The phrase “genetic engineering” often brings to mind a mad scientist manipulating mutant genes or a Frankenstein-like creation emerging from a test tube. Brought to the forefront by heated debates over genetically modified crops, genetic engineering has long been viewed as a difficult, risky process fraught with errors.1
The intentional use of CRISPRs, short for clustered regularly interspaced sport palindromic repeats, turned the world of genetic engineering on its head. Pioneered by Jennifer Doudna of Berkeley2 in 2012 and praised as the “Model T” of genetic engineering,3 CRISPR as a tool is both transforming what it means to edit genes and raising difficult ethical and moral questions about genetic engineering as a discipline.
CRISPR itself is no new discovery. The repeats are sequences used by bacteria and microorganisms to protect against viral infections. Upon invasion by a virus, CRISPR identifies the DNA segments from the invading virus, processes them into “spacers,” or short palindromic repeats of DNA, and inserts them back into the bacterial genome.4 When the bacterial DNA undergoes transcription, the resulting RNA is a single-chain molecule that acts as a guide to destroy viral material. In a way, the RNA functions as a blacklist for the bacterial cell: re-invasion attempts by the same virus are quickly identified using the DNA record and subsequently stopped. That same blacklist enables CRISPR to be a powerful engineering tool. The spacers act as easily identifiable flags in the genome, allowing for high precision when manipulating individual nucleotide sequences in genes.5 The old biotechnology system can be perceived as a confused traveler holding an inaccurate map, with a general location and vague person to meet. By the same analogy, CRISPR provides a mugshot of the person to meet and the precise coordinates of where to find them. Scientists have taken advantage of this precision and now use modified proteins, such as Cas-9, to activate gene expression as opposed to cutting the DNA,6 an innovative style of genetic engineering. Traditional genetic engineering can be a shot in the dark, but with the accuracy of CRISPR, mutations are very rare.7 For the first time, scientists are able to pinpoint the exact location of genes, cut the desired sequence, and leave no damage. Another benefit of CRISPR is the reincorporation of genes that have become lost, either by breeding or evolution, bringing back extinct qualities. For example, scientists have succeeded in introducing mammoth genes into living elephant cells.8,9 Even better, CRISPR is very inexpensive, costing around $75 to edit a gene at Baylor College of Medicine,10 and accessible to anyone with biological expertise, starting with graduate students.11 The term “Model T of genetic engineering” could hardly be more appropriate.
CRISPR stretches the boundaries of bioengineering. One enterprising team from China led by oncologist Dr. Lu You has already begun trials on humans. They plan on injecting cells modified using the CRISPR-Cas9 system into patients with metastatic non-small cell lung cancer--patients who otherwise have little hope of survival.12 To prevent attacks on healthy cells, extracted critical immune mediators called T cells will be edited with the CRISPR-Cas9 system. CRISPR will identify and “snip” out a gene that encodes PD-1, a protein that acts as a check on the T-cell’s capacity to launch an immune response. Essentially, Lu’s team is creating super-T-cells, ones that have no mercy for any suspicious activity. This operation is very risky. CRISPR’s mechanisms are not thoroughly understood, and mistakes with gene editing could have drastic consequences.11 In addition, the super T cells could attack in an autoimmune reaction, leading to degradation of critical organs. In an attempt to prevent such a response, Lu’s team will extract T-cells from the tumor itself, as those T-cells would likely have already specialized in attacking cancer cells. To ensure patient safety, the team will examine the effects of three different dosage regimens on ten patients, watching closely for side effects and responsiveness.
Trials involving such cutting-edge technology raise many questions. With ease of use and accessibility, CRISPR has the potential to become a tool worthy of science fiction horror. Several ethics groups have raised concerns over the inappropriate use of CRISPR: they worry that the technology could be used by amateurs and thus yield dangerous results. In spite of these concerns, China greenlit direct editing of human embryos, creating international uproar and a moratorium on further human embryo testing.13 But such editing could lead to new breakthroughs: CRISPR could reveal how genes regulate early embryonic development, leading to a better understanding of infertility and miscarriages.14
This double-edged nature defines CRISPR-Cas9’s increasing relevance at the helm of bioengineering. The momentum behind CRISPR and its seemingly endless applications continue to broach long-unanswered questions in biology, disease treatment, and genetic engineering. Still, with that momentum comes caution: with CRISPR’s discoveries come increasingly blurred ethical distinctions.
- Union of Concerned Scientists. http://www.ucsusa.org/food_and_agriculture/our-failing-food-system/genetic-engineering/risks-of-genetic-engineering.html#.WBvf3DKZPox (accessed Sept. 30, 2016).
- Doudna, J. Nature [Online] 2015, 7583, 469-471. http://www.nature.com/news/genome-editing-revolution-my-whirlwind-year-with-crispr-1.19063 (accessed Oct. 5, 2016).
- Mariscal, C.; Petropanagos, A. Monash Bioeth. Rev. [Online] 2016, 102, 1-16. http://link.springer.com/article/10.1007%2Fs40592-016-0062-2 (accessed Oct. 5, 2016).
- Broad Institute. https://www.broadinstitute.org/what-broad/areas-focus/project-spotlight/questions-and-answers-about-crispr (accessed Sept. 30, 2016).
- Pak, E. CRISPR: A game-changing genetic engineering technique. Harvard Medical School, July 31, 2015. http://sitn.hms.harvard.edu/flash/2014/crispr-a-game-changing-genetic-engineering-technique/ (accessed Sept. 30, 2016)
- Hendel, A. et al. Nature Biotech. 2015, 33, 985-989.
- Kleinstiver, B. et al. Nature. 2016, 529, 490-495.
- Shapiro, B. Genome Biology. [Online] 2015, 228. N.p. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4632474/ (accessed Nov. 1, 2016).
- Reardon, S. Nature. [Online] 2016, 7593, 160-163. http://www.nature.com/news/welcome-to-the-crispr-zoo-1.19537 (accessed Nov. 1, 2016).
- Baylor College of Medicine. https://www.bcm.edu/research/advanced-technology-core-labs/lab-listing/mouse-embryonic-stem-cell-core/services/crispr-service-schedule (accessed Sept. 30, 2016).
- Ledford, H. Nature. [Online] 2015, 7554, 20-24. http://www.nature.com/news/crispr-the-disruptor-1.17673 (accessed Oct. 11, 2016).
- Cyranoski, D. Nature. [Online] 2016, 7613, 476-477. http://www.nature.com/news/chinese-scientists-to-pioneer-first-human-crispr-trial-1.20302 (accessed Sept. 30, 2016).
- Kolata, G. Chinese Scientists Edit Genes of Human Embryos, Raising Concerns. The New York Times, April 23, 2015. http://www.nytimes.com/2015/04/24/health/chinese-scientists-edit-genes-of-human-embryos-raising-concerns.html?_r=0 (accessed Oct. 2, 2016).
- Stein, R. Breaking Taboo, Swedish Scientist Seeks To Edit DNA of Healthy Human Embryos. NPR, Sept. 22, 2016. http://www.npr.org/sections/health-shots/2016/09/22/494591738/breaking-taboo-swedish-scientist-seeks-to-edit-dna-of-healthy-human-embryos (accessed Sept. 22, 2016).