It's reasonable to expect small improvements in the risk profile, but I think blood cancer is going to be a side effect for any drug following this basic idea. You will always need some chemo to destroy the defective blood-making stem cells before replacing them with the genetically-modified blood-making stem cells, and any chemo that is strong enough to kill all of the blood-making stem cells in your body is necessarily going to have a risk of damaging healthy cells and turning them into pre-cancer cells. So the risk can be reduced but probably not eliminated.
> Does anyone know if changing the drug would require a new FDA approval for the entire regimen, or could the protocol be easily changed?
The FDA-approved prescribing information will recommend a particular chemotherapy regimen, but clinicians will be free to substitute alternatives if they believe those are clinically superior. They won't need permission from the FDA or the manufacturer to do that; clinicians deviate from the FDA-approved manufacturer recommendations all the time ("off-label prescribing").
If the manufacturer wants to update the official recommendations in the prescribing information, then they'll need FDA approval for that. But it is possible for clinicians to publish their own treatment guidelines (e.g. in medical journal articles), independent of the manufacturer, and the FDA has no control over those.
What a weird system: there's something better, but the manufacturer isn't allowed to tell you about it. What if they, like, slide the journal article across the desk, whilst holding their finger alongside their nose and winking?
> What a weird system: there's something better, but the manufacturer isn't allowed to tell you about it.
It is the way medicine works – not just in the US, in most countries worldwide. Not just about gene therapy, about all drugs and devices.
The FDA and its international equivalents (the EMA in the EU, the TGA in Australia, etc) regulate the manufacturers, not the clinicians. They control what the manufacturers sell and even what the manufacturers are allowed to say about their products (in product packaging, prescribing information, advertisements and marketing collateral). They don't control what the treating clinicians do with those products – to the extent that is regulated, it is the job of other regulatory agencies (e.g. professional licensing boards, civil courts hearing medical malpractice claims, etc)
> What if they, like, slide the journal article across the desk, whilst holding their finger alongside their nose and winking?
What they'll do instead: there will be a conference where (among other things) the journal article author will present their findings/recommendations, and the manufacturer will sponsor (and hence help pay for) the conference. They never actually said anything, they just made sure you were there to hear about it.
I'm not a doctor but my mother is. When I was a teenager, she'd be invited to these free dinners at fancy restaurants paid for by pharmaceutical companies, and a couple of times they allowed her to take me along (she was allowed to bring her spouse/partner to some of them, so she just asked "can I bring my teenage son instead"?). During the dinner, some academic would do a presentation on their research into how wonderful one of the company's drugs was, and also do some Q&A. So the manufacturer wasn't technically saying anything, everything was said by some academic (whose research they were funding). I didn't understand it all, but I found it rather interesting. Still didn't follow her footsteps into medicine though (although my younger brother has).
But, she tells me the regulators have cracked down on free perks from pharmaceutical companies, so they are forced to be a lot less generous nowadays than they were back in the 1990s. (This is not the US though, this is Australia.)
Does anyone know if changing the drug would require a new FDA approval for the entire regimen, or could the protocol be easily changed?