In vivo HIV-1 infection of CD45RA(+)CD4(+) T cells is established primarily by syncytium-inducing variants and correlates with the rate of CD4(+) T cell decline

Abstract

Switch from non-syncytium-inducing (NSI) to syncytium-inducing (SI) HIV type 1 (HIV-1) is associated with accelerated CD4(+) T cell depletion, which might partially be explained by higher virulence of SI variants compared with NSI variants. Because NSI and SI variants use different coreceptors for entry of target cells, altered tropism might offer an explanation for increased pathogenesis associated with SI HIV-1 infection. To investigate whether SI and NSI HIV-1 variants infect different CD4(+) T cell subsets in vivo, the distribution of SI and NSI variants over CD4(+) memory (CD45RA(-)RO(+)) and naive (CD45RA(+)RO(-)) cells was studied by using limiting dilution cultures. In contrast to NSI variants that were mainly present in CD45RO(+) cells, SI variants were equally distributed over CD45RO(+) and CD45RA(+) cells. Infection of memory cells by both NSI and SI HIV-1 and infection of naive cells primarily by SI HIV-1 corresponded closely with the differential cell surface expression of CXCR4 and CCR5. The frequency of SI-infected CD45RA(+) CD4(+) T cells, but not the frequency of NSI- or SI-infected CD45RO(+) CD4(+) T cells, correlated with the rate of CD4(+) T cell depletion. Infection of naive cells by SI HIV-1 may interfere with CD4(+) T cell production and thus account for rapid CD4(+) T cell depletion.

Figure 1

Ratio of virus load in CD45RA⁺ and CD45RO⁺ CD4⁺ T cells. The ratio between the frequency of infected CD45RA⁺CD4⁺ T cells and the frequency of infected CD45RO⁺CD4⁺ T cells is shown for individuals with only NSI variants and individuals with both SI and NSI variants. Individuals with an undetectable virus load in the CD45RA⁺ cells were excluded (N1, N8, S7, S12; Table 1). The numbers and bars in the graph indicate median values.

Figure 2

Distribution of SI and NSI variants in total CD4⁺ T cells, CD45RA⁺, and CD45RO⁺ CD4 T cells. The total number of biological virus clones that were obtained by cocultivation with healthy donor PBL of total PBMC (a, Top), CD45RO⁺CD4⁺ T cells (a, Middle), and CD45RA⁺CD4⁺ T cells (a, Bottom) of SI carrying individuals are depicted at the top of each panel in a. The open bars represent the proportion of NSI clones, and filled bars represent the proportion of SI clones. Total PBMC from patient S5 was not analyzed (a, Top). No biological clones were obtained from CD45RA⁺CD4⁺ T cells from patient S7 (a, Bottom). The difference in the proportion of SI variants in CD45RO⁺ and CD45RA⁺ cells was analyzed for the individuals with detectable CD45RA⁺ load (b). The numbers and bars in the graph indicate median values. NT, Not tested. NA, not applicable.

Figure 3

CCR5 and CXCR4 expression on CD45RA⁺ and CD45RO⁺ CD4 T cells. Using three-color flow cytometry, the percentages CCR5- and CXCR4-positive naive and memory cells were determined. FACScan images of one representative patient (S11) are shown (a). CD4⁺ lymphocytes were gated according to their forward and side scatter and CD4 staining. (Left) CD45RA vs. CD45RO staining. (Middle) CD45RO vs. CXCR4 staining. (Right) CD45RA vs. CCR5 staining. The proportion of CD45RA^high cells corresponded with the proportion of CD45RO⁻ cells, and the proportion of CD45RA⁻ cells corresponded with the proportion of CD45RO^high cells; the percentages are depicted on the outside of the graphs. The percentages of CXCR4-expressing CD45RO⁺ (RA⁻) and CD45RO⁻ (RA⁺) cells and percentages of CCR5-expressing CD45RA⁺ (RO⁻) and CD45RA⁻ (RO⁺) cells are depicted in the graphs. For all individuals, with NSI variants only (○) or with SI variants (●), these percentages are shown in b. The numbers and bars in the graph indicate median values.

Figure 4

CD4⁺ T cell decline and virus load for the 2-yr period spanning the moment of virus isolation and virus load determination (t = 0). The average CD4⁺ T cell counts per 3-mo interval were calculated for individuals with NSI variants only (○) and individuals with SI variants (●) (a). At the top of a, the number of included patients is shown. The linear regression coefficients (R_c) are depicted. Bars indicate the SEM. For the SI-carrying individuals, the correlation between CD4⁺ T cell decline and the relative virus load (Left) as well as the absolute SI load in the CD45RA⁺ cells (Right) was analyzed (b), and the correlations between the CD45RA⁺ SI load and the decline in CD45RA⁺ (Left) and CD45RO⁺ CD4⁺ T cells (Right) were analyzed (c). The Spearman correlation coefficients (R_s) and the P values are shown.