to a "self-restricting persistent infection" by HIV-1 and propose that this may explain the low percentage of infected cells in the circulation of AIDS patients.

High rate of HTLV-II infection in seropositive i.v. drug abusers in New Orleans

Confirmed infection with HTLV-II (human T cell leukemia virus type II) has been described only in rare cases. The major limitation to serological diagnosis of HTLV-II has been the difficulty of distinguishing HTLV-II from HTLV-I (human T cell leukemia virus type I) infection, because of substantial cross-reactivity between the viruses. A sensitive modification of the polymerase chain reaction method was used to provide unambiguous molecular evidence that a significant proportion of intravenous drug abusers are infected with HTLV, and the majority of these individuals are infected with HTLV-II rather than HTLV-I. Of 23 individuals confirmed by polymerase chain reaction analysis to be infected with HTLV, 21 were identified to be infected with HTLV-II, and 2 were infected with HTLV-I. Molecular identification of an HTLV-II--infected population provides an opportunity to investigate the pathogenicity of HTLV-II in humans.

HIV-1 production from infected peripheral blood T cells after HTLV-I induced mitogenic stimulation

The human immunodeficiency virus type 1 (HIV-1) and human T-cell leukemia virus type I (HTLV-I) are two distinct human retroviruses that infect T cells. Recent epidemiologic studies have identified a cohort of individuals that are coinfected with both viruses. It is reported here that human peripheral blood leukocytes infected with HIV-1 in vitro can be induced to produce large quantities of HIV-1 after mitogenic stimulation by noninfectious HTLV-I virions. It is also shown that HTLV-I virions may exert this effect prior to, immediately following, or well after the cells are infected with HIV-1. These results provide further impetus for epidemiologic studies of dually infected individuals to determine whether HTLV-I may act as a cofactor for acquired immunodeficiency syndrome (AIDS).

The mortality experience of workers exposed to tetrachlorodibenzodioxin in a trichlorophenol process accident

A standardized mortality analysis was conducted on workers exposed to tetrachlorodibenzodioxin in a trichlorophenol process accident at the Monsanto Company plant in Nitro, West Virginia. One hundred and twenty-one workers who developed chloracne resulting from this accident on March 8, 1949, were selected for study. Follow-up of this group was 100% complete. The standardized mortality ratio for all causes of death was shown to be 0.69, with 32 deaths observed and 46.41 expected. For the categories of malignant neoplasms and circulatory diseases, the standardized mortality ratios were 1.00 and 0.68, respectively. Because of the small size of the cohort and the relatively small number of deaths observed, the results of this study cannot be considered conclusive. However, it is important that no apparent excess in total mortality or in deaths from malignant neoplasms or diseases of the circulatory system was observed in a group of workers with a high peak exposure to tetrachlorodibenzodioxin who were followed over a period of nearly 30 years. The results of this study will be incorporated with those of a larger study which will include plant workers exposed in the course of 2,4,5-trichlorophenoxyacetic acid production during the period 1948 to 1969.