Figure 1. HTLV-1 disease and clonal expansion of separate T cell subsets.

After HTLV-1 infection, both CD4⁺ and CD8⁺ T cell subpopulations exhibit clonal expansion. In this issue of the JCI, Sibon et al. (3) examined each subpopulation using a sophisticated ex vivo model system. The authors observed that although each infected cell type displayed clonal expansion, loss of genomic integrity, which is a necessary predisposition for neoplasia, was observed only in the CD4⁺ T cell population. Clonal expansion of the HTLV-1–infected CD8⁺ T cell population is associated with increased cell division and resistance to apoptosis. The interaction between the 2 molecular pathways toward clonal expansion utilized by each T cell subset could have significant impact upon which HTLV-1 disease will develop in an infected individual.