Abstract 4836: Immune-tolerance due to aberrant expression of Natural Killer-Cell Immunoglobulin-like Receptors (KIRs) on cancer cells and enhanced cancer-platelet interactions
Authors: Chan Daniel C. , Zhang Zhiyong , Zheng Di , Chan Tiffany , Berg Mary , Horwitz Kathryn , Ahn Natalie , Lanier Lewis , Bunn Paul 
Published: May 2015

Abstract
Background: Metastatic cancer cells spread through blood vessels where they constantly interact with platelets and leukocytes, forming tumor microemboli and thereby protected from otherwise rapid elimination from host immune defense cells such as NK cells. We previously demonstrated that metastatic cancer cells with aberrant expression or with forced ectopic expression of Natural Killer Immunoglobulin-like Receptors (KIRs) are more resistant to NK killing than those with null or low KIR expression. Here we report that KIR-expressing cancer cells interact more strongly with platelets leading to significantly increase in NK tolerance than those cancer cells with null or low KIR expression. We have demonstrated that certain anti-platelet antagonists are capable of reversing the NK tolerance of these cancer cells in vitro.
Methods: Aberrant expressions of KIR genes in metastatic cancers derived from orthotopic rat models were detected by DNA microarray analysis and verified with immunohistochemistry and flow cytometry. Stable transformants with ectopic expression of KIR2DL1 or KIR3DL1 were enriched by cell sorting. Binding of cancer cells with human platelets were analyzed by flow cytometry. NK killing of GFP-tagged cancer cells with differential KIR expressions in the presence and absence of human platelets, with or without pretreatment of anti-platelet antagonists or anti-KIR antibodies, was accessed with a fluorescent plate reader.
Results: Using in vitro NK cytotoxic assays, we have found that KIR (aberrant or ectopic) expression or platelet coating on cancers clearly increased their resistance to NK cell killing when compared with parental cells. Interestingly, platelet coating on those metastatic cancer cells with high (aberrant or ectopic) KIR expression increased their IC50 values by 6 to 14 folds respectively when compared with parental cells. We show that NK tolerance correlates positively with platelet coating and the levels of KIR expression on the cancer cells (with correlation coefficient = 0.90 to 0.98), and that the NK resistance is significantly increased when both KIR aberrant expression and platelet coating are present on the cancer cells. However, pretreatment with anti-KIR antibodies and anti-platelet antagonists effectively reverse NK resistance.
Conclusion: Aberrant KIR expression on cancer cells enhances their interaction with platelets leading to significant increase in NK tolerance. Anti-platelet antagonists and anti-KIR antibodies alone or in combination may have clinical potential for the treatment or prevention of metastatic and immune resistant cancer cells.
Citation Format: Daniel CF Chan, Zhiyong Zhang, Di Zheng, Tiffany Chan, Mary Berg, Kathryn Horwitz, Natalie Ahn, Lewis Lanier, Paul Bunn. Immune-tolerance due to aberrant expression of Natural Killer-Cell Immunoglobulin-like Receptors (KIRs) on cancer cells and enhanced cancer-platelet interactions. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4836. doi:10.1158/1538-7445.AM2014-4836