Background: The therapeutic landscape for relapsed or refractory (R/R) B-cell non-Hodgkin lymphoma (B-NHL) is evolving to include targeted T-cell based immunotherapies, including CD19-targeted CAR-T and CD3xCD20 T-cell engaging (TCE) bispecific antibodies. Yet, there remains an unmet medical need for patients who are refractory to, or ineligible for these treatments. Leveraging natural killer (NK) cells emerges as a promising strategy in hematological malignancies, as shown in a Phase 1 study with IPH6101/SAR’579 in R/R AML (Stein, ASCO 2023; Bajel, ASH 2023). Methods: We developed IPH6501, a tetraspecific antibody-based NK cell engager that simultaneously targets on NK cells the CD16a and NKp46 receptors, the IL-2 receptor with an engineered IL-2 variant (IL2v) and on B-NHL cells the CD20 antigen. This approach boosts NK cell activation and proliferation, cytotoxicity against tumor cells, and cytokine production. The IL-2 variant is designed with mutations that prevent binding to CD25 (IL-2Rα), limiting Treg activation and potential IL-2-related side effects. IPH6501 has been evaluated in mouse, non-human primate, and human-derived models, including cells from R/R B-NHL patients. Results: In vivo studies in non-human primates and tumor mouse models revealed that IPH6501, at well-tolerated doses, significantly boosted peripheral NK cell proliferation, drove their accumulation at tumor locations, and effectively eradicated CD20+ cells in blood and tissues. In human derived-models, IPH6501 significantly induced NK cell proliferation and cytotoxicity. Notably, IPH6501 showed potent activity against a range of B-NHL cell lines, including those with low CD20 expression. In addition, IPH6501 upregulated the expression of activating receptors on NK cells, such as NKG2D, essential for the recognition and killing of malignant cells, thereby introducing another mode of action enabling the elimination of CD20-negative tumor cells. In a comparative analysis with a CD3xCD20 TCE, IPH6501 induced lower cytokine secretion, suggesting a potentially safer profile. Additionally, IPH6501 showed higher killing efficacy compared to the TCE in samples from healthy individuals as well as R/R B-NHL patients, underscoring its therapeutic potential. Conclusions: The preclinical demonstrations of IPH6501 activities across various in vivo models and its effectiveness in ex vivo assays using cells from R/R B-NHL patients provide compelling evidence of its therapeutic potential and tolerability. IPH6501 is emerging as a promising new candidate within the treatment landscape for R/R B-NHL and is currently being investigated in a global, first-in-human phase 1/2 study (NCT 06088654).