Transcriptional reprogramming in immune cells of HTLV-1 asymptomatic carriers and HAM/TSP patients following antiretroviral therapy

Human T-cell lymphotropic virus type 1 (HTLV-1) causes HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP), a chronic, immune-mediated spinal cord disease in which peripheral immune activation is thought to fuel central neuroinflammation. To delineate cell type-specific programs linked to disease, we performed single-cell RNA sequencing on the peripheral blood mononuclear cells (PBMCs) of the HTLV-1 infected asymptomatic carrier (AC) and HAM/TSP patient. Differential expression and pathway analysis localized the most pronounced transcriptional divergence to the monocyte compartment, revealing coordinated remodeling of macrophage classical (M1-like) activation, IL-10-regulatory signaling, leukocyte adhesion/diapedesis, and trans-endothelial migration pathway, and cytokine storm-related modules. Ingenuity Pathway Analysis highlighted overlap with multiple sclerosis-associated signaling, consistent with myeloid-driven neuroinflammation and potential blood-spinal cord barrier involvement. In an independent validation phase, we assayed the selected subsets of up- and down-regulated monocyte genes in AC and HAM/TSP participants enrolled in a randomized, open-label pilot trial in Brazil. Expression of several inflammatory markers was higher at baseline in HAM/TSP and decreased during dolutegravir (DTG) therapy, paralleling reductions in HTLV-1 proviral load (PVL) in the DTG arm. Collectively, these data suggest that antiviral strategies may modulate immune cell transcriptional programs that help reduce HTLV-1 PVL.