Belimumab in Patients With Chronic Lymphocytic Leukemia

This study is a phase II trial of belimumab in combination with rituximab/venetoclax in patients with refractory or relapsed chronic lymphocytic leukemia (CLL). Treatment of CLL has drastically changed in the past years as new therapeutic agents have gained clinical approval. The combination rituximab/venetoclax over a course of two years is approved as second line therapy especially in patients with high risk CLL (del17p), showing high remission rates and achievement of MRD (minimal residual disease) negativity. The next goals in CLL therapy are now to increase the rate of MRD negativity and to achieve an earlier MRD negativity during the course of treatment to allow for a reduction of treatment time and therefore treatment-induced toxicities. In line with other hematologic diseases, progression free survival depends on remission status, especially MRD negativity, after last treatment as MRD positivity after therapy indicates the persistence of treatment resistant CLL cells. One mechanism of therapy resistance has been described as reduced sensitivity to rituximab-induced antibody dependent cell-mediated cytotoxicity (ADCC) by natural killer (NK) cell production of B-lymphocyte stimulator (BlyS, also called BAFF), which can be bound by belimumab, a human anti-BAFF antibody. Moreover, recombinant human (rh)BAFF can dose dependently reverse cytotoxic effects of venetoclax, which could also be restored by the application of belimumab. This led to the conceptualization of this clinical trial, in which belimumab is applied as a weekly subcutaneous injection in combination with standardrituximab/venetoclax treatment for up to 24 months in relapsed and refractory CLL patients. By removing BAFF from the CLL microenvironment we aim to increase the efficacy of rituximab/venetoclax treatment to achieve higher and earlier MRD negativity rates and allow for an abbreviated treatment.