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Summary:A total of 415 leukaphereses in 201 patients stimulated with growth factor (GF; n ¼ 119) or chemotherapy-GF (n ¼ 296) were studied to determine CD34 þ cell collection efficiency (CE). The pre-apheresis leukocyte count was 1-93 Â 10 9 /l (median 20), and peripheral blood CD34 count (PBCD34) was 1-1104/ll (median 19). The total number of CD34 þ cells collected was 4-6531 Â 10 6 (median 151); corresponding to 0.1-111.4 Â 10 6 (median 2.3) per kg. There was strong correlation between PBCD34 and the number of CD34 þ cells collected (r ¼ 0.9; Po0.0001). CE was 7-145% (median 46). On multiple regression analysis, a higher leukocyte count (Po0.0001) was the most important predictor of lower CE. CE with leukocytes o20 was 7-145% (median 53%) compared to 10-132% (median 40%) with leukocyte X20 (Po0.0001). In all, 61% of the apheresis procedures performed after chemotherapy-GF occurred when leukocytes were o20 compared to 21% of those performed after GF alone (Po0.0001). We conclude that mobilizing patients with the combination of chemotherapy and GF rather than GF alone leads to leukapheresis being performed when the leukocyte count is low -in a range that results in optimum CD34 þ cell CE. Autologous stem cells should be mobilized with chemotherapy-GF rather than GF alone whenever possible. Bone Marrow Transplantation (2005) 35, 243-246.

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High-dose (HD) IL-2 is approved to treat renal cell carcinoma (RCC) with modest response rates and significant toxicity. Enhancement of cytotoxic T-cell activity by IL-2 is 1 mechanism of action. IL-2 also stimulates regulatory T lymphocytes (Tregs), which are associated with poor prognosis. Favorable outcomes are associated with greater rebound absolute lymphocyte count (Fumagalli 2003). DD depletes IL-2 receptor (CD25 component) expressing cells. We hypothesized that sequential therapy could complement each other; DD would deplete Tregs so IL-2 could more effectively stimulate proliferation and activity of cytotoxic T lymphocytes. Patients (n=18) received standard HD IL-2 and 1 dose of DD daily for 3 days; periodic flow cytometry and complete blood counts were performed. Group A included 3 patients to assess safety only with DD 6 μg/kg between the IL-2 courses. Group B included 9 patients at 9 μg/kg DD before the IL-2 courses. Group C included 6 patients at 9 μg/kg DD between the IL-2 courses. Efficacy using the RECIST criteria was assessed after the treatment. Fifteen patients from a study of IL-2 without DD served as controls for toxicity comparison and 13 of these for flow cytometry comparisons. No unusual toxicity was noted. For group B/C patients receiving DD, the median decline in Tregs was 56.3% from pre-DD to post-DD (P=0.013). Peak absolute lymphocyte count change from baseline was +9980/μL for group B, +4470/μL for group C, and +4720/μL for the controls (P=0.005 B vs. C). The overall response rate was 5 of 15 (33%); 3 of 9 (33%) and 2 of 6 (33%) for groups B and C, respectively, including 2 patients with sarcomatoid RCC and 1 with earlier sunitinib therapy.