Safety and biologic activity of a canine anti‐CD20 monoclonal antibody in dogs with diffuse large B‐cell lymphoma

Background To explore the safety and utility of combining low dose single‐agent doxorubicin with a canine specific anti‐CD20 monoclonal antibody (1E4‐cIgGB) in client owned dogs with untreated B‐cell lymphoma. Animals Forty‐two client‐owned dogs with untreated B‐cell lymphoma. Methods A prospective, single arm, open label clinical trial of dogs with B‐cell lymphoma were enrolled to receive 1E4‐cIgGB and doxorubicin in addition to 1 of 3 immunomodulatory regimens. B‐cell depletion was monitored by flow cytometry performed on peripheral blood samples at each visit. Results Dogs demonstrated a statistically significant depletion in CD21+ B‐cells 7 days following the first antibody infusion (median fraction of baseline at 7 days = 0.04, P 0.5 of baseline, indicating sustained B cell depletion at 4+ months after the final treatment. 1E4‐cIgGB was well tolerated with only 1 dog exhibiting a hypersensitivity event within minutes of the last antibody infusion. Conclusions The canine 1E4‐cIgGB anti‐CD20 monoclonal antibody is apparently safe when administered with doxorubicin and effectively depletes B‐cells in dogs with DLBCL.