Eva Maria Fenyö

A new classification for HIV-1

The phenotype of HIV-1 isolates is defined by the cells in which they replicate in vitro, but these phenotypes can change in vivo with profound implications for viral transmission, pathogenesis and disease progression. Here we propose a new classification system based on co-receptor use, providing a more accurate description of viral phenotype than the present imprecise and often misleading classification schemes.

REPLICATIVE CAPACITY OF HUMAN IMMUNODEFICIENCY VIRUS FROM PATIENTS WITH VARYING SEVERITY OF HIV INFECTION

T-lymphotropic viruses were isolated from 31 patients with different clinical manifestations of human immunodeficiency virus (HIV) infection. Lymphocyte cultures from patients with the acquired immunodeficiency syndrome (AIDS) or pre-AIDS yielded virus rapidly, as indicated by high levels of reverse transcriptase (RT) activity in culture fluids. These viruses were able to establish a persistent infection in several T4-antigen-positive tumour cell-lines. In contrast, lymphocyte cultures from patients with mild or no symptoms yielded virus more slowly and the RT activity was low. Co-cultivation of slow/low-yielding lymphocytes with T4-positive tumour cell-lines showed no or only transient virus production. In 14 out of 23 cases virus could be detected by their fatal cytopathic effects on tumour cells. The relation between severity of illness and in-vitro replication potential of the viruses suggests that in the course of an infection selection may occur for HIV variants that replicate efficiently in T4 cells.

ANTIBODY RESPONSE IN PRIMARY HUMAN IMMUNODEFICIENCY VIRUS INFECTION

The antibody response in 20 homosexual men with symptomatic primary HIV infection was studied with ten different antibody assays (enzyme-linked immunosorbent assays, indirect immunofluorescence assays, radioimmunoprecipitation [RIPA], and western blot). HIV antibodies were detectable by all the assays within 2 months after onset of illness. RIPA and western blot were more sensitive than the other assays--all serum samples obtained at 2 weeks and after were reactive. In all cases, the first serum sample reactive by RIPA precipitated gp160 whereas, by western blot, antibodies to p24 were first recognised. This study shows the necessity of including gp160 and p24 in any assay to detect early antibody response in primary HIV infection. 5 patients were studied by virus isolation. During the 2 first weeks after onset of symptoms, HIV was demonstrated in cell-free plasma in all cases and, in 4 cases, also in peripheral blood mononuclear cells. Samples obtained later contained demonstrable infectious virus in only 1 of 4 cases. Thus a phase of viraemia precedes the antibody response in symptomatic primary HIV infection.

Characteristics of new cell lines derived from Burkitt lymphomas

Thirty‐five cell lines were established from 47 Burkitt lymphoma biopsies. In different biopsies the modal cell size was found to vary and the tumor was often built up by larger cells if the patients received chemotherapy. In all cases the predominant cell size shifted towards larger values during cultivation. All cells in three biopsies from one patient and in the culture lines derived showed surface reactivity with anti‐IgM and antikappa light chain reagents. This trait was maintained in all three lines for about 21 weeks but was lost thereafter. A fourth biopsy—taken after the patient had been treated with cytosine arabinoside—did not have this immunoglobulin reactivity. Chromosomal analysis revealed that one of the IgM reactive lines had 46 as stemline number and normal diploid karyotype, while the nonreactive line had 47 as stemline number with an extra C chromosome in addition to the normal male karyotype. One or two C chromosomes, corresponding in size with pair 10 were formed as markers with subterminal constriction on their long arms. The unusual cellular trait—IgM specificity—being present on both the biopsy and its derived cell line, indicates the representativeness of the culture line for the in‐vivo tumor in this case.

Susceptibility to infection by the human immunodeficiency virus (HIV) correlates with T4 expression in a parental monocytoid cell line and its subclones

The monocytoid tumor cell line U-937 and five derived subclones were infected with the HTLV-IIIB isolate of the human immunodeficiency virus (HIV). Susceptibility to infection and sensitivity to the cytopathic effects correlated with the expression of the T4 antigen on the cell surface. On the basis of these characteristics the lines could be divided into three groups. Less than 10% T4 positive cells were present in the parental line and clone 4; hence productive infection could only be established after a long latency or with a high virus inoculum. These lines showed no or only marginal cytopathic effect. Clone 16 contained more than 95% T4 positive cells and was the most sensitive line to infection with HTLV-IIIB and its cytopathic effect. Cell death was so extensive following infection that no continuous virus producer line could ever be established from clone 16 cells. Cultures with intermediate T4 expression (50-70% T4+ cells) also had intermediate susceptibility to virus infection. Cytopathic changes, even if pronounced, could be overcome in the infected cultures by the addition of uninfected cells and, in each case, a producer line could be established. HTLV-IIIB infection of clone 16 cells could be blocked by preincubation with monoclonal anti-T4 antibodies indicating a close similarity between the HTLV-IIIB receptor on T4 positive T cells and monocytoid cells. The results thus show that T4 positive monocytoid cells can function as target cells for the HIV.

Polymerase chain reaction, virus isolation and antigen assay in HIV-1-antibody-positive mothers and their children

Diagnosis of perinatal HIV-1 infection is complicated by the persistence of maternal antibodies and the conflicting reports on polymerase chain reaction (PCR) reactivity in children born to HIV-1-seropositive mothers. We have compared PCR with other diagnostic methods for perinatal HIV-1 infection and have attempted also to identify maternal markers which correlate with risk of transmission. PCR was the most sensitive method for early diagnosis of perinatal transmission of HIV-1, but the PCR-positive children (n = 11) developed at least one additional sign of infection. The PCR-negative children (n = 76) were clinically healthy, virus isolation negative, and their serum was HIV-1-antigen-negative. All children who had become seronegative (n = 36) were both PCR- and isolation-negative. Antigenaemia in the mothers correlated significantly with higher risk of perinatal transmission of HIV-1, while no other parameters (clinical stage, lymphocyte subsets, PCR and isolation) showed such a correlation. This indicates that the level of virus expression may be of key importance for the risk of vertical transmission of HIV-1 infection.

Isolate-specific neutralizing antibodies in patients with progressive HIV-1-related disease.

Four individuals with increasing severity of HIV-1 infection were studied for serum neutralizing activity against their own virus isolates collected during 1-3 years. Sequential serum samples and HIV-1 isolates were available from these patients from the stage of lymphadenopathy to severe immunodeficiency. The replicative capacity of isolates changed from slow/low to rapid/high in each patient during the study period. Sequential virus isolates showed differences in sensitivity to neutralization by autologous as well heterologous area. Taken together with our previous results demonstrating that variant viruses resistant to neutralization by autologous sera emerge during the year following primary infection, neutralization-resistant variants seem to emerge during the entire course of HIV-1 infection. The ability to produce neutralizing antibodies to autologous virus appears to correlate with replicative capacity of the virus and the degree of immunodeficiency in the patient.

Human immunodeficiency virus infection of the brain: I. Virus isolation and detection of HIV specific antibodies in the cerebrospinal fluid of patients with varying clinical conditions

Isolation of the human immunodeficiency virus (HIV) has been attempted from the cerebrospinal fluid (CSF) of 29 subjects with varying severity of HIV infection. Virus could be isolated from patients in all stages of disease including patients with primary HIV infection and asymptomatic carriers. In the early stages of infection free virus was infrequently present in the CSF but could be isolated from the cells present in CSF. This suggests that HIV may reach the brain at a very early stage of infection and that initially there is little production of virus from infected cells. In the late stages of HIV infection, associated with increasing severity of immunodeficiency, free virus could readily be isolated from the CSF. With one exception, all of these patients had neurological and/or psychiatric symptoms, as compared to only 2 (of 13) subjects in the early stages of infection. All patients with HIV-specific antibodies in serum had antibodies also in CSF. Examined by a radioimmunoprecipitation assay, CSF was more often found to contain antibodies to the precursor (p55) of viral core proteins than the corresponding serum of the patients. We propose that immune disturbances have an essential pathogenic role in the neurological/psychiatric symptoms associated with HIV infection, possibly through allowing increased viral expression in the central nervous system.

BROAD CROSS-NEUTRALIZING ACTIVITY IN SERUM IS ASSOCIATED WITH SLOW PROGRESSION AND LOW RISK OF TRANSMISSION IN PRIMATE LENTIVIRUS INFECTIONS

Sera from human immunodeficiency virus type 1 and type 2 (HIV-1 and HIV-2)-infected humans were tested with autologous (from the same individual) and heterologous (from other individuals) virus isolates in a neutralization assay. Similarly, sera from experimentally simian immunodeficiency virus (SIVsm from sooty mangabey) or HIV-2SBL6669-infected cynomolgus macaques were tested for neutralizing activity against autologous and heterologous reisolates. In the neutralization assay, the virus dose ranged between 10-75 50% infectious dose (ID50), sera were used in five 2- or 4-fold dilutions, beginning with 1:20, and human peripheral blood mononuclear cells (PBMCs) served as target cells. The readout of the 7-day assay was a HIV-1 or HIV-2 antigen enzyme-linked immunosorbent assay (ELISA). Our results show that SIVsm-inoculated monkeys who develop early immunodeficiency lack serum neutralizing activity or develop a neutralizing antibody response with narrow specificity. Long survival is associated with the ability to neutralize several autologous and heterologous SIVsm reisolates. Infection of macaques with HIV-2SBL6669 did not cause disease within the 5 years observation time and elicited a broadly cross-reactive neutralizing antibody response, including neutralization of other, independently obtained, HIV-2 isolates. In HIV-1-infected humans, neutralizing antibodies can only be detected in up to 50% of cases. Neutralizing activity, whenever present, may show a broad specificity, that is, neutralization may occur across genetic subtypes. Presence of broadly cross-reactive neutralizing antibodies is associated with a lower risk of HIV-1 (subtype B) transmission both from mother to child and sexually from male to female. Unlike HIV-1 infection, serum neutralizing activity is regularly present in HIV-2 infection. In view of the differences between HIV-1 and HIV-2 pathogenesis, we suggest that an effective neutralizing antibody response may contribute to a delay in disease progression and to a decrease in risk of transmission.

Neurotropism of human immunodeficiency virus.

Three major characteristics of human immunodeficiency virus (HIV) infection define HIV as neurotropic. 1) Clinically, distinct neurological syndromes are associated with HIV infection and 2) presence of the virus as well as 3) pathological changes can be demonstrated in the central nervous system. Spread of HIV to the brain seems to be the general rule. Virus expression appears to be restricted during the asymptomatic period but increases with severity of HIV infection. Whether this reflects the emergence of virus variants with increased replica‐tive capacity in brain cells has yet to be elucidated.