The envelope glycoprotein ectodomains determine the efficiency of CD4+ T lymphocyte depletion in simian-human immunodeficiency virus-infected macaques

Abstract

CD4+ T lymphocyte depletion in human immunodeficiency virus type 1 (HIV-1)-infected humans underlies the development of acquired immune deficiency syndrome. Using a model in which rhesus macaques were infected with chimeric simian-human immunodeficiency viruses (SHIVs), we show that both the level of viremia and the structure of the HIV-1 envelope glycoprotein ectodomains individually contributed to the efficiency with which CD4(+) T lymphocytes were depleted. The envelope glycoproteins of recombinant SHIVs that efficiently caused loss of CD4(+) T lymphocytes exhibited increased chemokine receptor binding and membrane-fusing capacity compared with those of less pathogenic viruses. These studies identify the HIV-1 envelope glycoprotein ectodomains as determinants of CD4(+) T lymphocyte loss in vivo and provide a foundation for studying pathogenic mechanisms.

Figure 1

Genomic organization of SHIV variants. The SHIV proviral genome is shown on the top. Sequences from SIV_mac239 are shown in gray boxes and sequences from HIV-1 are shown in white (, 52). Enzyme restriction sites relevant for cloning of the SHIV variants are shown. The proviral structures of the SHIV variants used in this study are depicted beneath. SHIV-89.6* is identical to the parental SHIV-89.6, except that it contains the passage-associated tat and LTR changes (34). The other three variants differ from SHIV-89.6* only in the sequence of the envelope glycoproteins. SHIV-KB9 has the passage-associated amino acid changes in the gp120/gp41 ectodomains and the gp41 cytoplasmic tail change compared with SHIV-89.6*. SHIV-KB9ct has only the gp41 cytoplasmic tail change, and SHIV-KB9ecto has only the gp120/gp41 ectodomain changes.

Figure 2

Absolute CD4⁺ T cell counts and plasma p27 antigenemia in infected monkeys. (A) The absolute CD4⁺ T cell counts in the peripheral blood of animals infected with SHIV-89.6*, SHIV-KB9ct, SHIV-KB9ecto, and SHIV-KB9 during the first 36 d of infection are shown. (B) The p27 antigen levels in the plasma of SHIV-infected animals are shown.

Figure 2

Absolute CD4⁺ T cell counts and plasma p27 antigenemia in infected monkeys. (A) The absolute CD4⁺ T cell counts in the peripheral blood of animals infected with SHIV-89.6*, SHIV-KB9ct, SHIV-KB9ecto, and SHIV-KB9 during the first 36 d of infection are shown. (B) The p27 antigen levels in the plasma of SHIV-infected animals are shown.

Figure 3

Relationship between viremia and CD4⁺ T lymphocyte counts for SHIV variants with different envelope glycoprotein domains. A “set-point” value for the absolute CD4⁺ T lymphocyte count in each animal (the median of the CD4 counts recorded on days 14–36 after infection) was plotted against the cumulative p27 antigenemia (area under the p27 versus time curves in Fig. 2 B). The data were grouped according to the sequences (either wild-type 89.6 or containing the KB9 passage- associated changes) of the viral envelope glycoprotein ectodomains (A) or cytoplasmic tails (B). The curves are fitted to the data using a nonlinear exponential decay model.

Figure 3

Relationship between viremia and CD4⁺ T lymphocyte counts for SHIV variants with different envelope glycoprotein domains. A “set-point” value for the absolute CD4⁺ T lymphocyte count in each animal (the median of the CD4 counts recorded on days 14–36 after infection) was plotted against the cumulative p27 antigenemia (area under the p27 versus time curves in Fig. 2 B). The data were grouped according to the sequences (either wild-type 89.6 or containing the KB9 passage- associated changes) of the viral envelope glycoprotein ectodomains (A) or cytoplasmic tails (B). The curves are fitted to the data using a nonlinear exponential decay model.

Figure 4

Relationship between infected lymph node cells and CD4⁺ T lymphocyte counts. The number of viral RNA–positive cells in the T cell zone of lymph nodes, which were taken from the animals at day 10 after inoculation, was compared with the “set point” values for the peripheral blood CD4⁺ T lymphocyte counts. The animal identification numbers for three of the data points discussed in the text are provided.

Figure 5

Replication and syncytium-forming ability of SHIV variants. (A) Rhesus PBMCs were PHA-stimulated and infected with equal amounts of SHIV-89.6, SHIV-89.6*, SHIV-KB9ct, SHIV-KB9ecto, and SHIV-KB9. Cells were maintained in the presence of IL-2 for the duration of the experiment and an aliquot of the culture medium was removed every day for RT analysis. (B) Uninfected CEM×174 cultures (mock) were compared with cultures infected with SHIV-89.6, SHIV-KB9ecto, and SHIV-KB9 for the presence of syncytia. (C) COS-1 cells, transiently expressing the 89.6, KB9ct, KB9ecto, or KB9 envelope glycoproteins, were cocultivated with CEM×174 cells for 6 h at 37°C. The number of syncytia was scored and normalized to that observed for the parental 89.6 envelope glycoproteins. The mean values and SE derived from three independent experiments are shown.

Figure 6

Receptor-binding of the 89.6 and KB9 gp120 envelope glycoproteins. (A) The binding of the 89.6 and KB9 gp120 glycoproteins to human sCD4 absorbed onto the surface of an ELISA plate is shown. Values represent the mean and standard deviations from two independent experiments, each containing four replicate samples. (B) The ability of the 89.6 and KB9 gp120 glycoproteins to compete with MIP-1β binding to mouse cells expressing human CCR5 was assessed in the presence of 100 nM sCD4. The results shown are representative of two independent experiments, each performed with duplicate samples at each concentration of competitor. Relative inhibitory constants for MIP-1β (positive control), 89.6 gp120, and KB9 gp120 were 0.20 nM, 39.0 nM, and 4.4 nM, respectively. The YU2ΔV1/2/3 glycoprotein, which lacks the V3 loop and thus is unable to bind CCR5 (19), was included as a negative control.

Figure 6

Receptor-binding of the 89.6 and KB9 gp120 envelope glycoproteins. (A) The binding of the 89.6 and KB9 gp120 glycoproteins to human sCD4 absorbed onto the surface of an ELISA plate is shown. Values represent the mean and standard deviations from two independent experiments, each containing four replicate samples. (B) The ability of the 89.6 and KB9 gp120 glycoproteins to compete with MIP-1β binding to mouse cells expressing human CCR5 was assessed in the presence of 100 nM sCD4. The results shown are representative of two independent experiments, each performed with duplicate samples at each concentration of competitor. Relative inhibitory constants for MIP-1β (positive control), 89.6 gp120, and KB9 gp120 were 0.20 nM, 39.0 nM, and 4.4 nM, respectively. The YU2ΔV1/2/3 glycoprotein, which lacks the V3 loop and thus is unable to bind CCR5 (19), was included as a negative control.

Figure 7

Neutralization of viruses with the 89.6, KB9ct and KB9 envelope glycoproteins. Recombinant viruses encoding CAT and bearing either the 89.6, KB9ct, or KB9 envelope glycoproteins were incubated with different concentrations of IgG1b12 (A), AG1121 (B), or sCD4 (C). The viruses were then incubated with CEM×174 cells. CAT activity in the CEM×174 cells was assessed 3 d later and is expressed as the percentage of CAT activity seen in the absence of antibody or sCD4. The results shown are representative of those obtained in at least two independent experiments.

Figure 7

Neutralization of viruses with the 89.6, KB9ct and KB9 envelope glycoproteins. Recombinant viruses encoding CAT and bearing either the 89.6, KB9ct, or KB9 envelope glycoproteins were incubated with different concentrations of IgG1b12 (A), AG1121 (B), or sCD4 (C). The viruses were then incubated with CEM×174 cells. CAT activity in the CEM×174 cells was assessed 3 d later and is expressed as the percentage of CAT activity seen in the absence of antibody or sCD4. The results shown are representative of those obtained in at least two independent experiments.