Tafasitamab in Combination with a CD20xCD3 Bispecific T-Cell Engager Significantly Prolongs Survival in Preclinical Lymphoma Models
Authors: Schaadt Eveline , Heitmüller Christina , Peters Solveig , Ilieva Kristina , Blair Derek , Huth Christiane , Bartel Dominik , Zapf Sandra , Eberl Markus , Mangelberger-Eberl Doris , Giles Frank , Corvey Carsten 
Published: December 2023

R-CHOP remains the standard of care for newly diagnosed DLBCL patients. However, 30-40% of patients are refractory or relapse after initial response to the immunochemotherapy, indicating a high-unmet medical need for these patients.
Tafasitamab is a CD19-targeting, Fc-modified humanized monoclonal antibody mediating antibody-dependent cellular cytotoxicity (ADCC), antibody-dependent cellular phagocytosis (ADCP) and direct cytotoxicity. Tafasitamab was granted accelerated approval by the FDA in 2020 and conditional marketing authorization by the EMA in 2021 for the treatment of transplant-ineligible adult patients with relapsed or refractory (R/R) DLBCL in combination with the immunomodulatory drug lenalidomide.
CD20xCD3 T-cell engagers are currently under clinical investigation or recently received FDA approval in 2L+ DLBCL (Thieblemont 2023; Dickinson 2022).
CD19- and CD20-targeting antibodies might complement each other, as I) CD19 could compensate for CD20-low/ -negative settings and vice versa and II) monoclonal antibodies and T-cell engagers combine powerful and distinct immune pathways holding great potential to increase responses in patients who may need additional therapeutic options.
The aim of this study was to investigate the combination of tafasitamab and MOR212, a proprietary proof-of-concept CD20xCD3 T-cell engaging antibody, in preclinical models of lymphoma.
First, MOR212 was characterized in vitro and in vivo to ensure comparability with other CD20xCD3 bispecific antibodies (comp1-3) currently under clinical investigation.
In in vitro cytotoxicity assays, MOR212 demonstrated similar (comp1-2), or improved (comp3) cytotoxicity (MOR212 vs comp1 and 2 p&gt;0.05 vs comp3 p=0.03; exemplary data for EC50 in SU-DHL-4 cells; n=6), cytokine secretion (MOR212 vs comp1-3 p&gt;0.05; exemplary data for EC50 TNFα; n=4) and T-cell activation (MOR212 vs comp1 p=0.05; vs comp2 p&gt;0.05 vs comp3 p=0.003; exemplary data for % CD69 on CD8 T-cells; n=6) in cell lines expressing different levels of CD20.
In a lymphoma in vivo model co-engrafted with human T-cells, MOR212 prolonged progression-free survival of mice to a similar extent as two comparator molecules that were tested head-to-head (MOR212 vs comp1 and 3 p&gt;0.05;) at a dose of 0.1 mg/kg.
Next, we investigated the combination of tafasitamab and MOR212 in vitro. Due to the differential killing kinetics of a monoclonal antibody and a T-cell engager, we made use of a real time live-cell imaging assay. Lymphoma cells were co-cultured with healthy donor peripheral blood mononuclear cells (PBMCs) and tafasitamab and MOR212 were added in different concentration combinations. Tumor cell killing was monitored every 3 hours for 72 hours and revealed improved target cell killing by the combination of both compounds (signal/background caspase 3/7 staining at 48h: MOR212 24.2 vs tafasitamab 28.2 vs MOR212+tafasitamab 111.5; n=1). To confirm these findings in vivo, we used human CD34+ engrafted NCG mice with a huIL15 boost allowing for the development of human T-cells as well as NK-cells, as essential effector cells for the combination of both compounds. Raji lymphoma cells were engrafted and treatment with the single or combination therapy was started once tumors reached a pulpable size. Combination of tafasitamab and MOR212 significantly improved progression-free survival in animals compared to monotherapy treatment (tafasitamab+MOR212 vs tafasitamab only p=0.0002 and MOR212 only p=0.0098). In addition, the combined treatment regimen appeared to be safe in mice as no side effects on both body weight loss and clinical score were recorded throughout the entire observation period.
Our findings prove that the combination of tafasitamab and a CD20xCD3 T-cell engaging antibody significantly increases tumor cell eradication both in vitro and in vivo and lay the ground to potentially translate the results into improved outcome for patients with aggressive lymphoma in future clinical trials.