Lbl-043, a Novel LILRB4xCD3 T Cell Engager, for the Treatment of Relapsed/Refractory Multiple Myeloma

Background:

Multiple myeloma (MM) is a clonal plasma cell proliferative disorder characterized by abnormal increase of monoclonal immunoglobulins. Despite newly developed novel therapeutic agents have greatly improved the outcome of MM patients in the past decades, MM is still an incurable hematological malignancy. Several CD3 bispecific immunotherapies that harness T cells against MM are at various stages of preclinical and clinical development, but most of them are hampered by the refractory and drug-resistant mechanisms. Leukocyte immunoglobulin-like receptor B4 (LILRB4) is an immune checkpoint inhibitory receptor, which is highly expressed on both MM cells, AML cells, plasmablasts and myeloid-derived suppressive cells (MDSCs), which is crucial to completely eliminate tumor cells from MM patients. What's more, not expressing on hematopoietic stem cells and progenitor cells is a significant advantage of using LILRB4 for hematological malignancy immunotherapy. Patients with high LILRB4 expression had significantly worse prognosis in both NDMM (newly diagnosed MM) and RRMM (relapsed/refractory MM) cohort. All of these indicate that LILRB4 represents a promising target for MM. Herein a novel bispecific antibody targeting LILRB4 and CD3, LBL-043, is developed to specifically kill LILRB4 expressing MM cells by engaging T cells.

Methods:

LBL-043 was constructed using our proprietary LeadsBody^TM T cell engager platform, which is a 2:1 format bispecific antibody with two VHH arms targeting LILRB4 with high affinity and one scFv arm targeting CD3 with fine-tuned low affinity. The binding affinity of LBL-043 to LILRB4 and CD3 was determined with Fortebio, while the activity was measured using several cell based assays including reporter gene and TDCC assays on multiple myeloma cell lines. The anti-tumor activity of LBL-043 was investigated in B-NDG/hu-PBMC reconstructed mice implanted with NCI-H929 (human multiple myeloma cell line) tumor model. In addition, the potential toxicity profile of LBL-043 was examined in a non-GLP dose range finding (DRF) study in cynomolgus monkeys via IV infusion, once a week for a total of 4 doses, followed by a 7-day recovery period.

Results:

The binding affinity of LBL-043 to LILRB4 and CD3 protein was 0.724 nM and 35.7 nM, respectively. In CD3 reporter gene assays, LBL-043 could activate the NFAT reporter signaling through LILRB4 binding dependent CD3 cross-linking with an EC50 value of 2.459 nM. LBL-043 was shown a potent TDCC activity in different LILRB4 expression level on MM.1R cells and NCI-H929 cells with T cell activation and cytokine release. In B-NDG/hu-PBMC reconstructed mice implanted with NCI-H929 tumor cells, LBL-043 was shown significant anti-tumor activity. Furthermore, we did not find the obvious off-tumor toxicity, as weight and animal observation data showed in mice. DRF Study in Drug Toxicology Assessments demonstrated that LBL-043 has good safety profile in cynomolgus monkeys. There were no LBL-043 related changes of cardiac parameters, clinical chemistry, hematology, urinalysis, organ weight and gross pathology (except for decreased size of thymus).

Conclusion:

LBL-043, a novel bispecific antibody targeting CD3 and LILRB4 with affinity differentiation, induces T cell killing of MM cells by simultaneously binding LILRB4 expressed on tumor cells and CD3 on T cells, redirecting T cells to effectively killing of MM cells. It is also shown a great anti-tumor efficacy in NCI-H929 CDX mouse model. DRF of LBL-043 (0.2~10 mg/kg) in cynomolgus monkeys was well tolerated, and the highest non-severely toxic dose (HNSTD) was considered to be 10 mg/kg. These data support LBL-043 as a promising therapeutic bispecific antibody for the treatment of LILRB4 positive MM patients.

No relevant conflicts of interest to declare.