Loss of SMAD4 Is Associated With Poor Tumor Immunogenicity and Reduced PD-L1 Expression in Pancreatic Cancer

Abstract

Transforming Growth Factor β (TGFβ) is a key mediator of immune evasion in pancreatic ductal adenocarcinoma (PDAC), and the addition of TGFβ inhibitors in select immunotherapy regimens shows early promise. Though the TGFβ target SMAD4 is deleted in approximately 55% of PDAC tumors, the effects of SMAD4 loss on tumor immunity have yet to be fully explored. Using a combination of genomic databases and PDAC specimens, we found that tumors with loss of SMAD4 have a comparatively poor T-cell infiltrate. SMAD4 loss was also associated with a reduction in several chemokines with known roles in T-cell recruitment, which was recapitulated using knockdown of SMAD4 in PDAC cell lines. Accordingly, JURKAT T-cells were poorly attracted to conditioned media from PDAC cells with knockdown of SMAD4 and lost their ability to produce IFNγ. However, while exogenous TGFβ modestly reduced PD-L1 expression in SMAD4-intact cell lines, SMAD4 and PD-L1 positively correlated in human PDAC samples. PD-L1 status was closely related to tumor-infiltrating lymphocytes, particularly IFNγ-producing T-cells, which were more abundant in SMAD4-expressing tumors. Low concentrations of IFNγ upregulated PD-L1 in tumor cells in vitro, even when administered alongside high concentrations of TGFβ. Hence, while SMAD4 may have a modest inhibitory effect on PD-L1 in tumor cells, SMAD4 indirectly promotes PD-L1 expression in the pancreatic tumor microenvironment by enhancing T-cell infiltration and IFNγ biosynthesis. These data suggest that pancreatic cancers with loss of SMAD4 represent a poorly immunogenic disease subtype, and SMAD4 status warrants further exploration as a predictive biomarker for cancer immunotherapy.

Loss of functionSMAD4nonstop mutations in human cancer

“…15 Loss of SMAD4 expression has been associated with poor survival in multiple tumour types, including pancreatic, 16 colon, 17 and oesophageal 18 cancers. Loss of SMAD4 is also associated with decreased lymphocyte infiltration of tumoral and peritumoral tissue, 19 decreased responsiveness to immune checkpoint inhibitor therapy, 20 increased resistance to 5-fluorouracil 21 and radiotherapy, 22 and increased invasion and metastasis. 23 Paiella et al found that among patients with locally-advanced pancreatic cancer treated with radiofrequency ablation, cancers with retained SMAD4 expression had a better response to treatment than cancers with loss of SMAD4 expression.…”

The effect of SMAD4 on the prognosis and immune response in hypopharyngeal carcinoma

“…Kim et al suggested that Smad4-dependent signaling in T cells makes decreases the susceptibility to spontaneous gastrointestinal tumorigenesis by maintaining homeostasis, indicating that SMAD4 signaling in T cells is required to suppress gastrointestinal cancer ( 35 ). Furthermore, Principe et al suggested that SMAD4-intact increased T cell infiltration by recruiting more T cells and therefore SMAD4 is an indicator of a survival advantage in patients with pancreatic ductal carcinoma ( 36 ). SMAD4 is required for the differentiation of CD8 + T cells during inflammatory response ( 37 , 38 ).…”

Leukocyte subtyping predicts for treatment failure and poor survival in anal squamous cell carcinoma

“…Results were arranged by the Tukey method. Time-to-event survival data was evaluated via the Kaplan-Meier method [21,22]. Data were considered significant at p < 0.05 unless otherwise noted.…”