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 story quotes me as follows:

Sydney University lecturer in health law Dr Christopher Rudge told 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.”


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.

Updates from ‘Cellular Horizons’

Medical Research Future Fund project investigating how to to improve decisions about accessing cellular therapies

I recently presented updates from our MRFF project, which investigates how to improve decision-making, primarily among patients, about how and whether to access cellular therapies. The project has so far focused primarily on mesenchymal stem cell interventions: ie, ‘regenerative medicine’ treatments for osteoarthritis and conditions involving cell dysfunction. As a chief investigator in the ‘legal and regulatory affairs’ sub-team on the project, my focus has been on how these treatments are regulated.

New cellular therapies

However, as new cell-based interventions emerge as we speak, the project will likely also consider these novel interventions. In a very recent trial, immune cells (CAR-T cells) have been ‘programmed’ to attack cancerous T-cells by means of CRISPR ‘base editing.’ Specifically, this trial is aimed at treating a patient with T-cell acute lymphoblastic leukemia, or T-ALL.

There have been two issues for treating this disorder in the past.

The first relates to what is called T-cell aplasia. This is a process whereby the antigens on the T-cells are attacked, which destroys not only the cancerous T-cells but also destroys the normal T-cells. The means that T-cell numbers are decreased significantly.

Cell aplasia happens when patients undergo CAR T-cell therapy. Thus, when the cancer is a B-cell malignancy, the patient will generally experience B-cell aplasia. However, with B-cell aplasia, immunoglobulin replacement therapy can be administered to manage the problem. This is not so for T-cell aplasia. T-cell aplasia is not generally tolerated in humans, and persistent T-cell aplasia is life threatenting. Therefore, CAR T-cell therapy has generally not been possible for T-ALL.

The second issue is that CAR-T cells programmed to recognise and destroy T-cell antigens will inevitably attack healthy T-cells too in what is described as ‘T-cell fratricide.’ Sometimes, this problem is called ‘T v T’ fratiricide. This is described in the video below, which is a basic introduction to base editing published by Great Ormond Street Hospital:

While it is an extremely complicated molecular process, in CRISPR base editing, nucleotide bases in donor cells are edited at the atomic level so that the gene for CD7 (a genetic marker in blood cancers) is changed from cytosine to a thymine. In this process, the base editing produces a so-called ‘stop codon’ that terminates the production of CD7 (acting like a molecular ‘full-stop’). These edited cells are then transplanted into the patient to treat relapsed lymphoblastic leukaemia.

In an article published in Leukemia, authored by the team that are conducting the trial, the authors write that

Base editing offers the possibility of seamless disruption of gene expression of problematic antigens through creation of stop codons or elimination of splice sites. We describe the generation of fratricide-resistant T cells by orderly removal of TCR/CD3 and CD7 ahead of lentiviral-mediated expression of CARs specific for CD3 or CD7. Molecular interrogation of base-edited cells confirmed elimination of chromosomal translocations detected in conventional Cas9 treated cells.

While it is far too early to determine whether base editing might present an option to patients with T-ALL and whose options are exhausted, it is promising to see that base editing appears to be possible in humans. Using CRISPR base-edited cells in humans represents a new form of cellullar therapy — it could be called somatic cell genome editing; the only other trial for SCGE that I’m aware of is the trial for exagamglogene autotemcel  or exa-cel (formerly known as CTX-001); however, that is not a base-edited genome therapy. Rather, Exa-cel uses CRISPR to treat blood disorders (hemoglobinopathies) such as sickle-cell disorder.

Unlike T-ALL base editing treatment above, where base editing is applied to donor cells, exa-cel edits the patient’s own cells (ie, it is an autologous treatment), which are removed prior to the treatment. With the cells removed, the patient is given ablative therapy while the hematopoietic stem cells are edited using CRISPR-Cas9 to produce high level of fetal hemoglobin. This treatment promises to ensure that vaso-occlusive crises (blocked blood flow, depriving tissues of oxygen, and usually caused by the ‘sickle’ shape of the red blood cell), which is a symptom of the blood disorders, is avoided.

New Priority Review Pathway for Biologicals

In the context of such cellular therapies emerging in recent times, the Australian drug regulator, the Therapeutic Goods Administration, has recently introduced new expedited pathways for drug sponsors and manufacturers to fast-track novel biological therapies (another name for therapies involving cell and tissue products) through the approval process. In a recent article published in the Journal of Law and Medicine, our team analysed the new ‘priority pathway,’ which has since been approved. We also wrote a submission to the TGA, which can be found here.

In early December, I presented some of our work on these matters to another team of experts working on cellular therapies in Australia. Presentation slides from that meeting are available here.

Earlier in the year, in April, I presented a brief introduction on the same subject to our internal team. That presentation is also made available here.

Two conference papers to wrap up the year

In November I delivered two conference papers. I summarise them below.

From cell transplants to genome edits: Regulation and bioethics of existing and emerging interventions for sickle cell disease

This first paper was a ‘rapid-fire’ talk at the Australian Association of Bioethics and Health Law (AABHL) conference (‘Making Connections’) in Hobart, Tasmania, on 17 November. This talk summarised some of the work I have done on the bioethics of somatic cell genome editing with my colleague Prof Dianne Nicol. The most promising and translation-ready genome editing treatment around today seems to be CTX-001, manufactured by Vertex Pharmaceuticals. CTX-001 has been developed to treat sickle-cell disorders (SCDs).

SCDs comprise a group of genetic disorders of red blood cells (RBCs). Hemoglobin in RBCs usually carries oxygen from the lungs to the tissues and removes carbon dioxide. In the SCDs, a ‘sickle’ hemoglobin (‘HbS’) molecule is expressed within the RBCs. Generally speaking, if you have two HbS genes, you might have sickle-cell anaemia. If you have one HbS gene (heterozygous), you might have beta thalassemia.

The HbS molecule in the RBCs comes from the HbS gene. The HbS gene is a mutation thyat occurs when glutamic acid is replaced by valine. GAG becomes GTG on the HbS gene (at chromosome 11p15.5), which results in the HbS gene. Pathophysiologically, once the HbS gene mutation occurs, the HbS molecule within the RBCs results in a situation where, under reduced oxygen tension, you get polymerisation of the RBC, and this turns the cells (erythrocytes) into the characteristic sickle cell shape. When the RBCs are in this sickle shape, they obstruct blood flow, causing ischemias or vaso-occlusive crises. This then deprives the tissues of oxygen, creating respiratory issues that can be very serious.

CTX-001 is a new treatment to treat and potentially cure SCD. This paper examined SCD and its prevalence, identified its significant impacts on African American and African populations and analysed the bioethics of the best existing treatment (the allogeneic hematopoietic stem cell transplant, or a bone-marrow transplant). The paper then contrasted the bone-marrow transplant with the CTX-001, the yet-to-be-approved somatic cell genome therapy, and briefly noted the bioethical implications of administering CTX-001.

The paper was largely based on a book chapter contribution that I have written with Dianne Nicol titled Bioethical decision-making about somatic cell genome editing; Sickle-cell disease as a case study, which has been accepted by the editors of the Springer Handbook of Bioethical Decisions and will presumably be published in 2023. Slides from my talk (title page below) are viewable here.

Teaching constraints: Why we should (but don’t) teach the Commonwealth ‘spending’ power (among other things)

The second paper was presented at a symposium of law academics from around Australia held at the University of Sydney on 29 and 30 November and called Teaching Material: Symposium On The Pedagogy Of Political Economy In Australian Law Schools (program here).

This paper was one of my first serious attempts as a legal scholar to write about public finance law. In writing the paper, I learnt a lot, including from Will Bateman’s excellent book Public Finance and Parliamentary Constitutionalism (CUP, 2020). The essence of my talk was the ‘spending power,’ which is generally understood to be reposed in section 83 of the Australian Constitution. However, sections 81, 3 and 66 also deal with the Executive Government’s ability to spend by reference to Consolidated Revenue Fund, and so I made reference to those sections as well. But the main claims I was making were as follows.

There is no textbook dealing with public finance law in Australia, or in the UK, Canada or New Zealand; this represents an almost unbelievable lacuna in legal knowledge that shall continue to dog learning and epistemic understanding until we build a textual knowledge base.

There are three examples of how complicated public finance law can be; but, when we look at these examples, we can readily see (1) just how easily these complications can be resolved, and (2) why it is so important to resolve them.

The first complication is the notion of the spending power under s 81 of the Constitution; that power is not generally a parliamentary power but one exercised exclusively by the Executive Government of the Commonwealth; in other words, federal MPs not a part of the Executive are powerless to block spending or ‘block supply,’ with the effect being that there is really nothing anyone can do outside the Executive to control how much, or how little, the Commonwealth spend on its projects

The second complication is that the Consolidated Revenue Fund, which exists by dint of the ‘appropriations power’ (Constitution s 81; but also ss 83, 3, 66) is not actually a finite ‘kitty’ into which taxpayers’ taxes are deposited (eg, by the Australian Taxation Office), as appears to be largely assumed. Rather, the CRF is more complicated. It is a legal concept; and it is notionally self-executing and does not actually appear to be accessible, or its full quantum knowable, at any single point in time. This may be as confusing for students as it has been for apex courts!

The third complication is the seemingly unknown fact that special appropriations and standing appropriations can set aside (‘hypothecate’) or even ‘bake in’ an unspecified amount to be spent on a government program over an unspecified period of time. This means that spending can be effectively automated. For example, Medicare: will a person entitled to a rebate ever have their request declined because there are ‘insufficient funds’ in the CRF? No.

The point of bringing this into relief is to show that, as with legal knowledge about the legal ‘abstraction’ that is the CRF, knowledge about appropriations, and specifically ‘special appropriations’ (including knowledge about the common law and operations of the finance department), shows us: (1) precisely how government can lawfully spend money (for what purposes); (2) how it determined this (and it appears to be self-determined and open-ended (see Brown v West; Combet v Cth); (3) whether an appropriation that is an ‘Advance to the Finance Minister’ (AFM), for example, is lawful (it is: see Wilkie v Cth; Aus Marriage Equality Ltd v Minister for Finance); and (4) whether appropriations can include money that is not government money (seemingly they can, through ‘net appropriation’ agreements determined by the Finance Minister under the Financial Management and Accountability Act 1997 (Cth) s 31).

As the slides reveal, for each of these ‘complications’, there is a respective ‘teachable’ that shows us so much more about the reality of government spending. The paper then goes on to illustrate its claims through an example of a fictitious Act, the Bigger Medicare Act 2022 (Cth). I am hoping to write this up as a paper in the new year, once I finish some other work. The slides (title below) are viewable here.