Here we describe the integration of CRISPR gene-editing technology to improve the CAR T therapy design. Other alternative CAR T designs include mRNA vectors to create temporary CAR T cells and the use of antibody switches to control CAR T cell activation. Previous episodes deal with the CAR T fundamentals and its applications for B cell cancers, multiple myeloma, lupus and the heart.
Researchers find that combining new gene-editing CRISPR technology with CAR T therapy could simplify and improve CAR T therapy in one fell swoop.
Traditional CAR T therapy
A remarkable feat in cancer care, today people with difficult-to-treat blood cancers can receive CAR T therapy, a personalized “drug” made from their own immune cells. VSchimerical Antigen Rreceiver J cell therapy (CAR T) relies on extracting immune cells from a patient and modifying them in the laboratory with a new synthetic receptor.
The new receptor allows the white blood cell to target and destroy cancer cells once reinjected into the bloodstream. Evoking the patched image of a mythical chimera, these receptors fuse typical T-cell signaling machinery with an antibody-derived sensing region to create a potent “living drug” that continually grows inside the body. Figure 1 highlights the basic design of a CAR T cell, while Figure 2 illustrates the step-by-step process in more depth.
Gene editing with viral vectors
To make CAR T cells, the T cell’s own genes must be modified to express the chimeric antigen receptor. Gene editing therefore forms the basis of therapy.
Integration of CAR genes normally requires the use of a viral vector. Retroviruses in particular have the unique ability to permanently insert and fuse their own foreign genetic material into human cells. This allows viruses to use the host’s machinery to produce viral proteins.
Scientists have repurposed this force to deliver CAR genes into T cells. An inactivated form of the virus is packed with genetic material that codes for CAR. The desired genes are then transferred from the virus into T cells by a process called transduction (see Figure 3). As if reading biological instructions, the T cell uses the genetic information to construct the receptor before expressing it on the cell surface.
The industry standard may depend on viral vectors, but the procedure is lacking in some respects. This step in the CAR T process is the longest and most expensive; producing a batch of viral vectors can take a year or more and can cost up to $50,000 per dose. For these reasons, researchers now hope to turn to CRISPR technology, a recent scientific breakthrough in gene editing, to solve these problems.
Enter CRISPR/Cas9 gene editing
CRISPR comes from organisms such as bacteria and plays a major role in their defense. The acronym CRISPR stands for VSchandelier Rregularly Ispaced out Sshort Palindromic Repeats – in essence, they are short, repeating sequences of DNA that read the same forward or backward, similar to words like “MADAM” or “DEED”. Between these repeats are protospacers, a genetic history of the viruses encountered by the bacterium (see Figure 5).
When a virus tries to insert its genetic information into the bacterium, the bacterium can recognize the sequence from its catalog of protospacers. The bacterium transcribes the DNA of the protospacer into RNA; this RNA guides enzymes such as Cas9 to the viral DNA to cut and deactivate it.
The same CRISPR/Cas9 interface can also cut human DNA. As seen in Figure 6, an RNA guide can be made to cut DNA at a specific site. Broken DNA, eager to repair itself, can easily adopt a new DNA sequence at this location.
By translating this concept into CAR T therapy, researchers could directly modify the DNA of T cells to express a new receptor. Synthesizing guide RNA is cheaper and more efficient than culturing retroviral vectors. If successful, CRISPR could simply solve two major drawbacks associated with CAR T therapy: price and delivery time.
CAR T therapy, while a triumph of human engineering in its own right, still has room for improvement. It is possible to advance the CAR T design by incorporating contemporary innovations such as CRISPR/Cas9 technology. Although this method still requires manipulation of T cells outside the body, this change could streamline the process while becoming more accessible. The most critical step now is to test the feasibility of this concept. The next installment in the series will explore the latest clinical results from PACT Pharma and the University of California, Los Angeles on their dual CRISPR/CAR T interface.