BCG024: A Novel DLL3 × CD3 × 4-1BB Trispecific T Cell Engager Enhances T-Cell Persistence and Safety
DLL3 × CD3 × 4-1BB Trispecific TCE Strategy for SCLC and NEC
- DLL3-directed tumor targeting: DLL3 is a tumor-associated antigen highly expressed in small cell lung cancer (SCLC) and neuroendocrine carcinomas (NECs). By targeting DLL3, BCG024 localizes immune activation to tumor cells, enabling selective T-cell engagement within the tumor microenvironment (TME).
- CD3-mediated T-cell redirection: BCG024 incorporates a clinically validated SP34-derived CD3 arm to redirect T cells toward DLL3-positive tumor cells. Its engineered head-to-tail architecture promotes efficient immunological synapse formation, while sterically attenuated CD3 binding may reduce excessive T-cell activation and help expand the therapeutic window.
- 4-1BB costimulation for sustained T-cell fitness: Conventional DLL3 × CD3 bispecific TCEs may be constrained by T-cell exhaustion and limited durability. BCG024 integrates 4-1BB (TNFRSF9) costimulation to enhance T-cell proliferation, survival, and long-term functional persistence, supporting sustained antitumor activity under repeated antigen exposure.
- Competitive differentiation: BCG024 builds on the clinically validated DLL3 × CD3 TCE mechanism by adding 4-1BB costimulation to enhance T-cell proliferation, persistence, and cytotoxic functionality. Its favorable preliminary safety, antibody-like PK, and repeat-dose tolerability support the translational development of this next-generation DLL3 T cell engager.
RenMice® and RenNano®-Derived Antibody Components for Trispecific TCE Development
Built on Biocytogen's antibody discovery platforms, BCG024 integrates a
RenMice®-derived DLL3 antibody, a
RenNano®-derived 4-1BB VHH, and a clinically validated SP34 CD3 arm into a compact DLL3 × CD3 × 4-1BB trispecific T cell engager format. The RenNano®-derived VHH supports efficient trispecific assembly and 4-1BB-mediated T-cell functionality, providing a developable foundation for next-generation DLL3 T cell engager engineering.
Excellent Preclinical Performance
- BCG024 leverages 4-1BB costimulation to enhance tumor growth inhibition, in vivo T-cell expansion, and dose-dependent T-cell proliferation without inducing T-cell apoptosis (Figure 1 & Figure 2).
- BCG024 showed strong cytotoxic activity under low effector-to-target (E:T) conditions and upregulated the anti-apoptotic marker Bcl-xL, supporting T-cell survival signaling and cytotoxic function (Figure 3).
- BCG024 maintained T-cell viability and function after repeated antigen stimulation, while benchmark and DLL3 × CD3 bispecific controls showed reduced activity (Figure 4).
- In a SCLC CDX model, BCG024 DLL3 TriAb exhibited robust antitumor efficacy in a monovalent DLL3-binding format compared with bivalent antigen-binding and AMG757-analog controls (Figure 5).
- BCG024 DLL3 TriAb displayed a favorable preliminary safety profile in CD3ε × 4-1BB humanized mice, with no significant body weight loss and cytokine levels remaining near background levels even at high doses (Figure 6). Preliminary cynomolgus monkey PK and repeat-dose tolerability data further support translational development.
Potential Indications
BCG024 is being evaluated as a DLL3 × CD3 × 4-1BB trispecific T cell engager, with a primary focus on small cell lung cancer (SCLC) and potential development in neuroendocrine carcinoma (NEC).
Preclinical Data Highlights Supporting BCG024 DLL3 × CD3 × 4-1BB Trispecific T Cell Engager Drug Development
The supporting preclinical data package for BCG024 includes 4-1BB-mediated T-cell costimulation, potent cytotoxic activity under low E:T conditions, sustained T-cell function after repeated antigen stimulation, robust antitumor efficacy in a SCLC CDX model, and favorable preliminary safety, PK, and tolerability profiles in humanized mice and cynomolgus monkeys, supporting the development of BCG024 as a next-generation DLL3 × CD3 × 4-1BB trispecific T cell engager for SCLC and NEC.
4-1BB Costimulation Drives Potent T-Cell Proliferation Without T-Cell Apoptosis
Figure 1. Tumor growth inhibition and T-cell expansion following DLL3 TriAb treatment. B-NDG mice were implanted with SHP-77 SCLC tumors and injected with human PBMCs. Antibody treatments (DLL3 BsAb and DLL3 TriAb) were administered on Days 10, 14, and 17, with samples collected on Day 21. DLL3 TriAb showed stronger tumor growth inhibition than DLL3 BsAb and increased CD4+ and CD8+ T-cell populations, supporting 4-1BB-mediated T-cell expansion and antitumor activity.
Figure 2. Dose-dependent T-cell proliferation without apoptosis. In a SHP-77 tumor-bearing PBMC-humanized mouse model, AMG757-analog and DLL3 TriAb were administered as a single intraperitoneal dose at 0.1, 0.5, 2.5, or 5 mg/kg, and serum hCD3-positive T-cell counts were measured 21 days after treatment. DLL3 TriAb promoted dose-dependent T-cell proliferation without inducing T-cell apoptosis, supporting enhanced T-cell expansion while preserving T-cell viability.
BCG024 Induces Superior Cytotoxic Activity at Low E:T Ratios and Upregulates Bcl-xL
Figure 3. Cytotoxic activity against DLL3-positive tumor cells at low effector-to-target (E:T) co-culture and Bcl-xL upregulation. SHP-77 cells were co-cultivated with human PBMCs and a dose range of test articles for 7 days, and specific cytotoxicity was assessed by flow cytometry. At low E:T ratios of 1:2 and 1:1, BCG024 DLL3 TriAb showed superior cytotoxic activity compared with benchmark and DLL3 BsAb controls. BCG024 also upregulated the anti-apoptotic marker Bcl-xL, supporting enhanced T-cell survival signaling and cytotoxic function.
BCG024 Maintains T-Cell Function Under Repeated Antigen Stimulation
Figure 4. PBMC viability, live cell count, and cytotoxicity after repeated DLL3 antigen stimulation. PBMCs were incubated with the coated DLL3 protein and test article. For each subsequent round of stimulation (2-3 days), PBMCs were harvested, counted, and re-stimulated with fresh test article (5 nM). Across later stimulation rounds, BCG024 DLL3 TriAb maintained higher PBMC viability and live cell counts compared with AMG757-analog and DLL3 BsAb controls. After stimulation 4, BCG024 also preserved stronger cytotoxic activity, supporting sustained T-cell function under repeated antigen stimulation.
BCG024 Demonstrates Potent Antitumor Activity in a DLL3-Positive SCLC CDX Model
Figure 5. Antitumor efficacy in the NCI-H889 SCLC CDX model. B-NDG mice were subcutaneously implanted with NCI-H889 SCLC cells and injected with human PBMCs. Test articles were administered intraperitoneally on Day 0 and Day 7, including BCG024 DLL3 TriAb at 4 mg/kg, 2TAA DLL3 TriAb at 5.5 mg/kg, and AMG757-analog at 3 mg/kg. BCG024 showed potent antitumor activity, supporting the tumor growth inhibition potential of a monovalent DLL3-binding trispecific T cell engager format.
BCG024 Shows a Favorable Preliminary Safety Profile in CD3ε × 4-1BB Humanized Mice
Figure 6. Body weight and cytokine assessment in CD3ε × 4-1BB humanized mice. B-hCD3E/h4-1BB humanized mice were intravenously dosed on Days 3, 7, and 10 with non-specific TriAb control or BCG024 DLL3 TriAb at 1, 10, and 50 mg/kg. Body weight was monitored from Day 0 to Day 17, and no significant body weight loss was observed following BCG024 DLL3 TriAb treatment. IL-2, IFN-γ, and IL-6 levels were shown in pg/mL, with BCG024 DLL3 TriAb-treated groups remaining close to background levels, while the non-specific TriAb control induced marked cytokine elevation.
In addition, preliminary cynomolgus monkey data showed an antibody-like PK profile and favorable repeat-dose tolerability for BCG024 DLL3 TriAb, with no major drug-related clinical observations and limited cytokine release, supporting further translational development.
Explore BCG024 Partnership Opportunities
Explore BCG024 Partnership Opportunities
Frequently Asked Questions (FAQs) About BCG024 DLL3 × CD3 × 4-1BB Trispecific T Cell Engager
1. What makes BCG024 a differentiated DLL3 T cell engager?
BCG024 is designed to address two major challenges associated with conventional T cell engagers: CRS risk and limited T-cell durability. By integrating DLL3-targeted tumor engagement, CD3-mediated T-cell redirection, and 4-1BB costimulation in a single molecule, BCG024 is engineered to support sustained antitumor activity while expanding the therapeutic window.
2. What role does 4-1BB costimulation play in BCG024?
4-1BB provides a costimulatory signal within the DLL3 T cell engager format, helping reinforce T-cell activation beyond CD3 engagement alone. In BCG024, this 4-1BB component supports T-cell survival signaling, functional persistence, and cytotoxic activity under repeated or low effector-to-target stimulation conditions.
3. How does RenNano® support the design of BCG024?
BCG024 incorporates a RenNano®-derived 4-1BB VHH as a compact and flexible costimulatory module. RenNano® mice generate heavy chain-only antibodies that do not require in vitro humanization, supporting a faster and more cost-effective discovery workflow. RenNano®-derived components also provide sequence diversity, optimal affinity, and favorable PK properties for modular multispecific antibody engineering.
4. What safety profile supports BCG024 development?
BCG024 showed a favorable preliminary safety profile in CD3ε × 4-1BB humanized mice, with no significant body weight loss and limited cytokine induction compared with non-specific TriAb control. Preliminary cynomolgus monkey data further supported antibody-like PK, repeat-dose tolerability, and limited cytokine release.
5. Which indications may be relevant for BCG024 development?
The primary focus for BCG024 is SCLC, supported by high tumor-associated DLL3 expression and clinical validation of DLL3-targeted T-cell engagement in extensive-stage disease. DLL3-positive NEC may represent an additional development opportunity.
