CD45RO expression on peripheral lymphocytes as a prognostic marker for adult T-cell leukemia

Adult T-cell leukemia (ATL) is an aggressive hematological malignancy etiologically linked to HTLV-I. The clinical subtype classification, age, performance status, serum calcium and LDH levels are major prognostic factors of ATL, but these criteria and factors do not always correlate with prognosis. CD45 is expressed on cells of the hematopoietic system, and plays a pivotal role in antigen-stimulated proliferation of T-lymphocytes. CD45RO is a very light weight isoform of CD45 expressed on activated T-cells. Recent studies have shown that peripheral lymphocytes show two patterns of CD45RO expression in HTLV-I infected individuals which appears to correlate with their clinical outcome. The acute type ATL patients have pattern A with CD45RO+ lymphocytes with intermediate expression (CD45ROint cells), and show a better prognosis than those who do not have any CD45ROint cells. Further studies demonstrated that CD45ROint cells were not infected with HTLV-I, and as a result we suggest that CD45RO expression be considered a marker of host immunity in acute type ATL clinical course, in contrast to the levels of WBC or LDH which are regarded as tumor markers and indicators of tumor mass.