Experimental treatments that use the body's own immune system to fight cancer are nothing short of amazing. At the year's biggest scientific conference for cancer drug developers, bluebird bio (NASDAQ:BLUE) showed us that its candidate can prolong the lives of people who had exhausted all available options.

Despite the highly positive results released after the bell on Friday, the stock ticked up just a few percentage points on Monday. If you're scratching your head over the disconnect, there are a few things you need to know about bluebird bio and a hyper-competitive environment for groundbreaking new cancer therapies.

Three scientists working in a laboratory.

Image source: Getty Images.

1. Expectations were sky-high

Last December, bluebird showed us data from 21 advanced-stage multiple myeloma patients after they received a dose of bb2121, an experimental chimeric antigen receptor t-cell (CAR-T) therapy partnered with Celgene Corporation (NASDAQ:CELG). All of these patients had undergone at least three lines of treatment, and most had seen seven or more. To see any of these patients respond would be impressive, so it's no wonder investors sent the stock surging when the partners showed us responses from 17 of 18 patients infused with at least 150 million cells.

That set the bar pretty high for follow-up data recently presented at the American Society for Clinical Oncology's (ASCO) annual conference. The 94% overall response rate in the 150 million and up group trumpeted in December fell to 81%, largely due to less than durable responses among patients given 150 million bb2121 cells.

Celgene and bluebird bio were quick to point out that 21 of 22 patients infused with at least 450 million cells showed responses to treatment as of a March 29, 2018, cutoff date. Moreover, half of this group was in complete remission. If the partners made any mistake, it was portraying the 150 million cell dose as "active" when presenting data from the October 2, 2017, cut-off date late last year.

2. The safety side of the equation

CAR-T therapies like bb2121 are essentially a bag of a patient's own cells that have been trained off-site to recognize a protein called beta-cell maturation antigen (BCMA) on the surface of cancer cells. The therapy isn't toxic itself, but once it starts working, the contents of millions of destroyed cancer cells entering the bloodstream all at once cause a series of reactions known as cytokine release syndrome (CRS).

Last year, we saw Juno Therapeutics scuttle its lead candidate following five patient deaths, and investors are understandably nervous about safety issues. Investigators tracked down CRS events in a frightening 82% of patients dosed with at least 150 million bb2121 cells, which seems like trouble on the surface. It's important to point out that only two of 22 patients in this group were actually hospitalized with CRS, and neither case was considered life-threatening.

Blood samples with bar codes.

Image source: Getty Images.

3. It's getting crowded in here

Another reason bluebird bio investors weren't exactly thrilled with the company's latest update is that some have noticed the increasingly competitive environment that immuno-oncology stocks operate in. As of March 30, 2018, bb2121 was one of 17 BCMA-directed CAR-T therapies in clinical trials around the world.

So far, two CAR-T therapies have earned FDA approval, and the more modestly priced option carries a $373,000 list price. Roughly 31,000 Americans receive their first multiple myeloma diagnosis each year, and far fewer become eligible for fourth-line treatments. Bluebird could end up competing with several similar treatments for a relatively small patient pool.

Remember, treatment with bb2121 involves a lengthy complex process because a new batch needs to be made for each patient, and it's hard to see how it would ever compete with an off-the-shelf solution. Right now, investors excited about the prospect of simple-to-administer CAR-T therapies appear willing throw money at just about any company that attempts to develop them, and it's probably just a matter of time until one of them succeeds. 

Looking ahead

Beyond cutting-edge cancer treatments, bluebird's very close to filing new drug applications for a gene therapy called LentiGlobin that helps patients with sickle-cell disease and beta-thalassemia dramatically reduce their lifelong dependence on expensive, painful, and time-consuming blood transfusions with a single dose.

The company intends to send LentiGlobin's application to European regulators in the second half of the year, and a related therapy called Lenti-D isn't far behind. The treatment has helped children born with a rare and metabolic disorder called cerebral adrenoleukodystrophy produce a protein they need to avoid severe neurological damage. 

The latest CAR-T update may not have thrilled bluebird investors, but the company will get plenty of chances to shine in the months ahead.

Cory Renauer owns shares of Celgene. The Motley Fool owns shares of and recommends Bluebird Bio and Celgene. The Motley Fool has a disclosure policy.