Effect of the Adminstration of Rituximab between Mobilization Chemotherapy and Leukapheresis on Stem Cell Collection Parameters: A Study of Fifty NHL Patients Mobilized Using Intermediate Dose Cyclophosphamide and Sequential GM-CSF and G-CSF.

Abstract We have previously reported that intermediate dose cyclophosphamide followed by sequential GM-CSF and G-CSF (iCy/GM/G) provides efficient mobilization for patients undergoing autografting. Furthermore, the predictable time course of mobilization with this regimen obviates the need for weekend leukaphereses (Blood 2003: 957a). Recently, the addition of rituximab to mobilization regimens for B-cell NHL has been shown to be effective at depleting contaminating B-cells from the leukapheresis product. However, the effect of rituximab administered for in-vivo purging, on mobilization and stem cell collection parameters is unclear. We compared leukapheresis (LP) yield parameters, and the time course of stem cell mobilization in 23 consecutive B-cell NHL patients mobilized with iCy/GM/G plus rituximab (group 1) with 27 consecutive B-cell NHL patients mobilized with the same regimen without rituximab (group 2). The iCy/GM/G regimen consisted of cyclophosphamide 1.5g/m2 (d1), GM-CSF 500 mcg/d (d 3–7), G-CSF (d 8 until completion of LP) 600mcg/d for weight ≤80kg, 960 mcg for weight > 80 kg. Rituxan was administered at 375mg/m2 as a single dose on d8. LP was begun on d 11 irrespective of WBC. D1 was usually a Friday in order to avoid weekend LP. Patients underwent up to 20 liter LP for ≤ 5 days (median =3, range 1–5 for both groups) with a target collection of > 5 x 10e6 CD34+ cells/kg. The groups were well matched for median age, gender, number of prior chemotherapy regimens (median=2 for both groups), prior pelvic XRT and histological subtype of B-NHL (p=NS in all cases). The estimated (Kaplan-Meier) cumulative probability of achieving a target collection of 2 x 10e6 CD34+ cells/kg on d 1–5 was 0.43, 0.70, 0.78, 0.84, 0.84 respectively for group 1 and 0.22, 0.69, 0.77, 0.84, 0.84 respectively for group 2. The corresponding probabilites of achieving 5 x 10e6 CD34+ cells/kg on d 1–5 were 0.22, 0.39, 0.57, 0.57, 0.57 (group 1) and 0.11, 0.30, 0.46, 0.59, 0.59 (group 2) (p=NS Log-rank test). Percentage of CD34+ cells in the LP product (LP CD34%) was measured daily. Maximums LP CD34% was seen on LP d1 for both groups with a fall on subsequent days (p=NS between groups 1 and 2). Toxicities experienced were generally mild consisting mostly of bone pain and fevers and were similar in both gropups. No patient required admission for febrile neutropenia. The number of CD34+ cells infused were similar for both groups (median 5.9 vs.5.7 x10e6 CD 34+ cells/kg). Median time to reach ANC > 500/mm3 and platelets > 20,000/mm3 were identical between groups 1 and 2 (d11 and d 10 respectively). These data show that the addition of rituximab administered on d 8 to the iCy/GM/G regimen in patients with B-NHL does not impair the yield of CD34+ cells, or the tolerability of the regimen. Furthermore, the time course of the mobilization and therefore the predictbility of the collection is not compromised. Maximum cumulative yield of CD34+ cells is achieved within 4 days of LP with no patient benefitting from a fifth day of collection. The additional cost and inconvenience of weekend leukapheresis can be avoided in all cases using this regimen.