XPO1 and tropical spastic paraparesis: In this regard, it is important to underline that cytoplasmic localization of HBZ in PBMC of HAM/TSP patients was not modified by the treatment of the cells with Leptomycin B, a drug that blocks the CRM1-dependent nuclear-cytoplasmic shuttling of the proteins, strongly indicating that HBZ is a cytoplasmic resident, non migrating protein in HAM/TSP.