Kathelyn S. Steimer

Infection by the Retrovirus Associated with the Acquired Immunodeficiency Syndrome: Clinical, Biological, and Molecular Features

Peripheral mononuclear cells from more than 160 persons from groups at risk for the acquired immunodeficiency syndrome (AIDS) have yielded AIDS-associated retroviruses (ARV). Antibodies to ARV can also be found in these risk groups. Antibody-negative, virus-positive persons have been identified with early infection or possible viremia with immune complex formation. Established lines of human T and B cells, monocytes, and promyelocytes have been infected with ARV. Moreover, infectious virus has been recovered from macrophages cultured from the blood of some persons with AIDS. The cytopathic effects of ARV in T cells is associated with the accumulation of unintegrated viral forms in the infected cells. The ARV has also been isolated from plasma, serum, saliva, semen, urine, cerebrospinal fluid, and brain tissue. All these results reflect the wide host range of ARV and support its role in neurologic abnormalities seen in some patients. Molecular studies of independent ARV isolates indicate a polymorphism of nucleotide sequences, particularly in the viral envelope region. All these features place ARV in the lentivirus subfamily of human retroviruses.

Differential antibody responses of individuals infected with AIDS-associated retroviruses surveyed using the viral core antigen p25gag expressed in bacteria.

Infection with the retrovirus that is the etiological agent of acquired immune deficiency syndrome (AIDS) is characterized by the development of antiviral antibodies. To generate reagents for studying immune responses to individual viral proteins, we have produced viral antigens in microorganisms by recombinant DNA techniques. Large amounts of the major core protein (p25gag) of an isolate of the AIDS retrovirus (AIDS-associated retrovirus; ARV-2) have been directly expressed in Escherichia coli. Recombinant p25gag (R-p25gag) has been purified and used in an enzyme-linked immunosorbent assay (ELISA) for antibodies to p25gag. Serum samples obtained from 100 individuals with AIDS, AIDS-related complex (ARC), or potential exposure to the virus through sexual contact with AIDS or ARC patients (contacts) were tested first in an ELISA with disrupted whole virus to determine which of the subjects had mounted an antibody response to the virus (virus seropositive) and then in the p25gag ELISA to determine if they had antibodies to this particular viral antigen. We observed a decrease in the proportion of virus seropositive individuals with antibodies to p25gag among patients groups in which the disease was more advanced; contacts were often positive (71%), ARC patients less frequently positive (48%), and AIDS patients only rarely positive (16%). Our results suggest that monitoring p25gag seropositivity of infected individuals may be useful for predicting either the prognosis or the stage of the disease.

Antibody-dependent cellular cytotoxicity is directed against both the gp120 and gp41 envelope proteins of HIV.

To define the target antigens for antibody-dependent cellular cytotoxicity (ADCC), assays were performed using affinity-purified human immunoglobulin (Ig) or polyclonal rabbit sera directed against specific proteins of HIV. ADCC was not found using affinity-purified anti-core (p25) human Ig or sera obtained from rabbits hyper-immunized with recombinant p25. However, when affinity-purified human Ig or rabbit antisera specific for the envelope glycoproteins, gp120 or gp41, were used in ADCC assays, killing of HIV-infected cells was observed. These results indicate that antibodies in the infected individual that mediate ADCC are directed against both the gp120 and gp41 HIV envelope proteins and not against the viral core protein.

Neutralization of a Clade B Primary Isolate by Sera from Human Immunodeficiency Virus-Uninfected Recipients of Candidate AIDS Vaccines

The inability of antibodies induced by experimental human immunodeficiency virus type 1 (HIV-1) vaccines to neutralize HIV-1 primary isolates may be due to a failure to elicit such antibodies, antigenic differences between the vaccine and the strains tested, insensitivity of the assays used, or to a combination of factors. New neutralization assays were used to determine the ability of candidate AIDS vaccines to generate neutralizing antibodies for clade B primary isolate BZ167, which is closely related in portions of its envelope to the immunizing strains. Sera from HIV-uninfected volunteers in vaccine trials were tested, and neutralizing activity was found in recipients of recombinant (r) gp120MN or of rgp160MN-containing canarypox boosted with rgp120SF-2. Detection of antibodies that neutralize primary isolate BZ167 correlated with neutralizing activity for homologous vaccine strains. These data demonstrate that certain candidate AIDS vaccines can elicit antibodies that neutralize a primary isolate of HIV-1.

Infection of baboons with simian/human immunodeficiency viruses.

Baboons were evaluated for their utility to serve as a model for testing envelope-based vaccines against human immunodeficiency virus type 1 (HIV-1). The ability of HIV-1 strains IIIB, RF, and SF2 to infect baboons was compared with that of simian/human immunodeficiency virus (SHIV) recombinant viruses comprised of either HXB2 or SF2 env, tat, rev, and vpu genes inserted into the SIVmac239 backbone. Both SHIV recombinants replicated in baboon PBMC in vitro, while no evidence of replication was noted for HIV-1 strains (MN, IIIB, SF2). Infection of baboons in vivo correlated with the restriction of infection in vitro. Virus was recovered by cocultivation methods early after SHIV (HXBc2) infection of two baboons with seroconversion profiles that parallel those observed in simian immunodeficiency virus (SIV)mac-infected rhesus monkeys. One of two baboons inoculated with SHIV(SF2) also seroconverted within 4 weeks; however, the kinetics of infection in a second animal appeared much later, with seroconversion to gp120 not evident until 20 weeks and no virus recovery during 32 weeks following infection. Viral DNA was detected in the lymph nodes of the SHIV-inoculated animals by nested polymerase chain reaction (PCR) amplification. Histopathologic changes were evident in lymph nodes, yet no overt clinical disease was observed. When HIV-1 strains (IIIB, RF, and SF2) were inoculated into baboons, virus was not recovered and no seroconversion to the major HIV-1 antigens was observed. However, viral DNA from the lymph nodes of four animals inoculated with HIV-1 strains could be detected by nested PCR, indicating a persistent but diminutive infection of HIV-1. The baboon thus represents a new animal model for testing HIV-1 envelope-based vaccines including the evaluation of new immunogens, dosages, routes, and adjuvants that act in eliciting protective responses.

Infection by the Retrovirus Associated With the Acquired Immunodeficiency Syndrome: Clinical, Biological, and Molecular Features

Abstract Peripheral mononuclear cells from more than 160 persons from groups at risk for the acquired immunodeficiency syndrome (AIDS) have yielded AIDS-associated retroviruses (ARV). Antibodies to...