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Roskopf, Claudia Christina (2018): T cell-dependent lysis of CD19-positive leukemia cells mediated by single-chain triplebodies with dual-targeting. Dissertation, LMU München: Fakultät für Chemie und Pharmazie



Targeted tumor therapy with multispecific antibody formats bears great potential to improve the efficacy of cancer immunotherapy: The simultaneous interaction of antibody derivatives with immune effector cells and multiple tumor-associated antigens is expected to increase cancer cell selectivity, to block cancer cell survival mechanisms and to hamper immune escape. For this purpose a large number of bi- and multispecific molecular platforms have been developed including the single-chain triplebody format. Triplebodies are composed of three antibody-derived single-chain variable fragments interconnected by flexible glycine-serine peptide linkers. They are used for re-targeting of cytotoxic immune effector cells towards cancer cells, which are bound bivalently by the triplebody. In the present work the triplebody-mediated engagement of T cells for the lysis of B lymphoid leukemia cells was established. A prototype with specificity for B lymphoid differentiation antigen CD19 and T cell trigger antigen CD3-epsilon – triplebody 19-3-19 – was shown to activate T lymphocytes at picomolar concentrations and to engage them for the efficient, serial lysis of target antigen-positive cancer cells. The triplebody 19-3-19 also induced T cell proliferation, which can lead to the partial regeneration of a patient’s immune effector cell pool. In these capacities the triplebody 19-3-19 was comparable to the bispecific T cell engager (BiTE®) blinatumomab, which is approved for the treatment of relapsed or refractory acute precursor B lymphoid leukemia in the USA and in the European Union since late 2014/2015. Furthermore, it was shown with the trispecific triplebody 33-3-19 that dual targeting of CD19 and myeloid surface marker CD33 on biphenotypic leukemia blasts results in selective lysis of these target cells. The CD19 and CD33 double-positive blasts were 145-fold more sensitive to treatment with the triplebody 33-3-19 than CD19 single-positive cells. Parts of the author’s work also contributed to the functional characterization of two previously developed NK cell-recruiting triplebodies – SPM-1 (19-16-19) and SPM-2 (33-16-123) – which are candidates for clinical development. The results of this thesis project have established the triplebody format as a molecular platform, which can be employed for the recruitment of any cytotoxic effector cell population as required in a particular therapeutic setting. Furthermore, the improved target cell selectivity that was achieved in vitro with the dual-targeting triplebody 33-3-19 adds weight to the concept of improved therapeutic efficacy of multispecific antibodies.