NFκB in Pancreatic Stellate Cells Reduces Infiltration of Tumors by Cytotoxic T Cells and Killing of Cancer Cells, via Up-regulation of CXCL12.

Background & Aims: Immunotherapies are ineffective against pancreatic cancer. We investigated whether the activity of nuclear factor (NF)κB in pancreatic stromal cells contributes to an environment that suppresses antitumor immune response.

Methods: Pancreata of C57BL/6 or Rag1 mice were given pancreatic injections of a combination of Kras; Trp53 ; Pdx-1cre (KPC) pancreatic cancer cells and pancreatic stellate cells (PSCs) extracted from C57BL/6 (control) or mice with disruption of the gene encoding the NFκB p50 subunit (Nfkb1 or p50 mice). Tumor growth was measured as an endpoint. Other mice were given injections of Lewis lung carcinoma (LLC) lung cancer cells or B16-F10 melanoma cells with control or p50 fibroblasts. Cytotoxic T cells were depleted from C57BL/6 mice by administration of antibodies against CD8 (anti-CD8), and growth of tumors from KPC cells, with or without control or p50 PSCs, was measured. Some mice were given an inhibitor of CXCL12 (AMD3100) and tumor growth was measured. T-cell migration toward cancer cells was measured using the Boyden chamber assay.

Results: C57BL/6 mice coinjected with KPC cells (or LLC or B16-F10 cells) and p50 PSCs developed smaller tumors than mice given injections of the cancer cells along with control PSCs. Tumors that formed when KPC cells were injected along with p50 PSCs had increased infiltration by activated cytotoxic T cells along with decreased levels of CXCL12, compared with tumors grown from KPC cells injected along with control PSCs. KPC cells, when coinjected with control or p50 PSCs, developed the same-size tumors when CD8 T cells were depleted from C57BL/6 mice or in Rag1 mice. The CXCL12 inhibitor slowed tumor growth and increased tumor infiltration by cytotoxic T cells. In vitro expression of p50 by PSCs reduced T-cell migration toward and killing of cancer cells. When cultured with cancer cells, control PSCs expressed 10-fold higher levels of CXCL12 than p50 PSCs. The CXCL12 inhibitor increased migration of T cells toward KPC cells in culture.

Conclusions: In studies of mice and cell lines, we found that NFκB activity in PSCs promotes tumor growth by increasing expression of CXCL12, which prevents cytotoxic T cells from infiltrating the tumor and killing cancer cells. Strategies to block CXCL12 in pancreatic tumor cells might increase antitumor immunity.