Abstract
Human T-cell lymphotropic virus type 1 (HTLV-1)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) develops in 1–5% of HTLV-1-infected individuals. Previous studies by us and others have shown that the expression of negative immune checkpoint receptors (NCRs) is significantly increased on CD8 T cells in various chronic viral infections and are associated with poor anti-viral immunity. We have previously identified the differential expression of NCRs on CD8 T cells in blood from patients with HAM/TSP and in central nervous system (CNS) tissues of HTLV-1 infected humanized mice and defined the association with neurological complications. In this study, we determined the co-expression patterns of several key NCRs (PD-1, TIGIT, TIM-3, and LAG-3) and their cognate ligands in HTLV-1 infection and assessed how combination strategies targeting these pathways would impact HTLV-1-specific CD8 T-cell effector functions as an approach to reduce CNS disease outcomes. We found that global CD8 T cells from HAM/TSP patients co-express multiple NCRs at significantly higher frequencies than asymptomatic carriers (AC). Moreover, NCR ligands (PVR and PD-LI) on both plasmacytoid and myeloid dendritic cells were also expressed at higher frequencies in HAM/TSP compared to AC. In both AC and HAM/TSP subjects, combination dual PD-L1/TIGIT or triple PD-L1/TIGIT/TIM-3 blockade with monoclonal antibodies resulted in increases in intracellular cytokine expression in CD8 T cells after virus stimulation, particularly CD107a, a marker of degranulation, and TNF-α, a key cytokine that can directly inhibit viral replication. Interestingly, almost all blockade combinations resulted in reduced IL-2+ HTLV-1-specific CD8 T cell frequencies in HAM/TSP subjects, but not in AC. These results define a novel combinatorial NCR immunotherapeutic blockade strategy to reduce HAM/TSP disease burden.
Highlights
Despite nearly 40 years since the discovery of human T-cell lymphotropic virus type 1 (HTLV-1), there is no vaccine or effective treatment for Human T-cell lymphotropic virus type 1 (HTLV-1)-associated myelopathy/tropical spastic paraparesis (HAM/TSP), a debilitating and progressive neurological disorder that manifests is 1–5% of infected individuals
To evaluate the relative expression of single and multiple co-expressed negative immune checkpoint receptors (NCRs) on CD4 and CD8 T cells during HTLV1 infection, cryopreserved peripheral blood mononuclear cells (PBMCs) from HTLV-1-infected asymptomatic carriers (AC, n = 20), HTLV-1-infected individuals diagnosed with HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) (HAM/TSP, n = 6) and seronegative controls (SC, n = 12) were assessed for expression of PD-1, TIGIT, T-cell immunoglobulin and mucin-containing domain 3 (TIM-3), and lymphocyte-activation gene 3 (LAG-3) (Table 1, Figure 1; Supplementary Figure 1)
We observed significantly increased global single TIM-3+ and LAG-3+ CD4 T cells and TIM-3+ CD8 T cells in HAM/TSP subjects when compared to SN controls (Figures 1A,B)
Summary
Despite nearly 40 years since the discovery of human T-cell lymphotropic virus type 1 (HTLV-1), there is no vaccine or effective treatment for HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP), a debilitating and progressive neurological disorder that manifests is 1–5% of infected individuals. This is, in part, due to a limited understanding of the interplay between viral and host factors that contribute to HTLV-1 disease pathogenesis. Immune checkpoint receptors on T cells modulate the magnitude and duration of activation by providing further stimulatory or suppressive signals [1]. NCRs have been implicated as key contributors in several disease processes that culminate in T-cell “exhaustion,” where T cells are rendered dysfunctional and exhibit poor recall responses [3,4,5,6]
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