Lymphocytosis decline is not responsible for tumor progression in cancer patients chronically treated with interleukin-2

The antitumor activity of IL-2 is mediated by an increase in lymphocyte number. Moreover, our previous studies have shown that therapy for 1 week/month with low-dose subcutaneous IL-2 is sufficient to maintain high levels of lymphocytes in cancer patient who have had tumor regression or stable disease (SD) in response to IL-2 immunotherapeutic cycles. This study was performed to establish whether tumor progression in cancer patients chronically treated with IL-2 may be associated with lymphocyte number decline.

The study included 53 metastatic renal cell cancer patients, who were treated with 2 induction cycles of IL-2 subcutaneous immunotherapy (6 million IU/day for 5 days/week for 6 weeks, corresponding to one cycle). Tumor regression occurred in 15/53 patients, 20 patients had a SD, and the remaining 18 cases progressed. Non progressed patients (n = 35) underwent a maintenance therapy consisting of one week of therapy every month. After a median follow-up of 18 months, 26/35 patients with response or SD had progressed. The immune investigation consisted of lymphocyte, T lymphocyte, NK cell number determination and sCD25 level detection.

The mean number of lymphocytes, T lymphocytes and NK cells observed on IL-2 maintenance therapy was significantly higher than that seen before beginning the immunotherapy. Moreover, mean number of lymphocytes and mean levels of sCD25 observed at the time of tumor progression were respectively lower and higher than those seen on maintenance therapy in the same patients, without, however, significant differences.

Despite the importance of lymphocytes in mediating the antitumor activity of IL-2, this study shows that tumor progression in cancer patients chronically treated with low-dose IL-2 after response or SD during IL-2 induction cycles is not associated with a significant decline in lymphocyte, T lymphocyte or NK cell numbers. Further studies, carried out to analyze the functional status of immune cells at the time of tumor progression, will be necessary to define the role of immunity in cancer patients progressing under IL-2 chronic therapy.