Intrinsic susceptibility of rhesus macaque peripheral CD4(+) T cells to simian immunodeficiency virus in vitro is predictive of in vivo viral replication

Abstract

Previous studies with simian immunodeficiency virus (SIV) infection of rhesus macaques suggested that the intrinsic susceptibility of peripheral blood mononuclear cells (PBMC) to infection with SIV in vitro was predictive of relative viremia after SIV challenge. The present study was conducted to evaluate this parameter in a well-characterized cohort of six rhesus macaques selected for marked differences in susceptibility to SIV infection in vitro. Rank order relative susceptibility of PBMC to SIVsmE543-3-infection in vitro was maintained over a 1-year period of evaluation. Differential susceptibility of different donors was maintained in CD8(+) T-cell-depleted PBMC, macrophages, and CD4(+) T-cell lines derived by transformation of PBMC with herpesvirus saimiri, suggesting that this phenomenon is an intrinsic property of CD4(+) target cells. Following intravenous infection of these macaques with SIVsmE543-3, we observed a wide range in plasma viremia which followed the same rank order as the relative susceptibility established by in vitro studies. A significant correlation was observed between plasma viremia at 2 and 8 weeks postinoculation and in vitro susceptibility (P < 0.05). The observation that the two most susceptible macaques were seropositive for simian T-lymphotropic virus type 1 may suggests a role for this viral infection in enhancing susceptibility to SIV infection in vitro and in vivo. In summary, intrinsic susceptibility of CD4(+) target cells appears to be an important factor influencing early virus replication patterns in vivo that should be considered in the design and interpretation of vaccine studies using the SIV/macaque model.

FIG. 1

Bar graph of the distribution of in vitro susceptibility of PBMC of 22 macaques as assessed by relative TCID of the SIVsmE543-3 stock. STLV-1-seropositive macaques are indicated with black bars; STLV-1-negative macaques are indicated with shaded bars.

FIG. 2

RT activity in culture supernatants collected at 11 days postinfection from PBMC of six macaques infected with serial 10-fold dilutions of SIVsmE543-3. Numbers at the top and bottom represent the log₁₀ dilution of virus input (i.e., 6 = 10⁶). The minimal TCIDs for these six donors are shown to the right.

FIG. 3

Correlation between TCID of SIVsmE543-3 or SIVmac251 in six donors. The bar graph shows relative TCIDs of these two stocks in a representative experiment where all infections were performed in parallel. This result was confirmed in two independent experiments.

FIG. 4

Correlation between susceptibility to SIVsmE543-3 of PBMC and HVS-transformed T-cell lines. The bar graph shows relative TCIDs of SIVsmE543 in PBMC and HVS lines of the six macaques.

FIG. 5

Flow cytometric analysis of CD3⁺ T cells in HVS-transformed T-cell lines for expression of CCR5 using monoclonal antibody 2D7. The percentage of cells expressing CCR5 is shown at the top right of each panel. Analysis of the Maji/CCR5 cell line is shown on the bottom right as a positive control for staining of CCR5.

FIG. 6

Plasma viremia and the correlation between plasma viremia and in vitro susceptibility. (A) Plasma viremia in the cohort of six macaques is shown graphically over the first 18 weeks after inoculation. Plasma samples were collected at 0, 3, 7, 10, 14, 17, 21, and 28 days and every 2 weeks thereafter. (B) The statistically significant correlation observed between peak primary plasma viremia and TCID determined in vitro is shown in a scatter plot.