CHICAGO -- The negative whispers that hit Bluebird Bio's (BLUE) stock price coming into the American Society of Clinical Oncology (ASCO) annual meeting were wrong. There was nothing much to worry about the company's anti-BCMA CAR-T therapy for multiple myeloma.

Response rate at the three active doses: 100%.

Number of patients relapsing: Zero.

Safety: Still good, with just two patients experiencing grade 3 cytokine release syndrome that resolved within 24 hours.

The details: The clinical trial of Bluebird's CAR-T, known as BB2121, enrolled 21 multiple myeloma patients no longer responsive to a prior stem cell transplant and a median of seven prior therapies. These were very sick patients.

Eighteen multiple myelomas patients were treated with one of three escalating "active" doses of BB2121, with 15 patient evaluable for response as of May 4, the data cutoff. [The other three patients were treated with a fourth and lowest dose of bb2121 that was discontinued prior to this update.]

Four of the 15 patients, or 27%, achieved a complete response. Another seven patients (47%) achieved a very good partial response. The remaining four patients were in a partial response.

All 15 patients with bone marrow involvement at baseline had no detectable multiple myeloma cells in their bone marrow on Day 14 or beyond. Of four patients evaluable for Minimal Residual Disease (MRD), all four were found to be MRD-negative.

The efficacy of BB2121 and the duration of follow up (8 to 54 weeks) is further described in this swimmer's plot:

 

And here is the key safety slide from Bluebird's presentation:

Nothing is perfect, so what nit will investors find to pick? Patient No. 4 (see the chart above), one of the complete responders, degraded to a very good partial response near 48 weeks.

"This is not a clinical relapse or progression," said Bluebird spokesperson Manisha Pai. "It is a phenomenon that has been seen with other therapies."

Next steps: Bluebird and partner Celgene (CELG) plan to enroll additional multiple myeloma patients in this study at a specific, but as-yet-undisclosed BB2121 dose. Investors might grow impatient that Bluebird and Celgene won't yet announce definitive plans to start another clinical trial needed for BB2121'a approval.

What is BB2121 and how does it work? To make BB2121, Bluebird extracts immune T cells from multiple myeloma patients, and in a lab, genetically engineers them to recognize a protein known as B-cell maturation antigen (BCMA). The BCMA protein is found on malignant and healthy plasma cells. Once injected back into the patient, the altered T cells seek out and kill BCMA-containing cells.

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Adam Feuerstein writes regularly for TheStreet. In keeping with company editorial policy, he doesn't own or short individual stocks, although he owns stock in TheStreet. He also doesn't invest in hedge funds or other private investment partnerships. Feuerstein appreciates your feedback; click here to send him an email.

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