Investors of bluebird bio (BLUE) got a serious case of the blues this week. Shares sunk deep into the red after the gene therapy specialist put the brakes on two of its clinical trials.

Specifically, bluebird temporarily halted the Phase 1/2 (HGB-206) and Phase 3 (HGB-210) studies of LentiGlobin, the company’s experimental gene therapy for sickle cell disease (SCD) after it became known that a former patient in the HGB-206 study has developed acute myeloid leukemia (AML), a cancer of the blood and bone marrow.

Additionally, another patient from a different HGB-206 group was found to be suffering from myelodysplastic syndrome (MDS), another type of blood cancer.

The AML case is a patient who participated in the study over 5 years ago, and whether the illness is due to the LentiGlobin treatment, is still not known. However, out of precaution, bluebird decided to halt the studies until it finds out if the gene therapy is to blame.

In the meantime, the company has also paused Zynteglo’s marketing push in Europe.

Zynteglo is bluebird’s treatment for transfusion-dependent beta-thalassemia, and shares the same lentiviral vector (a virus-derived vehicle for gene delivery) as LentiGlobin. While no cancer cases have been reported from patients treated with Zynteglo, the company is understandably taking no chances.

According to a 2017 study, compared to the general population, SCD patients have a threefold chance of developing AML.

Oppenheimer analyst Mark Breidenbach believes the setback “could impact bluebird’s entire gene therapy pipeline.”

“While many factors could be contributing to the development of malignant disease—including the busulfan-based pre-conditioning, oncogenic lentiviral insertions, or unrelated underlying patient predisposition—we lower our estimated POS for bluebird’s gene therapy pipeline given what we see as a fundamental shift in its risk/reward profile,” the 5-star analyst commented.

Along with reducing the entire gene therapy program’s chances of success to 20%, Breidenbach downgraded bluebird’s rating from Outperform (i.e. Buy) to Perform (i.e. Hold) and took his price target off the table. (To watch Breidenbach’s track record, click here)

Turning now to the rest of the Street, where bluebird still qualifies with a Moderate Buy consensus rating, based on 4 Buys and 12 Holds. Presently, the average price target remains a bullish one; at $51.83, the figure suggests gains of 85% over the next 12 months. (See BLUE stock analysis on TipRanks)

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Disclaimer: The opinions expressed in this article are solely those of the featured analyst. The content is intended to be used for informational purposes only. It is very important to do your own analysis before making any investment.