Inhibition of ABL1 tyrosine kinase reduces HTLV-1 in peripheral blood mononuclear cells from HTLV-1-associated myelopathy/tropical spastic paraparesis patients

Human T-cell leukemia virus type 1 (HTLV-1) causes incurable adult T-cell leukemia and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). Patients with HAM/TSP have increased levels of HTLV-1-infected cells compared with asymptomatic HTLV-1 carriers. However, the roles played by cellular genes in HTLV-1-infected CD4+ T cells await discovery. We combined microarray data and pathway analysis, and found that the ABL1 tyrosine kinase gene is a critical gene in HAM/TSP. ABL1 is a known survival factor for T- and B-lymphocytes. ABL1 is also part of the fused gene (BCR-ABL) known to be responsible for chronic myelogenous leukemia (CML), and tyrosine kinase inhibitors (TKI), including imatinib, nilotinib, and dasatinib, are in safe clinical use for treating CML. To evaluate whether ABL1 is indeed critical for the pathogenesis of HAM/TSP, we investigated the effect of ABL1 inhibitors on HTLV-1-infected cells. We developed a propidium monoazide-HTLV-1 viability quantitative PCR assay, which distinguishes DNA from live cells and DNA from dead cells. Using this method, we were able to measure the HTLV-1 proviral load (PVL) in live cells alone when peripheral blood mononuclear cells (PBMCs) from HAM/TSP cases were treated with TKI. Treating the PBMCs with nilotinib or dasatinib produced significant reductions in the PVL (21.0% and 17.5%, respectively) in live cells. Furthermore, a retrospective survey based on our clinical records found a rare case of HAM/TSP, where the patient also suffered from CML. The patient showed an 84.2% PVL reduction after CML treatment with imatinib. We conclude that inhibiting the ABL1 tyrosine kinase specifically reduced the PVL in PBMCs from patients with HAM/TSP, suggesting that ABL1 is a significant gene for the survival of HTLV-1-infected cells and that TKI may be a potential therapeutic agent for HAM/TSP. Human T-cell virus type 1 (HTLV-1) causes adult T-cell leukemia and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). We performed microarray experiments using GPL4133 Platform Agilent-14850 Whole Human Genome cDNA microarray G4112F (Feature number version, 85 columns x 532 rows) 1-color protocol (Cy3) and total RNA from HTLV-1 main reservoir, CD4+ T cells taken from patients with HAM/TSP (N=4), asymptomatic carriers (N=4), and HTLV-1 negative controls (N=4). Following to GeneSpring GX ver 7.3.1 manual, raw signal intensities data were filtered on flags and raw signal intensities less than 5.0 were set to 5.0. All signal intensities were transformed with base 2 log. For the per chip normalization, 50 percentile of transformed data were normalized to 1.0. By combination of differentially expressed genes up-regulated greater or less than 2-fold change only in HAM/TSP compared with NC and significant genes by 3 group comparison with one-way ANOVA (P < 0.01), we refined 310 genes. Furthermore, we identified 177 genes up-regulated only in HAM/TSP from these 310 genes by Venn mapping. Furthermore, these genes were mapped to pathway database TRANSPATH and performed Fisher’s exact test, we extracted 12 significant pathways. Eleven among these 12 pathways included ABL1 tyrosine kinase gene in common, therefore we decided this gene as the target to assay. Finally, we demonstrated that inhibition of ABL1 tyrosine kinase reduced HTLV-1 proviral loads in peripheral blood mononuclear cells from patients with HAM/TSP.