How Far Away Is In Vivo Gene Therapy? A Real Timeline
In vivo gene therapy for genetic disease is likely more than a decade away, and the delay is not regulatory, it is scientific. Today's approved gene therapies for conditions like sickle cell are mostly ex vivo: a patient's cells are removed, edited in a lab, and reinfused. In vivo means editing the cell directly inside the body, with no lab step, and that is a much harder problem to get right. Jaap Jan Boelens, Chief Medical Officer of the International Society for Cell and Gene Therapy (ISCT), drew the distinction carefully in his Open Door Salon conversation with ISCT President-Elect Bambi Grilley.
How far away is in vivo gene therapy?
It depends entirely on which kind you mean, and Boelens was quick to split the question rather than give one number. In vivo CAR, aimed at cancer, is closer. In vivo gene therapy to correct a genetic disease is the longer road.
For the CAR in vivo I think it's closer than one decade away, but I think the in vivo gene therapy is likely more than a decade away, and then it's an issue with the dosing: how much to give to get sufficient cells in vivo and not overload the system.
He noted there is genuinely encouraging early in vivo data, some of it presented at recent oncology meetings in multiple myeloma, though the patient numbers are small and the selection criteria aren't fully clear yet. The promise is real. The timeline is honest about how much is still unsolved.
Why is dosing the hard part?
Because in vivo editing has no lab step to control the dose, so getting the amount right inside a living body is the central engineering problem. Give too much and you risk toxicity. Give too little and nothing happens. As Boelens put it, the challenge is delivering enough to work without overloading the system, and there is no reset button once the therapy is inside the patient. That narrow window, effective but not toxic, is what pushes the genetic-disease version past the decade mark.
Why does durability matter more for genetic disease than for cancer?
Because a cancer therapy can succeed in weeks, while a genetic-disease cure has to last a lifetime, and lasting that long inside the body is unproven. Boelens contrasted the two directly.
In the cancer therapy you may get away with a couple of weeks or a month effect, but in ex vivo gene therapy for sickle cell you need decades.
He added a second durability trap specific to the in vivo route: the body can mount an immune response against the therapy and simply reject it. So the in vivo approach has to clear two bars at once, sustain a genetic correction for decades and avoid being neutralized by the patient's own immune system. That is why he sees far more hurdles for in vivo gene therapy than for in vivo CAR, where a shorter effect can still be a win. The durability question is the same reason real-world monitoring is non-negotiable, a point that connects to why these therapies are so expensive to develop and follow.
What safety question comes with editing cells inside the body?
The same unknowns that govern whether it works also govern whether it is safe, and there may be no way to shut it off. Grilley added the concern that sits inside Boelens's black box.
You have to know that two years after you infuse, you don't cause them to develop diabetes or cancer or some bad thing.
Her point is that efficacy, durability, and safety are not separate boxes to check in sequence. They are the same unknown. Once an in vivo therapy is working inside a patient, the field needs a way to monitor it for years and, ideally, a way to turn it off if something goes wrong, and that control doesn't fully exist yet. It is a sober counterweight to the field's real progress, seen in patient stories like Emily Whitehead's CAR-T recovery.
The honest read from ISCT's leaders is that in vivo gene therapy is coming, but the genetic-disease version is a decade-plus problem of dosing, durability, and control, not a paperwork delay. Sponsors and researchers tracking that road can work with Open Door Salon or follow the science at ISCT. The wait has a cost the field does not discuss enough, which is what desperate families do while a real therapy is still a decade away.
Drawn from the recorded, on-the-record Open Door Salon conversation with Jaap Jan Boelens and Bambi Grilley of ISCT. For a primer on the difference between in vivo and ex vivo gene editing, see the NIH National Human Genome Research Institute.