Abstract
Background:
CD169+ macrophages in lymph nodes (LNs) activate cytotoxic T lymphocytes (CTLs), which play a crucial role in anticancer immunity, through antigen presentation and co-stimulation by CD169. Interferon alpha (IFNα) is capable of inducing the CD169+ phenotype of macrophages; however, its clinical applications have been hindered by pharmacokinetic limitations-low LN distribution and an inability to target macrophages. To overcome these issues, this study genetically fused mouse IFNα (mIFNα) with mannosylated mouse serum albumin (Man-MSA), and investigated the antitumor effects of the hybrid protein (Man-MSA-mIFNα) or its add-on effects with programmed death-ligand 1 (PD-L1) blockade.
Methods:
To confirm the possibility of CD169+ macrophage-mediated T cell priming, positional information about individual immune cells in LNs of cancer patients was obtained. Traits of Man-MSA-mIFNα, which was prepared using Pichia pastoris to form the high-mannose structure, were characterized by several physicochemical methods. To evaluate the lymphatic drainage of Man-MSA-mIFNα, radioiodine or Cy5-labeled Man-MSA-mIFNα was subcutaneously administered in mice, and then the radioactivity or fluorescence in LNs was analyzed. CD169-diphtheria toxin (DT) receptor (CD169-DTR) mice in which LN CD169+ macrophages can be depleted by DT injection were used to verify whether the antitumor effect of Man-MSA-mIFNα is dependent on LN CD169+ macrophages.
Results:
Multiplex tissue imaging predicted close proximity of CD169+ macrophages and T cells and positive correlation between the number of CD169+ macrophages and T cells in neighborhoods in LNs of cancer patients. Physicochemical analyses showed that Man-MSA-mIFNα was formed from the fusion of the intact Man-MSA and mIFNα. Man-MSA-mIFNα efficiently induced the CD169+ phenotype of macrophages by its high LN distribution and macrophage-targeting capability, and significantly exerted antitumor activity through CD8+ T cell activation in the LNs, whereas its antitumor effects were canceled in CD169-DTR mice. Finally, combination therapy with PD-L1 blockade markedly suppressed tumor growth in MB49-bearing mice, which exhibit resistance to PD-L1 blockade monotherapy.
Conclusions:
The present study successfully designed and developed Man-MSA-mIFNα, which efficiently induces the CD169+ phenotype in LN macrophages, contributing to the antitumor immunity. The findings suggest that our novel strategy targeting CD169⁺ macrophages could be a promising immunotherapy for cancer patients who are unresponsive to immune checkpoint inhibitors.