By David Warmflash, MD | 23 May 2016
Genetic Literacy Project
We’re in the midst of a CRISPR craze, both in research and media, where the last three years have brought numerous stories on how CRISPR-CAS9 gene editing will change the world. Particularly those stories written over the last 18 months, journalists and biotechnology experts have been explaining that designer babies do not constitute the principal application of the technology. They have been warning that we’re not close to ready to begin modifying human embryos for sake of creating babies and this includes Jennifer Doudna, one of the CRISPR discoverers, who has been interviewed in several key stories about CRISPR. They have been explaining that, while the prospect of gene editing to design babies has inspired formal discussions between biotech experts and bioethicists, genetic modification of human embryos is years in the future and not a current application of CRISPR.
Rather, CRISPR is revolutionizing the biomedical research world and is poised to improve treatment and prevention of various diseases in the years to come. This idea comes up frequently within stories by media such as PBS, the BBC, and others with respectable track records on science reporting. The interviewers and writers have the correct perspective—that what’s hot in CRISPR has nothing to do with designer babies—but you wouldn’t know it from many of the headlines. Here are some samples:
- PBS: 2015’s Biggest Breakthrough Could Deliver Designer Babies (December 30, 2015)
- Mother Jones: We Are This Close to Designer Babies (February 8, 2016)
- Huffington Post: Diving Into The Ethics of The Technology Behind Designer Babies (December 4, 2015)
- Popular Science: Are We Ready For Designer Babies? (March 21, 2016)
- The Economist: Editing Humanity (August 22, 2015)
- BBC: ‘Designer babies’ debate should start, scientists say (January 19, 2015)
With all of these, clicking on the links and reading through the story will give you a pretty realistic idea or where CRISPR gene editing is today, where it’s going, and that designer babies, though on the bioethics radar screen, are not the fist thing that should come into mind when you hear about editing of genes or genomes. But in the age of Facebook shares and Twitter retweets, sometimes the headline is all an audience sees, and in the case of CRISPR that can lead to people missing on some of the coolest applications of the technology. Removing viral sequences from the DNA of an HIV infected patient, eliminating the malaria parasite from mosquitos, delivering gene therapy, even creating humanized organs from organs of pigs—all of these are just some of the CRISPR applications that loom on the horizon. We’ll take a glance at them a little later, after a brief discussion on what CRISPR actually is.
US scientists have succeeded in genetically editing the immune systems of three cancer patients using CRISPR, without creating any side effects, a first for the tool which is revolutionizing biomedical research https://t.co/4FOVBt0q2d
— Channa Prakash (@AgBioWorld) February 9, 2020
CRISPR-CAS: An immune system for microorganisms
CRISPR stands for Clustered Regularly-Interspaced Short Palindromic Repeats. This phrase describes DNA sequences that—like so many phenomenon in genetics—were discovered initially in the bacterial species Escherichia coli. That was back in the 1980s and gradually CRISPRs also were identified in numerous other single-celled organisms, not just those in the Bacterial domain, but also within Earth’s other domain of prokaryotes, the Archaea. Further complicating the terminology, additional sequences were identified nearby the CRISPR sequences, so they were named CRISPR-associated sequences (CAS). It may be a lot of terminology to swallow all at once, but doing so will make it a lot easier to grasp why so many powerful CRISPR applications are in the works.
Over the course of decades, molecular biologists came to understand that CRISPR and CAS sequences were a microbial immune system. The “I” of CRISPR, for “interspersed”, tells you that some other sequences must exist that separate the CRISPR sequences. In turns out that they’re separated by sequences that correspond DNA to sequences of viruses that have attacked the microorganism, or its ancestors, in the past. In other words, just like your own immune system, microorganisms retain a molecular record of infections. Instead of using the record to make antibodies and T-lymphocytes, however, the microorganisms use the record to make something called a guide RNA. Then, if the organism is invaded by a virus, the guide RNA recognizes the viral DNA and works with the CRISPR sequences and with proteins encoded by the CAS sequences to unravel and chop up the viral DNA.
CRISPR as gene editing 2.0
Given how well it seemed to work, researchers set out to try to hijack a bacterial CRISPR-CAS system and see how it might be put to use in genetic engineering. That led to the identification of a CRISPR system in bacterial species Streptococcus pyogenes, in which Jennifer Doudna, and another researcher, Emmanuelle Charpentier, found something different. Rather than making multiple CAS proteins, S. pyogenes produced one really capable CAS, called CAS-9, which performs several different jobs that other species usually dish out to multiple CAS proteins. They and other researchers tweaked the S. pyogenes CRISPR-CAS9 system so that it could be repurposed for numerous gene editing applications by simply changing around the sequences of the guide RNA.
Going back earlier than 2012 when the potential of CRISPR-CAS9 was recognized, biotechnologists have been utilizing other gene editing systems, such as TALENs and zinc fingers. Compared with these older technologies, however, CRISPR-CAS9 provides orders of magnitude more gene editing for the amount of preparation and cost that must be devoted to the project. This has to do the fact that the system needs just one CAS protein, namely the CAS-9 and that CAS9 can work with any guide RNA regardless of the sequence. That’s a dramatic improvement over TALENs and zinc fingers, which require custom-designed proteins for each new gene editing job. The need for just a new guide RNA sequence for each new application makes CRISPR far more adaptable than older technologies, and something like 1 percent the cost. Furthermore, CRISPR can be used for deletions and/or replacements of multiple genes at once in different areas of an organism’s genome. This means that an enormous amount of genetic engineering capability now beckons, raising that question of what researchers are doing with it.
The short answer is that they’re going to do a lot. While customizing human embryos could eventually become an application, it’s not currently on the task list, except in limited cases, such as the recent, highly publicized Chinese experiment that used human embryos that were never going to be implanted anyway. People are not on the verge of using gene editing to give their children blue eyes instead of brown, or anything like that, since the underlying genetics of that is actually more complex than was once thought, so just maybe the emphasis on “designer babies” at least in headlines is premature.
— Church and State (@ChurchAndStateN) February 10, 2021
Instead, here are a few potentially life-saving CRISPR applications that are in the works right now:
Removing HIV genes from a patient’s genome: Present day therapies can keep an HIV-positive individual from developing AIDS for years and years, but once an infection gets into a person’s chromosomes it’s permanent. As a retrovirus, HIV violates the Central Dogma of Biology in which genetic information flows in one direction, from DNA to messenger RNA to protein. HIV’s genetic information is carried as RNA, which includes a gene for the enzyme reverse transcriptase, which copies all of the viral genes from RNA into DNA, which then integrates into the chromosomes of infected human cells. With CRISPR-CAS9, however, one simply designs guide RNAs to locate all of the HIV genes as easily as the “find” function on your computer locates one particular word or phrase in a written document, then the system will delete them out. To be sure, it’s a kind of gene therapy conducted inside the body, which entails years of clinical testing, but the research has begun.
Curing disease caused by mutation of specific genes: There are a whole sting of conditions caused by abnormalities in just one or a few genes, many of which are targets of current gene therapy research. Leber congenital amaurosis (LCA) and retinitis pigmentosa (RP) are examples of retinal diseases that lead to blindness and that currently are in clinical trials of gene therapy. Trials on gene therapy also are advancing for Duchenne muscular dystrophy and various blood diseases, such as hemophilia, thalassemia, and sickle cell anemia. There are literally hundreds more diseases that could be treated with gene therapy, but while collectively they affect millions of people individually they are quite rare. At present, gene therapies need to designed specifically for each disease with great cost in time and money, but CRISPR beckons as a potential strategy for an almost one-size-fits-all approach—not that you could treat all genetic diseases the same, but there could be a common gene delivery system and protocol using CRISPR with a need only to design new guide RNAs to tackle different diseases. Additionally, CRISPR provides greater accuracy in terms of where one can deliver genetic payload within a person’s genome, and that in turn reduces the risk of any long-term negative effects.
Eliminating vector-borne disease: CRISPR can make reality of a process known as gene driving, that previously was science fiction. The process has been proposed as a means of entire populations of animal vectors that carry human diseases, such as insects that carry malaria, dengue fever, and Zika virus, resistant to the causative microorganisms.
We may look into the details of these emerging CRISPR applications in future articles, but they are just a small sample of what’s on the horizon. What they all have in common is that they represent applications of CRISPR to non-humans, or to human somatic cells, but not to the human germ cells or embryos. The latter is a still more technically complex undertaking, which is why even the Chinese study that caused so much alarm involved human embryos that would not be implanted. It’s also why the focus of embryo editing is on non-human animals, such as pigs, for instance to create humanized organs for transplantation—yet one more example of the amazing potential of CRISPR to revolutionize medicine. So while it is important for all of the ethics discussions to continue at full speed in anticipation of the possibility of gene editing to create genetically modified humans, we must not lose site of the CRISPR advances in other areas—advances that that could save your life.
Reprinted with permission from the author.
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