Phase III Randomized Stem Cell Mobilization Trial Comparing Standard Vs Double-Dose G-CSF Vs Standard Doses of G-CSF Plus GM-CSF in Hard to Mobilize Patients Undergoing An Autologous Hematopoietic Stem Cell Transplant (HSCT).

Using standard dose G-CSF (10 μg/kg) for stem cell mobilization, 25-40% of patients, deemed to be hard to mobilize based on prior therapy, will not collect sufficient HSC (> 2-2.5 × 10⁶ CD34/kg) to proceed to a prompt autotransplant. Strategies to improve CD34/kg yields have included dose escalating G-CSF up to 30 μg/kg or combining G-CSF and GM-CSF. While dose escalated G-CSF is effective in increasing CD34 yields in normal donors as is the combination of G-CSF and GM-CSF, their comparative value in pre-treated patients has not been tested. To determine the value of these strategies, we performed a randomized comparison of high dose G-CSF (30 μg/kg as 2 doses 12 hours apart), to the combination of simultaneous single daily doses of G-CSF (10 μg/kg) plus GM-CSF (5 μg/kg), to a control group receiving G-CSF at an equivalent total dose of cytokine to the combination arm (15μg/kg) as a single dose.

Patients were eligible if heavily pre-treated, defined as: a minimum of 10 total cycles of combination chemotherapy and two prior regimens, or a total of 6 chemotherapy cycles if the patient also received RT to marrow bearing sites, platinum-based chemotherapy or 2 or more cycles of any BCNU or fludarabine containing regimen. Baseline WBC had to be > 3000/μl, ANC > 1500/μl and a platelets > 100,000/μl. Twelve liter aphereses began on day 5 of mobilization, and continued until ≥ 4 × 10⁶ CD34/kg were collected or a maximum of 5 aphereses. Patients typically proceeded to transplant if they had ≥ 2.5 × 10⁶ CD34/kg collected and were always re-mobilized if they collected < 2.0 × 10⁶ CD34/kg. CD34 subsets (CD34⁺/CD33^- and CD34⁺/CD38^-) were also assessed for the 3 groups to determine if more primitive HSC were mobilized by the 2 novel strategies. The sample size was calculated based as follows: 60% of the control group would collect 2.5 × 10⁶ CD34/kg and this would rise to 90% in one or both study arms. The detection of such differences with a power of 80% and a 2-sided alpha level of 0.025 required a total sample of 120 patients.

A total of 120 patients were randomized; 119 were eligible. Patient demographics, shown in the Table, were matched among the three groups:

The % of patients collecting ≥2.5 × 10⁶ CD34/kg was: standard G: 60%, high dose G: 57% (p = 1.0), G + GM: 41% (p = 0.1). Median CD34 collected in first mobilization were, 3.6 × 10⁶/kg, 3.0 × 10⁶/kg (p = 0.22) and 2.0 × 10⁶/kg (p = 0.05) respectively in a median of 4, 4, and 5 aphereses (p = NS). Re-mobilization rates: standard G; 37.5%, high dose G: 35%; G + GM: 50% (p = NS). Total median CD34 collected from first and any second mobilizations were: standard G: 4.8 × 10⁶/kg, high dose G: 3.9 × 10⁶/kg, and G + GM: 3.5 × 10⁶/kg. One patient in the standard G arm and 3 in high dose G did not proceed to transplant due to poor initial mobilization and progression in 2, and one each for progression or poor mobilization alone. There were no significant differences in median engraftment times: for ANC, 10, 11 and 15 days respectively for the standard G-, high dose G- and G + GM arms and for platelets, 11, 13 and 14 days respectively. The overall survivals @ the median f/u time of 37 months were 59.8%, 61.8% and 48.1% respectively (p = 0.272) for the three groups. The % primitive HSC (CD34⁺/CD33^- and CD34⁺/CD38^-) from the first mobilization were identical in the 3 patient groups.

We found no advantage to dose escalated G-CSF nor to the combination of G-CSF and GM-CSF to mobilize HSC for autotransplantation in heavily pre-treated patients. We also did not find higher numbers of more primitive CD34 subsets mobilized by these newer strategies. Alternative approaches, e.g. the combination of plerixifor + standard dose G-CSF (Stiff et al: BBMT; 15:249-56, 2009) would appear to be the preferred method of initial HSC mobilization for heavily pre-treated patients.

Stiff:Genzyme: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding.