NK Cells in Hodgkin Lymphoma Are Impaired but Can Be Activated

NK cells represent the key component of the innate immune system to recognize and eliminate cancer cells. Defects in NK cell function including impaired cytotoxicity/cytokine secretion, aberrant receptor expression profile, NK cell number and NK cell anergy are reported in non Hodgkin lymphoma and correlate with a bad prognosis. So far, nothing is known about the phenotype of peripheral NK cells and serum levels of ligands for NK cell receptors in Hodgkin Lymphoma (HL) patients. Here, cytotoxicity, expression pattern of activating NK cell receptors and the serum levels of several ligands for the key cytotoxic receptors NKG2D and NKp30 are determined.

The cytotoxicity of NK cells isolated from HL patients was analysed by europium release assay using the HL cell line L428 as target cells. The serum level of the NKp30-ligand BAT3 and ligands for NKG2D (MICA, MICB and ULBP1,2,3) was estimated in sera of 117 HL patients and 40 healthy donors by ELISA. The expression pattern of NKp30, NKp44, NKp46, CD16 and the activation markers CD25, CD69 and CD71 was determined by 4-colour FACS analysis of peripheral blood lymphocytes.

The cytotoxicity assays reveal a significantly reduced killing efficacy of NK cells from HL patients against the Hodgkin cell line L428 in comparison to NK cells from healthy donors. Correlating with the impaired NK cell function, we observed that the serum level for BAT3 and MICA was significantly elevated in HL patients, whereas other ligands (MICB and ULBP1,2,3) remained unchanged. NKG2D showed a significantly decreased expression on NK cells of HL patients. No significant difference was observed for all other receptors and activation markers tested.

Our results suggest that soluble BAT3 and MICA, ligands for NKp30 and NKG2D, contribute to the NK cell inhibition in HL patients. Since soluble ligands for NK cell receptors are known to inhibit NK cell-cytotoxicity, the release of these ligands might represent an immune escape mechanism of HL tumors to avoid detection and killing by the innate immune system. To overcome NK cell inhibition in HL patients we design, express and purify bispecific proteins (immunoligands) that target NKG2D and a HL-specific tumorantigen. Work to activate HL-derived NK cells with immunoligands ex vivo will be discussed.

Engert:Affimed Therapeutics AG: Honoraria, Research Funding.