Background: Multiple factors, including dense stroma and high infiltration of suppressive immune cells make pancreatic ductal adenocarcinoma (PDA) challenging to treat with immunotherapy. The presence of intra-tumoral T cells positively correlates with improved survival for PDA patients. Gamma chain cytokines (GCCs) can augment T cell mediated anti-tumor immunity and various GCC agonist drugs have been applied in clinical trials for cancer. Besides evaluating the effect of GCC derived agonists using recovered blood or biopsies of treated patients, it is challenging to mechanistically study the effect of GCCs on tumor-resident immune cells in human samples.

Methods: Here we apply organotypic slice culture of surgically resected tumor tissues to study the effect of GCCs on intra-tumoral immune cells. We treated slices of PDAs with GCCs (IL-2, IL-7, IL-15 and IL-21) for 6 days. Immune cells, especially T cells emigrated from the tumor slices into the culture supernatant. On day 6 we fixed intact tumor slices for multiplex immunohistochemistry (mIHC) and analyzed emigrated cells using flow cytometry.

Results: IL-15 and IL-7 potently induced T cell proliferation. The effect of IL-7 and IL-15 on T cell proliferation was higher for T cells that expressed markers of antigen experience such as CD39 and PD1 (Table 1). While IL-15 had the strongest effect on tumor-derived T cells, IL-15 and IL-7 were similar in their effect on T cells in the blood of the same patient, suggesting that IL-15 is especially effective in inducing the proliferation of tumor-infiltrating T cells. The effect of IL-15 on enhanced T cell proliferation was also seen within tumor slices, as revealed by mIHC.

Conclusion: Our data suggest that IL-15 is the most potent GCC at inducing in situ expansion of tumor-resident T cells, including T cells that show signs of antigen experience.

Table 1.

IL-15 induces in situ T cell proliferation in PDA.

AssayGroupsUntreatedIL-2IL-7IL-15IL-21
Parameter
Flow Cytometry %Ki67+CD8+cells of live cells 0.090.04 0.360.59 5.001.35 14.331.20 0.310.14 
 %CD39+CD103+of CD8+ 0.130.15 0.110.04 0.290.14 0.620.18 0.130.08 
 %PD1+of CD8+ 25.107.22 23.233.10 30.484.74 46.483.50 37.402.32 
mIHC %CD8+Ki67+ of all cells 0.16 0.04(n=2) 0.83 (n=1) 0.550.38(n=2) 2.200.04(n=2) 0.490.41(n=2) 
AssayGroupsUntreatedIL-2IL-7IL-15IL-21
Parameter
Flow Cytometry %Ki67+CD8+cells of live cells 0.090.04 0.360.59 5.001.35 14.331.20 0.310.14 
 %CD39+CD103+of CD8+ 0.130.15 0.110.04 0.290.14 0.620.18 0.130.08 
 %PD1+of CD8+ 25.107.22 23.233.10 30.484.74 46.483.50 37.402.32 
mIHC %CD8+Ki67+ of all cells 0.16 0.04(n=2) 0.83 (n=1) 0.550.38(n=2) 2.200.04(n=2) 0.490.41(n=2) 

n=4 slices for each group for flow cytometry. Data are from one experiment*. MeanSD is shown. Two doses (10-fold difference) for each cytokine were tested and results only for the low dose are shown.*Another experiment with groups IL-2 and IL-2+IL-15 was performed and had similar results for the effect of IL-15

Citation Format: Karan Kohli, Shihong Zhang, Xiuyun Jiang, Cynthia Hsu, Arezou Abbasi, Teresa S. Kim, Venu G. Pillarisetty. IL-15 is the most potent of tested gamma chain cytokines at inducing in situ proliferation of T cells in human pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 607.