Allogeneic Hematopoietic Stem Cell Transplantation After Reduced-intensity Conditioning for Relapsed Follicular Lymphoma

Follicular lymphomas are chemosensitive neoplasms characterized by a relentless succession of remissions and relapses when treated with conventional chemotherapy. The successive periods of remission are of shorter duration and patients invariably die of their disease. At first line, patients are treated with conventional chemotherapy. At first relapse, intensive chemotherapy with autologous stem cell transplantation (SCT) is often proposed. Allogeneic hematopoietic stem cell transplantation after reduced-intensity conditioning (RIC-allo) is an option for patients relapsing after autologous SCT, allowing long-term progression free survival of 50 to 60%. The toxic mortality related to severe acute graft versus host disease (GVHD) remains a critical issue. The goal of our study is to test in a multicentric approach a strategy of RIC-allo including rituximab in order to reduce the incidence of acute GVHD. Around half of patients with relapsed or refractory follicular lymphomas treated with allogeneic SCT achieve long-term progression free survival whatever the conditioning regimen. Because the median age of patients with follicular lymphoma is 55 years, a reduced intensity conditioning is the most appropriate option in this setting. The outcome of patients with a chemoresistant disease is usually poor because of a high toxic mortality. As a consequence, only patients with a chemosensitive disease will be included in this study. To further reduce the toxic mortality, it is critical to reduce the incidence of severe acute GVHD. A low incidence of acute GVHD could be obtained by the use of Rituximab before and after the transplantation as reported by the MD Anderson's experience in several hematological malignancies including follicular lymphoma. Their results are impressive in patients with follicular lymphoma with long-term survival of 85%. The favored hypothesis is a depletion of patient and donor B cells reducing the presentation of minor histocompatibility alloantigens. The benefit of Rituximab could also be explained by its anti-lymphoma effects that could compensate the putative reduction of a graft versus lymphoma effect due to a better control of GVHD. The primary objective is to estimate 2-year overall survival in this setting.