In tax positive clones derived from in vitro infection, the HTLV-1 tax mRNA load ranged from 16.7 to 474.5 AU (mean ± se of mean 114.1 ± 61.0) without significant difference between CD4+ (mean ± se of mean 43.0 ± 11.1) and CD8+ cells (mean ± se of mean 208.7 ± 134.1). Here, CD4 is linked to infection.