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Chimeric monkey sheds light on what can be done with embryonic stem cells

I was quoted in this article today regarding a newly published study in Cell that demonstrates, in the author’s words, that ‘mammalian pluripotent stem cells possess preimplantation embryonic cell-like (naive) pluripotency.’ As the summary notes, this discovery about embryonic stem cells can now be said to have been demonstrated experimentally through the generation of a chimeric animal — a monkey whose embryonic development has been ‘complemented’ by homologous embryonic stem cells derived from another ‘donated’ line of cells. The monkey, in short, has developed from a blastocyst that is a compound of two embryonic stem cell lines.

Unsurprisingly, news stories have been focusing on one of the eye-grabbing aspects of this experiment: that the monkey in question has fluorescent green fingers and eyes. Unfortunately, the monkey died after only 10 days — which is still the longest period of time for which such a chimeric organism has lived before.

The reason that the monkey has these features is because the researchers used green fluorescent protein (GFP) to ‘label’ the embryonic stem cells (ESCs) that were incorporated into the host embryo at the blastocyst stage. And so what one is looking at when one sees the monkey with green fingers and eyes (visible even to the naked eye) is visual evidence that the embryonic stem cells have survived the process of being ‘complemented’ into the blastocyst of the host monkey and have spread throughout its body. In other words, the cells have been incorporated into the monkey’s cellular DNA; the monkey has both its ‘natural’ DNA and a ‘foreign’ line of DNA. Indeed, as the images indicate, there is a proliferation of these complemented ESCs throughout the monkey’s organs, including plenty in the brain and ileum (small intestine).

As the ‘Highlights’ section of the article points out, when these embryonic stem cells (ESCs) in the body of the monkey were ‘characterised’ (assessed), it was revealed that they remained in a so-called pluripotent state. In other words, the ESCs seem to have been able to differentiate into the different kinds of cellular categories: glial (brain) cells, heart cells (myocytes), lung cells (epithelial cells), and so on. Indeed, they continue to be in this pluripotent state, even as they maintain a ‘functional’ presence in the monkey’s body.

The news.com.au story quotes me as follows:

Sydney University lecturer in health law Dr Christopher Rudge told new.com.au the medical experiment had been on the cards for a long time.

“This is another step along the journey,” he said.

“The advancement here is that scientists have never been able to show such a prolific survival / proliferation of donated (or ‘complemented’) embryonic cells through a single organism.

“You’ve got more of these donated or secondary cells throughout the organism in a mammal.”

But he cautioned whether it would lead to anything substantive.

“Regenerative medicine has been hyped since the late 1990s,” he said. “Unfortunately it has not borne fruit.”

See https://www.news.com.au/technology/science/stunning-monkey-born-with-glowing-eyes-and-fingers/news-story/27d84700628476da1579968e76cbda5d

Obviously this scientific study demonstrates that certain new techniques can be adopted to expand the capacity of scientists to create chimeras. Scientists have long had the capacity to infuse mouse and rat blastocysts with pluripotent stem cells to generate live chimeric animals that feature this high proliferation of homologous cells. What is new here is that this capacity now extends to non-human primates — a species of animal much closer, in evolutionary terms, to humans.

It is arguably another step along the way in discovering how stem cells, including pluripotent embryonic stem cells, can be used as technologies of biological inquiry (for diagnosis, and to study developmental mechanisms) and, ultimately, to biological treatments. Of course, there is still so much more to learn.

Whether an experiment of this nature would be approved in Australia is an interesting question. If nothing else, this finding indicates that discoveries in stem cell medicine are continuing apace. Of course, given that this involved the effective fusing of two monkey embryos (or embryonic cell lines), the more serious bioethical questions regarding human-monkey chimeras, which have been posed before, do not arise in this instance.

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Exa-cel on review at the FDA

Just last week, on 31 October, the FDA’s Cellular, Tissue, and Gene Therapies Advisory Committee met to discuss Vertex Pharma’s Biologics License Application for Exagamglogene autotemcel (or exa-cel, and formerly known as CTX-001) — a cell-based gene therapy designed to treat sickle-cell diseases.

I have written about exa-cel many times before, both on this blog (here) and in published academic writing too. I have also spoken about it in this podcast. Exa-cel is a therapeutic product that is composed of the patient’s own (autologous) hematopoietic stem cells; however, those cells — specifically differentiation 34+ (CD34+) cells, have been edited using CRISPR/Cas 9 editing machinery (CRISPR).

In short, a CRISPR-Cas endonuclease system (CRISPRs) is a naturally occurring adaptive immune system that exists in most bacteria. These systems prevent bacteria from being infected by foreign genetic elements, such as viruses and phages. Where an infection exists, the Cas9 protein in the CRISPR will cleave or cut one strand each of double-stranded DNA to cause a double-strand break and thus decrease production of progeny viruses. Following that DSB, the genome will be repaired naturally, usually through a naturally occurring process called non-homologous end joining or NHEJ.

But this CRISPR/Cas 9 system can be ‘hijacked’ by science for therapeutic purposes. Using a guided template, the DSBs made by the Cas9 protein can be repaired in a precise and controllable manner, allowing the editing machinery of cell repair to be redirected toward doing repairs or edits that it would otherwise not do unguided.

This is how exa-cel works (in a nutshell). After the patient’s cells have been extracted, they are subject to guided disruption and repair by CRISPR. The CRISPR system make precise DSBs at the erythroid lineage specific enhancer region of B-cell lymphoma/leukemia 11A (BCL11A) gene on chromosome 2. In turn, this process disrupts GATA1 binding and abrogates BCL11A expression. Having turned off the expression of BCL11A, another gene, γ-globin (HBG1/HGB2) is expressed, creating fetal hemoglobin (HbF) production. It is quite complicated; but, in essence, the production of fetal hemoglobin allows people with sickle-cell diseases (red blood cells shaped like sickles because the cells are starved of oxygen) to be restored to health.

There are many issues and risks with this therapy, including the fact that sickle-cell disorder could be a protective disorder against malaria. But one especially concerning prospect, which is really at the core of the BLA on review currently, is the chance that the CRISPR may create cuts or DSBs at a site on the genome locus that is not in the right place. These misplaced or unforeseen cuts are known as ‘off-target effects’ or, alternatively, as indels — which means (usually unintended) insertions or deletions. The BLA puts the risks well:

One of the main concerns related to genome editing technology is risk of cleavage of genomic DNA at unintended sites due to imperfect pairing between the gRNA and the target DNA sequence. A subset of these imperfectly paired sites can be cleaved by the Cas9 endonuclease resulting in unintended edits across the genome. These sites can tolerate up to 6-mismatches between the gRNA and the genomic DNA. Since unintended edits can disrupt gene expression if present in the coding or regulatory DNA sequences, it is critical that the specificity of the gRNA be thoroughly screened to ensure off-target genome editing is minimized.

https://www.fda.gov/media/173414/download

I am still trying to get my head around the recent report of the results of the off-target analysis present in the BLA. The FDA’s BLA report states as follows:

For the cellular off-target analysis, the Applicant used three samples from healthy donors and three samples from subjects with SCD of African American ethnicity. Given the impact of the SCD on [hematopoietic stem cell] function, which can potentially change the chromatin landscape and can impact off-target editing, the merits of using healthy donor samples for such analysis is not clear.

Additionally, it is not clear if the small number of samples used in the cellular GUIDE-seq offtarget analysis is sufficient to adequately assess off-target editing in exa-cel.

https://www.fda.gov/media/173414/download

The report then continues:

4.1.1.1 In Silico Analysis Off-Target Analysis Data for Exa-cel

The Applicant used three publicly available in silico algorithms to nominate potential off-target sites for the sgRNA SPY101 (Figure 6) based on its homology to the reference sequence.

https://www.fda.gov/media/173414/download

Notably, however, when you get to the next page on the analysis of these risks, there are a number of redactions, no doubt because these are commercially protected contents that the regulator must not disclose. On first view, it appears that these ‘in silico algorithms’ to nominate potential off-target sites is, as is said below, a ‘part of the tool.’ I am not quite sure whether that means that the tool — the CRISPR system used be Vertex — is also the same system that conducts the off-target search, or something else. Have a read:

In any case, it looks like the so-called ‘indel frequency’ is very low. As the report noted later, “In this analysis, there were no statistically significant off-target editing events observed at any of the off-targets nominated using in silico analysis.” Although it remains unclear to me precisely how the indel assessment takes place, it is worth noting that the report’s view of the findings of the sponsor are very ambiguous, and tend towards a finding that the results of the study are inadequate. As the report notes in its conclusion of the safety summary section (4.1.2):

These changes have the potential to impact the chromatin landscape of SCD donor derived CD34+ HSPCs. Since chromatin accessibility can influence off-target activity, it is not clear if GUIDE-seq analysis of healthy donor derived CD34+ HSPCs can adequately capture potential off-target editing occurring in patient cells. However, availability of SCD donor cells can be limited and should also be considered. The Applicant used a total of four samples that were from donors of African American ethnicity. Three of these samples were from SCD donors that were used in the GUIDE-seq experiment and hybrid capture sequencing experiment, and one sample was from healthy donor that was used in the hybrid capture sequencing experiment. Given the limited number of SCD samples that were used in the cellular off-target analysis, it is not clear if the GUIDE-seq analysis adequately assessed the potential off-target editing by exa-cel.

Given the ambiguity of the FDA’s assessment, which states that Vertex’s pharmacovigilance plan is still under review, it remains to be seen whether more studies will need to be provided before the FDA consider exa-cel ready for the clinic.

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Updates for September: Cosmetics and COVID-19

This month has been a busy month for my semi-scholarly work. At the start of the month, I wrote a piece for the Conversation about the so-called crackdown on the cosmetics procedures sector announced by AHPRA around 7 September 2023.

Following the publication of that piece, I was lucky to be asked to appear on a long interview for Mamamia’s The Quicky. It was a great talk and I thank host Claire Murphy for the great interview.

Over the last few days, when it was announced that a COVID-19 inquiry would be run by the Commonwealth government, its terms of reference came under scrutiny. Having co-authored and published an article earlier in the year on COVID-19 mandates — an article that I was very proud to have written, especially when it was given plaudits from now Justice of the High Court of Australia Hon Robert Beech-Jones — I was keen to provide my view on the terms of reference.

Several commentators around the country have argued that the terms of reference are unduly restrictive and a cause for complaint. That, in some ways, is understandable. After all, it is essential that critical minds and governments examine how the public health legislation was deployed during the pandemic, especially where profound human rights issues arise from coercive interventions.

However, as I argued ion ABC News Radio on Friday 22 September, the Inquiry expressly will cover questions of governance, including

the role of the Commonwealth Government, responsibilities of state and territory governments, national governance mechanisms (such as National Cabinet, the National Coordination Mechanism and the Australian Health Protection Principal Committee) and advisory bodies supporting responses to COVID-19.

See Inquiry TORs

Given that our Constitution does not confer on the Commonwealth a competency to make laws with respect to public health, however, the terms of reference strike me as sensible and practical.

After all, it is the states, including New South Wales, that hold the power to regulate public health within their polities. Sections of the states’ public health Acts confer different conditional powers on their relevant health ministers; and, in New South Wales, it is section 7 that gives the Minister massive powers to do whatever they consider to be necessary when, on reasonable grounds, they consider that a situation has arisen that is likely to be a risk to public health, and they seek to deal with the risk and its possible consequences. My phrasing, above, is a little garbled, because it seeks to paraphrase the wording of the provision, which is as follows:

7 Power to deal with public health risks generally
(cf 1991 Act, s 5)

(1) This section applies if the Minister considers on reasonable grounds that a situation has arisen that is, or is likely to be, a risk to public health.

(2) In those circumstances, the Minister–

(a) may take such action, and
(b) may by order give such directions,

as the Minister considers necessary to deal with the risk and its possible consequences.

All of the NSW public health orders were made pursuant to section 7, above.

The Victorian Act, by contrast, requires that a ‘pandemic declaration’ be made before the minister’s powers are enlivened. Following the making of any such declaration, the Minister of Health may exercise their powers to make orders under s 165AI of the Public Health and Wellbeing Act 2008 (Vic), which states as follows:

PUBLIC HEALTH AND WELLBEING ACT 2008 – SECT 165AI

Minister may make a pandemic order

(1) The Minister may, at any time on or after the making of a pandemic declaration, make any order (a pandemic order) that the Minister believes is reasonably necessary to protect public health.

…

As is obvious, these powers are held by state ministers. They are not controlled or controllable by the Commonwealth government, or any Commonwealth minister. Arguably, any influence exerted by a Commonwealth minister over a state minister to exercise their powers in a particular way may give rise to a misuse of the power, inasmuch as the requisite ‘consideration’ (New South Wales) or ‘belief’ (Victoria) of the health minister has to be held by that relevant state minister. Sure, a health minister’s belief or consideration may be reconfigured by additional information from other actors, including their equivalent ministers in other Australian governments. But the legal fact is that the Commonwealth cannot really repeal, remake or otherwise alter or even influence this power; and this is a point that I have found has been missing from the public debate about the scope of the COVID-19 inquiry.

What would be the best outcome of an inquiry into the way the state health ministers exercised their powers? Would the Commonwealth recommend that the state ministers must have approval from the Commonwealth before exercising these powers? Would they be required to consult? This would seem to be completely contrary to the design of the Constitution, which, as Quick and Garran point out time and again, was premised on a fair compromise between the new central government and the colonies: the states would retain independent powers across a range of areas, including, as I think it must be inferred, health. I am not opposed to more centralisation; however, I think it;’s important to understand what we are proposing when we ask for a Commonwealth inquiry into the exercise of state power. And so I was pleased to feed that into the debate via national radio.

My request, alas, remains with ABC Archives for a copy of the recording! (It cannot be replayed like some other programs on ABC listen, etc).

In the meantime, I feel more compelled than ever to revise and rewrite the serious consideration that I developed in 2018 on the division of health power in Australia — an article that, for various reasons, did not make it through peer review at the top journals but which I have been told several times since would make a sorely needed contribution to the literature in this area. The best articles on the topic I have found are two oldies and a newie: