Naive T-cell depletion related to infection by X4 human immunodeficiency virus type 1 in poor immunological responders to highly active antiretroviral therapy

Abstract

The reasons for poor CD4+ T-cell recovery in some human immunodeficiency virus (HIV)-infected subjects despite effective highly active antiretroviral therapy (HAART) remain unclear. We recently reported that CXCR4-using (X4) HIV-1 could be gradually selected in cellular reservoirs during sustained HAART. Because of the differential expression of HIV-1 coreceptors CCR5 and CXCR4 on distinct T-cell subsets, the residual replication of R5 and X4 viruses could have different impacts on T-cell homeostasis during immune reconstitution on HAART. We examined this hypothesis and the mechanisms of CD4+ T-cell restoration by comparing the virological and immunological features of 15 poor and 15 good immunological responders to HAART. We found a high frequency of X4 viruses in the poor immunological responders. But the levels of intrathymic proliferation of the two groups were similar regardless of whether they were infected by R5 or X4 virus. The frequency of recent thymic emigrants in the poor immunological responders was also similar to that found in the good immunological responders, despite their reduced numbers of naïve CD4+ T cells. Our data, rather, suggest that the naïve T-cell compartment is drained by a high rate of mature naïve cell loss in the periphery due to bystander apoptosis or activation-induced differentiation. X4 viruses could play a role in the depletion of naïve T cells in poor immunological responders to HAART by triggering persistent T-cell activation and bystander apoptosis via gp120-CXCR4 interactions.

FIG. 1.

High frequency of CXCR4-using viruses in poor immunological responders. (A) Cell-associated HIV-1 DNA load in PBMCs. (B) Genotypic (geno) and phenotypic (pheno) characterization of HIV-1 isolates. Patients whose quasispecies included only pure R5 clones are classified as “R5,” and those with some pure X4 or R5X4 dual-tropic clones are classified as “X4.” Also see Fig. S2 in the supplemental material for an analysis of quasispecies in the two groups.

FIG. 2.

Similar levels of intrathymic proliferation in poor and good immunological responders. (A) Percentage of the CD45RA⁺ CD27⁺ CD4⁺ and CD8⁺ T-cell populations of poor immunological responders (PIR) and good immunological responders (GIR). (B) Measure of the sj/βTREC ratio. Closed red circles, PIR harboring some X4 viruses; closed red circles with blue rings, PIR harboring R5 viruses with an “X4-like” genotype; gray circles, PIR in whom coreceptor usage could not be determined; open red circles, GIR harboring some X4 viruses; open blue circles, GIR harboring R5 viruses; open gray circles, GIR in whom coreceptor usage could not be determined. (C) Correlation between the sj/βTREC ratio and age. Closed circles, PIR; open circles, GIR. (D) Lack of correlation between the sj/βTREC ratio and the percentage of CD45RA⁺ CD27⁺ CD4⁺ T cells. Closed circles, PIR; open circles, GIR.

FIG. 3.

Similar frequencies of RTEs in the CD31⁺-naïve CD4⁺ T-cell subsets of the poor and good immunological responders. (A) sjTREC content of the CD31⁺- and CD31⁻-naive CD4⁺ T-cell subsets. *, statistically significant difference between groups. (B) Frequency of CD31⁺ cells in naive CD4⁺ T cells. (C) Correlation between the percentage of CD31⁺ cells among naive CD4⁺ T cells and age. Closed circles, PIR; open circles, GIR. (D) sjTREC content of the CD31⁺- and CD31⁻-naive CD4⁺ T-cell subsets.

FIG. 4.

Similar levels of cellular virus load in naïve CD4⁺ T-cell subsets of the poor and good immunological responders.

FIG. 5.

Persistent T-cell activation in the poor immunological responders. Level of CD4⁺ (A) and CD8⁺ (B) T-cell activation. Closed red circles, PIR harboring some X4 viruses; closed red circles with a blue ring, PIR harboring R5 viruses with an “X4-like” genotype; closed gray circles, PIR in whom coreceptor usage could not be determined; open red circles, GIR harboring some X4 viruses; open blue circles, GIR harboring R5 viruses; open gray circles, GIR in whom coreceptor usage could not be determined. (C) Frequency of naïve T cells (T_N, CD45RA⁺ CD27⁺), central memory cells (T_CM, CD45RA⁻ CD27⁺), effector memory cells (T_EM, CD45RA⁻ CD27⁻), and terminally differentiated effector memory cells (T_TEM, CD45RA⁺ CD27⁻). The proportion of T_TEM in the CD4⁺ T-cell subset was negligible and is thus not represented. *, statistically significant difference between the two groups. (D) Proportion of cells bearing the Ki67 cell cycle marker in CD45RA⁺ CD27⁺ CD4⁺ and CD8⁺ T cells. (E) Cell death rate in CD45RA⁺ CD27⁺ CD4⁺ T cells measured using 7-AAD staining. (F) Correlation between CD4⁺ T-cell activation and the percentage of CD45RA⁺ CD27⁺ CD4⁺ T cells. (G) Correlation between CD8⁺ T-cell activation and the percentage of CD45RA⁺ CD27⁺ CD8⁺ T cells. Closed circles, PIR; open circles, GIR.