An Engineered Protein Helps Phagocytes Gobble Up Diseased Cells

When cells die or the body no longer needs them, phagocytic cells arrive to engulf them. This process relies upon the cells destined for destruction to express a protein that serves as an “eat me” signal. An adaptor molecule grabs onto this signal and then tethers itself to a protein on phagocytes, bridging the two cells. This binding activates the phagocyte to pull in the unwanted cell and chow down on it.

A research team at Kyoto University wondered whether they could adapt this cell removal system as a therapeutic to eliminate cells involved in disease. They modified the adaptor protein to recognize an antigen on a target cell of their choosing and demonstrated that this promoted selective elimination by phagocytes.¹ The findings, published in Nature Biomedical Engineering, offer a potential new approach to treat a variety of diseases.

To test their idea, the team first replaced the antigen-target domain on the adaptor protein with an antibody fragment, a nanobody, that recognized green fluorescent protein (GFP). They dubbed this new construct: connector for removal of unwanted cell habitat (Crunch). They showed that GFP-targeting Crunch bound to GFP on cell membranes in vitro and activated engulfment of these cells by phagocytes.

Next, they assessed whether GFP-targeting Crunch also promoted elimination in vivo. They showed that their Crunch construct reduced GFP-expressing splenocytes as well as melanoma tumors expressing GFP injected into otherwise healthy mice.

To evaluate whether they could adapt this system to disease-relevant antigens, they fused different small antibody constructs to their antigen-binding domain. They targeted two different antigens: one against a melanoma protein, while the other bound to CD19, a B cell marker.

Both Crunch constructs recognized their targets in mice. The melanoma-targeting Crunch reduced tumor growth, increasing the animals’ survival. Meanwhile, the CD19-targeting Crunch promoted engulfment of CD19⁺ splenocytes in mouse blood and spleens. When the team injected this construct into mice that modeled systemic lupus erythematosus, which is driven by autoantibodies, they observed decreased numbers of CD19⁺ B cells in the animals’ blood and spleens. This also decreased the accumulation of antibodies in the kidneys and the presence of autoantibodies in the serum.

“We think this could become a new kind of therapy that can be adapted to many conditions. We can also adopt the targeting sensors from antibodies and CAR-T. It’s the ecosystem for the various therapeutic tools,” said Jun Suzuki, a biochemist at Kyoto University and study coauthor, in a press release.