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#apaperaday: Unexpected Death of a Duchenne Muscular Dystrophy Patient in an N-of-1 Trial of rAAV9-delivered CRISPR-transactivator

In today’s #apaperaday, Prof. Aartsma-Rus reads and comments on the paper titled: Unexpected Death of a Duchenne Muscular Dystrophy Patient in an N-of-1 Trial of rAAV9-delivered CRISPR-transactivator

Today’s pick is Duchenne themed again to commemorate TREAT-NMD Duchenne masterclass. Today’s pick is the preprint from MedRxiv by Lek et al on the sad passing of the first Duchenne patient treated with genome editing.

Before summarizing the paper, first I want to commend the authors for sharing the results so quickly so everyone can learn from this. Reading it was hard, but it must have been much more difficult to write it for the people who were closely involved. The patient treated with genome editing was a Duchenne patient in his 20s, who had a deletion of exon 1 of the muscle dystrophin. He produced a very low amount of dystrophin from the Dp427c promoter in muscle, but this was not enough to prevent Duchenne.

Authors point out that patients with a deletion of muscle exon 1 can also have Becker or present only with heart problems. In these patients the Dp427c promoter is used at higher levels resulting in higher amounts of dystrophin in skeletal muscle.

The therapeutic approach they devised for this patient is not the traditional genome editing, where cas9 causes a double stranded break. Rather, they used a dead cas9 (dcas9) to modify the Dp427c promotor to increase its use and thereby upregulate dystrophin production.

The approach was tested in a mouse model, before the authors requested approval to treat the patient with FDA. The patient was non ambulant, had been treated with steroids for over 20 years, had low muscle mass, pulmonary deficiency (FVC 36%) and mild heart dysfunction (LVEEF 54%).

The dcas9 and guideRNAs were delivered with AAV9. Before treatment it was confirmed that the patient did not have AAV9 antibodies or T-cells. 13 days before treatment an immune suppression protocol was started (prednisolone and just before treatment sirolimus). 1.10(14) viral genomes per kg were injected intravenously. 1 day after treatment the patient showed heart problems, had increased heart damage markers and showed pulmonary distress. After 6 days he had acute respiratory failure and the ejection fraction declined to 45-50%.

He was placed on ECMO (extra corporeal membrane oxygenation) but despite this he passed away 8 days after treatment due to multiorgan failure and neurological injury. Post mortem analysis showed the patient had severe cardiomyopathy (due to disease not due to treatment).

No inflammation of the heart was found. The lungs however were oedemic and there was alveolar damage. The brain damage was likely due to poor perfusion due to the cardiac/pulmonary distress. Authors concluded that likely death occurred due to an acute innate immune response.

They tried treating this but this was unsuccessful. Vector distribution was analyzed with qPCR, showing vectors in the heart and muscle, more in lung and a lot in liver. Transgene expression was only detected at very low levels in liver. No anti cas9 immunity was detected.

Authors discuss that so short after treatment it was not expected to have transgene expression (with AAV this usually takes at least 14 days). They also discuss that the innate immune response likely resulted in a cytokine release and capillary leakage in the lungs.

They highlight another non ambulatory Duchenne patient treated with AAV (micro-dystrophin) who passed away. Here cause of death was speculated to be cardiac problems. Authors stress older, more advanced patients may not have the ‘buffer’ to handle innate immune response to AAV.

So the death was not due to genome editing effects, but due to a response to AAV. This is important information with the gene therapy micro-dystrophin FDA verdict coming up later this month.

It appears older patients are more at risk for being unable to cope with the immediate immune response to AAV and so far this has resulted in the most severe side effect for 2 Duchenne patients. While this is not good news, it is good to be aware of these risks.

I appreciate the authors and family of the patient who were willing to share the results so quickly. Not peer reviewed yet, but still good to have the data available.