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)kappa B 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(G12D/+); Trp53(R172H/+); 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 NF kappa B 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 NF kappa B 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.