Immune checkpoint inhibitors (ICIs), such as anti-programmed cell death protein 1/anti-programmed cell death 1 ligand 1 (PD-1/PD-L1) monoclonal antibodies, have made great success in the treatment of malignancies. Achievements in non-small-cell lung cancer (NSCLC), colorectal cancer (CRC), and melanoma have resulted in durable responses [1], [2], [3], [4]. However, limited patients benefited from such treatments due to primary or acquired resistance attributed to loss of neoantigens, defective antigen presentation, and upregulation of immune checkpoints other than PD-1/PD-L1 [5], [6], [7], [8]. In fact, objective response rates (ORR) in patients with positive expression of the PD-L1 biomarker range from 10 % to 40 % [9], [10], [11], [12], [13]. Therefore, it is necessary to explore new therapeutic strategies, such as combination therapy, to overcome drug resistance to ICIs.

Type I IFNs have enormous antitumor capabilities attributed to direct inhibition of tumor cell proliferation and tumor angiogenesis, as well as immunomodulatory effects [14], [15], [16], [17]. Emerging evidence suggests that type I IFNs can significantly induce tumor cell apoptosis and inhibit tumor cell proliferation and metastasis [15], [18]. In addition, type I IFNs stimulate dendritic cell (DC) differentiation and maturation, thereby enhancing DC activity [19]. Adequate type I IFN promotes DC activation and T cell cross-priming [20]. Thus, type I IFNs may be ideal collaborators for ICIs to enhance the therapeutic efficacy, especially in subpopulations of cancer patients with deficient antigen presentation and T cell priming.

Among the subtypes of type I IFNs, interferon alfa (IFNα) and Pegylated interferon alfa (PEG-IFNα) are of interest. IFNα [21] and PEG-IFNα [22], [23] have been approved for the treatment of cancer. Compared to IFNα, another member of type I IFNs, interferon beta (IFNβ) exhibits better antitumor potency which correlates with more potent receptor binding, DC activation and antiproliferative activity [24], [25], [26], [27], [28], [29]. In the clinical setting, IFNβ and pegylated interferon beta (PEG-IFNβ) have been approved as disease-modifying therapies for multiple sclerosis (MS) [30], [31]. To date, IFNβ monotherapy, with moderate efficacy mainly through early phase studies [32], [33] and ongoing phase III clinical trials [34], is approved only in Japan for the treatment of cancer [35]. The potency of IFNβ in combination with ICIs has been explored preliminarily in clinical trials in melanoma patients [36] and preclinical studies of mouse IFNβ in murine melanoma models [37], [38]. A comprehensive preclinical elucidation of the efficacy of IFNβ as monotherapy or in combination with ICIs in tumor models other than melanoma is warranted.

In this study, human IFNβ was conjugated with polyethylene glycol (named PEG-IFNβ) to conquer the deficiencies of cytokine-based therapies, such as rapid clearance and short half-life [39], [40]. The efficacy of PEG-IFNβ as monotherapy or in combination with anti-PD-1 antibody in lung cancer, colon cancer, and melanoma mouse models was elucidated. In addition, we compared the effect of PEG-IFNβ and pegylated human IFNα-2b (PEG-IFNα-2b) on proliferation of human tumor cell lines (lung cancer, colon cancer, and melanoma) and activation of human monocyte-derived dendritic cells (MoDCs).