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Medical breakthroughs usually occur when science and industry collide through combinations of various disciplines. Right now, we are on the verge of witnessing a potential medical breakthrough for the treatment of cancer as three discoveries converge:

Invention of CAR-T (Carl June, a scientist from University of Pennsylvania, pioneered CAR-T technology. Dr. June started treating cancer patients with it in 2010. In 2017, U.S. FDA approved the first two CAR-T medicines for the treatment of blood cancers)
Introduction of Checkpoint Inhibitors (Bristol-Myers’s Opdivo and Merck’s Keytruda were approved by FDA for the treatment of cancer in 2014/2016, respectively. Since then, the agency has approved these medicines for the treatment of various types of cancer)
Discovery of CRISP-Cas9 gene editing (In 2012, Jennifer Doudna, Emmanuelle Charpentier and Feng Zhang were credited for this eureka moment, as these scientists independently discovered CRISPR-Cas9 technology and predicted its significant potential. Jennifer (University of California, San Francisco), Emmanuelle Charpentier (Max Planck Institute) and Feng Zhang (Massachusetts Institute of Technology, MIT) were the inventors, respectively, of the technologies given rise to three emerging biotech companies: Intellia Therapeutics, CRISPR Therapeutics and Editas Medicine).

“Chimeric Antigen Receptor T cell therapy” (CAR-T) is a gene therapy designed to harness the potency of antibodies and T-lymphocytes into one single medicine for the treatment of cancer. CAR-T therapy could be viewed as a “living anti-cancer drug” as the medicine itself consists of a living cell, which is genetically engineered as a pharmaceutical “chimera” to find and destroy cancer cells (see Parts 1/2 of these series). Gene editing tools, such as CRISPR-Cas9, could be utilized to generate more effective CAR-T medicines (Figure 1).

Figure 1. Gene editing to engineer a “CAR-T medicine”. A picture containing clock, device

Description automatically generated

Source: “T-cell tweaks to target tumors”. Nature 2017, 543:48-49

Traditional CAR-T Design. Traditional CARs (shown in yellow) are inserted at a random location into the genome (DNA) of T cells. If the CAR-T is expressed constitutively (constant synthesis), the cells often enter a state called “exhaustion” (become inactive).
Use of CRISPR-Cas9. Gene-editing tool CRISPR–Cas9 used to replace the cell's TCR-encoding gene (TCR – “natural T-cell receptor”, shown in green) with a CAR-T encoding sequence (shown in yellow).
Gene-edited CAR-T. CRISPR–Cas9-edited T cells express only one type of TCR, the CAR-T (shown in yellow and red), providing better anti-tumor responses than traditional CAR T cells. The natural TCR (green) has been removed.

Click here to read Part 1 or Part 2 of this series on the revolutionary advances happening in the science of cancer treatment.

Using “Gene-edited CAR-T Medicines” to Overcome Checkpoint Inhibition. Using CRISPR-Cas9, a potent gene editing tool, it is possible to generate an anti-cancer weapon that overcomes checkpoint inhibition. Checkpoint inhibitors such as Merck’s Keytruda have been the most effective immunotherapy for the treatment of cancer. These medicines revert inhibitory signals generated by PD-1 checkpoint, thus significantly stimulating anti-cancer immune responses (“like triggering car acceleration by releasing the brakes”). Scientists at the University of Southern California, Los Angeles, have engineered a CAR-T medicine designed to continuously secrete anti-PD1 antibody, thus blocking inhibitory PD-1 signals, which result in heightened potency for CAR-T treatments (Clinical Cancer Research 2017, 23(22): 6982-6992). In a similar fashion, also utilizing CRISPR-Cas9 as a gene editing method, scientists at the University of Pennsylvania have developed universal CAR-T cells (“off-the-shelf”, “allogeneic”, “universal donor”) resistant to PD-1 inhibition. These CAR-T cells lack the gene for expression of PD-1 checkpoint protein. Without PD-1 inhibition, these CAR-T cells show enhanced anti-tumor killing effects in experimental cancer models (Clinical Cancer Research 2017, 23(9) 2255-2266). These results are important because they show the potential of combining checkpoint inhibition theory, CRISPR-Cas9 gene editing, and CAR-T technologies to potentially develop one potent anti-cancer weapon.

Hurdles to Overcome Before “Gene-edited CAR-Ts” Become a Reality. CAR-T cells are engineered to infiltrate the tumor mass and persist in it over long periods, which is required to kill cancer cells. However, objective tumor responses (tumor shrinkage) seen with this treatment in solid tumors are frequently short-lived, as the tumor microenvironment generate inhibitory signals rendering CAR-T cells inert. Inhibitory signals primarily come from a different type of T-lymphocytes known as “regulatory T cells” (Tregs), and from checkpoint molecules (CTLA-4, PD-1, LAG3, or TIM-3) expressed on the cell surface, which shut down CAR-T cells. CRISPR-Cas9-edited CAR-T cells could potentially overcome some of these limitations. However, gene editing does not come without its own challenges. The risk of genetic “off-target” gene insertions/deletions in the genome (DNA) of the patient, and side effects caused by Cas9 enzymatic activity, could hinder the potential of this technology. Off-target effects could introduce random mutations, impact the role of tumor suppressor genes and oncogenes, resulting in tumorigenic potential. Experiments performed by scientists at Stanford University, Palo Alto, California, found many unintended mutations in the genome of a mouse after using CRISPR-Cas9 gene editing (Nat Methods 2017, 14:547-8). The results of this study raise concerns related to the technology’s safety, especially given the inherent risks of undesired/secondary mutations. The experiment revealed the presence of secondary mutations in regions not targeted by the “single guide RNA” (sgRNA), one of the main components of the CRISPR-Cas9 system.

Biotechnology Innovations in CRISPR-Cas9/CAR-T Technologies. In recent years, significant advances in CAR-T technologies have been implemented by various companies in the biotechnology industry. Although there are still hurdles to overcome, especially to develop efficacious CAR-T candidate medicines for the treatment of solid tumors, the industry continues to innovate. Better knowledge of T-cell receptor functions, improved understanding of anti-cancer immunology and a wider industry participation on these endeavors should generate better results in CAR-T human clinical trials. CRISPR Therapeutics, Mustang Bio and Intellia Therapeutics are examples of emerging biotechnology companies using CRISP-Cas9 to engineer better CAR-T medicines.

CRISPR Therapeutics (Nasdaq: CRSP) is developing CTX130 as an allogeneic CRISPR/Cas9 gene-edited CAR-T cell therapy targeting CD70 expressing cancers, including hematological (blood) and solid tumors. According to the medical literature, CRISPR/Cas9 gene editing is faster, cheaper and easier to use than competing gene editing systems such as “transcription activator-like effector nucleases” (TALENs), and zinc-finger nucleases (ZFNs).

In 2017, Mustang Bio (Nasdaq: MBIO) entered into a licensing agreement and research collaboration with Harvard University to develop CRISPR-Cas9-enhanced CAR-T medicines for the treatment of blood cancers and solid tumors. Mustang Bio is developing MB-102/MB-106 (CD123/CD20 CAR-Ts) for the treatment of blood cancers, MB-101 (IL13Ra2 CAR-T) for the treatment of glioblastoma, and other CAR-Ts for the treatment of prostate, pancreatic and metastatic breast cancers. Another competitor in the area is Intellia Therapeutics (Nasdaq: NTLA), which is using its CRISPR-Cas9 gene editing technology in collaboration with “Novartis Institutes for Biomedical Research” to develop CAR-T medicines for the treatment of cancer.

In summary, the consensus among academics and industry experts is that research and development in CAR-T area will only intensify in coming years, fueled by technological advancements in checkpoint inhibition and gene editing. A potential medical breakthrough emanating from these developments will be welcome news for patients, who eagerly wait for a triumph in the war against cancer.

In case you missed them, click here to read Part 1 or Part 2 of this series on CAR-T medicines for the treatment of cancer.

Sources:

“Chimeric Antigen Receptor (CAR) T Cell Therapy for Malignant Pleural Mesothelioma (MPM)”. Cancers 2017, 9(9) p115

“Fine and Predictable Tuning of TALEN Gene Editing Targeting for Improved T Cell Adoptive Immunotherapy”. Molecular Therapy: Nucleic Acids Vol. 9 December 15, 2017.

“Programming CAR-T cells to kill cancer”. Nature Biomedical Engineering 2018, Vol 2, June 2018, p377-391

Switching on the green light for chimeric antigen receptor T-cell therapy. Clinical & Translational Immunology 2019, Vol 8, e1046

“CAR-T with License to Kill Solid Tumors in Search of a Winning Strategy”. International Journal of Molecular Sciences 2019, Vol 20, p1903

“Chimeric-antigen receptor T (CAR-T) cell therapy for solid tumors: challenges and opportunities”. Oncotarget 2015, Vol 8(52), p90521-90531

“Two-Dimensional Regulation of CAR-T Cell Therapy with Orthogonal Switches”. Molecular Therapy - Oncolytics 2018 Dec 20;12:124-137

“Therapeutic potential of CRISPR/Cas9 gene editing in engineered T-cell therapy”. Cancer Medicine 2019, DOI: 10.1002/cam4.2257

“Targeting a CAR to the TRAC locus with CRISPR/Cas9 enhances tumour rejection”. Nature 2017; 543(7643): 113-117

“A long way to the battlefront: CAR T cell therapy against solid cancers”. Journal of Cancer 2019; 10(14): 3112-3123

“Enhanced cancer immunotherapy by chimeric antigen receptor-modified T cells engineered to secrete checkpoint inhibitors”. Clinical Cancer Research 2017, 23(22): 6982-6992

“Multiplex genome editing to generate universal CAR T cells resistant to PD-1 inhibition”. Clinical Cancer Research 2017, 23(9) 2255-2266

“Unexpected mutations after CRISPR-Cas9 editing in vivo”. Nat Methods 2017, 14:547-8

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