Natural killer cell therapy

NK cells make up roughly 5-20% of the lymphocytes (a type of white blood cell) circulating in your blood. They belong to the innate immune system, the fast-response arm that acts within hours.

Researchers first described NK cells in 1975, after noticing lymphocytes that killed tumour cells in the laboratory with no prior exposure to them. Most immune cells need to be shown a specific target before they act but the benefit of NK cells is that they arrive ready.

Natural Killer cells are constantly weighing two kinds of signal:

• Stop signals. Healthy cells carry molecules called MHC class I on their surface, inhibitory receptors tell NK cells it to stand down.
• Go signals. Cells under stress, including many cancer cells, display distress markers on their surface. Activating receptors on the NK cell, such as NKG2D, pick these up.

Many cancer cells hide from T-cells (part of the adaptive immune system) by reducing their MHC class I badges, but this removes the stop signal for NK cells which is one reason NK cells are seen as a complement to T-cell-based treatments rather than a duplicate of them.

When the go signals win, the NK cell attaches to its target and releases two proteins, perforin and granzymes. Perforin opens small pores in the target cell's membrane; granzymes pass through and trigger the cell's built-in self-destruct process (apoptosis). NK cells also release messenger molecules, including interferon-gamma, that help recruit and activate other parts of the immune system.

NK cell therapy is usually considered for people whose immune defences may be under strain, from the cancer itself, from conventional treatment, or both.

We review proposed cellular treatment alongside your medical history and current oncology plan. Suitability is assessed individually. Our doctors look at cancer type and stage, current and recent treatments, blood counts, immune function and overall health as NK cell therapy may not be appropriate for everyone.

The clearest results so far come from blood cancers and from studies that combine NK cells with other treatments. In solid tumours, NK cell therapy has generally been well tolerated, with response rates that vary widely by cancer type, cell source and combination partner.

Two patterns stand out across the research. NK cells appear to do more when combined with another treatment than on their own. And cells from healthy donors have tended to outperform a patient's own cells, likely because a patient's NK cells may already be weakened by cancer and prior treatment.