Allogeneic Stem Cell Transplantation (Allo-SCT) after Treatment with Programmed Cell Death-1 (PD-1) Checkpoint Inhibitors for Relapsed/Refractory Classic Hodgkin Lymphoma (R/R cHL) Is Associated with an Unprecedented Low Relapse Rate

Introduction: Phase 1/2 trials using the programmed cell death-1 (PD-1) checkpoint inhibitors Nivolumab and Pembrolizumab in relapsed/refractory classic Hodgkin lymphoma (R/R cHL) who had failed autologous-SCT (Auto-SCT) showed high response rates and durable responses in the majority of patients. However, with extended follow-up, progression-free survival (PFS) curves from the CheckMate 205 trial failed to show a plateau, thus suggesting the need for a consolidation therapy in cHL responding to anti-PD-1. Reported here is the retrospective analysis of the outcome of 34 cHL patients who received an Allo-SCT after treatment with PD-1 inhibitors. Patients and Methods: From Nov 2014 to Apr 2017, 44 R/R cHL enrolled in the CA209-205, CA209-254 and MK3475087trials(median age, 31 years; range, 18-81) received nivolumab (n=42) or pembrolizumab (n=2) until complete remission (CR), very good partial remission (PR) defined as a tumor burden reduction >80%, or progressive disease (PD).At study entry, 30 patients (84%) had refractory disease, 39 (89%) had failed BV and 38 (86%) Auto-SCT. Tumor assessment was performed according to Cheson et al (JCO, 2014). Non-relapse mortality (NRM) was defined as death by any reason other than disease progression. Cumulative incidence of relapse, NRM, and graft-versus-host disease (GVHD) was assessed using the Kaplan-Meier method. Results: After a median duration of anti-PD-1 therapy of 10 months (range, 3-33), 18 patients (41%) experienced CR or PR whereas 26 (59%) progressed. Sixteen of 18 responding patients were allografted. Eighteen of 26 patients who progressed during anti-PD-1 therapy received additional chemotherapy and were finally allografted. Overall, 34 of 44 patients were allografted. Allografting was not performed due to age (n=1), PD (n=4), patient refusal (n=5). The median time from last nivolumab to Allo-SCT was 49 days (range, 23 - 372). At Allo-SCT, 22 patients (65%) were in CR, 11 (32%) in PR and 1 (3%) in PD. Donors were haploidentical sibling (n=23), matched sibling (n=5), or matched unrelated (n=6). Stem cell source was bone marrow (n=15) and peripheral blood (n=19).Acute graft-versus-host disease (aGVHD) was recorded in 15 patients.The cumulative incidence (CI) of grade 2-4 and grade 3-4 aGVHD at 100 days was 46% and 12%, respectively; the 2-year CI of cGVHD was 27%. Non-infectious complications including febrile syndrome, macrophage activation syndrome and cytokine release syndrome, as well as infectious complications occurring until day +100 post-allografting are detailed in a companion abstract.With a median follow-up of 18 months (range, 1.8-39.3), one patient died due to relapse and 5 to non-relapse mortality (NRM) [(acute Graft-versus-Host Disease (aGVHD) (n=1), CMV pneumonia (n=1), immune-mediated pneumonia (n=1) heart failure (n=1), post-transplant lymphoproliferative disorder (PTLD) (n=1)]. The 2-year cumulative incidence (CI) of relapse and NRM was 3.1% and 19.7%, respectively. The 2-year OS and PFS were 76% and 76%, respectively. Conclusions: With an extended follow-up, data reported herein clearly show that Allo-SCT performed after PD-1 inhibitors or the sequence PD-1 inhibitors/chemotherapy is a feasible consolidation strategy associated with an unprecedented low relapse incidence. Early transplant-related complications prompt at identification and implementation of risk-minimizing strategies. PD-1 inhibitors eventually combined with salvage chemotherapy and Allo-SCT represent a paradigm shift in the treatment of refractory cHL.