Cancer stem cells that drive tumor growth were halved by Medi-551, an experimental antibody treatment for multiple myeloma, according to results of a small preliminary clinical trial presented at the American Association for Cancer Research (AACR) Annual Meeting.1

A total of 15 patients with newly diagnosed multiple myeloma were treated with Medi-551, along with a monthly regimen of lenalidomide and dexamethasone, which are already FDA approved for multiple myeloma.

The impact of the drugs on cancer stem cells was measured by counting stem cells in bone marrow and blood samples drawn from patients at several points throughout the 7-month study.

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At first, bone marrow-derived cancer stem cells increased by an average of 2.5-fold after 2 cycles of lenalidomide and dexamethasone alone. MEDI-551 was added in the third and fourth months of treatment, and the number of cancer stem cells decreased by half, on average, in 14 of the 15 patients.

In contrast, numbers of cancer stem cells in 5 patients with newly diagnosed multiple myeloma who did not receive the extra antibody treatment increased 9.3-fold after an average of 4 months of treatment with the other 2 drugs.

No serious adverse events occurred among the patients who received the antibody.

MEDI-551 targets CD19, a specific protein found on the surface of multiple myeloma stem cells.

“We chose to carry out this clinical trial in newly diagnosed patients because our original data showed that CD19 was almost always expressed by myeloma stem cells in these patients, whereas we don’t know if that is the case in more advanced patients,” said William Matsui, MD, of Johns Hopkins Kimmel Cancer Center in Baltimore, Maryland, an expert on multiple myeloma and coauthor of the study.

The researchers tested stem cells with both bone marrow and blood samples, and saw nearly identical results. Therefore, because blood is much easier to draw than bone marrow, they plan to primarily use blood samples to track multiple myeloma stem cells in the future.

Although most of the patients experienced a decrease in multiple myeloma stem cells after 3 doses of MEDI-551, these stem cells increased in 2 patients, each of whom had their cancer grow or spread during the course of the study.


1. Huff CA, Gladstone D, Borrello I, et al. Clinical cancer stem cell targeting in multiple myeloma: an early phase trial of the anti-CD19 monoclonal antibody Medi-551 in combination with lenalidomide and dexamethasone. Presentation at: American Association for Cancer Research Annual Meeting; April 16-20, 2016; New Orleans, Louisiana. Abstract CT102.