Reduced susceptibility of NK cells to cancer cells is associated with long term NK cell culture and over-expression of TIMP3

Natural killer (NK) cell/cancer cell conjugation leads to reciprocal cellular damage. Nature and specificity of this phenomenon in NK cells remain unclear. Using standard immunological methods, we assessed the effects of human and mouse cancer cells on human and mouse NK cells. Human, allogeneic, malignant cells triggered human NK cell alteration (NKCA) including FcgRIII (CD16) down-regulation, NK cell loss and apoptosis. In contrast, allogeneic peripheral blood mononuclear cells (PBMCs) depleted of NK cells failed to produce significant NKCA. Mouse allogeneic leukemia cells induced mouse NK cell loss and apoptosis while syngeneic, allogenic mouse splenocytes depleted of NK cells and xenogenic cancer cells did not, suggesting that NKCA preferentially involved allogeneic, malignant cells. After 10 days of PBMCs culture, in the absence of cancer cells, post-activated and unstimulated NK cells showed some CD16 antigen down-regulation. More importantly, they became resistant to cancer cell based NKCA but maintained their cytotoxic activity. Actinomycin D restored NKCA in the long term NK (LTNK) cells suggesting that the resistance to NKCA required de novo RNA transcription. TAPI-0,a functional analogue of the tissue inhibitors of metalloproteinases (TIMP) 3 inhibited cancer cell based NKCA underlying a role for a restricted number of metalloproteinases (MMPs) on the generation of this phenomenon. Finally, we found an association between TIMP3 gene over-expression and TIMP3 protein release in the supernatant of LTNK cells culture resistant to cancer cell based NKCA. This study provides evidence that TIMP3 plays a role in the protection of LTNK cells from cancer cell based NKCA.