A Novel Therapeutic Approach for Multiple Myeloma: Development of a CD38 and CD47 Bispecific Bipartopic Antibody-CAR-T Molecule Discovery Topic-Tekbiotech-Yeast and Phage Display CRO, Expert in Nano-body and Antibody Drug Development

A Novel Therapeutic Approach for Multiple Myeloma: Development of a CD38 and CD47 Bispecific Bipartopic Antibody

Antibody engineering enables the customization of therapeutic antibody design and activity to improve efficacy or achieve favorable clinical properties. Grandclement et al. [1] developed a fully human bispecific antibody, ISB1442, designed to reconstitute synthetic immunity for CD38+ hematologic malignancies. ISB1442 is currently in Phase I clinical trials for relapsed/refractory multiple myeloma. ISB1442 comprises two anti-CD38 arms targeting two distinct epitopes, preferentially driving binding to tumor cells. It can also block proximal CD47 receptors on the same cell through avidity-induced binding while preventing on-target off-tumor binding to healthy cells. The Fc portion of ISB1442 is engineered to enhance complement-dependent cytotoxicity, antibody-dependent cellular cytotoxicity, and antibody-dependent cellular phagocytosis. Therefore, ISB1442 represents a CD47 bispecific antibody that combines biparatopic targeting of a tumor-associated antigen with enhanced antibody effector functions to overcome potential resistance mechanisms hindering monospecific anti-CD38 antibody therapy for myeloma.

Main Research Content

ISB1442 consists of two anti-CD38 Fab fragments, each linked via a flexible glycine-serine peptide linker consisting of 15 amino acids (G4Sx3) to a BEAT? B chain, while an anti-CD47 Fab fragment is linked to a BEAT? A chain.

Figure 1: Schematic representation of ISB1442.

To enable CD38-driven avidity binding to engage proximal CD47 receptors, the study selected the H2 Fab within the 2+1 bispecific format of the ISB1442 antibody. This H2 Fab exhibited a KD value of 0.9 μM for CD47 (Figure 2A, B). As a monomeric Fab, H2 Fab could block the weak interaction between CD47 and SIRPα (KD ~1 μM) (competition binding assays using BLI showed that the anti-CD47-H2 Fab or magrolimab (huSF9) Fab blocked the CD47-SIRPα interaction) (Figure 2C). In the context of the 2+1 bispecific antibody format, H2 Fab induced CD47-SIRPα blockade similar to the high-affinity anti-CD47 (magrolimab, huSF9) monoclonal antibody in CD38+/CD47+ cell-based assays (Figure 2D).

Figure 2: Validation of the mechanism of action of the bispecific antibody ISB1442.

All ISB1442 binding domains exhibited similar binding characteristics to cynomolgus monkey CD38 and CD47 antigens (Figure 3A, B). ISB1442 induced significant phagocytosis of tumor cells, indicating that CD47 inhibition is sufficient to enable macrophage-mediated phagocytosis of multiple tumor cells in vitro (Figure 3C, D).

Figure 3: Cross-species antigen reactivity and cellular validation of the bispecific antibody ISB1442.

The study generated single-subunit variants of the ISB1442 antibody, where both CD38 Fab domains targeted the same epitope (ISB1442E2RecAxE2RecA and ISB1442B6-D9xB6-D9). Their activity was then compared to the dual-subunit ISB1442 (Figure 4A). Compared to ISB1442E2RecAxE2RecA or ISB1442B6-D9xB6-D9, ISB1442 demonstrated superior binding to tumor cells (Figure 4B, C). The binding of ISB1442 was significantly better than the ISB1442E2RecAxE2RecA variant, but the difference in binding compared to ISB1442B6-D9xB6-D9 was less pronounced. ISB1442 exhibited greater tumor cell killing via CDC compared to the ISB1442E2RecAxE2RecA and ISB1442B6-D9xB6-D9 single-subunit variants (Figure 4D, E). This indicates that the dual-subunit targeting modality enhances the CDC activity of ISB1442.

Figure 4: Functional validation of binding and killing by different domains of the bispecific antibody ISB1442.

In cells with low CD38 expression, ISB1442 induced an average phagocytosis of 56%, significantly higher than the 31% phagocytosis induced by daratumumab (Figure 5A, B). Furthermore, phagocytosis of CD38+ and CD38 knockout multiple myeloma cells was analyzed using live-cell imaging confocal microscopy. ISB1442 induced selective phagocytosis only of CD38+ multiple myeloma cells, whereas hu5F9 induced phagocytosis to a similar extent against both CD38+ and CD38 knockout tumor cells (Figure 5C, D), supporting the specificity of ISB1442 for CD38-expressing tumor cells. In addition to phagocytosis, ISB1442 exhibited higher tumor cell killing via the CDC pathway compared to daratumumab (Figure 5E, F). Furthermore, compared to daratumumab, its potency via ADCC was higher, although maximum killing efficacy was comparable (Figure 5G, H).

Figure 5: Efficacy of ISB1442 compared to anti-CD38 and anti-CD47 monospecific antibody controls.

This study presents the design rationale, mechanism of action, and efficacy evaluation of ISB1442. ISB1442 is a bispecific, bipartopic antibody capable of inducing synthetic immunity through multiple effector mechanisms while circumventing certain tumor escape mechanisms that can diminish the activity of monospecific antibodies. ISB1442 is envisioned as a next-generation innate cell engager for CD38+ hematologic malignancies and is currently in Phase I clinical trials for relapsed/refractory multiple myeloma. This research provides a new approach and reference for the future development of therapeutic antibody drugs for difficult-to-treat oncologic diseases.

Tek Biotech (Tianjin) Co., Ltd. specializes in phage display and yeast display antibody discovery services as its core business. We are committed to providing high-quality bispecific antibody development services to scientists worldwide. We also offer comprehensive supporting services including downstream in vitro affinity validation (comprising EC50 validation, BLI validation, and SPR validation), flow cytometry validation, cell killing validation, and in vivo animal imaging services, providing robust technical support for our partners' drug development programs.

References

[1] Grandclement, C., Estoppey, C., Dheilly, E. et al. Development of ISB 1442, a CD38 and CD47 bispecific bipartopic antibody innate cell modulator for the treatment of multiple myeloma. Nat Commun 15, 2054 (2024).

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