A stock market uncertain about the commercial viability of gene therapies has been tough on gene-editing stocks. CRISPR Therapeutics (NASDAQ:CRSP) has fallen 35% since the end of August, and Editas Medicine (NASDAQ:EDIT) has given back 20% over the same time frame.

Forward sales estimates are always tricky when it comes to early-stage experimental drugs, but the Food and Drug Administration is clearly willing to work with these companies to get their treatments to patients who need them. Let's compare these beaten-down biotechs side by side to see which has a better chance to deliver market-beating gains in the years ahead.

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The case for CRISPR Therapeutics

The moment we've all been waiting for is getting closer. Late last year, CRISPR Therapeutics and its collaboration partner Vertex Pharmaceuticals (NASDAQ:VRTX) began the first human proof-of-concept trials with a CRISPR-based drug. 

In the U.S., 45 people with severe sickle cell disease will receive an infusion of CTX001, which is really just their own stem cells that have been modified by CRISPR off-site to produce fetal hemoglobin. Investigators will be looking for safety signals and, of course, signs of fetal hemoglobin production. In Europe, another 45 patients will receive CTX001 treatment, but this group has a different hemoglobin-related disorder called transfusion-dependent beta-thalassemia.

The beta-thalassemia population that CTX001 is aimed at can't live without regular blood transfusions, which comes with a lot of problems of its own. That's why investigators will measure the percentage of patients who need fewer transfusions, or none at all, from nine to 24 months after a single infusion of CRISPR's lead candidate.

If CTX001 succeeds, it could end up competing with an experimental gene therapy further along the development timeline. LentiGlobin from bluebird bio doesn't employ CRISPR's technique, but it has produced results that CTX001 will be measured against. If CTX001 looks unable to keep up, enthusiasm for CRISPR could evaporate.

In the first half of 2019, CRISPR will also start a clinical trial with a CAR-T therapy, called CTX110, which works the same as both CAR-T therapies on the market today but with an important advantage: Today's pricey CAR-T therapies are tailor-made for each patient, but CRISPR's working on an off-the-shelf solution.

Vertex will share costs related to CTX001, but CRISPR Therapeutics has to develop its experimental cancer drugs on its own dime. CRISPR Therapeutics finished September with $487 million in cash after losing $117 million during the first nine months of 2018. That should give the company enough time to produce proof-of-concept results for CTX001 and its wholly owned cancer drug.

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The case for Editas Medicine

Editas Medicine won't be the first company to test a CRISPR-based drug, but it will probably be the first to inject one into the eyeballs of infants. EDIT-101 was designed to help babies born with a bad gene that leads to a deficiency of a protein vital to healthy retina cells, a condition called Leber congenital amaurosis type-10 (LCA 10).

Retinas of infants born with LCA 10 usually stop working, leaving them blind before their first birthday. If everything works out as intended, though, a single injection of EDIT-101 in each eye should allow their retinal cells to produce the protein they need on their own, permanently. 

LCA 10 affects around 15,000 patients in North America and Europe, but it can be caused by any one of over a dozen mutated genes. As a treatment for LCA 10, EDIT-101 could start with a tiny addressable patient population that could be the beginning of something much bigger. In addition to all the other forms of LCA, dozens of different inherited gene mutations cause progressive vision loss for over 100,000 Americans.

Last summer, Editas Medicine's collaboration partner Allergan (NYSE:AGN) exercised its option to split the costs of development and potential profits from EDIT-101. If successful, Allergan can ask Editas to get at least four more candidates ready for clinical trials.

Editas was developing CAR-T therapies in partnership with Juno Therapeutics, which has already been acquired twice. Bristol-Myers Squibb will soon inherit the partnership from Celgene, and the big pharma's plans for Editas are still anybody's guess. Down the road, Editas could also begin clinical studies with a candidate aimed at the same beta-thalassemia and sickle cell disease patients as CTX001. 

At the end of September, Editas had $337 million in cash and securities after burning through $85 million during the first nine months of the year. With Allergan sharing expenses for EDIT-101 and nothing new beginning clinical trials in the near future, that cash cushion should last long enough to know if it really can stall blindness for LCA 10 patients.

If early results for EDIT-101 fail to impress, though, the company might not have any clinical-stage candidates in development yet to fall back on.

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The better buy

It seems silly to think about potential sales before we've seen human proof-of-concept data, but Editas Medicine's LCA 10 program could be a lot easier to sell than another hemoglobin treatment from CRISPR Therapeutics. Editas can also use the same delivery system to make treatments aimed at more mutations associated with vision loss.

Trial results later this year could turn the tables, but right now Editas Medicine looks like the better stock to buy.

Cory Renauer has no position in any of the stocks mentioned. The Motley Fool owns shares of and recommends Bluebird Bio and Editas Medicine. The Motley Fool owns shares of CRISPR Therapeutics. The Motley Fool recommends Vertex Pharmaceuticals. The Motley Fool has a disclosure policy.