In spite of the widespread use of Rituximab, a chimeric monoclonal antibody with demonstrated efficacy in the treatment of non-Hodgkin’s lymphomas, there is a recognized need to develop fully human antibodies with improved efficacy. Towards this end, using XenoMouse™ technology, a fully human IgG1 monoclonal antibody specific to human CD20 was generated. This antibody, denoted mAb 1.5.3, evoked enhanced pro-apoptotic activity in vitro, as compared to Rituximab, in the Ramos human lymphoma cell line. In addition, mAb 1.5.3 was active in mediating complement dependent cytotoxicity (CDC) and elicited improved antibody-dependent cellular cytotoxicity (ADCC) relative to Rituximab in Ramos, Raji, and Daudi human B-lymphoma lines. To recapitulate various aspects of acquired resistance to Rituximab, as observed in a subpopulation of patients, Rituximab-resistant clones were established from lymphoma lines. Interestingly, mAb 1.5.3 demonstrated superior cytolytic activity against engineered Rituximab-refractory lymphoma clones, as well as across multiple human B-lymphoma and chronic B-cell leukemia lines in an in vitro whole blood assay. Furthermore, mAb 1.5.3 exhibited enhanced anti-tumor activity in Rituximab-sensitive cell lines and -refractory engineered lymphoma clones in vivo. Lastly, mAb 1.5.3 produced a superior B-cell depletion profile in lymph node organs and bone marrow as compared to Rituximab in a primate PD model. In contrast to Rituximab, mAb 1.5.3 is a fully human antibody and is thus anticipated to exhibit a longer serum half-life with minimal immunogenicity following repeated administration. In sum, these results demonstrate the superior anti-tumor activity of mAb 1.5.3 relative to Rituximab and its potential for improved clinical activity in the treatment of B-cell malignancies.
Disclosure:Employment: The authors are employees of Amgen and AstraZeneca.