A novel anti-PD-L1/IL-8 bispecific antibody BP2402 enhances antitumor immunity and modulates inflammatory signaling in triple-negative breast cancer mice model.

Background: Triple-negative breast cancer (TNBC) is an aggressive malignancy with limited therapeutic options. Immune checkpoint inhibitors targeting the programmed death-ligand 1 (PD-L1) pathway show restricted efficacy in TNBC, with response rates of only 5-10% as monotherapy. Interleukin-8 (IL-8/CXCL8) signaling promotes immunosuppression and mediates resistance to anti-PD-L1 therapy, necessitating combination approaches to overcome these limitations. However, the underlying mechanisms of enhanced efficacy from dual pathway targeting require further investigation.

Methods: We generated humanized mouse models by reconstituting immunodeficient mice with human PBMCs from five donors (n = 5 mice/group). MDA-MB-231 TNBC cells were implanted subcutaneously, and mice were treated with vehicle control, atezolizumab (anti-PD-L1), HuMax-IL8 (anti-IL-8), combination therapy, or a novel bispecific antibody BP2402 targeting both PD-L1 and IL-8. Antitumor activity was assessed alongside single-cell RNA sequencing of tumors and mechanistic analyses including immunofluorescence and Western blot.

Results: Combination therapy demonstrated significantly enhanced tumor growth inhibition compared to atezolizumab monotherapy in responsive donor models (51.28% vs. 39.13% for donor 3, p < 0.01; 44.01% vs. 6.57% for donor 4, p < 0.01). Single-cell RNA sequencing showed higher intratumoral T-cell fractions with combination therapy (donor 3: 80.5% vs. 26.7%; donor 4: 63.6% vs. 13.0% compared to control). BP2402 maintained high binding affinity for both IL-8 (KD = 2.132 nM) and PD-L1 (KD = 1.473 nM), and demonstrated superior antitumor efficacy compared to monotherapies (p < 0.001 vs. vehicle, p < 0.01 vs. individual antibodies). BP2402 treatment significantly reduced CXCL8 and VEGFA expression, suppressed JAK1/STAT1 signaling pathway activation, and upregulated pro-apoptotic proteins including FAS and BAX while effectively modulating T cell exhaustion markers PD-1 and TIM-3.

Conclusions: These results indicate that dual targeting of PD-L1 and IL-8 pathways represents a promising therapeutic strategy for TNBC. The bispecific antibody approach offers superior therapeutic potential by simultaneously modulating immune checkpoints, inflammatory signaling, and angiogenesis, effectively addressing resistance mechanisms. Additional preclinical optimization and clinical studies are required to fully assess the therapeutic potential of this novel immunotherapeutic approach.