Human macrophage phagocytosis of lung cancer cells induced by CD47 blockade is augmented after knockdown of phagocytosis checkpoints mediated by siRNA-loaded lipid nanoparticles

Macrophages can phagocytose tumor cells. However, tumor cells may avoid phagocytosis by activating macrophage-expressed phagocytosis checkpoints such as SIRPα, LILRB1, or Siglec-10. Here, we investigated if LNPs loaded with siRNA (siRNA-LNPs) specifically neutralizing these checkpoints may be used as a counter-regulatory approach to augment cancer cell phagocytosis in human macrophages. The NanoAssemblr Ignite platform was used to prepare siRNA-LNPs targeting genes of interest. Human monocyte-derived macrophages were generated in vitro from healthy anonymous blood donors and treated with one or more siRNA-LNPs under various conditions. Following treatments, abundance of mRNA was analyzed by RT-qPCR, while membrane protein and soluble protein was measured by flow cytometry and ELISA, respectively. Phagocytosis was assessed by flow cytometry and fluorescence microscopy. Target mRNAs were efficiently downregulated by siRNA-LNPs in a dose-dependent manner. Combination treatment targeting all three genes of interest was similar in knockdown effectiveness to single treatment for each target. A single dose resulted in significant downregulation of mRNA and protein for up to 7 days and did not reduce macrophage viability. Repeated dosing further reduced target abundance. Importantly, we observed a synergy between LILRB1-siRNA-LNPs and CD47 blockade that increased macrophage phagocytosis of NCI-H196 lung cancer cells. In conclusion, transfection with siRNA-LNPs resulted in an efficient simultaneous downregulation of phagocytosis checkpoints in human macrophages and augmented macrophage phagocytosis of tumor cells in response to CD47 blockade in vitro. Using siRNA-LNPs in cancer therapy may be a promising potential approach to augment phagocytosis and the innate immune response against tumor growth.