Chemistery

Antigen Escape Antigen Escape is one of the most concerning challenges during the clinical development of CAR-T cell therapy. A robust initial response is often followed by a relapse in many trials. This is often due to the downregulation or the complete loss of target antigens on the tumor cells. Introduction Antigen escape describes the development of tumor resistance to a single antigen targeting CAR construct. After the initial encounter with the CAR-T cells, the malignant cells mutate and show partial or complete loss of the target antigen expression.  In patients with ALL treated with CD19-targeted CAR-T cell therapy, a downregulation or loss of CD19 antigens was observed.  In patients with myeloma treated with BCMA-targeted CAR-T cell therapy, a downregulation or loss of BCMA expression was observed.  In patients with glioblastoma, a solid tumor treated with IL13Ra2-targeted CAR-T cell therapy, a downregulation of IL13Ra2 expression was observed.  Improve...

Transmembrane Domains Among the four components of a chimeric antigen receptor (CAR), the transmembrane domain is the least studied one. How different transmembrane domains affect and contribute to each other's functions is also not well studied. That being said, we will go through the function of a transmembrane domain of a CAR, the CD3ζ transmembrane domain, and the CD8α transmembrane domain.  Introduction of the transmembrane domain The transmembrane domain is where the transmembrane proteins are located. In a CAR, the transmembrane domain has the function to anchor the CAR to the T cell membrane. How strong the CAR is anchored to the T cell membrane affects the CAR expression level and stability.  Currently, the commonly used transmembrane domain is derived from proteins such as CD3ζ, CD4, CD8α, and CD28. The CD3ζ transmembrane domain Among the transmembrane domains mentioned, the CD3ζ transmembrane may improve CAR-mediated T cell action as the CD3ζ transmembrane medi...

Antigen Binding Domains The antigen-binding domain of a chimeric antigen receptor is like the head of a train. It determines the target antigen specificity.  The antigen-binding site is made up of a heavy chain and a light chain joined together to form a single-chain variable fragment (scFv).  Single-chain variable fragment (scFv) scFv targets extracellular surface cancer antigens, the biomarkers of the tumor cells. Classically, CD19 is presented in B cells in leukemia. Hence, CD19 is the biomarker that we want the CAR to recognize and bind with it. Once the scFv of a CAR binds with the target antigen, the immune response, major histocompatibility complex (MHC)-independent T cell activation, results. This is when a cascade of molecular signaling starts to trigger an immune response to kill the tumor cells.  MHC-dependent, T cell receptors (TCR)-mimic CARs Some may call it an improvement, but a T cell receptor (TCR)-mimic CAR functions well when it targets intracellular tu...

Intracellular Signaling Domain(s) Intracellular signaling domains get the most attention as we talk about CAR-T cell therapy because it affects how CAR constructs are generated in the T cells and initiate CAR co-stimulation.  The intracellular signaling domain is the research topic where all the cell engineering happens and gets all the attention for future improvement. What co-stimulatory domain(s) is/are presented in the CAR? What co-stimulatory domains need to be avoided to decrease the likelihood of activation-induced cell death (AICD)? These are questions that cell engineers and researchers ask as they finetune the fourth component of a chimeric antigen receptor to target tumor cells.  Since the first generation of CARs is built in the late 1990s, we now mainly have three generations of CARs as the iteration happened.  First-generation CARs The very first generation of CARs built in the late 1990s contains a CD3ζ or FcRγ signaling domain. Clinical Responses Most of t...

The Hinge Region Let's talk about the hinge region, the second component of a chimeric antigen receptor (CAR).  Refresher: A CAR is a synthetic receptor that consists of four components: an extracellular target antigen-binding domain, a hinge region, a transmembrane domain, and one or more intracellular signaling domains.  A. Structure and function of the hinge region Before we dive into how the length of the hinge region could affect the CAR functionality, let's cover what the hinge region is and its function.  What is the hinge region? A structural region that extends the binding units from the transmembrane domain.  What is the function of the hinge region?  It makes the receptor flexible to overcome steric hindrance and adds to the length to allow the antigen-binding domain to access the epitope of the target. Which CAR functionality does the hinge region affect?  The hinge region is important because it affects several aspects of a CAR. It could affect...