Gene-editing - CRISPR and beyond Image

Gene-editing - CRISPR and beyond

Posted: 08/03/2016

In recent weeks, it has been announced that a licence for gene-editing has been granted by the Human Fertilisation and Embryology Authority (HFEA). Jim Kinnier Wilson, head of the life sciences group at Penningtons Manches, brings us up to speed on the latest developments.

What is the background on gene-editing?

Gene-editing is a technique which is performed on the DNA itself rather than the cell and the organelles.

Using a system by which bacteria protect themselves from viral attack, a short section of ribonucleic acid (RNA), (which more usually has a role in the formation of proteins in cells) binds to specific sites on DNA. These RNA strands are known as clustered regularly interspersed short palindromic repeats (or CRISPR) after the location where they were found in bacteria. Attached to these RNA strands is an enzyme which cleaves the DNA strand. These are known as CRISPR-associated proteins or Cas. There are a number of these Cas proteins.

The CRISPR-Cas system gives researchers the ability to create RNA that will bind to the exact target sequences and cleave the DNA at a precise point or points. It can therefore be used to remove a single base or base pair in DNA which can be substituted with another, more suitable base.

Some diseases are associated with variations in DNA where a single base position in normal DNA is substituted with another base in defective DNA. This can lead to incorrect amino acids in a protein, and malfunction of the protein (ie disease) all from a single nucleotide substitution. Such a nucleotide substitution is known as a single nucleotide polymorphism (SNP or snip). The National Centre for Biotechnology Information (NCBI) lists all known snips that might cause human diseases, from which it lists 8,041 as being ‘likely pathogenic’ including some breast cancers, some cardiomyopathies, some kidney diseases etc. The ability to be able to treat these diseases using accurate ‘molecular scissors’ to replace an aberrant snip is very exciting.

In the UK, the link between these two is that research using human embryos, whether involving CRISPR techniques or mitochondrial DNA, requires a licence from the HFEA.

How does this contrast with the position in other countries (including activity that has already taken place in China)? What are the legal and ethical concerns?

Around April 2015, the journal ‘Nature’ reported that it had declined to publish a paper on human embryo manipulation with CRISPR as a peer-reviewed paper but it did publish a news item some days later about the same work once it had been published in a Chinese online journal ‘Protein and Cell’. The issue raised in the news item was that the work was the first evidence that China had been conducting so-called ‘germline’ modification on human embryos. This article raised a storm among scientists decrying what seemed to have been done.

Germline manipulation is the genetic modification of the genes in eggs, sperm, or early embryos such that the modifications can be passed on to successive generations (although some argue that the modification of embryos without the possibility of generational effect could still amount to germline modification). It has with it connotations of eugenics (improving a population by breeding methods to increase the occurrence of desirable inheritable characteristics and reduce undesirable ones) or the deliberate manipulation of offspring to select gender. There are legal and ethical issues globally in relation to such practices, but they vary across the world.

By contrast, somatic cell gene manipulation can cure genetic illnesses in a particular patient, but the modifications do not affect the eggs and/or sperm and so are not inheritable by subsequent generations.

The UK has probably the most highly-developed laws surrounding genetic manipulation and modification in the world, based on international conventions and customs. Those involving animals may be covered by the Animals (Scientific Procedures) Act 1986 which requires a three-level licensing of the premises, personnel and project involving animals by the Home Office. Experiments involving human stem cells and embryos are covered by a licence from HFEA, under the Human Fertilisation and Embryology Act 1990 (as amended, HFEA 1990)

HFEA 1990 has codified into UK law the guideline requirement that embryos on which research is carried out are not allowed to survive beyond 14 days after first creation. Elsewhere, this 14-day prohibition is an international guideline, without the force of law. Nevertheless, the 14-day guideline appears to have been adhered to in the Chinese research.

Outside the UK, many countries ban stem cell and embryo research completely—others permit it on excess embryos (ie those from IVF clinics which are created pending implantation, but are not needed) up to no more than the 14-day mark.

The US has a ban on federal funding of any research that destroys or puts at risk human embryos. Any research in the US would therefore need to be conducted with private funds, but such research would still require Research Ethics Committee (REC) or Institutional Review Board (IRB) approval before it could be commenced.

While information about the status of REC in China is difficult to assess with accuracy, a news item in the journal ‘Science’ of 24 April 2015 reported that the Chinese ethical review procedures are similar to those of the US and are based on the same principles. It is likely (though not reported) that the Chinese work was approved by the hospital’s IRB before the work commenced.

For the record, the Chinese research involved modifying the gene responsible for beta-thalassaemia using CRISPR-Cas9 in non-viable embryos from local IVF clinics. These embryos had in fact each been fertilised by two sperm, meaning they had three sets of DNA. Two days after the embryos had been treated with CRISPR, only 54 of the original 86 embryos had survived. Of those 54, only four embryos exhibited the changes that had been sought. In each case, not every cell in the four embryos displayed all or the same changes. The conclusions from this is that at present the CRISPR technique, while a major advance scientifically, is not likely to represent a viable clinical tool without significant further research.

Nevertheless the paper caused a flurry of concern across the globe, with scientists supporting or condemning the research. Much of the criticism speculated that there might be other research for clinical uses of CRISPR that had been conducted in China but unpublished, but there appears to be no evidence to corroborate the rumours on which these claims are based.

To try to obtain some global consensus, a three-day international summit was organised by the US National Academy of Science, the US National Academy of Medicine, the UK’s Royal Society, and the Chinese Academy of Sciences in December 2015. That meeting produced a summary statement requesting a continuing forum where these issues can be debated and where steps to reach broad consensus can be begun. The issues were highlighted in the statement at the end of the summit which established that:

  • if the process of research involved gene editing of embryos or germline cells, the modified cells should not be used to establish a pregnancy
  • somatic clinical use should only be permitted once the risks and benefits are better understood but that the current and evolving regulatory systems are likely to be able to make appropriate assessments for approval, and
  • there are substantial and unknown effects from the potential for germline editing in clinical use and it would be irresponsible to proceed with any clinical use of the techniques until not only have the issues been fully resolved, but also when there is societal consensus about the appropriateness of its use—this looks a long way off, but should be revisited on a regular basis

So while legal and ethical issues remain across the globe, attempts are being made to address them in a consensual and practical way. Properly regulated and reviewed, human embryo research in the existing regimes can perform a very useful function.

What is the background to the recent HFEA approval? What scientific procedures are now allowed?

The HFEA is the UK’s authority that, among other things, oversees fertility clinics and grants licences for human embryo research. Since HFEA 1990, research projects into a human embryo must:

  • be carried out under a licence granted by HFEA, and in suitable, specified premises
  • have satisfied the HFEA that the research fulfils at least one of the statutory purposes and that the use of human embryos is necessary
  • have informed consent from the egg or sperm donors that they consent to their eggs or sperm being used for research
  • not allow any embryo created or used in research to develop beyond 14 days after fertilisation
  • not permit any embryo created or used in research to be transferred into a woman.

In addition, before any research can be begun it needs to receive approval from the local REC.

The recent authorisation from HFEA arose from an application to renew a research licence. The application for a renewal was made by the Francis Crick Institute in North London. It has held a licence for embryo research since 2005, with the most recent licence granted for three years in 2013. That licence was due to expire in March 2016.

As part of the renewal application, the Crick Institute amended the terms as it is now seeking to understand which genes are involved in normal human embryo development, and what effect gene disruption has on development. This gene disruption is proposed using CRISPR–Cas9 (Cas9 Cleaves double stranded caps DNA, allowing better analysis of the effect of gene disruption than single strand cleavage would). After two peer-reviewed reports on the amended application, and substantial replies to questions or alternatives proposed by the peer reviewers, and after advice from HFEA’s legal advisor, a positive assessment of the application was made by the HFEA Executive. The HFEA Executive determined that the use of human embryos for this research was necessary, as the gene products under investigation were not present in mouse embryos at the same developmental stage.

All of this information then went to the HFEA Licence Committee for review and, if appropriate, approval. Approval was granted for a further three years on a condition that the new research added to the existing licence was to be the subject of a fresh application for approval from the local REC.

So, aside from the use of CRISPR to investigate human embryos due to the absence of a suitable model in mice - very much a question of fact for the application being considered - no new, general scientific procedures are ‘approved’. Rather, provided the research is justifiable scientifically (and is supported by peer review assessment), and justifiable as against the criteria for a licence, then it seems that a licence may be grantable notwithstanding untested techniques in human embryos.

What are the connections between mitochondrial donation and gene-editing? How, if at all, does this development tie in with the licensing of mitochondrial donation which was allowed at the end of last year?

Technically the two are very different. In mitochondrial donation techniques one is working with whole cells. An egg cell from a mother that is susceptible to mitochondrial disease has its nuclear DNA (the DNA in the nucleus) removed from the cell. An egg from a donor that has healthy mitochondria also has its nuclear DNA removed. Then the mother’s DNA is inserted into the donor egg, resulting in mother’s nuclear DNA in a healthy (but donated) egg cell. Such an egg can then be fertilised with the father’s sperm and implanted in the usual way, via IVF implantation. It is also possible to use this process on cells where fertilisation has just occurred, but there are greater ethical concerns about the destruction of the fertilised donor nucleus as compared to pre-fertilisation.

What safeguards are in place? Will the system be able to cope?

Even though it was enacted in 1990 and amended in 2008 (in anticipation of the mitochondrial donation debate and vote which eventually took place in 2015), HFEA 1990 is a remarkably resilient piece of legislation. Its basic provisions still provide for sufficient safeguards:

  • all activities in the space must only be undertaken pursuant to a licence
  • no embryo for research may be placed into a woman, and
  • no research embryo may be allowed to survive beyond 14 days at the latest

The issue of genetic manipulation was, to some extent, addressed in the amendments in the Human Fertilisation and Embryology Act 2008 (HFEA 2008).

HFEA 1990, s 3ZA(4), (introduced by HFEA 2008) says:

‘(4) an embryo is a permitted embryo if—

(a) it has been created by the fertilisation of a permitted egg by permitted sperm;

(b) no nuclear or mitochondrial DNA of any cell of the embryo has been altered; and

(c) no cell has been added to it other than by division of the embryo’s own cells.’

Gene-editing would ‘alter’ the mitochondrial or nuclear DNA of the cells of the embryo, and would thus not result in a permitted embryo (and by HFEA 1990, s 3(2) only a permitted embryo may be placed in a woman).

The words of HFEA 1990, s 3ZA(4) were thought to be slightly strained by mitochondrial donation (though HFEA 1990, s 3ZA(5) allows regulations to be passed to allow ‘permitted embryo’ status to embryos that have undergone processes aimed at preventing serious mitochondrial disease in offspring), and the mitochondrial donation regulations (Human Fertilisation And Embryology (Mitochondrial Donation) Regulations 2015, SI 2015/572), address this. These regulations came into effect on 29 October 2015.

Regulation 4 describes the process of mitochondrial donation from eggs I outlined earlier, and Regulation 3 makes such an egg a permitted egg only if:

‘(c) there have been no alterations in the nuclear or mitochondrial DNA of egg P [the permitted egg] since it was created.’

In relation to the second alternative mitochondrial donation method I mentioned earlier—where a fertilised egg (technically an embryo) has its nuclear DNA substituted by the mother’s fertilised nuclear DNA, the regulations provide at regulation 6(c):

‘(c) since embryo P was created by means of the application of that process—

(i) there have been no alterations in the nuclear or mitochondrial DNA of any cell of embryo P, and

(ii) no cell has been added to embryo P other than by the division of embryo P’s own cells.’

Both of these provisions refer to alterations of DNA after the creation of the egg or embryo (respectively), with no reference to the possibility of modifications to egg or sperm before the mitochondrial donation processes are applied, but such an egg or embryo would fall under HFEA 1990, s 3ZA(4), and thus also not be a permitted egg. HFEA 1990 therefore already provides mechanisms to prevent gamete or embryo modification pre-fertilisation except for experimental purposes, which must be strictly licensed.

What trends do you foresee?

It is clear that the CRISPR technology is much more accessible, easier to use and more precise than the existing gene modification techniques—zinc finger nucleases and TALENS—so there will be a strong impetus for continuing research into CRISPR in animal models. Eventually that will be translated into human embryo study, which can be accommodated within the UK’s regulatory pathway.

However, as the techniques are already being used around the globe, unless there is a truly global harmonised approach those who wish to take advantage of the system for gene-editing will gravitate to countries with a less stringent regime. If we truly want to address the legal and ethical issues that surround gene-editing, this will need to be done on a global approach with all states signing up to the regime.

One issue that affects that is the creation of new CRISPR-based spin-out companies, and the battles to secure patent rights on CRISPR that are being waged in the US and at the EPO, but that is another conversation.

This article was published in Lexis®PSL in February 2016. 

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