What happened

Juno Therapeutics (NASDAQ:JUNO), a clinical-stage biotech, saw its shares gain a whopping 87% in January, according to S&P Global Market Intelligence.

The stock took flight after the company reportedly agreed to a $9 billion all-cash buyout offer from its largest stakeholder and development partner Celgene Corp. (NASDAQ:CELG) last month.

A rocket taking off.

Image source: Getty Images.

So what

While Juno's shareholders likely cheered this news, Celgene's have been decidedly less enthusiastic, with the biotech's stock price falling by nearly 5% ever since the initial rumor of this deal was leaked in mid-January.

The culprit? The overarching problem is that this rather pricey deal won't have an immediate impact on Celgene's top line. Juno's lead CAR-T therapy candidate, JCAR017, isn't expected to hit the market as a treatment for advanced B-cell non-Hodgkin lymphoma until 2019, after all. 

Now what

The long-term value of this deal to Celgene's shareholders is also in serious doubt for one clear reason: JCAR017 requires individualized procedures that make it exceedingly difficult to manufacture on a commercial scale.

During clinical trials, for instance, the current cohort of Food and Drug Administration-approved CAR-T therapies were assessed on hundreds of patients -- not the thousands required to push their sales into the billions. Unfortunately, this scalability problem, which has plagued CAR-Ts from the onset, has yet to be adequately addressed.

The long and short of it is that the complex manufacturing process behind these first-generation CAR-Ts may limit their commercial potential in a significant way -- implying that Celgene might have just grossly overpaid for Juno.