Switching off leukaemia

A way to reprogramme leukaemia cells to disable their malignant tendencies has been announced by scientists in the US.

Acute B-cell lymphoblastic leukaemia (B-ALL) is a cancer of the white blood cells that fight infection.

Normally, doctors treat the disease by giving drugs to destroy the stem cells that are producing the leukaemia cells, and this is sometimes followed by a transplant with healthy bone marrow cells to restore the patient's immune system. But this is a complicated and risky procedure.

Now, scientists at Stanford University in the US have discovered that, by administering a certain cocktail of growth factors, they can trigger cultured leukaemia cells to switch from cancer cells into healthy immune cells called macrophages.

Writing in PNAS, James Scott McClellan and his colleagues treated cultures of B-ALL cells with chemicals called cytokines which act as immune signals and trigger cells of the developing immune system to specialise.

When a cocktail containing the signals IL3, M-CSF, GM-CSF, IL7 and FLT-3L was added the unspecialised, rapidly-growing B-ALL cells, the cells turned into entities called macrophages, or "giant eaters" that lacked any cancerous features.

Unlike the B-ALL cells from which they came, which would rapidly cause cancers and kill experimental animals into which they were injected, the newly-made macrophages could be transplanted without harm, proving that they had lost their malignant potential.

And the macrophages were also fully functional and capable of engulfing bacteria, which is the normal role of macrophages in the body. This suggests that a treatment based on this approach might achieve a double benefit, nailing the malignancy and also bolstering the immune system in the process.

However, the results should be regarded with caution because the study was done only in a dish and has yet to be demonstrated in people. Also, not all of the cells in the culture responded to the growth signals, and even if only a small number slipped through the net this would be enough to bring the cancer back.

The researchers suggest that this might reflect the fact that their system hasn't yet been optimised. That said, other forms of leukaemia, including the condition acute promyelocytic leukaemia, are being "cured" with up to 95% success using these sorts of approaches.