Abstract 3656: Therapeutic effects of anti-KIR antibodies against metastatic cancer cells with aberrant expression of Natural Killer-Cell Immunoglobulin-like Receptors (KIRs)

Background: The aim of this study is to investigate the mechanism of immune-escape and cancer metastasis due to an aberrant expression of the natural killer (NK) cell immunoglobulin-like receptors (KIRs) on human lung cancer. We previously reported that metastatic cancer cells acquired immune-resistance by aberrantly expressing KIRs on their surface (AACR 2009 and 2010). Here we report the effects of anti-KIR antibodies on the cancer cells with aberrant expression of KIRs enhanced cytolytic killing of cancer cells by human Natural Killer cells. Method: KIR2DL1 (LL454) and KIR3DL1 (LL456) plasmids were used to transfect target cells (H2122-GFP) for individual KIR subtype or both KIR subtype expression. Stable transformants (termed as 2DL1 or 3DL1) were enriched by cell sorting. H2122 parental and KIR expressing cells were pre-treated with two different anti-KIR antibodies respectively (DX9 or DX27) and then exposed to various amounts of human NK-92MI cell line. Anti-proliferative effects by NK cells were accessed by a fluorescent microplate reader. IC50s were determined based on the Effector (NK) / Target Ratio (ETR). Result: When exposed to various amount of NK-92MI cell line, the parental line was most sensitive to NK-92MI killing with an IC50 ETR=1.12, followed by 2DL1(1.8), KIR3+ (1.8) and 3DL1 (3.5). After these cancer cells were pretreated with anti-KIR2DL2/3 antibodies (DX27) or anti-KIR3DL1 antibodies (DX9) respectively, sensitivities (based on IC50 ETR) to NK killing were all downshifted when compared to the untreated samples respectively. (a) After DX27 pretreatment: parent decreased by 3.3 folds (ETR 1.10 → 0.33), KIR3+ decreased by 3.3 folds (ETR 1.9 → 0.57), 2DL1 decreased by 5 folds (ETR 1.8 → 0.36), and 3DL1 decreased by 7.9 folds (ETR 3.4 → 0.43). (b) After DX9 pretreatment: parent decreased by 1.9 folds (ETR 1.13 → 0.58), KIR3+ decreased by 2.71 folds (ETR 1.9 → 0.7), 2DL1 decreased by 3.27 folds (ETR 1.8 →0.55) and 3DL1 decreased by 6.3 folds (ETR 3.5 → 0.56) respectively. Our data clearly demonstrated that aberrant expression of KIR on lung cancer cells either by in vivo immune selection in orthotopic nude rat model or by forced expression of KIRs confers resistance to NK cytolytic killing. Pretreatment with anti-KIR antibodies not only reversed resistance but increased their sensitivity to NK cytolytic killing. Conclusion: We have discovered a novel mechanism of immune resistance to NK cells due to aberrant expressions of KIRs on cancer cells. This immune resistance can be reversed by the treatment with anti-KIR antibodies, suggesting that anti-KIR antibodies have clinical potential for the treatment of aggressive and immune resistant cancer cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3656. doi:10.1158/1538-7445.AM2011-3656