Dynamic evolution of antibody populations in a rhesus macaque infected with attenuated simian immunodeficiency virus identified by surface plasmon resonance

BACKGROUND

Increasing evidence suggests that an effective AIDS vaccine will need to elicit broadly neutralizing antibody responses. However, the mechanisms of antibody-mediated neutralization have not been defined. Previous studies from our lab have identified significant differences in the rates of antibody binding to trimeric SIV envelope proteins that correlate with neutralization sensitivity. Importantly, these results demonstrate differences in monoclonal antibody (MAb) binding to neutralization-sensitive and neutralization-resistant envelope proteins, suggesting that one mechanism for virus neutralization may be related to the stability of antibody binding. To date, little has been done to evaluate the binding properties of polyclonal serum antibodies elicited by SIV infection or vaccination.

METHODS

In the current study, we translate these findings with MAbs to study antibody binding properties of polyclonal serum antibody responses generated in rhesus macaques infected with attenuated SIV. Quantitative and qualitative binding properties of well-characterized longitudinal serum samples to trimeric, recombinant SIV gp140 envelope proteins were analyzed using surface plasmon resonance (SPR) technology (Biacore).

RESULTS

Results from these studies identified two antibody populations in most of the samples analyzed; one antibody population exhibited fast association/dissociation rates (unstable) while the other population demonstrated slower association/dissociation rates (stable). Over time, the percentage of the total binding response of each antibody population evolved, demonstrating a dynamic evolution of the antibody response that was consistent with the maturation of antibody responses defined using our standard panel of serological assays. However, the current studies provided a higher resolution analysis of polyclonal antibody binding properties, particularly with respect to the early time-points post-infection (PI), that is not possible with standard serological assays. More importantly, the increased stability of the antibody population with time PI corresponded with potent neutralization of homologous SIV in vitro.

CONCLUSIONS

These results suggest that the stability of the antibody-envelope interaction may be an important mechanism of serum antibody virus neutralization. In addition, measurements of the 'apparent' rates of association and dissociation may offer unique numerical descriptors to characterize the level of antibody maturation achieved by candidate vaccine strategies capable of eliciting broadly neutralizing antibody responses.

Induction of cell-cycle regulators in simian immunodeficiency virus encephalitis

Neuronal degeneration associated with human immunodeficiency virus encephalitis has been attributed to neurotoxicity of signaling molecules secreted by activated, infected macrophages. We hypothesized that the barrage of signals present in the extracellular milieu of human immunodeficiency virus-infiltrated brain causes inappropriate activation of neuronal cell-cycle machinery. We examined the presence of three members of the cell-cycle control machinery: pRb, E2F1, and p53 in the simian immunodeficiency virus encephalitis (SIVE) model. Compared to noninfected and simian immunodeficiency virus-infected, nonencephalitic controls, we observed increased protein expression of E2F1 and p53 and aberrant cellular localization of E2F1 and pRb. In SIVE, E2F1 was abundant in the cytoplasm of neurons in both neurons and astrocytes proximal to SIVE pathology in the basal ganglia. pRb staining was nuclear and cytoplasmic in cortical neurons of SIVE cases. Antibodies to phosphorylated pRb also labeled the cytoplasm of cortical neurons. These data suggest that in SIVE, cell signaling results in phosphorylation of pRb which may result in subsequent alteration in E2F1 activity. As increased E2F1 and p53 activities have been linked to cell death, these data suggest that the neurodegeneration in SIVE could in part be because of changes in expression and activity of cell-cycle machinery.

Differential tumor necrosis factor alpha production in simian immunodeficiency virus-infected rhesus macaques coinfected with Mycobacterium avium

Mycobacterium avium infections are the third most common opportunistic infection in patients with AIDS. Simian immunodeficiency virus (SIV)-infected rhesus macaques naturally acquire M. avium infections from the environment, and their clinical symptoms are similar to those observed in AIDS patients. We characterized concurrent infection with SIV and M. avium in monkeys on the basis of the growth of the bacteria in macrophages (Mphis) from rhesus macaques and the ability of M. avium to induce SIV replication and tumor necrosis factor alpha (TNF-alpha) production. The simian M. avium isolate grew significantly better than did an isolate from an AIDS patient or a chicken isolate (P = .001); it induced significantly more TNF-alpha production in Mphis from SIV-positive and SIV-negative monkeys than did the isolate from an AIDS patient (P = .013). No significant increase in SIV replication was seen in the M. avium isolates, and no correlation was found between increased SIV replication and increased TNF-alpha production. In addition, Mphis from monkeys infected with M. avium during late-stage SIV disease produced less TNF-alpha when stimulated with virulent M. avium.

Evaluation of a candidate human immunodeficiency virus type 1 (HIV-1) vaccine in macaques: effect of vaccination with HIV-1 gp120 on subsequent challenge with heterologous simian immunodeficiency virus-HIV-1 chimeric virus

Human immunodeficiency virus type 1 (HIV-1) envelope vaccines can now be evaluated for efficacy in macaques by challenging with chimeric viruses in which the env, tat and rev genes of simian immunodeficiency virus (SIV) have been replaced by those of HIV-1. Most experiments have so far been conducted using gp120 molecules derived from T-cell-adapted LAI or MN strains of HIV-1, which predominantly use the CXCR-4 co-receptor. These vaccines protect against infection by apathogenic chimeric virus carrying the same envelope sequences. In the experiment described here, four macaques were vaccinated with W61D gp120 derived from a low passage Dutch isolate and capable of inhibiting the binding of MIP1beta to the co-receptor CCR-5. This vaccine was potent, inducing high titres of binding and neutralizing antibodies against the homologous HIV-1 and tenfold lower titres against a heterologous challenge virus (SHIV(SF33)) in which the env, tat and rev genes of SIV had been replaced by those of a San Francisco isolate, HIV-1(SF33). Despite strong immune responses to the vaccine there was no evidence that it protected against challenge with this chimeric virus. The antigenic divergence between vaccine and challenge virus or the increased virulence of the challenge virus may be responsible for the inability of this vaccine to protect against infection by SHIV(SF33).

Detection of respiratory syncytial virus in nasopharyngeal secretions by DNA-RNA hybridization

We have developed an RNA-cDNA hybridization assay for the detection of respiratory syncytial virus (RSV) RNA in nasopharyngeal samples. We chose to use as probe a cDNA complementary to the nucleocapsid protein gene of RSV, integrated into the plasmid vector pBR322. The lower limit of sensitivity of the assay is 8.2 X 10(2) PFU of the Long strain of RSV. In throat washes with added cell-free virus, the assay can detect 3.3 X 10(3) PFU of RSV. Respiratory secretions were collected from a group of 104 infants in New Orleans, and 73 of the samples were tested for RSV by immunofluorescence (IF). All were then frozen at -70 degrees C for later testing by hybridization, and 67 were tested for RSV antigens by enzyme immunoassay (EIA). A second set of respiratory secretions from 48 infants in Denver were cultured for virus, assayed for RSV antigen by EIA, and then frozen for later testing by hybridization. For those samples on which IF was performed, hybridization, compared with IF, had a sensitivity of 49% and a specificity of 66%. For samples tested by EIA, hybridization had a sensitivity of 60% and a specificity of 81% compared with EIA. Compared with virus isolation, hybridization assay had a sensitivity of 73% and a specificity of 92%. With clinical samples, the sensitivity and specificity of the assay were improved with the addition of a control blot, which was hybridized to the plasmid vector (pBR322). The performance of the hybridization assay can be expected to improve when the assay is used with fresh clinical material rather than frozen samples.