Radioimmunotherapy with Yttrium-90-Ibritumomab Tiuxetan as Part of a Reduced Intensity Conditioning Regimen for Allogeneic Hematopoietic Cell Transplantation in Patients with Advanced Non-Hodgkin Lymphoma: A Phase I/II Study.

Allogeneic hematopoietic cell transplantation (HCT) using reduced intensity conditioning (RIC) regimens offers a potential curative therapy to patients with advanced NHL. RIC HCT induces potent graft-versus-lymphoma effects with best results in patients with low tumor burden at time of HCT. Combined use of radioimmunotherapy (RIT) with RIC may increase anti-lymphoma activity of RIC while HCT provides rescue from hematologic toxicity of RIT. This may allow dose escalation of RIT. A multicenter phase I/II study of allogeneic HCT combining RIT using yttrium-90-ibritumomab tiuxetan (Y90-CD20) with two RIC regimens for treatment of patients with NHL has been initiated. Patients with indolent NHL (Arm A) receive RIT with Y90-CD20 (0.4 mCi/kg) on day −14 combined with RIC using fludarabine (30 mg/m^2 day −4 to−2) and 2 Gy TBI (day 0). Patients with aggressive NHL (Arm B) receive an escalated dose of Y90-CD20 (0,6–0,8 mCi/kg) on day −14 combined with RIC using fludarabine (30 mg/m^2 day −8 to−4), melphalan (140 mg/m^2 day −3) and campath (20–30 mg day −3 to−2). For postgrafting immunosuppression either CSA/MMF (Arm A) or CSA alone (Arm B) is used. To date, 31 patients have been enrolled (Arm A=23, Arm B=8). Diagnoses in Arm A were FL (n=12), MCL (n=6), CLL (n=4) and Immunocytoma (n=1). Diagnoses in Arm B were DLBCL (n=6), blastoid MCL (n=1) and transformed CLL (n=1). Median age was 55 (range, 34–67) years. PBSC grafts were either from matched related (n=10) or matched unrelated donors (n=21). All patients were high risk with refractory disease or relapse after preceding HCT. Disease status after salvage therapy at time of HCT was in Arm A: CR=1, PR=18, SD=4 and in Arm B: PR=8. No additional toxicity due to RIT was observed. Engraftment was rapid and sustained with no graft rejections. In Arm A median time to >500 granulocytes/μL was 13 (range, 0–69) days and to >20000 platelets/μL 3 (range, 0–69) days (in 11 patients platelets never dropped <20000/μL). In Arm B median time to >500 granulocytes/μL was 17 (range, 9–23) days and to >20000 platelets/μL 11 (range, 8–29) days. TRM in the first 100 days was 3%, overall 19%. Incidence of grade II-IV GVHD in Arm A was 35% (II=3, III=4, IV=1) and in Arm B 25% (II=2). Best disease response observed was in Arm A: CR=18, PR=5 and in Arm B: CR=3, PR=5. To date, 16/23 patients in Arm A and 6/8 patients in Arm B are alive with a median follow-up of 271 (range, 20–390) days, resulting in a Kaplan-Meier 1 year survival estimate of 65% in Arm A and 62% in Arm B. Causes of death were infection=5, GVHD=1, relapse=1 in Arm A and relapse=2 in Arm B. A combination of RIT with RIC is feasible with no additional toxicity due to RIT and stable engraftment in all patients. Preliminary response data suggest that this strategy may improve early post-transplant disease control, but long-term disease-free survival remains to be determined.