Key Points

  • A T-cell bispecific antibody targeting intracellular WT1 presented on HLA-A*02 for treatment of AML is characterized in vitro and in vivo.

  • The novel, clinical-stage WT1-TCB mediated high-level killing of primary AML cells, which was enhanced by the addition of lenalidomide.

Antibody-based immunotherapy is a promising strategy for targeting chemo-resistant leukemic cells. However, classical antibody-based approaches are restricted to targeting lineage-specific cell-surface antigens. By targeting intracellular antigens, a large number of other leukemia-associated targets would become accessible. In this study, we evaluated a novel T-cell bispecific (TCB) antibody, generated using CrossMab and knob-into-holes technology, containing a bivalent T-cell receptor-like binding domain that recognizes the RMFPNAPYL peptide derived from the intracellular tumor antigen Wilms' tumor 1 (WT1) in the context of human leukocyte antigen (HLA) A*02. Binding to CD3ε recruits T cells irrespective of their T-cell receptor specificity. WT1-TCB elicited antibody-mediated T-cell cytotoxicity against AML cell lines in a WT1- and HLA-restricted manner. Specific lysis of primary AML cells was mediated in ex vivo long-term co-cultures utilizing allogenic (mean specific lysis: 67±6% after 13-14 days; ±SEM; n=18) or autologous, patient-derived T cells (mean specific lysis: 54±12% after 11-14 days; ±SEM; n=8). WT1-TCB-treated T cells exhibited higher cytotoxicity against primary AML cells than an HLA-A*02 RMF-specific T-cell clone. Combining WT1-TCB with the immunomodulatory drug lenalidomide further enhanced antibody-mediated T-cell cytotoxicity against primary AML cells (mean specific lysis on day 3-4: 45.4±9.0% vs 70.8±8.3%; p=0.015; ±SEM; n=9-10). In vivo, WT1-TCB-treated humanized mice bearing SKM-1 tumors showed a significant and dose-dependent reduction in tumor growth. In summary, we show that WT1-TCB facilitates potent in vitro, ex vivo and in vivo killing of AML cell lines and primary AML cells; these results led to the initiation of a phase I trial in patients with r/r AML (NCT04580121).

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