Senior author Stephen Gottschalk, M.D., (left) and corresponding author Peter Chockley, Ph.D., (right) both of the St. Jude Department of Bone Marrow Transplantation and Cellular Therapy.
Adding a molecular anchor to the key protein that recognizes cancer in cellular immunotherapies can make treatments significantly more effective. Scientists at St. Jude Children's Research Hospital found that immune cells with the anchored protein increased cancer killing, regardless of the cancer's cell type or the form of cancer targeted. The molecular anchor concept is a new design for improving chimeric antigen receptor (CAR)-based-immunotherapies. CARs have shown some promise in the clinic but have yet to deliver widespread success across tumor types. The findings were published today in Nature Biotechnology.
"We've come up with a new way to more efficiently and effectively bind and target cancer cells," said first and corresponding author Peter Chockley, Ph.D., St. Jude Department of Bone Marrow Transplantation and Cellular Therapy. "The anchor domain design is modular and universal. We showed it worked in multiple CARs and multiple immune cell types - including both Natural Killer (NK) and T cells."
Scientists can reprogram human immune cells to target cancer cells by adding engineered CAR proteins to their surface. CAR T cells have shown some success in the clinic for certain cancers, such as relapsed leukemia. However, CAR T cells have failed to deliver such success for solid tumors, partially due to problems with immune cell activation. The St. Jude group found a way to "anchor" the CAR molecule within immune cells, allowing the cells to become activated more easily and kill cancer more effectively than conventional CARs. The anchored CARs increased survival in animal models of multiple tumor types, including lung, bone and brain cancers.
"The anchor domain discovery is easily translatable into early phase clinical testing," said senior author Stephen Gottschalk, M.D., St. Jude Department of Bone Marrow Transplantation and Cellular Therapy chair. "It doesn't require any other new technology. We strongly believe that this approach needs to get tested in the clinic because no one has tried it before, and it looks very promising in our preclinical work."
Carefully structured CARs kill cancers better
CARs are a key molecule to the cancer-killing process. The outside of the molecule recognizes a protein on the cancer cell. This forms a complex of molecules and proteins between the two cells called the immune synapse. Once the immune synapse is formed, the part of the CAR inside the immune cell receives signals from the portions outside the cell. These interactions send the 'go' signal to activate and kill the cancer cell, however these complex communications can be difficult for conventional CAR T and NK cells to interpret.
"Our approach is different because it focuses on organization," Chockley said. "CAR immune cells form synapses that are very disorganized. The anchoring domain we added organizes internal scaffolding proteins and makes a better synapse, and then brings in other extant signaling proteins. The simple addition of organization improves CARs dramatically."
Picture the back of a desktop computer with many tangled cords and cables. CAR activation requires untangling the cords and cables to add a monitor. If the cords are disorganized, it can be incredibly difficult. If someone has organized the cables well a task that may have taken hours becomes easy. Conventional CARs develop a disorganized immune synapse like a desk covered in a mess of cords, causing delayed signaling within the cells. By adding an anchoring domain to the bottom side of the CAR, the scientists organized the CARs - the molecular equivalent of adding cable ties to organize computer cables.
St. Jude researchers added a new anchor domain (PDZ) to CARs in NK cells (green), which efficiently invade and kill a tumor (red) in cell culture.
An attractive approach to improve any CAR system
"The most attractive thing about this approach," said senior author Stephen Gottschalk, M.D., St. Jude Department of Bone Marrow Transplantation and Cellular Therapy chair, "is that you can add the anchor domain to any CAR or other antigen-specific receptor you like. The engineering is simple and easily translatable to a broad range of cellular immunotherapies that are currently being developed."
The scientists added the molecular anchor by including a specific four amino acid sequence to the end of the conventional CAR. These amino acids then bound to the protein Scribble, which is involved in signaling and attaching to the internal scaffolding structure of the cell. The proteins, amino acids and signaling involved would be familiar to those working in skin (epithelial) cells, but not necessarily to an immunologist working on CARs. The discovery required a cross pollination of at least three different major disciplines, which Chockley has expertise in. His work shows that innovation in the field of CAR-modified cells can significantly benefit from paying attention to other basic scientific fields to find new ways to order and tune the immune synapse.
"There's a lot more to an immune cell-cancer cell interaction than we've been working with," Chockley said. "We're entering a new design realm with this domain. We have plenty to do and explore now."
Authors and funding
The study's other authors are Jorge Ibanez-Vega, Giedre Krenciute and Lindsay Talbot, all of St. Jude.
The study was supported by grants from the St. Jude Sumara Fellowship, ChadTough Defeat DIPG Foundation, National Institute of Neurological Disorders and Stroke (R01NS121249), the Rally Foundation for Childhood Cancer Research, The Garwood Postdoctoral Fellowship, the National Cancer Institute (P30 CA021765), the National Institutes of Health grants (P01CA096832 and R50CA211481) and ALSAC, the fundraising and awareness organization of St. Jude.
St. Jude is seeking a corporate partner to further develop this technology. If interested, you may learn more about the PDZ CARs (SJ-22-0011)
