Popularity can sometimes drive stocks higher in the short term, even if the companies behind them aren't performing particularly well. But that's not a bet investors focused on the long term want to make. Ultimately, corporations that aren't the biggest or the most famous names in their sectors can perform well in the long run, provided their businesses are robust.

With that said, let's examine two biotech stocks that could be excellent long-term bets: CRISPR Therapeutics (CRSP -4.25%) and Sarepta Therapeutics (SRPT 1.14%). These aren't the best-known drugmakers out there, and both are still unprofitable, which makes them a bit more risky than average. But both also carry substantial upside potential. Here's why. 

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1. CRISPR Therapeutics

CRISPR Therapeutics is a clinical-stage biotech. It focuses on developing gene-editing therapies for severe illnesses. The company's targets include several forms of cancer and two rare blood-related conditions called sickle cell disease (SCD) and transfusion-dependent beta-thalassemia (TDT). CRISPR may be inching closer to an important regulatory approval for exa-cel, its potential TDT and SCD therapy.

It is co-developing this treatment with Vertex Pharmaceuticals. The two drugmakers plan to submit regulatory applications for the treatment in the U.S. and Europe by the first quarter of 2023. Exa-cel's chances look great as patients treated with the gene-editing therapy have experienced substantial improvements.

For instance, 42 of the 44 patients who underwent treatment in a late-stage study became transfusion-independent, while the remaining two saw substantial decreases in the volume of transfusions they needed.

Exa-cel could earn approval within the next 18 months. Vertex and CRISPR Therapeutics will share the profits and costs associated with it on a 60/40 basis -- 40% of the profits and the costs will go to CRISPR Therapeutics. Vertex Pharmaceuticals has spent hundreds of millions purchasing its share of the rights to this medicine from CRISPR. 

As of the end of the second quarter, the gene-editing specialist had $2.1 billion in cash and cash equivalents -- a handsome sum for a clinical-stage biotech -- although it decreased from the $2.4 billion in cash and equivalents it had as of the end of 2021.

CRISPR Therapeutics estimates a combined addressable market of at least 32,000 patients for exa-cel in treating TDT and SCD. That may not seem like a lot, but gene-editing therapies are typically costly. Bluebird Bio's Zynteglo, also a gene-editing treatment for some TDT patients, costs a whopping $2.8 million per treatment.

Suppose CRISPR and Vertex can grab just 20% of this target market: 6,400 patients. At a price of $2.8 million, the two partners could generate an impressive $17.9 billion in sales. CRISPR will also be able to push forward its other pipeline programs thanks to its existing cash pile and the money it will likely generate from exa-cel. The company boasts several potential cancer treatments, among others.

CRISPR Therapeutics is well on its way to gaining prominence thanks to its innovative programs that could produce more breakthrough therapies after exa-cel. 

2. Sarepta Therapeutics

Sarepta Therapeutics primarily focuses on developing medicines for rare illnesses. The biotech has received U.S. approval for three treatments that target Duchenne muscular dystrophy (DMD). DMD is a rare genetic, progressive, and fatal condition that causes patients' muscles to become weak. It is typically diagnosed in early childhood and affects males primarily. The prevalence of DMD is about 1 in 3,500 to 1 in 5,000 males.

Sareptas' DMD treatments were the first and only approved for the disease. However, since various mutations cause DMD, not all patients are eligible for the company's products. Thankfully, several of the more than 40 programs Sarepta Therapeutics is working on could help it target even more DMD patients. The company submitted an application for another potential DMD therapy, SRP-9001, in September.

Sarepta Therapeutics' revenue increased by 42% year over year in the second quarter to $233.5 million. It also ended the quarter with $1.9 billion in cash and equivalents, down from the $2.1 billion it had at the end of 2021.

The company still has plenty of work ahead of it. It'll be a few years before it earns approval for any non-DMD therapy. However, the biotech has already proven that it can successfully develop treatments for rare and difficult-to-treat illnesses. The company will likely continue to expand its DMD portfolio in the coming years -- and eventually earn the green light for treatments that target other diseases.

Sarepta may not be the most recognizable name in the biotech industry, but for patient investors, it could be a solid stock to buy and hold for a while.