Xmab™ Fc-engineered anti-cd19 monoclonal antibodies with in vitro and in vivo efficacy against lymphoma and leukemia
Authors: Eugene Zhukovsky, Matthew Bernett, Seung Chu, Sher Karki, Holly Horton, John Richards, Erik Pong, Patrick Joyce, Matthias Peipp, Roland Repp, John Desjarlais
Journal: Cancer Research (2008)

AACR Annual Meeting-- Apr 12-16, 2008; San Diego, CA

4903 

CD19 is a pan-B cell surface receptor expressed from early stages of pre-B cell development through terminal differentiation into plasma cells. It is an attractive target for cancers of lymphoid origin since it is expressed on the vast majority of Non-Hodgkin Lymphoma (NHL) as well as different types of leukemia, including those lacking CD20 expression. The majority of NHL patients will relapse after the current treatment regimen of chemotherapy combined with rituximab (CHOP-R) despite major improvements in response rates and progression free survival. Thus salvage regimens with novel non-cross resistant antibody therapies are warranted. We present the characterization of a novel Fc-engineered and humanized anti-CD19 antibody (XmAbCD19) that was generated using our XmAb antibody engineering technologies. This novel antibody is highly cytotoxic against a panel of lymphoma and leukemia cell lines as well as primary cancer cells. The main features of this antibody are: i) increased affinity for Fc gamma receptors (FcγR), ii) improved effector function, and iii) significantly increased antitumor potency. Humanization and affinity maturation were applied to this antibody in order to: i) decrease immunogenicity, ii) increase affinity, and iii) increase stability of the engineered antibody. Since internalization is expected to impact a naked antibody’s effector functions, we assayed its internalization rate using Eu-labeled XmAbCD19 and observed an unexpectedly low rate of internalization. Thus, we proceeded to investigate several direct and indirect (Fc-mediated) mechanisms of antibody-mediated cytotoxicity. The potency of XmAbCD19 in antibody-dependent cell-mediated cytotoxicity (ADCC) increased 10- to 100-fold relative to a native/non Fc-engineered version (anti-CD19 IgG1) of the antibody in a screen of 16 NHL and leukemia cell lines. ADCC potency (EC50) and efficacy (% Lysis) of the Fc-engineered anti-CD19 antibody were superior to that of rituximab: in CLL - 10- and 1.5-fold higher, in B-ALL - 10- and 100-fold higher, and in HCL - 6- and 1.2-fold higher, respectively. Unlike XmAbCD19, native anti-CD19 IgG1 mediated little ADCC. Moreover, XmAbCD19 mediated potent ADCC of primary patient-derived ALL and MCL cells that was also significantly increased in potency and efficacy relative to rituximab and anti-CD19 IgG1. Additionally, XmAbCD19 demonstrated enhanced phagocytosis relative to anti-CD19 IgG1. XmAbCD19 also exhibited robust anti-proliferative apoptotic activity that was significantly more potent than that of rituximab. Finally, both xenograft mouse models, subQ tumor growth and iv metastasis, showed that XmAbCD19 has remarkable protection in both paradigms. In summary, our data suggest that our anti-CD19 Fc variant antibody engineered for increased effector function is a promising next-generation immunotherapeutic for a variety of leukemias and lymphomas.