OP0221 LBL-047, A NOVEL AFUCOSYLATED ANTI-BDCA2/TACI FUSION PROTEIN WITH YTE MUTATION, INHIBITS THE FUNCTIONS OF BOTH pDCs AND B CELLS

Background: Both plasmacytoid dendritic cells (pDCs) and B cells play pivotal roles in various autoimmune diseases, such as systemic lupus erythematosus (SLE), systemic sclerosis, and rheumatoid arthritis 1-4. Blood DC antigen 2 (BDCA2) is exclusively expressed on pDCs and its antibody BIIB059 has demonstrated preliminary efficacy and excellent safety in patients with SLE or cutaneous lupus erythematosus via pDC depletion and inhibition of cytokines release such as IFN-α 5. On the other hand, BAFF (B-cell activating factor) and APRIL (a proliferation-inducing ligand) are critical for B cell proliferation, and antibody production. One of the receptors for BAFF and APRIL is the transmembrane activator and CAML interactor (TACI). Telitacicept, an approved recombinant fusion protein of TACI has shown great clinical benefits in autoimmune diseases 6,7. Therefore, a novel bifunctional fusion protein, LBL-047, targeting both pDCs and B cells was designed and exhibited superior activity in inhibiting multiple autoimmune mechanisms and disease progression in in vitro and in vivo studies, and may hold promise in the treatment of autoimmune diseases. Objectives: Develop a new drug that inhibits both pDC and B-cell functions for the treatment of autoimmune diseases. Methods: An anti-BDCA2 antibody was generated from mouse hybridoma and humanized by CDR grafting. The afucosylated antibody was then produced using fucosyltransferase inhibitor or a FUT8 knock-out cell line. The anti-BDCA2/TACI fusion protein, was obtained by fusing engineered TACI to the humanized, afucosylated anti-BDCA2 antibody. The YTE mutation was introduced to extend the half-life, creating the final molecule: LBL-047. Binding affinity was assessed using Fortebio. Human peripheral blood mononuclear cells (PBMCs) were cocultured with molecules to test the antibody-dependent cellular cytotoxicity (ADCC) potency. IFN-α inhibition assays were conducted using PBMCs cocultured with the TLR9 agonist and drugs. The IFN-α in the supernatants was detected using homogeneous time-resolved fluorescence method. B-cell-proliferation inhibition assays were conducted using B cells cocultured with BAFF, APRIL and drugs, and B cell counts were measured using the CellCounting-Lite system. Human CD34+ stem cells were injected into NCG mice to generate a humanized mouse model (huHSC-NCG model). These mice were injected with drugs to test the efficacy of pDC depletion in vivo. Keyhole limpet hemocyanin (KLH)–immunized balb/c mice were treated with drugs to test the efficacy of reducing splenic B cells and plasma cells. Single-dose PK studies were conducted in rats and humanized FcRn mice. Results: We have developed an afucosylated anti-BDCA2/TACI fusion protein, LBL-047, with an extended half-life due to the YTE mutation. LBL-047 exhibited high binding affinity to BDCA2, BAFF and APRIL. In vitro, LBL-047 potently inhibited IFN-α release and efficiently depletes pDCs in PBMC ADCC assays and in huHSC-NCG mice, surpassing the efficacy of BIIB059. Additionally, LBL-047 more effectively inhibited B cell proliferation in vitro compared to telitacicept. In the KLH-immunized mice model, LBL-047 (No YTE) reduced more splenic B cells and plasma cells than telitacicept. In rats, LBL-047(No YTE) exhibited a longer half-life than telitacicept, and the introduction of YTE mutation further extended half-life in humanized FcRn mice. Conclusion: A novel afucosylated bifunctional anti-BDCA2/TACI fusion protein with the YTE mutation, LBL-047 is developed. It is demonstrated extended half-life and dual immunosuppressive functions, simultaneously inhibiting pDC and B cell functions, indicating promising clinical applications for the treatment of autoimmune diseases. REFERENCES: 1 A. Kaul et al. Nat Rev Dis Primers 2, 16039 (2016). 2 I. S. Silva et al. Biology (Basel) 12, (2023). 3 R. Nehmar et al. Trends Mol Med 24, 338-347 (2018). 4 F. Wu et al. Front Immunol 12, 750753 (2021). 5 Cho Y M et al. Immunotherapy, 2024, 16(1): 15-20. 6 D. Wu et al. Ann Rheum Dis, (2023). 7 Wang L et al. Arthritis Rheumatol 75 (suppl 9), (2023). Acknowledgements: NIL. Disclosure of Interests: None declared.