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Background Preclinical studies have firmly established the CD47-signal-regulatory protein (SIRP)α axis as a myeloid immune checkpoint in cancer, and this is corroborated by available evidence from the first clinical studies with CD47 blockers. However, CD47 is ubiquitously expressed and mediates functional interactions with other ligands as well, and therefore targeting of the primarily myeloid cell-restricted inhibitory immunoreceptor SIRPα may represent a better strategy.Method We generated BYON4228, a novel SIRPα-directed antibody. An extensive preclinical characterization was performed, including direct comparisons to previously reported anti-SIRPα antibodies.Results BYON4228 is an antibody directed against SIRPα that recognizes both allelic variants of SIRPα in the human population, thereby maximizing its potential clinical applicability. Notably, BYON4228 does not recognize the closely related T-cell expressed SIRPγ that mediates interactions with CD47 as well, which are known to be instrumental in T-cell extravasation and activation. BYON4228 binds to the N-terminal Ig-like domain of SIRPα and its epitope largely overlaps with the CD47-binding site. BYON4228 blocks binding of CD47 to SIRPα and inhibits signaling through the CD47-SIRPα axis. Functional studies show that BYON4228 potentiates macrophage-mediated and neutrophil-mediated killing of hematologic and solid cancer cells in vitro in the presence of a variety of tumor-targeting antibodies, including trastuzumab, rituximab, daratumumab and cetuximab. The silenced Fc region of BYON4228 precludes immune cell-mediated elimination of SIRPα-positive myeloid cells, implying anticipated preservation of myeloid immune effector cells in patients. The unique profile of BYON4228 clearly distinguishes it from previously reported antibodies representative of agents in clinical development, which either lack recognition of one of the two SIRPα polymorphic variants (HEFLB), or cross-react with SIRPγ and inhibit CD47-SIRPγ interactions (SIRPAB-11-K322A, 1H9), and/or have functional Fc regions thereby displaying myeloid cell depletion activity (SIRPAB-11-K322A). In vivo, BYON4228 increases the antitumor activity of rituximab in a B-cell Raji xenograft model in human SIRPαBIT transgenic mice. Finally, BYON4228 shows a favorable safety profile in cynomolgus monkeys.Conclusions Collectively, this defines BYON4228 as a preclinically highly differentiating pan-allelic SIRPα antibody without T-cell SIRPγ recognition that promotes the destruction of antibody-opsonized cancer cells. Clinical studies are planned to start in 2023.

Background Current immunotherapy for patients with high-risk neuroblastoma involves the therapeutic antibody dinutuximab that targets GD2, a ganglioside expressed on the majority of neuroblastoma tumors. Opsonized tumor cells are killed through antibody-dependent cellular cytotoxicity (ADCC), a process mediated by various immune cells, including neutrophils. The capacity of neutrophils to kill dinutuximab-opsonized tumor cells can be further enhanced by granulocyte-macrophage colony-stimulating factor (GM-CSF), which has been shown in the past to improve responses to anti-GD2 immunotherapy. However, access to GM-CSF (sargramostim) is limited outside of Northern America, creating a high clinical need for an alternative method to stimulate dinutuximab responsiveness in the treatment of neuroblastoma. In this in vitro study, we have investigated whether clinically well-established granulocyte colony-stimulating factor (G-CSF) can be a potentially suitable alternative for GM-CSF in the dinutuximab immunotherapy regimen of patients with neuroblastoma.Methods We compared the capacity of neutrophils stimulated either in vitro or in vivo with GM-CSF or G-CSF to kill dinutuximab-opsonized GD2-positive neuroblastoma cell lines and primary patient tumor material. Blocking experiments with antibodies inhibiting either respective Fc gamma receptors (FcγR) or neutrophil integrin CD11b/CD18 demonstrated the involvement of these receptors in the process of ADCC. Flow cytometry and live cell microscopy were used to quantify and visualize neutrophil-neuroblastoma interactions.Results We found that G-CSF was as potent as GM-CSF in enhancing the killing capacity of neutrophils towards neuroblastoma cells. This was observed with in vitro stimulated neutrophils, and with in vivo stimulated neutrophils from both patients with neuroblastoma and healthy donors. Enhanced killing due to GM-CSF or G-CSF stimulation was consistent regardless of dinutuximab concentration, tumor-to-neutrophil ratio and concentration of the stimulating cytokine. Both GM-CSF and G-CSF stimulated neutrophils required FcγRIIa and CD11b/CD18 integrin to perform ADCC, and this was accompanied by trogocytosis of tumor material by neutrophils and tumor cell death in both stimulation conditions.Conclusions Our preclinical data support the use of G-CSF as an alternative stimulating cytokine to GM-CSF in the treatment of high-risk neuroblastoma with dinutuximab, warranting further testing of G-CSF in a clinical setting.