Generation of a Half-Life Extended Anti-CD19 BiTE^® Antibody Construct Compatible with Once-Weekly Dosing for Treatment of CD19-Positive Malignancies

CD19 is an immunoglobulin family member expressed ubiquitously on B cell lineage cells, from the pre-B cell to the mature B cell stage, until downregulation during terminal differentiation into plasma cells. CD19 is important for B cell activation, maturation and proliferation, and is widely expressed on the majority of B cell neoplasms.

The T cell engaging bispecific antibody construct (BiTE^®) blinatumomab, which targets CD19, is approved for the treatment of relapsed or refractory B cell precursor acute lymphoblastic leukemia in adults and children in the US and has shown great promise for treating other CD19-positive hematological malignancies. The short serum half-life of blinatumomab necessitates administration by continuous IV infusion to maintain therapeutic serum concentrations. To extend the half-life and allow for a more convenient administration, a next generation BiTE^® antibody construct designated CD19 HLE BiTE^® has been generated. The CD19 HLE BiTE^® comprises a new CD19- and CD3-targeting tandem single-chain Fv antibody fused to an Fc domain.

The biological properties of CD19 HLE BiTE^® were evaluated in vitro and in vivo . CD19 HLE BiTE^® binds with high affinity to both human and non-human primate (NHP) CD19 as well as CD3. In vitro experiments demonstrated that CD19 HLE BiTE^® can recruit and activate human and NHP T cells, mediating redirected lysis of CD19-expressing cells at half-maximal effective concentrations in the low picomolar range. The fusion to an Fc domain resulted in a serum half-life of 210 hours following a single intravenous administration of a 5 µg/kg dose in NHP. In a repeat-dose study CD19 HLE BiTE^® caused robust depletion of circulating B cells, B lineage bone marrow cells, and peripheral lymphoid organ B cells in NHPs, whilst no overt signs of toxicity were observed in clinical and laboratory examinations of the animals.

These results demonstrate that CD19 HLE BiTE^® effectively eliminated CD19-positive cells in vitro and in vivo, and may be suitable for once weekly dosing in patients with CD19-positive malignancies.