HIV-Associated Structural and Functional Brain Alterations in Homosexual Males

Dynamics of peripheral T cell exhaustion and monocyte subpopulations in neurocognitive impairment and brain atrophy in chronic HIV infection

BACKGROUND

HIV-associated neurocognitive disorders (HAND) is hypothesized to be a result of myeloid cell-induced neuro-inflammation in the central nervous system that may be initiated in the periphery, but the contribution of peripheral T cells in HAND pathogenesis remains poorly understood.

METHODS

We assessed markers of T cell activation (HLA-DR + CD38+), immunosenescence (CD57 + CD28-), and immune-exhaustion (TIM-3, PD-1 and TIGIT) as well as monocyte subsets (classical, intermediate, and non-classical) by flow cytometry in peripheral blood derived from individuals with HIV on long-term stable anti-retroviral therapy (ART). Additionally, normalized neuropsychological (NP) composite test z-scores were obtained and regional brain volumes were assessed by magnetic resonance imaging (MRI). Relationships between proportions of immune phenotypes (of T-cells and monocytes), NP z-scores, and brain volumes were analyzed using Pearson correlations and multiple linear regression models.

RESULTS

Of N = 51 participants, 84.3% were male, 86.3% had undetectable HIV RNA < 50 copies/ml, median age was 52 [47, 57] years and median CD4 T cell count was 479 [376, 717] cells/uL. Higher CD4 T cells expressing PD-1 + and/or TIM-3 + were associated with lower executive function and working memory and higher CD8 T cells expressing PD-1+ and/or TIM-3+ were associated with reduced brain volumes in multiple regions (putamen, nucleus accumbens, cerebellar cortex, and subcortical gray matter). Furthermore, higher single or dual frequencies of PD-1 + and TIM-3 + expressing CD4 and CD8 T-cells correlated with higher CD16 + monocyte numbers.

CONCLUSIONS

This study reinforces evidence that T cells, particularly those with immune exhaustion phenotypes, are associated with neurocognitive impairment and brain atrophy in people living with HIV on ART. Relationships revealed between T-cell immune exhaustion and inflammatory in CD16+ monocytes uncover interrelated cellular processes likely involved in the immunopathogenesis of HAND.

Circulating endothelial and angiogenic cells predict hippocampal volume as a function of HIV status

Circulating endothelial cells (CECs) and myeloid angiogenic cells (MACs) have the capacity to stabilize human blood vessels in vivo. Evidence suggests that these cells are depleted in dementia and in persons living with HIV (PWH), who have a higher prevalence of dementia and other cognitive deficits associated with aging. However, the associations of CECs and MACs with MRI-based measures of aging brain health, such as hippocampal gray matter volume, have not been previously demonstrated. The present study examined differences in these associations in 51 postmenopausal women with and without HIV infection. Gray matter volume was quantified using MRI. CECs and MACs were enumerated using fluorescence-activated cell sorting. Analyses examined the association of these cell counts with left and right hippocampal gray matter volume while controlling for age and hypertension status. The main finding was an interaction suggesting that compared to controls, postmenopausal PWH with greater levels of CECs and MACs had significantly greater hippocampus GMV. Further research is necessary to examine potential underlying pathophysiological mechanisms in HIV infection linking morpho-functional circulatory reparative processes with more diminished hippocampal volume in postmenopausal women.