Response to rituximab in B-CLL patients is adversely impacted by frequency of IL-10 competent B cells and FcγRIIIa polymorphism. A study of FCGCLL/WM and GOELAMS groups

Rituximab (MabThera, Rituxan) in vivo mechanisms of action remain incompletely understood and could differ depending on the subtype of B-lymphoproliferative disorders. Rituximab has been shown to induce apoptosis, complement-mediated lysis, antibody-dependent cellular cytotoxicity (ADCC) and antibodydependent phagocytosis (ADPC) in vitro and there is some evidence pointing towards an involvement of these mechanisms in vivo. Factors affecting rituximab response have been previously described including histology, tumor burden and rituximab pharmacokinetics. We previously observed that FcγRIIIa-158 V/F polymorphism also impacts on clinical response. Because this polymorphism affects human IgG1 affinity for FcγRIIIa expressed on both natural killer cells and macrophages, we postulated that ADCC was an important mechanism of rituximab activity in follicular lymphoma. New anti-CD20 antibodies, with higher affinity for FcγRIIIa and ADCC such as obinutuzumab, have been therefore developed and are currently in clinical development. Regulatory B cells have been identified in human and mice as a subset of B lymphocytes competent to secrete interleukin-10 (IL-10). These cells, also named B10 in mice, are characterized by their ability to modulate inflammation, autoimmunity and adaptive and innate immune response through the production of IL-10. In mouse model, B10 cells would inhibit lymphoma cell clearance induced by anti-CD20 monoclonal antibodies (mAbs) through the regulation of monocyte Fc-mediated functions. Recently, it has been demonstrated that clonal chronic lymphocytic leukemia (CLL) cells displayed such IL-10 competence and immunosuppressive functions. We therefore hypothesized that IL-10-competent B-CLL cells could influence the clinical efficacy of rituximab in CLL patients. A prospective, randomized phase II study (NCT01370772) including 140 patients was conducted between June 2012 and January 2013 in France. Treatment-naive patients (aged 18–66 years) diagnosed with Binet stage C or active Binet stage A or B CLL were enrolled. Inclusion criteria are described in the supplementary Methods available on the Blood Cancer Journal website. In the experimental arm, standard fludarabine-cyclophosphamide-rituximab (FCR) courses (six 28-day courses of rituximab: 375 mg/m D1 C1 and 500 mg/m D1 C2–C6; fludarabine: 40 mg/m/d D2–4, cyclophosphamide: 250 mg/m/d D2–4) were preceded by a prephase of rituximab: 500 mg on D0 and 2000 mg on D1, D8 and D15. Immuno-chemotherapy was planned to begin at D22. Primary end point results have been previously published. We considered that lymphocyte depletion after rituximab monotherapy assessed at D22 was a surrogate marker of in vivo rituximab activity, allowing thus to analyze influence of IL-10competent B-CLL cells on in vivo rituximab efficacy, in the 68 patients included in the experimental arm. Median lymphocyte count before the four doses of rituximab (D0) was 91.13 g/l (range: 3.74–497.40) and was 2.60 g/l (range: 0.14–189.40) at the end of rituximab prephase (D22). Thus the median lymphocyte depletion after rituximab prephase (D22) was 95.1% (range: − 77.0 to +99.9), among them 66% obtained more than 90% depletion. Patients’ characteristic and their distribution according to 90% lymphodepletion are presented in Table 1. No significant correlation was found between 90% lymphodepletion and clinical (age, sex, Binet