OXS-1550 is a bispecific scFv recombinant fusion protein-drug conjugate composed of the variable regions of the heavy and light chains of anti-CD19 and anti-CD22 antibodies and a modified form of diphtheria toxin as its cytotoxic drug payload.  CD19 is a membrane glycoprotein present on the surface of all stages of B-lymphocyte development, and is also expressed on most B-cell mature lymphoma cells and leukemia cells.  CD22 is a glycoprotein expressed on B-lineage lymphoid precursors, including precursor acute lymphoblastic leukemia, and often is co-expressed with CD19 on mature B-cell malignancies such as lymphoma.

OXS-1550 targets cancer cells expressing the CD19 receptor or CD22 receptor or both receptors.  When OXS-1550 binds to cancer cells, the cancer cells internalize OXS-1550, and are killed due to the action of drug’s cytotoxic diphtheria toxin payload.  OXS-1550 has demonstrated success in a Phase 1 human clinical trial in patients with relapsed/refractory B-cell lymphoma or leukemia.