ATLL cells exhibits characteristic lymphocytes with a “flower cell” aspect, and express a mature T-cell phenotype: CD2+, CD3+, CD4+, CD8-, CD25+, CD7-, CD5+, CD25+ (strong and uniform), CD29+, CD45RO+, TCR αβ+, and HLA-DR+. Here, CD4 is linked to adult T-cell leukemia/lymphoma.