Activated γδ T cells express the natural cytotoxicity receptor natural killer p44 and show cytotoxic activity against myeloma cells

Summary γδ T cells account for up to 10% of T lymphocytes in the peripheral blood of healthy donors. They can be activated by cytokines such as interleukin (IL)‐2, IL‐12 and IL‐15, express natural killer (NK) cell markers such as NKG2D and show cytotoxic activity against several tumour cells, including multiple myeloma. Here, we present activated polyclonal γδ T cells from healthy donors with an NK T cell‐like phenotype expressing the natural cytotoxicity receptor NKp44. Natural cytotoxicity receptors NKp30, NKp44 and NKp46 have been regarded as specific NK receptors; only two γδ T cell clones described so far expressed NKp44. Isolated polyclonal γδ T cells cultured for 7 days according to the cytokine‐induced killer cell (CIK) protocol with additional IL‐15 revealed a surface expression of NKp44 of 8 ± 7% ( n  = 22). This could be confirmed by detection of NKp44 mRNA by reverse transcription–polymerase chain reaction (RT–PCR). γδ T cells exhibited a marked cytotoxic activity against myeloma cells, which could be reduced by inhibition of NKp44. To our knowledge, this is the first description of the expression of NKp44 on polyclonal γδ T cells.