Researchers find that combining novel 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. Chimeric Antigen Receptor T cell (CAR T) therapy relies on extracting a patient’s immune cells and modifying them in the lab with a new, synthetic receptor.

CAR T cell design
FIGURE 1: A T cell and a chimeric antigen receptor combine to create a CAR T cell. Most approved CAR … [+]MESOTHELIOMA.COM
Process of CAR T therapy
FIGURE 2: In CAR T therapy, 1) T cells are first isolated from the patient’s collected blood. 2) In … [+]CANCER.GOV

Gene Editing with Viral Vectors

To craft CAR T cells, the very genes of the T cells must be altered to express the chimeric antigen receptor. Gene editing, therefore, provides the foundation for the therapy.

Integrating CAR genes normally requires the use of a viral vector. Retroviruses in particular have the unique ability to insert and meld their own foreign genetic material into human cells permanently. This allows viruses to use host machinery to produce viral proteins.

Scientists have repurposed this strength to deliver CAR genes into T cells. An inactivated form of the virus is filled with genetic material which encodes for CAR. The desired genes are then transferred from the virus into the T cells through 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 onto the cell surface.

retorvirus transduction of car t cells
FIGURE 3: How to modify T cells to express chimeric antigen receptors. A) Essential viral genes are … [+]MORGAN AND BOYERINAS
Retrovirus transduction
Figure 4: Retroviral transduction of T Cells. Translation of the synthetic genes results in the … [+]MOLECULAR THERAPY, 2016

The industry standard may depend on viral vectors, but the procedure lacks in some aspects. This stage of the CAR T process is the most time-consuming and expensive; it can take a year or longer to produce a batch of viral vectors, 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 resolve these issues.

Enter CRISPR/Cas9 Gene Editing

CRISPR originates from organisms such as bacteria and plays a major role in their defense. The acronym CRISPR stands for Clustered Regularly Interspaced Short Palindromic Repeats—in essence, they are short, repeating DNA sequences which read the same forwards or backwards, similarly to words such as “MADAM” or “DEED.” Sandwiched between these repeats are protospacers, a genetic history of viruses the bacteria encounters (see Figure 5).

When a virus tries to insert its genetic information into the bacteria, the bacteria can recognize the sequence from its protospacer catalog. The bacteria transcribes the protospacer DNA 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 snip human DNA. As seen in Figure 6, an RNA guide can be made to cut DNA at a specific site. The broken DNA, eager to repair itself, can easily adopt a new DNA sequence in that location.

Translating this concept to CAR T therapy, researchers could modify T cell DNA directly to express a new receptor. Synthesizing an RNA guide is cheaper and more efficient than cultivating retroviral vectors. If successful, CRISPR could simply solve two major drawbacks associated with CAR T therapy: price and time-to-delivery.

CRISPR DNA made of spacers and repeats
FIGURE 5: CRISPR consists of spacers—unique, virus-derived DNA sequences—sandwiched between short, … [+]SCIENCE BUDDIES
Cas9 enzyme cuts DNA
FIGURE 6: Researchers leverage CRISPR/Cas9 to cut and insert genes at a desired site on the genome. … [+]LABIOTECH


CAR T therapy, although a triumph of human engineering in its own regard, still has room for improvement. There is potential to propel CAR T design forward by integrating contemporary innovations such as CRISPR/Cas9 technology. Although this method still requires T cell manipulation outside the body, this change could streamline the process while becoming more accessible.

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