Breast cancer (BC) is the most common malignancy diagnosed in women worldwide, and the second cause of cancer-related deaths.(Siegel et al., 2023) Since its approval by the FDA in 1998, trastuzumab has been successfully used in clinics and has improved the outcomes of patients with HER2+ BC.(Du et al., 2023a; Nahta and Esteva, 2006; Sheikh and Huang, 2022) However, most patients who achieve an initial response to trastuzumab-based regimens have been found to develop resistance within one year.(Du et al., 2023a; Nahta and Esteva, 2006) In addition, a considerable number of women do not benefit from this therapy.(Dahabreh et al., 2008; Valachis et al., 2011) Therefore, it is necessary to develop novel therapeutic approaches to resolve this clinical issue. Several potential trastuzumab resistance mechanisms have been reported in earlier studies, including HER family alterations, loss/masking of HER2 epitope, activation of compensatory pathways, HER2 heterogeneity, long non-coding RNA mediated mechanisms, and tyrosine phosphorylation-mediated mechanisms (Du et al., 2023b, Marra et al., 2024, Singh et al., 2022, Swain et al., 2023, Zou et al., 2024). However, the treatment for trastuzumab resistance needs further investigation.

Macrophages are the major infiltrating cells, and the extent of its infiltration tends to correlate with a poor prognosis in BC(Komohara et al., 2023; Ma et al., 2020; Nalio Ramos et al., 2022). It was found that the co-expression of CD47 and HER2 is frequently detected among recurrent BC patients with poor prognosis from The Cancer Genome Atlas (TCGA) datasets, as well as the immunohistochemistry and western blot for BC samples and cell lines.(Candas-Green et al., 2020) Many studies have demonstrated that inhibiting the interaction between CD47 and SIRPα exerted a significant influence on a synchronized innate and adaptive immune response against tumor cells, involving various cell types such as macrophages, DCs, neutrophils, and T cells.(Jiang et al., 2021; Sun et al., 2021; Yanagita et al., 2017; Zhao et al., 2011). However, the majority of studies have indicated that the sole inhibition of the CD47/SIRPα signaling pathway in-vivo exhibited restricted therapeutic efficacy against solid tumors, including BCs.(Liu et al., 2022; Qu et al., 2022; Sikic et al., 2018). While, the dual blockade of CD47 and HER2 has been found to significantly inhibit clonogenicity and enhance macrophage-mediated attacks in radioresistant BC cells.(Candas-Green et al., 2020) These findings provide a strong scientific rationale for simultaneously targeting the CD47/SIRPα and HER2 signaling pathways by anti-CD47/HER2 bispecific antibody (BsAb) for the optimal immune activation and effective tumor destruction.

In the present study, we developed a novel anti-CD47/HER2 BsAb, named IMM2902. IMM2902 is uniquely designed to block the CD47/SIRPα interaction only in the context of HER2 expression while also blocking HER2 signaling. IMM2902 demonstrated higher anti-tumor activities against trastuzumab-resistant BC cells than controls both in vitro and in vivo. In addition, IMM2902 yielded a high safety profile regarding anemia and non-specific cytokines release. These data illuminate a novel strategy for treatment against trastuzumab-resistant BC.