Your Guide to the CRISPR Babies

Imagine a future in which we can edit genes like a sentence in Microsoft Word. We could highlight, delete, and correct a section of a gene known to cause disease, virtually eliminating the devastating genetic illnesses that cost the world billions of dollars and countless hours of heartache every year. This is a future envisioned by many scientists working on the CRISPR-Cas9 system of gene editing. These researchers have used the technology to cure everything from liver disease to cataracts in mice. Ethical concerns have limited these experiments to model organisms and until recently, on-demand gene editing in humans seemed like more of a science fiction fantasy than a potential reality. All of that appears to have changed, however, with a Chinese scientist named He Jiankui claiming to have successfully used CRISPR to delete an HIV-related gene in two human babies late last year. This claim has stirred up quite a bit of controversy, to put it lightly, in the scientific community, but why is it such a big deal? Let’s take a closer look at the experiment and the hopes and concerns it brings to light.

A CRISPR introduction

CRISPR, short for CRISPR-Cas9, stands for “clusters of regularly interspaced palindromic repeats.” The major player in the CRISPR system is Cas9, which is a protein that acts like molecular scissors to chop up DNA. This system first evolved as a bacterial defense mechanism that targeted Cas9 to common sequences found in viruses, allowing the bacteria to chew up viral DNA and prevent infection. However, scientists then discovered that Cas9 could be targeted to just about any sequence of DNA they wanted. The secret lies in how Cas9 targets specific DNA sequences: the protein works together with a piece of RNA called guide RNA that matches up to the target DNA sequence. Modify this RNA and you can cause Cas9 to cut up whatever DNA you choose. Thanks to DNA repair, scientists can even provide a template sequence, say to correct a bad version of the gene, that can be incorporated into the DNA cut by Cas9 to fix a genetic mutation. These manipulations can be done in cells in a dish or even by injecting the CRISPR components into animals.

An overview of using CRISPR to delete a segment of DNA. Made using biorender.io.

The first CRISPR humans?

Until last November, using CRISPR to induce inheritable changes in live organisms was restricted to animals like fruit flies and mice. However, on November 26, 2018, the Associated Press reported that Chinese scientist He Jiankui claimed to have successfully used CRISPR to delete a gene associated with HIV infection in two human embryos. The edited embryos were created using in vitro fertilization (IVF), checked for successful editing after CRISPR treatment, and implanted back into the women who donated them. Allegedly, the edited embryos resulted in the birth of healthy twin girls. The gene Jiankui claims to have deleted encodes the protein CCR5, a human cell surface receptor that the HIV virus requires to infect immune cells. Essentially, deletion of CCR5 results in no HIV infection. This manipulation, Jiankui says, could protect the children from acquiring HIV and has broad implications for the management of HIV from a public health perspective. From a basic science perspective, the birth of children from CRISPR-edited embryos is an incredible achievement. However, as with almost every method of genome editing, the ethical controversy of Jiankui’s work has become just as important as the scientific implications.

Ethical and scientific concerns

One of the largest outstanding questions surrounding the alleged CRISPR babies is the fact that they are just that: alleged. Jiankui has not published the results of his manipulations in a peer-reviewed scientific journal and the identities of the children’s parents have been kept private to protect them from media scrutiny and potential backlash. However, let’s say that Jiankui actually did successfully delete the CCR5 gene in embryos that went on to become healthy human babies. What’s the problem with that? First, although some people have naturally occurring mutations that inactivate CCR5, the changes that Jiankui made in the embryos do not appear to mimic those natural mutations, leading to concerns about potential unintended consequences. Additionally, a well-known issue with CRISPR is its potential for off-target effects, or making changes in genes other than the targeted one. Finally, even if CCR5 was correctly inactivated with no off-target effects, the naturally occurring inactivating CCR5 mutations have been shown to have negative health effects, such as increasing the risk for infection and complications of West Nile virus. The scientific consensus is that using CRISPR to make such drastic, inheritable changes is unsafe simply because we don’t know enough about it yet. Ethically, a large concern with gene editing in humans is the old slippery slope argument: if we can delete disease-causing genes, what’s to stop people from editing embryos to select for traits like eye color or intelligence? Along the same lines, proponents of CRISPR gene editing in humans speak of “curing” conditions with a probable genetic basis like autism. However, advocacy organizations like Autism Speaks say this is a fundamental misunderstanding of this complex condition and that many people with autism view it as an inextricable part of themselves, not a disease to be cured. For these reasons and more, the larger scientific community has condemned Jiankui’s alleged experiments as risky and unethical. More extensive experiments in model organisms and strict ethical guidelines are needed before scientists can even think about bringing CRISPR into the mainstream.  Although this technology seems like it could be a magic bullet for genetic editing, it’s clear that the way forward is uncertain and each new advance creates more questions than it does answers. For now, at least, a world of CRISPR on-demand is still a distant future.

Peer edited by Rachel Battaglia and Breanna Turman.

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Superior Syntheses: Sustainable Routes to Life-Saving Drugs

While HIV treatment has come a long way over the past few decades, there is still a discrepancy between total number of HIV patients and those with access to life-saving antiretroviral therapies (ART). The inability to access medications is often directly linked to the cost of the medication, demonstrating the need for ways to make these medicines cheaper. In October 2018, Dr. B. Frank Gupton and Dr. Tyler McQuade of Virginia Commonwealth University were awarded a 2018 Green Chemistry Challenge Award for their innovative work on the affordable synthesis of nevirapine, an essential component of some HIV combination drug therapies.

https://www.flickr.com/photos/blyth/1074446532

Neviripine, a component of some HIV therapies.

For the past 22 years, the American Chemical Society (ACS) in partnership with the U.S. Environmental Protection Agency (EPA), has awarded scientists who have contributed to the development of processes that protect public health and the environment. Awardees have made significant contributions in reducing hazards linked to designing, manufacturing, and using chemicals. As of 2018, the prize-winning technologies have eliminated 826 million pounds of dangerous chemicals and solvents, enough to fill a train 47 miles long. The nominated technologies are judged on the level of science and innovation, the benefits to human health and the environment, and the impact of the discovery.

https://www.flickr.com/photos/37873897@N06/8277000022

Green Chemistry protects public health and the environment.

Gupton and McQuade were awarded the Green Chemistry Challenge Award for the development of a sustainable and efficient synthesis of nevirapine. The chemists argue that oftentimes, the process to produce a drug remains consistent over time, and is not improved to reflect new innovations and technologies in the field of chemistry, which could make syntheses easier, cheaper, and more environmentally friendly. Synthesizing a drug molecule is not unlike building a Lego tower; the tower starts with a single Lego and bricks are added one-by-one until it resembles a building. Researchers start with a simple chemical and add “chemical blocks” one-by-one until it is the desired drug molecule.  Gupton and McQuade demonstrated that by employing state-of-the-art chemical methods, they can significantly decrease the cost to synthesize nevirapine.

https://www.flickr.com/photos/billward/5818794375

Producing pharmaceutical molecules is like building a Lego house.

Before this discovery, there were two known routes toward the synthesis of nevirapine. Researchers used projections to determine which steps were the costliest. With this knowledge, they were able to improve the expensive step of the synthesis by developing a new reaction that used cheap reagents (“chemical blocks”) and proceeded in high yield. A chemical yield is the amount of product obtained relative to the amount of material used. The higher the yield, the more efficient the reaction. Reactions may have a poor yield because of alternative reactions that result in impurities, or unexpected, undesired products (byproducts). Pharmaceutical companies often quantify chemical efficiency by using the Process Mass Intensity (PMI), which is the mass of all materials used to produce 1 kg of product. Solvent, the medium in which the reaction takes place, is a big contributor to PMI because it is a material that is necessary for the reaction, but not incorporated into the final product. Gupton and McQuade were able to decrease the amount of solvent used because they streamlined reactions that reduced impurities, allowing them to recycle and reuse solvent. These improvements reduced the PMI to 11 relative to the industry standard PMI of 46.

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Molecular structure of nevirapine 

In addition to their synthesis of nevirapine, Gupton and McQuade also developed a series of core principles to improve drug access and affordability for all medications. The general principles include implementation of novel and innovative chemical technologies, a decrease in the total number of synthetic steps and solvent changes, and use of cheap starting materials. Oftentimes, the pharmaceutical industry focuses on starting with very complex molecules in order to decrease the number of steps needed to reach the target molecule. Interestingly/unfortunately, starting with complex “chemical blocks” is often the most expensive part of  producing a medication. By starting with simpler chemicals, they believe production costs can be significantly decreased. Virginia Commonwealth University recently established the Medicines for All Institute in collaboration with the Bill & Melinda Gates foundation, and Gupton and McQuade hope that by employing the process development principles, they will be able to more efficiently and affordably synthesize many life-saving medications.

Peer edited by Dominika Trzilova and Connor Wander.

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