The stocks of biotechs focused on gene editing haven't performed very well recently. Two have performed especially poorly. Shares of Editas Medicine (EDIT -9.11%) are down around 40% over the last 12 months, while Sangamo Therapeutics (SGMO -7.60%) stock plunged nearly 60% during the same period.

This dismal past performance doesn't necessarily mean that Editas and Sangamo won't be winners over the long run. Which of these two biotech stocks is the better pick for investors? Here's how Editas and Sangamo stack up against each other.

DNA helixes with a physician in background pointing to a sequence with a light flashing on it

Image source: Getty Images.

The case for Editas Medicine

Anytime a key executive leaves a small biotech, the speculation behind the departure can take a toll on the company's share price. That happened with Editas Medicine twice in recent months, with former CFO Andrew Hack announcing his departure in December followed by Katrine Bosley stepping down as CEO in January. However, Editas has kept on moving forward despite the turnover at the top, with industry veteran and board member Cynthia Collins acting as interim CEO until a replacement is found.

In several respects, Editas is in a better position than it's ever been. The biotech and its partner, Allergan, expect to begin a phase 1/2 clinical study in the second half of 2019 evaluating CRISPR gene-editing therapy EDIT-101 in treating patients with Leber congenital amaurosis type 10 (LCA10), the leading cause of genetic blindness. This will be the first in vivo (inside the body) CRISPR clinical trial conducted in humans.

Editas thinks that the approach taken with EDIT-101 lends itself well to treating other genetic causes of blindness. The next target is Usher syndrome type 2A (USH2A). Editas plans to present proof-of-concept data for its experimental USH2A gene-editing therapy at the American Society of Gene & Cell Therapy meeting in May.

The biotech's presentation at the American Society of Hematology (ASH) last year of data from its research into CRISPR therapies for treating rare blood diseases beta thalassemia and sickle cell disease was selected as one of 11 "best of ASH" abstracts chosen from more than 5,000 entries. Editas thinks that its approach to treating these diseases could be safer and more effective than other gene-editing therapies in development. 

Editas is also working with Celgene to develop engineered T cells to fight cancer. The company hasn't revealed too much about those efforts but expects to provide key updates later this year.

When it comes to CRISPR gene editing, Editas Medicine arguably claims the most impressive intellectual property around. The company has rights to CRISPR patents held by the Broad Institute, Harvard, Massachusetts Institute of Technology, and Massachusetts General Hospital. Editas licensed rights to the CRISPR/Cpf1 gene-editing technology discovered by its co-founder, Feng Zhang. And the biotech has over 70 issued patents of its own in addition to around 600 patent applications pending approval.

Check out the latest earnings call transcripts for Editas Medicine and Sangamo Therapeutics.

The case for Sangamo Therapeutics

Sangamo Therapeutics' chief worries haven't been about executives leaving. The biotech, however, has been hit hard by pipeline setbacks for a couple of its zinc-finger nuclease (ZFN) gene-editing therapies. In September, Sangamo announced disappointing interim results for SB-913 in treating rare genetic disease mucopolysaccharidosis type II (MPS II). The company also reported in February that another ZFN therapy, SB-318, didn't provide a significant clinical benefit to patients with MPS I, a genetic disease similar to MPS II.

With two disappointments, why should investors still consider buying Sangamo stock? The company has several other pipeline candidates as well as multiple big partners interested in its technology.

Pfizer teamed up with Sangamo to develop SB-525, a gene therapy (which introduces foreign DNA into cells rather than editing DNA) targeting treatment of hemophilia A. Sangamo expects to report key data from its early-stage clinical study of SB-525 later this year. The biotech also plans to announce data from a phase 1/2 study of its wholly owned program, SB-FIX, in hemophilia B in 2019.

Sangamo and Sanofi's Bioverativ subsidiary are working together on early-stage cell therapy ST-400 in treating beta thalassemia. Sanofi is also conducting a phase 1/2 study evaluating cell therapy BIVV-003 in treating sickle cell disease.

Gilead Sciences expects to file for approval to begin a clinical trial for cell therapy KITE-037 in the second half of 2019. KITE-037 is being developed using Sangamo's ZFN gene-editing technology. In addition, Sangamo hopes to advance a couple of its own programs to early-stage clinical testing this year -- gene therapy ST-920 in treating Fabry disease and cell therapy TX200 for the prevention of solid organ transplant rejection.

Better buy

Which of these stocks is the better buy? For many investors, the answer is neither. Both Editas Medicine and Sangamo Therapeutics are highly risky. There's no guarantee that either biotech's pipeline candidates will be successful.

Sangamo has more shots on goal than Editas does. Its clinical programs are also more advanced than Editas' programs are. Some investors who aren't averse to buying a speculative stock might prefer Sangamo since it arguably has higher prospects of getting an approved drug on the market sooner.

I personally own shares in Editas Medicine and still like the stock's long-term prospects more than I do Sangamo's. In my view, Editas' relationship with Feng Zhang, who continues to pioneer CRISPR gene-editing approaches, along with its solid intellectual property rights, make the biotech attractive for aggressive investors who are willing to wait a while.