SIGNIFICANCE OF SOLUBLE INTERLEUKIN-2 RECEPTOR LEVELS FOR EVALUATION OF THE PROGRESSION OF ADULT T-CELL LEUKEMIA

Background. The authors conducted a survey of a large cohort of patien ts with adult T-cell leukemia (ATL) and a group of human T-cell leukem ia virus type 1 (HTLV-1) carriers to elucidate whether measurements of soluble interleukin-2 receptor (sIL-2R) levels are indicative of ATL tumor burden and correlate with clinical progression. Methods. Using a sandwich enzyme immunoassay, the authors determined sIL-2R in the ser um of 135 patients with ATL diagnosed and subclassified according to t he Japan Lymphoma Study Group criteria and in the serum of healthy HTL V-1 seropositive persons. Also included were patients in the preleukem ic state of ATL (pre-ATL), which is characterized by only slight blood changes but does not fit the diagnostic criteria of ATL. In the five subjects who finally advanced to overt ATL, the authors prospectively performed serial measurements of the receptor. Results. Serial measure ments of sIL-2R levels taken until overt ATL developed showed that the se levels in the initial samples were higher than those of control sub jects, even when subjects were asymptomatic or in the pre-ATL state. T he serial levels of the five subjects gradually increased despite bein g in a clinically stable condition, finally reaching markedly high lev els at the time ATL became overt. The mean sIL-2R levels of the smolde ring, chronic, acute, and lymphoma subtypes of ATL were 1680 U/ml, 668 0 U/ml, 45,940 U/ml, and 34,620 U/ml, respectively (P < 0.01). The sIL -2R levels of each subtype at the time of diagnosis were more correlat ed with tumor burden, malignant behavior, and prognosis than lactate d ehydrogenase (LDH) levels. In the low, moderate, and high sIL-2R subgr oups, the median survival time and percent survival probability at 2 y ears was 30.2 months (46.0%), 16.5 months (25.0%), and 7.7 months (15. 3%), respectively. Conclusions. Serial measurements of sIL-2R levels a re of clinical importance because changes of the levels correlate with disease progression, especially in early phase of ATL. The data sugge st that sIL-2R may be more useful than LDH. In addition, emphasis may be placed on sIL-2R as an indicator of ATL progression status and prog nosis for survival. The value of this marker in clinical practice shou ld be confirmed prospectively.