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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.

https://doi.org/10.1038/s41375-021-01282-6

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.

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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.

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Mitochondrial donation law reform

Recently, a new Bill on mitochondrial donation, the Mitochondrial Donation Law Reform (Maeve’s Law) Bill 2021, was tabled in the federal Parliament. Although a vote was scheduled for last June, circumstances conspired against the parliamentary agenda, and it has been held over until later in the year.

The Bill proposes to introduce mitochondrial donation — and to legalise the intervention, which would be unlawful under current law — into the Australian health system. One of the reasons the Bill was needed is that, under current law, an act that alters a human genome is unlawful in Australia and will result in a penalty of 15 years imprisonment — one of the strictest penalties for genome alteration in the world.

That penalty is set out in section 15 of the Prohibition of Human Cloning for Reproduction Act 2002 (Cth) (the ‘PHCR Act’). That provision has remained unchanged since 2002, despite huge advancements in science, including the invention and discovery of several completely new forms of editing and altering human genomes. One such advancement was the discovery of a way of editing the human genome with great precision; this was the CRISPR Cas-9 (and related) techniques, and the discoverers won joint Nobel prizes for chemistry in 2020 for their achievements.

How Mitochondrial Donation Works

Mitochondrial donation involves taking healthy mitochondria from the egg of a donor and transferring that healthy mitochondria into the egg of a mother who has defective or diseased mitochondria. Replacing the defective mitochondria in the mother’s egg with healthy mitochondria from another woman’s healthy egg means that the child who will issue from the mother will not have mitochondrial disease or any other disease associated with defective mitochondria (such as Leigh syndrome). Where the procedure is not undertaken, a child born of a mother with defective mitochondria is virtually guaranteed to inherit mitochondrial disease or a related condition. Most of these conditions are not well treatable, and certainly not curable. After all, imagine if every cell (or most cells) in your body had a defect! The health implications of any mitochondrial defect are serious indeed.

Figure 1: Here is a diagram of mitochondrial donation.

This figure is taken from this article, pulished in Harvard University’s Science in the News website (CC BY 4.0). The figure is by Rebecca Clements.

As may be seen in figure 1, mitochondrial donation involes a few steps. First, a medical practitioner will remove the nuclear DNA from the donor egg, leaving an ’empty egg’ (an egg sans nucleus) containing healthy mitochondria (purple). Second, the medical practitioner will then remove the defective mitochondrial DNA from the birth mother’s nuclear DNA (teal). This creates a healthy nucleus with all of the defective mitochondrial material removed. Then, the altered nuclear DNA from the mother is transferred into the empty donor egg that is free of any defective mitochondria. The result is a newly engineered egg comprising the donor’s mitochondrial DNA and the mother’s nuclear DNA. This new egg is then fertilised by the father’s sperm outside of the body (ex vivo) and, once fertilised, implanted into the mother’s womb.

Once this transfer, fertilisation, and implantation process has taken place, the mother will possess a new egg. As noted, this will be an engineered egg — a product of the mother, the father, and the donor. Inside that egg, an embryo will develop that will now possess (1) nuclear DNA from the mother, (2) nuclear DNA from the father, as well as (3) the donated mitochondrial DNA from the donor’s egg. The defective mitochondrial DNA has been removed and in its place we have only healthy mitochondrial DNA.

The reason this is possible is because, fascinatingly, mitochondria have their own chromosomes and their own DNA. This DNA is separate from the DNA that we find in the nucleus of cells (the nuclear DNA). As such, it is possible to swap out the mitochondrial DNA in an egg without disturbing the nuclear DNA.

Since the nuclear DNA is the trait-giving DNA (that is, the DNA of primary genetic inheritance, imparting such things as eye colour, height, bone density, etc.), the child’s primary genetic inheritance will remain undisturbed by the addition of the donated mitochondrial DNA from the donor. In fact, the mitochondrial DNA is just that: DNA that relates only to the mitochondria in the cells. The anatomy of a cell is visible in figure 2, below. As we can see, the nuclear DNA and mitochondrial DNA are separated and rarely interdigitate. But while the mitochondrial genome is separate from the nuclear genome, its volume is much lower. The mitochondrial genome is built of 16,569 DNA base pairs, while the nuclear genome is made up of some 3.3 billion DNA base pairs.

Figure 2. The image above shows where mitochondria and nuclear DNA are distinct; it also shows the number of genes contained in the cell nucleus compared to the number of genes in the mitochondria, which sits outside the cell nucleus.

This figure is taken from this article, pulished in Harvard University’s Science in the News website (CC BY 4.0). The figure is by Rebecca Clements.

Hang on — what are mitochondria?

Mitochondria are known as the ‘energy powerhouses’ of our cells. They are membrane-bound organelles within our cells that generate enough energy to facilitate cellular activity. Mitochondria also contain their own chromosomes. They are essential in converting the energy we receive from exogenous sources (such as food and sunlight) into energy that the cell can use in the tissues or organs. Mitochondria create energy by storing it chemically in the form of adenosine triphosphate (ATP).

Different tissue and organ cells have varying numbers of mitochondria. A mature red blood cells or erythrocyte may have no mitochondria; by contrast, liver cells (hepatocytes) can have more than 2,000 mitochondria in a single cell. Mitochondria even exist in collagen-producing cells like fibroblasts (see figure 3, below).

Figure 3. Fluorescent microscopy image of the mitochondria (red) and cell nucleus (blue) of two mouse embryo fibroblast cells.

Image taken by the Institute of Molecular Medicine I, University of Düsseldorf (CC BY 4.0) and obtained here via this Wikimedia Commons page.

What does the Maeve’s Law Bill do?

Among other things, the Maeve’s Law Bill amends section 15 of the PHCR Act to carve out an exception for mitochondrial donation, essentially decriminalising the procedure. Recall that altering the human genome is unlawful, and that mitochondrial donation would have to be deemed an unlawful alteration of the human genome under the existing law. This is because, when a mitochondrial donation intervention takes place, the medical practitioner will be altering the human genome by transferring the DNA contained in the mitochondria into a new egg that will ultimately be implanted into a mother. Precisely how and when the alteration occurs (for instance, is it unlawful to alter the genome ex vivo?) is probably not worth considering. The provision seems broad enough to capture almost any kind of alteration, at least potentially. So, without the amendment in the Bill to make an exception for mitochondrial donation (and the Bill proposes to makes a huge number of amendments across three separate Acts), a practitioner who administers the treatment would be liable for up to 15 years imprisonment.

The question I have is as follows: Is the Maeve’s Law Bill a sign of things to come? Could we see further carve outs for CRISPR-style interventions in the near future? While interesting to contemplate, I do not think we shall see any such change. The reason is that we are still too far away from wielding CRISPR (or other genome editing techniques) in ways that would be safe and effective. Somatic cell genome editing, however: that may be a different matter. But I digress. Somatic cell editing is a different case altogether.

Federalism and Mitochondrial Donation

Despite many good aspects, the Maeve’s Law Bill does have some issues. Some of those relate to the ways in which the treatment is to be made available across the state and federal levels of government. As always in health, the dualism of our federal republic — and the indelible separation of the state and federal tiers on matters of health — threaten to complicate the roll out of any medical treatment.

On my analysis, it is quite possible that certain states, for whatever reason (perhaps ethical ones), may in the future enshrine a law prohibiting mitochondrial donation in that state, despite a Commonwealth laws that permits the intervention (Maeve’s Law). In such an instance, the current Bill is powerless to overcome that issue. Of course, it is arguable that federalism would require that to be just so, since the Commonwealth lacks a power to legislate on health. However, I wonder whether a National Cabinet memorandum of understanding could not be reached, and whether the states and territories could not refer their powers to legislate on this narrow area of health law to the Commonwealth under s 51 (xxxvii) of the Constitution.

Submission to Senate Inquiry

I and my colleague Professor Ainsley Newson set out some of our perceptions of the Bill in our submission to the Legislation Committee of the Senate Standing Committee on Community Affairs. Our submission is available here; it is submission number 49.