A Crack in Creation
Authors: Jennifer Doudna and Samuel Sternberg
If there is one innovation that truly deserves to be called paradigm-changing, then CRISPR-Cas9 deserves that accolade. With such cutting-edge applications as the gene editing of animals and the treatment of genetic disorders, the book aptly depicted CRISPR as ‘the newest and arguably most effective genetic engineering tool‘. Written by one of the pair of women scientists who won the Nobel Prize for discovering and refining the technology, the book’s objective was to publicise the method which has hitherto been hidden ‘behind the closed doors of laboratories and biotech startups‘. With clear prose, the book described the science behind CRISPR, a process that was adapted from the normal bacterial defence against viruses, and which has made reading ‘an organism’s entire DNA content’ almost as easy as reading ‘a simple piece of text’. The authors highlight both the monumental applications of CRISPR to healthcare, and the ethical conundrums this has thrown up for science and society. The book is also an exemplar of the human drama that characterises the scientific enterprise, illustrating such high points as the exhilaration of making groundbreaking discoveries, and low points such as the patents disputes that created ‘a disheartening twist to what had begun as collegial interactions’ (pages xv, xix, xxi-xxii, 89 and 97).
In providing the historical context leading to the discovery of CRISPR-Cas9, the authors traced the genesis of genetic engineering to the early attempts at gene therapy by Stanfield Rogers who used purified rabbit Shope papilloma virus in two girls with hyperargininaemia. Although the endeavour was unsuccessful, the authors nevertheless said it introduced the concept of viral vectors as ‘the ultimate Trojan horse‘ for gene therapy because they reach their targets ‘with nearly 100% efficiency‘. The book also referred to the birth, in the 1970’s, of the ‘cut and paste‘ technology that enables DNA segments to be inserted into the human genome; they noted that it was first used to treat adenosine deaminase deficiency, and subsequently cystic fibrosis, haemophilia, and Duchenne muscular dystrophy. In narrating the history of the other gene editing technologies that preceded CRISPR-Cas9, the authors recounted techniques such as Maria Jasin‘s yeast endonuclease which was limited by its inability to recognise long DNA sequences; Srinivasan Chandrasegaran‘s bacterial-derived chimeric nucleases which were too complex for practical purposes; and the virus-free homologous reconstituted genes of Mario Capecchi, Oliver Smithies and Martin Evans which were too indiscriminate. It is by its simplicity and specificity, the authors affirmed, that CRISPR emerged and superseded these ill-fated technologies (pages 16-31).
The central theme of the book is its detailed and graphic portrayal of the structure and function of CRISPR, an acronym that stands for clustered regularly interspersed short palindromic repeats. Characterising CRISPR as a bacterial ‘fifth weapons system‘, the authors portrayed it as a ‘molecular vaccination card‘, and as an ‘adaptive immunity‘ which enables bacteria to ‘steal snippets of phage DNA during an infection and use it to mount a future immune response’ (pages 39-57). In describing the physical properties of this antiviral defence system, the authors depicted it is an ensemble of short identical repeating segments of about thirty DNA letters, and these are all clustered in one region of the circular chromosome of bacteria. They also described how this palindromic structure, organised as diamond squares, reads the same in either direction, and is flanked by a region of a consistent set of CRISPR-associated genes or Cas. The most remarkable components of CRISPR however are the interspersed segments that are found between the squares which, by possessing the ability to rapidly evolve and adapt to viral invasion, act as the bacterial immune system. In underscoring the remarkable efficiency of this system, the authors referred to the works of Philippe Horvath and Rodolphe Barrangou, which demonstrated that the bacterial CRISPR DNA not only makes ‘perfect matches‘ with the DNA of viruses, it also transmits these matches when it replicates.
The autobiographical account of the co-author’s personal involvement in the discovery of the CRISPR system was a compelling feature of the book’s narrative. A biochemist, she was researching the RNA-RNA double helices of the antiviral immune system of plants and animals when she was fortuitously introduced to the bacterial CRISPR system. The book described how she teamed up with the geomicrobiologist Jillian Banfield to, amongst other things, establish how the CRISPR system actually targets the viral genome for destruction. Using pseudomonas phages, the pair worked out that the process is initiated when the CRISPR array is converted into matching ‘long RNA strands‘, and these strands function as ‘chemical cleavers‘ to cut the viral RNA into shorter strands of uniform length. The book also describes the author’s equally trailblazing subsequent discoveries, for example demonstrating that CRISPR could target both RNA and DNA for destruction, and that the Cas system is able to insert pieces of viral DNA into the CRISPR array. The author’s most influential contribution was however made during the course of a series of inspiring and ingenious investigations into the CRISPR type II system of streptococcus pyogenes; working with fellow Nobel prize winner Emmanuelle Charpentier, she demonstrated that Cas9 cuts up viral DNA at specific sites where the bacterial CRISPR RNA forms double helices with the viral DNA. It is therefore fitting that the book epitomised the CRISPR-Cas9 mechanism as ‘the perfect bacterial weapon – a virus-seeking missile that could strike quickly and with incredible precision‘ (pages 39, 53-69 and 71-82).
In its portrayal of the important and diverse practical applications of the CRISPR-Cas9 system, the authors characterised it as ‘a swiss army knife, with a panoply of functionalities’. For example, in exploring its gene editing function, the authors enthused that ‘out of this fifth bacterial weapons system, we had built the means to rewrite the code of life‘, pointing out the potential benefits – from creating gene-edited mice to editing human stem cells. The authors also emphasised CRISPR’s equally impressive non-cutting function in terms of controlling gene expression; they pointed out that this is ‘nearly as powerful as the ability to edit the genes themselves’, illustrating this with such capacities as the ability to visualise and to barcode genes within cells. The most beneficial applications of CRISPR are however in the treatment of diseases, and the authors cited such varied examples as the treatment of clotting disorders; the prevention of viral infections such as HIV; the immunotherapy of cancer; and the treatment of monogenic disorders such as cystic fibrosis, thalassemia, sickle cell disease, Duchenne muscular dystrophy, achondroplasia, Alzheimer’s disease, amyotrophic lateral sclerosis, diabetes, and fragile X syndrome. Because it is cheap and easy to use, the authors predicted that CRISPR ‘will increasingly become a tool of choice for all biologists, regardless of their line of work’ (pages 101-111, 82-98, 130-141, 157, 161-166, 172-177 and 181).
The ‘unsettling’ capacity of CRISPR-Cas9 to ‘tamper’ with the genetic code was a serious ethical concern that the book discussed, putting particular emphasis on its potential to alter the human germline. Apprehensive that ‘it won’t be long before CRISPR allows us to bend nature to our will’, the authors warn of the ‘unintentional or even calamitous consequences’ of the unregulated use of CRISPR. Beyond germline editing, the book also explored other ethically disturbing potential applications of the technology, and these included the aesthetic editing of animals such as the micropig; the ‘forcible extinction of unwanted animals’; the de-extinction of species such as woolly mammoths; and the gene-drive insertion of traits into wild animal populations such female sterility in malaria-carrying mosquitoes. Whilst the authors accept that some researchers have already crossed the line in some aspects, they were emphatic that scientists must refrain from germline editing until such a time that it is considered ‘safe to use in the clinic’. In an insightful reflection on the subject, they outlined a very balanced perspective on gene editing and genetic enhancement. In pushing forward the ethical agenda of CRISPR technology, and taking inspiration from the Asilomar conference on recombinant DNA technology, the book described how the author organised conferences which have led to the publication of guidelines to govern this rapidly evolving field ((pages 113-119, 142-153 and 193-222).
CRISPR is a new and influential technology and this book has set out the history that led to its discovery. The book clearly described how CRISPR works using a rather curious single-person narrative style for a co-authored book. The authors explored both the clinical and ethical dimensions of the subject, particularly noting its potential to alter the human gene. The use of diagrams greatly enhanced the book, although some were used to illustrate rather simple ideas that the text adequately reflected. The narrative most eloquently demonstrates how scientific breakthroughs take inspiration from the insights of the past, and how progress is achieved when diverse groups work together or in competition to build on each others research. Whilst the non-chronological approach made it difficult to readily grasp the concepts it conveyed, the book’s simple prose made the themes accessible to the lay reader.
The influence of the CRISPR-Cas9 technology is profound and impacts all spheres of life. The healthcare implications are perhaps the most important, and this book has explored this exhaustively. The promise of treating previously incurable diseases, and of preventing otherwise genetically-fated disorders, has the potential to alter the course of medicine itself. The book placed appropriate emphasis on both the practical benefits of CRISPR, and its potential repercussions on healthcare, and I highly recommend it to all doctors.
Publisher, Place, Year: Vintage, London, 2017
Number of chapters: 8
Number of pages: 281
Star rating: 5