Immune Mobilization of Autologous Peripheral Blood Progenitor Cells: IL-2 with GM-CSF and G-CSF Results in Effective Mobilization without Delay in Engraftment.

We initiated an immune mobilization trial in an attempt to mobilize cytotoxic effector cells, along with CD34+ hematopoietic progenitor cells. A Prospective Phase I trial was initiated using dose escalation of IL-2, in combination with GM-CSF and G-CSF. IL-2 began on Day 0 and continued as a daily SQ injection for 11 days. On Day 7, GM-CSF (7.5 mcg/kg/d) and G-CSF (5 mcg/kg/d) were initiated for 5 days (Days 7–11). On Day 11, leukapheresis was started if the peripheral blood CD34 + cell count was > 5 cells/mcl. The endpoint of collection was ≥ 3 × 10⁶ CD34+ cells/kg. After collection, patients received melphalan (200 mg/m²) followed by infusion of cryopreserved stem cells. Post-transplant GM-CSF began on Day +5 and terminated once the ANC reached 5000 cells/mcl. To date, 9 patients have been treated (myeloma, n = 8; NHL, n = 1) and 7 patients are evaluable. Six patients received IL-2 at Dose Level 1 (6 × 10⁵ IU/m²/d). The remaining 3 patients received IL-2 at Dose Level 2 (1 × 10⁶ IU/m²/d). The MTD of IL-2 has not been reached. One patient (NHL) was removed from the study due to progressive disease. The remaining 8 patients completed the regimen. Toxicities have been mild and have included Grade 2 fever (n=1) on Dose Level 2. All patients were successfully mobilized. The median number of CD34+ cells/kg and MNC/kg collected were 3.4 × 10⁶ (range 2.8 – 4.4 × 10⁶/kg) and 9.5 × 10⁸ (range 0.4 – 1.7 × 10⁹), respectively. Two large volume leukaphereses were required (median; range 1 – 3). Following transplant, the ANC recovered on Day 13 (median; range: 10 – 14 d) and platelets recovered on Day 12 (median; range 0 – 13 d). These preliminary results demonstrate that immune mobilization and collection of an adequate number of hematopoietic progenitor cells is feasible without suppression of hematopoiesis. Toxicities are minimal but the MTD of IL-2 has not yet been reached. Post-transplant engraftment is not delayed. As patient accrual continues, we are currently evaluating the qualitative and quantitative components of the collected cells, including Th1 vs. Th2 cells and the types of dendritic cells mobilized.