Abstract 1175: Interleukin-15 activates NK and CD8 T cells within the Prostate cancer microenvironment by expanding activatory NK cell receptors and attenuating inhibitory HLA ligands on tumor cells
Authors: Sakellariou Christina Alexandra , Elhage Oussama , Ukimura Osamu , Gill Inderbir , Smith Richard Anthony , Dasgupta Prokar , Galustian Christine 
Published: May 2015

Background

The prostate cancer microenvironment is profoundly immunosuppressive and NK and T cells infiltrating this environment are rendered anergic or suppressive. Recently, immunomodulatory checkpoints such as PDL1 have been shown to be important in this immunosuppression. Antibodies to such checkpoints have a moderate effect in suppressing tumor growth but many unknown immunosuppressive factors exist on tumor cells. We have shown that prostate cancer cells express many ligands that inhibit NK cell activity by binding to inhibitory Killer Ig like receptors (KIRs). These receptors are critical in modulating NK cell function. We have shown that IL-15, unlike other immunotherapeutic cytokines (e.g IL-12), increases NK and CD8-T-cell activity within the prostate cancer microenvironment. To investigate mechanisms of this activation, we studied effects of IL-15 on inhibitory and activatory receptors on NK cells and their corresponding ligands on prostate cancer cells.

Methods

The prostate cancer cell-lines PC3 and LNCaP were incubated with non-adherent PBMCs at effector:target ratios of 8:1 and cytokines IL-2 or IL-15. After 1 week, NK-cells in the cocultures were stained with antibodies to inhibitory KIRs (KIR2DL1,KIR2DL2,KIR3DL1) and activatory KIRs (NKp44,NKG2D, NKp46, and DNAM1). Tumor cells in the cocultures were stained with antibodies to inhibitory NK-receptor ligands HLA-class1-BW4 and HLA-G, and activatory receptor ligands Nectin-2 and MICA/MICB. Antibody to HLA-ABC was also used. Staining was followed by flow cytometric analysis.

Results

IL-15, but not IL-2 inhibited expression of the inhibitory-receptors KIR2DL1 and KIR3DL1 by upto 50%*on NK cells in PBMC-PCa cell cocultures. NKG2D was increased upto 40%* in these cells with IL-15 but not IL-2. On tumor cells, IL-15, but not IL-2 decreased the inhibitory-ligands HLA-Class-1-BW4 by upto 60%* on both LNCaP and PC3 cells. IL-15 also decreased the expression of HLA-G by 75%* on LNCaPs. HLA-A,B,C expression was increased by over 65%* in the two prostate cancer cell lines. Initial data showed that activatory-ligands were not affected on either PC3 or LNCaP tumor cells.

* =(p&lt;0.001,1-way-anova, post-hoc Newman-Keuls,n=5).

Conclusion

One mechanism by which IL-15 increases PCa killing by NK cells in PBMC-PCa cocultures is through upregulating activatory NKG2D and decreasing inhibitory KIR2DL1 and KIR3DL1 receptors. In addition, inhibitory ligands on PCa cells are downregulated, suggesting strong shifts toward NK activation vs inhibition in the cocultures. Increased HLA-A,B,C also favors stronger cytotoxic-T cell recognition. This suggests strong shifts toward NK activation vs inhibition in the cocultures. Increased HLA-A,B,C on the tumor cells also favors stronger cytotoxic-T cell recognition. The molecular basis of these effects are currently being investigated.

Citation Format: Christina Alexandra Sakellariou, Oussama Elhage, Osamu Ukimura, Inderbir Gill, Richard Anthony Smith, Prokar Dasgupta, Christine Galustian. Interleukin-15 activates NK and CD8 T cells within the Prostate cancer microenvironment by expanding activatory NK cell receptors and attenuating inhibitory HLA ligands on tumor cells. [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 1175. doi:10.1158/1538-7445.AM2014-1175