CD4 and tropical spastic paraparesis: Many biomarkers have been proposed as prognostic for development of either ATLL (PD-1/PD-L1, absence of CD7 in CD4+ T cells [41–43] or HAM (CXCL10, CXCL9, neopterin and HTLV-1 antibody titers in CSF, and gender [44–46], although the most studied is PVL.