Identification of a candidate therapeutic antibody for treatment of canine B-cell lymphoma

B-cell lymphoma is one of the most frequently observed non-cutaneous neoplasms in dogs. For both human and canine BCL, the standard of care treatment typically involves a combination chemotherapy, e.g. "CHOP" therapy. Treatment for human lymphoma greatly benefited from the addition of anti-CD20 targeted biological therapeutics to these chemotherapy protocols; this type of therapeutic has not been available to the veterinary oncologist. Here, we describe the generation and characterization of a rituximab-like anti-CD20 antibody intended as a candidate treatment for canine B-cell lymphoma. A panel of anti-canine CD20 monoclonal antibodies was generated using a mouse hybridoma approach. Mouse monoclonal antibody 1E4 was selected for construction of a canine chimeric molecule based on its rank ordering in a flow cytometry-based affinity assay. 1E4 binds to approximately the same location in the extracellular domain of CD20 as rituximab, and 1E4-based chimeric antibodies co-stain canine B cells in flow cytometric analysis of canine leukocytes using an anti-canine CD21 antibody. We show that two of the four reported canine IgG subclasses (cIgGB and cIgGC) can bind to canine CD16a, a receptor involved in antibody-dependent cellular cytotoxicity (ADCC). Chimeric monoclonal antibodies were assembled using canine heavy chain constant regions that incorporated the appropriate effector function along with the mouse monoclonal 1E4 anti-canine CD20 variable regions, and expressed in CHO cells. We observed that 1E4-cIgGB and 1E4-cIgGC significantly deplete B-cell levels in healthy beagle dogs. The in vivo half-life of 1E4-cIgGB in a healthy dog was ∼14 days. The antibody 1E4-cIgGB has been selected for further testing and development as an agent for the treatment of canine B-cell lymphoma.