CRISPR’d pig kidneys for xenotransplantation

Last week, the biotech firm eGenesis supplied a donor kidney sourced from a genome-edited pig to a surgical team at Massachusetts General Hospital (MGH) in the US. The donated kidney was transplanted into a patient with end-stage renal disease whose existing kidney transplant (‘allotransplanted’ from a human) was wearing out. The FDA had granted an expanded access authorisation for the procedure and, as of today’s date, the patient is reported to be doing well.

It is not clear to me from any of the materials online how exactly the pig was edited, other than that it was broadly subject to CRISPR/Cas9 editing of three kinds. First, there was so-called knock out editing of the glycan antigens (which lead to hyperacute rejection); second, there was knock in editing of seven human transgenes, which are thought to help with ‘acceptance’ (or which mitigate immunogenic rejection); and, finally, there was editing directed towards inactivating the genes known to cause porcine endogenous retroviruses (PERVs).

In total, eGenesis and MGH report that sixty-nine (69) discrete gene edits were made. That appears to be a record for a xenotransplantation, because the previous two pig-derived heart xenotransplants from 2022 and 2023 in the US are reported to have only been subject to about 10 edits.

I am assuming that the edits were made to the germline cells of a pig embryo fertilised in the laboratory, as opposed to being made on primordial germ cells or embryonic stem cells, but I am not able to find any specific protocols for this firm’s method. I suspect that somatic cell nuclear transfer (SCNT; ie, cloning) was not used, even though SCNT is technically legal in the US. In any event, I wrote a piece for the Conversation on some of the issues arising in relation to this recent news item here.

Casgevy: bioethical concerns should not be written off just yet — even though the treatment has been approved

On BioEdge, Dr Patrick Foong and I quickly run through the bioethical perturbations that have come with the relatively rapid approval of Casgevy, the first-ever approved genome-editing therapy that utilises CRISPR/Cas 9. In some ways, it could be said that Casgevy is the first-ever approved genome therapy ‘full-stop’, because other categories of gene therapy have not been understood to create ‘edits’ to the human genome, as such.

For instance, Luxturna (and other AAV therapies) are used to ‘swap out’ mutated genes with ‘healthy’ or unmutated versions of the same. While this may seem like an ‘edit,’ it is also arguably a form of “gene replacement therapy.”

Similarly, forms of therapy using CAR T cells have been characterised as therapies that use cell reprogramming or engineering, rather than cell ‘editing,’ to create their therapeutic effects. This is because the immune cells that are extracted from a patient in a CAR T therapy process, and then reprogrammed to recognise and target cancer cells, is not as much a process by which genes or cells are ‘edited’ as much as one in which they are adapted, ex vivo.

As I have noted previously on Cells and Statutes, one of the most concerning aspects of the process in which Casgevy was approved was that the admitted lack of acceptable data about so-called off-target effects was not deal-breaker: neither for the FDA in the United States nor the MHRA in the United Kingdom.

Closer to home, it will be interesting to see what happens when an evidence dossier lands with the Australian regulator: the TGA. Given the ongoing pivot towards making cell and gene therapies faster to approve, the broader governmental investment in cell and gene therapies (see the 2021 senate inquiry on the future of cell and gene therapy here), and the historical tendency of the TGA to follow the FDA’s decisions, both for scientific and regulatory reasons, I suspect it will be approved without too much agony.