CD19/CD3 bispecific antibodies induce potent response against chronic lymphocytic leukemia cells ex vivo

Abstract While treatment of chronic lymphocytic leukemia (CLL) has been advanced by introduction of targeted therapies such as tyrosine kinase inhibitors, there remains a need for adjunct therapies capable of inducing response in the setting of relapse on or resistance to first-line agents. Blinatumomab is a bispecific antibody (bsAb) against CD19/CD3, designed to target endogenous T cells against B cells via the formation of cytolytic synapses. It is approved for treatment of relapsed/refractory B-cell acute lymphoblastic leukemia, and has shown promise for use in non-Hodgkin’s lymphoma. Designed in the relatively small 54.1 kDa BiTE format, blinatumomab has a half-life of 2.1 hours and requires continuous intravenous infusion for clinical efficacy. In contrast, our novel anti-CD19/CD3 bsAb, designed in the 100 kDa single chain Fv-Fc format (CD19/CD3-scFv-Fc), has an approximately 100-fold longer half-life and could therefore be suitable for weekly dosing. We found that both blinatumomab and CD19/CD3-scFv-Fc induce potent killing of CLL cells ex vivo compared to cells treated with control HER2/CD3-scFv-Fc bsAb or medium alone. This response was associated with robust expansion of autologous CD4+ and CD8+ T cells, as shown by absolute cell counts and CFSE-detected population doubling. Notably, while HER2/CD3-scFv-Fc induced T cell expansion, no CLL directed cytotoxicity was observed. Our results identify CD19/CD3-scFv-Fc as a possible novel immune-based treatment for CLL.