Age but not disease progression defines CD4+ and CD8+ T stem cell memory levels in human retroviral infections: contrasting effects of HTLV-1 and HIV-1

BackgroundHuman CD4+ and CD8+ stem cell memory T cells (TSCM) represent a minor fraction of circulating lymphocytes characterized by stemness and long-term in vivo persistence. CD4+ TSCM are preferentially infected and constitute a reservoir for HIV-1, whereas CD8+ TSCM appear to play a protective role. However, little is known about CD4+ and CD8+ TSCM in the only other human pathogenic retroviral infection, human T-cell leukemia virus type 1 (HTLV-1). HTLV-1 is the etiological agent of both Adult T-cell Leukemia (ATL) and HTLV-1 associated myelopathy/tropical spastic paraperesis (HAM/TSP), a neuroinflammatory disorder. In ATL, CD4+ TSCM cells were identified as the hierarchical leukemic stem cell, but data in HAM/TSP are lacking. Age is a major risk factor for both ATL and HAM/TSP, as both diseases generally manifest several decades after infection. Therefore, we explored a possible link between TSCM, age and disease status in human retroviral infections in a cross-sectional study, using multiparametric flow cytometry.\n\nResultsWe found that CD4+ or CD8+ TSCM levels (quantified as CD3+CD45RA+CD45RO- CD27+CCR7+Fashi) do not differ between healthy controls and untreated HTLV-1 infected individuals with and without neuroinflammatory disorder. However, we found both TSCM as well as CD8+ TSCM significantly accumulated with age, resulting in a >400% increase in elderly HTLV-1 infected individuals (>60 years). A significant correlation between age and TSCM signature genes was validated at the transcriptome level in an independent cohort. CD8+ but not CD4+ TSCM were significantly decreased in untreated HIV-1 infection. Unexpectedly, CD8+ TSCM recovery upon successful antiretroviral treatment was essentially complete (92.2{+/-}11.0%) in younger (45 years) individuals (p=0.0003).\n\nConclusionIn HTLV-1 infection, an age-dependent accumulation of CD4+ and CD8+ TSCM points towards a possible protective role of CD8 TSCM in the elderly against leukemic but not neuroinflammatory disease. HIV-1-infected individuals lose their ability to restore CD8+ TSCM levels upon successful antiretroviral therapy at later age (>45 years), which might eventually lead to immunological failure and decreased vaccine efficacy.