AIDS. Defective viruses to blame?

Molecular determinants of the ratio of inert to infectious virus particles

The ratio of virus particles to infectious units is a classic measurement in virology and ranges widely from several million to below 10 for different viruses. Much evidence suggests a distinction be made between infectious and infecting particles or virions: out of many potentially infectious virions, few infect under regular experimental conditions, largely because of diffusion barriers. Still, some virions are inert from the start; others become defective through decay. And with increasing cell- and molecular-biological knowledge of each step in the replicative cycle for different viruses, it emerges that many processes entail considerable losses of potential viral infectivity. Furthermore, all-or-nothing assumptions about virion infectivity are flawed and should be replaced by descriptions that allow for spectra of infectious propensities. A more realistic understanding of the infectivity of individual virions has both practical and theoretical implications for virus neutralization, vaccine research, antiviral therapy, and the use of viral vectors.

Generation and role of defective proviruses in cytopathic feline leukemia virus (FeLV-FAIDS) infections

Cytopathic feline leukemia virus (FeLV) infections of feline T-cell line (FeT-cell) cultures led to the accumulation and maintenance of threefold more proviruses with deletions within the polymerase gene (pol) than minimally cytopathic FeLV infections. Over 60% of the viral DNA from cytopathic infections bore deletions in pol. Characterization of DNA sequences adjoining the deletions revealed that the junctions were most often flanked by RNA splice donor and acceptor consensus motifs. A thymidine-to-cytidine mutation introduced at the +2 position of one RNA splice donor-like motif inhibited formation of the two most prevalent viral DNA species with deletions, confirming the origin of many proviruses with deletions from reverse transcription of aberrantly spliced viral RNA species. An example of deletion by misalignment was also characterized. Viral inocula obtained from cells recovered after cytopathic infections were attenuated in their ability to cause cytopathic effects (CPE) and were able to confer superinfection resistance to naïve FeT-cells, despite maintaining envelope gene (env) sequences with full cytopathic potential. This suggested that viral genomes with deletions, rather than being required for cytopathicity, play a role in protecting cells from CPE. Indeed, expression of a molecularly cloned provirus bearing one of the characterized deletions attenuated CPE in FeT-cells caused by superinfecting cytopathic virus.

Possible supplemental mechanisms in the pathogenesis of AIDS

Multiple and diverse mechanisms have been proposed as supplements to the HIV-1 virus in the destruction of CD4+ cells and the pathogenesis of AIDS. But it is now realized that 100 times more CD4+ cells are infected with HIV-1 than was originally thought to be the case, and many antigen-presenting cells are infected as well. In addition to the direct cytopathic effect of the virus, one or a few supplemental mechanisms may well suffice to explain the progressive loss of CD4+ cells, e.g., the considerable variation in the virus and/or the destruction of uninfected CD4+ cells by one immunological mechanism or another. However, it is not yet possible to state confidently which additional mechanism(s) is important. Identification of the nature of this supplemental process has become essential for successful, nonharmful intervention.

HIV-1 in blood monocytes: frequency of detection of proviral DNA using PCR and comparison with the total CD4 count

In vivo infection of monocytes/macrophages by the human immunodeficiency virus (HIV) has been investigated in many studies since these cells were suggested to provide a reservoir for the virus. In this study, we wanted to find out whether HIV provirus could be detected in circulating monocytes and whether it could be compared with the provirus found in T lymphocytes (T-Ly). Twenty-one seropositive subjects were studied. The amplification method (PCR) was used with three different primer pairs (in gag, env, and long terminal repeat regions of the viral genome) to detect the HIV-1 genome in monocytes and T-Ly separated by an immunomagnetic isolation technique. Of 21 monocyte samples, 13 (61.9%) were positive with at least one primer pair. Furthermore, the provirus harboured in 9 of those 13 monocyte-positive samples differed, with respect to pattern of primer response, from the provirus found in T-Ly. When comparing primer responses of monocytes and T-Ly, most of the differences were found to have occurred with the env primers (8 of 9 cases). Dilution experiments with the 8 E5 cell line revealed that 9 of 12 T-Ly contained 15-150 HIV DNA copies per 150,000 cells while 8 of 11 positive monocytes contained less than 15 copies. However, monocyte samples from two asymptomatic individuals and an AIDS patient showed high levels of HIV DNA, comparable to those obtained in T-Ly. Finally, it was also found that the monocyte-positive subjects were more immunosuppressed than the negative ones, as shown by the total CD4 count of both groups (means of 269 T4/mm3 and 573 T4/mm3, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Human immunodeficiency virus type 1 envelope gene structure and diversity in vivo and after cocultivation in vitro

Nested-primer polymerase chain reaction (PCR) has been applied to the molecular cloning of 4.6-kb half-genome fragments of human immunodeficiency virus type 1 (HIV-1) taken directly from the peripheral blood mononuclear cells (PBMC) of an individual with neurological symptoms of HIV-1 infection. In a similar manner, gp120-coding portions of the envelope gene were cloned after PBMC from the same blood sample were cocultivated with uninfected PBMC for 28 days. The complete 1.6-kb nucleotide sequence of the gp120 gene was determined from each of 35 clones examined. Two of 13 (15%) PBMC-derived gp120 genes and 3 of 22 (14%) coculture-derived gp120 genes were defective as a result of frameshifts and an in-frame stop codon(s). Mean diversity between individual gp120-coding sequences in PBMC was fivefold greater (3.24%) than after coculture (0.65%). A predominant sequence of "strain" was found after coculture that was distinct from the diverse viral genotypes detected in vivo and therefore was selectively amplified during in vitro propagation. Multiple distinct third variable (V3) regions encoding the principal neutralizing domain of the envelope protein were detected in PBMC-derived genes, suggesting the presence of immunologic diversity of HIV env genes in vivo not reflected in the cocultured virus sample. The large size of the HIV fragments generated in this study will permit analysis of the diversity of immunologic reactivity, gene function, and pathogenicity of HIV genomes present within infected individuals, including the functional significance of the loss of diversity that occurs upon coculture.

AIDS acquired by drug consumption and other noncontagious risk factors

The hypothesis that human immunodeficiency virus (HIV) is a new, sexually transmitted virus that causes AIDS has been entirely unproductive in terms of public health benefits. Moreover, it fails to predict the epidemiology of AIDS, the annual AIDS risk and the very heterogeneous AIDS diseases of infected persons. The correct hypothesis must explain why: (1) AIDS includes 25 previously known diseases and two clinically and epidemiologically very different epidemics, one in America and Europe, the other in Africa; (2) almost all American (90%) and European (86%) AIDS patients are males over the age of 20, while African AIDS affects both sexes equally; (3) the annual AIDS risks of infected babies, intravenous drug users, homosexuals who use aphrodisiacs, hemophiliacs and Africans vary over 100-fold; (4) many AIDS patients have diseases that do not depend on immunodeficiency, such as Kaposi's sarcoma, lymphoma, dementia and wasting; (5) the AIDS diseases of Americans (97%) and Europeans (87%) are predetermined by prior health risks, including long-term consumption of illicit recreational drugs, the antiviral drug AZT and congenital deficiencies like hemophilia, and those of Africans are Africa-specific. Both negative and positive evidence shows that AIDS is not infectious: (1) the virus hypothesis fails all conventional criteria of causation; (2) over 100-fold different AIDS risks in different risk groups show that HIV is not sufficient for AIDS; (3) AIDS is only 'acquired,' if at all, years after HIV is neutralized by antibodies; (4) AIDS is new but HIV is a long-established, perinatally transmitted retrovirus; (5) alternative explanations disprove all assumptions and anecdotal cases cited in support of the virus hypothesis; (6) all AIDS-defining diseases occur in matched risk groups, at the same rate, in the absence of HIV; (7) there is no common, active microbe in all AIDS patients; (8) AIDS manifests in unpredictable and unrelated diseases; and (9) it does not spread randomly between the sexes in America and Europe. Based on numerous data documenting that drugs are necessary for HIV-positives and sufficient for HIV-negatives to develop AIDS diseases, it is proposed that all American/European AIDS diseases, that exceed their normal background, result from recreational and anti-HIV drugs. African AIDS is proposed to result from protein malnutrition, poor sanitation and subsequent parasitic infections. This hypothesis resolves all paradoxes of the virus-AIDS hypothesis. It is epidemiologically and experimentally testable and provides a rational basis for AIDS control.

The majority of cells infected with the defective murine AIDS virus belong to the B-cell lineage

Murine AIDS (MAIDS) is caused by a defective retrovirus which encodes a gag fusion protein (Pr60gag). We previously reported that this virus induced an oligoclonal proliferation of infected cells and suggested that this cell expansion was an important event in the pathogenesis of MAIDS. To identify these target cells, we constructed novel defective viruses whose genomes could be detected with specific probes. Helper-free stocks of these viruses induced MAIDS. Using in situ hybridization and immunocytochemistry and Southern analysis, we found that most infected cells belong to the B-cell lineage. Transformation of these B cells appears to be the primary event responsible for the development of immunodeficiency. This animal model may be relevant to our understanding of AIDS, of the immunodeficiencies associated with B-cell lymphoproliferative disorders, and of the role of B-cell proliferation and transformation in the effects of superantigens, since Pr60gag appears to be a superantigen.

Host range mutant of human immunodeficiency virus type 1: modification of cell tropism by a single point mutation at the neutralization epitope in the env gene

We have isolated a variant of human immunodeficiency virus type 1 (HIV-1) which is highly infectious to fibroblastlike cells (BT cells) derived from human brain as well as CD4-positive T cells. This variant HIV-1, named HIV[GUN-1V], was obtained by infecting BT cells with a prototype HIV-1 isolate, named HIV[GUN-1WT], which is highly infectious to T cells but barely infectious to BT cells. HIV[GUN-1V] infects BT cells productively and this infection appeared to be mediated by CD4. To elucidate the viral gene responsible for the host range difference between the variant and prototype HIV-1s, we cloned and analyzed the provirus genomes of the two viruses. Examination of the infectivities of BT cells by various recombinant viruses and analyses of the nucleotide sequences of HIV[GUN-1V] and HIV[GUN-1WT] showed that a single nucleotide exchange was responsible for their difference in infectivity of BT cells: HIV[GUN-1V] contains a thymine residue instead of the cytosine residue in HIV[GUN-1WT] at position 931 of the env coding sequence. Replacement of cytosine by thymine at this position of the env coding sequence of the HIV[GUN-1WT] genome induced the ability to infect BT cells. The base exchange at this position was expected to change amino acid 311 of the envelope glycoprotein, gp120, from proline to serine, which is located in a variable region containing type-specific immunodominant epitopes. Thus, HIV[GUN-1V] acquired a wider host range than HIV[GUN-1WT] by a single point mutation in the env gene.

Mechanisms associated with the generation of biologically active human immunodeficiency virus type 1 particles from defective proviruses

The human immunodeficiency virus (HIV) is the etiological agent of acquired immunodeficiency syndrome (AIDS). HIV exhibits extensive genetic diversity and it is apparent that an infected individual contains different populations of distinct viral strains, a large proportion of which has been found surprisingly to be defective for replication. A similar phenomenon has also been observed with some cell lines that are known to produce infectious viral particles but harbor defective proviral genomes. Here, we investigated the molecular basis of this phenomenon by cloning proviral genomes of HIV from a cell line that was capable of producing high titers of biologically active HIV particles that readily induced syncytia with CD4+ cell lines and peripheral blood lymphocytes. This cell line was found to contain five proviral genomes, all of which, when tested individually, failed to produce replication-competent viruses upon transfection into human cells. However, when a specific combination of two proviral genomes was used in such transfection studies, it was possible to obtain biologically active, replication-competent viral particles that infected and replicated in CD4+ cell lines and induced syncytia characteristic of HIV. Such a result may be due to homologous recombination between proviral DNAs occurring in cells after transfection and/or complementation of replication-defective proviral DNAs. The diploid nature of the viral RNA genome present in the viral particle may enable the persistence of defective HIV genomes.

A role for CD8+ T lymphocytes in the pathogenesis of AIDS

Experimental and clinical evidence is presented which supports the hypothesis that CD8+ T lymphocytes aimed at suppressing HIV replication in infected CD4+ T cells may have an important role in the pathogenesis of AIDS by directly causing a decrease in CD4+ T lymphocyte numbers. Possible models to test this hypothesis are discussed.

HIV2 chronic infection of promonocytic cells

HIV1 infection of mononuclear phagocytes is now well established, whereas HIV2 infection of these cells is less well documented. In this work, we studied the replication of the HIV2ROD strain in the U-937 promonocytic cell line and compared it with that of the HIV1BRU strain. p24 antigen and RT (reverse transcriptase) activity were assessed at regular intervals in cell-free supernatants, as was the infectiousness of the produced virus. In the case of HIV2, after a phase of high cell mortality, a chronically infected cell population releasing infectious virions was obtained (the infection remained stable after 60 days of culture). By contrast, for a given multiplicity of infection (i.e. 10,000 cpm RT/10(6) cells), HIV1 replication in U-937 cells was only transient (i.e. 14 days), leading to the synthesis of slightly infectious and probably defective viral particles. Abortive infection was finally obtained, as confirmed by a polymerase chain reaction which failed to detect any proviral HIV1 DNA in the cell line. These results indicate a marked difference between HIV1 and HIV2 in their in vitro interaction with mononuclear phagocytes.

RNA virus evolution and the control of viral disease

RNA viruses and other RNA genetic elements must be viewed as organized distributions of sequences termed quasi-species. This means that the viral genome is statistically defined but individually indeterminate. Stable distributions may be maintained for extremely long time periods under conditions of population equilibrium. Perturbation of equilibrium results in rapid distribution shifts. This genomic organization has many implications for viral pathogenesis and disease control. This review has emphasized the problem of selection of viral mutants resistant to antiviral drugs and the current difficulties encountered in the design of novel synthetic vaccines. Possible strategies for antiviral therapy and vaccine development have been discussed.