BYON4228 is a pan-allelic antagonistic SIRPα antibody that potentiates destruction of antibody-opsonized tumor cells and lacks binding to SIRPγ on T cells.

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.

G-CSF as a suitable alternative to GM-CSF to boost dinutuximab-mediated neutrophil cytotoxicity in neuroblastoma treatment.

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.

SIRPα on Mouse B1 Cells Restricts Lymphoid Tissue Migration and Natural Antibody Production.

The inhibitory immunoreceptor SIRPα is expressed on myeloid and neuronal cells and interacts with the broadly expressed CD47. CD47-SIRPα interactions form an innate immune checkpoint and its targeting has shown promising results in cancer patients. Here, we report expression of SIRPα on B1 lymphocytes, a subpopulation of murine B cells responsible for the production of natural antibodies. Mice defective in SIRPα signaling (SIRPαΔCYT mice) displayed an enhanced CD11b/CD18 integrin-dependent B1 cell migration from the peritoneal cavity to the spleen, local B1 cell accumulation, and enhanced circulating natural antibody levels, which was further amplified upon immunization with T-independent type 2 antigen. As natural antibodies are atheroprotective, we investigated the involvement of SIRPα signaling in atherosclerosis development. Bone marrow (SIRPαΔCYT>LDLR-/-) chimaeric mice developed reduced atherosclerosis accompanied by increased natural antibody production. Collectively, our data identify SIRPα as a unique B1 cell inhibitory receptor acting to control B1 cell migration, and imply SIRPα as a potential therapeutic target in atherosclerosis.