Carcinoma-associated pancreatic fibroblasts (CAFs) are the major type of cells in the stroma of pancreatic ductal adenocarcinomas and besides their pathological release of extracellular matrix proteins, they are also perceived as key contributors to immune evasion. Despite the known relevance of tumor infiltrating lymphocytes in cancers, the interactions between T-cells and CAFs remain largely unexplored. Here, we found that CAFs isolated from tumors of pancreatic cancer patients undergoing surgical resection ( n = 15) expressed higher levels of the PD-1 ligands PD-L1 and PD-L2 compared to primary skin fibroblasts from healthy donors. CAFs strongly inhibited T-cell proliferation in a contact-independent fashion. Blocking the activity of prostaglandin E 2 (PGE 2 ) by indomethacin partially restored the proliferative capacity of both CD4 + and CD8 + T-cells. After stimulation, the proportion of proliferating T-cells expressing HLA-DR and the proportion of memory T-cells were decreased when CAFs were present compared to T-cells proliferating in the absence of CAFs. Interestingly, CAFs promoted the expression of TIM-3, PD-1, CTLA-4 and LAG-3 in proliferating T-cells. Immunohistochemistry stainings further showed that T-cells residing within the desmoplastic stromal compartment express PD-1, indicating a role for CAFs on co-inhibitory marker expression also in vivo . We further found that PGE 2 promoted the expression of PD-1 and TIM-3 on T-cells. Functional assays showed that proliferating T-cells expressing immune checkpoints produced less IFN-γ, TNF-α, and CD107a after restimulation when CAFs had been present. Thus, this indicates that CAFs induce expression of immune checkpoints on CD4 + and CD8 + T-cells, which contribute to a diminished immune function.

Acute graft-versus-host disease (GvHD) is a severe adverse event after stem cell transplantation. Bone marrow-derived mesenchymal stromal cells (BM-MSCs) have been used to treat GvHD, but decidual stromal cells (DSCs) isolated from term fetal membrane have advantages compared with BM-MSCs, including increased allosuppression, unlimited supply, and high expression of integrins. We introduced the use of DSCs in patients with steroid refractory aGvHD. In this study, we investigated factors of importance in the reduction of alloreactivity by DSCs. We found that DSCs need to have cell-cell contact in order to mediate suppression in mixed lymphocyte reactions (MLRs). This contact dependency is consistent with an increased frequency of CD4(+)CD25(high)FOXP3(+) regulatory T cells (Tregs) and an augmented intensity of CD25 expression in CD4(+) T cells. Blocking of the activity of indoleamine-2,3-dioxygenase (IDO), prostaglandin E2, PD-L1, and IFN-γ impaired the antiproliferative ability of the DSCs in MLRs. Neutralization of IDO also reduced the frequency of Tregs. In contrast to BM-MSCs, pretreatment of DSCs with high concentrations of IFN-γ (100 U/mL) reduced their ability to suppress alloreactivity, but stimulation of DSCs with MLR supernatants containing low levels of IFN-γ had no effect on the suppressive capacity in MLR. To conclude, DSCs differ in several aspects from MSCs and need to be close to alloreactive lymphocytes to mediate a suppressive effect and increase the frequency of Tregs. Thus, DSCs may not only use paracrine factors for systemic immunosuppression, but also more specifically target T cells locally in affected tissues.

During pregnancy, the maternal immune system must tolerate the developing foetus, and yet retain a potent antimicrobial response to prevent infections. Mucosal associated invariant T (MAIT) cells recognize microbial-derived vitamin B metabolites presented on the MR1 molecule, but their presence and function at the foetal-maternal interface is not known. We here isolated mononuclear cells from paired samples of peripheral blood (PB), intervillous blood (IVB), and decidua parietalis (DP) following uncomplicated term pregnancies. Interestingly, MAIT cells were highly enriched in IVB compared to PB and DP. The activation status of IVB MAIT cells was similar to that of PB MAIT cells, except for a lower expression of PD-1. Both IVB MAIT cells and conventional T cells were more dominated by an effector memory phenotype compared to PB MAIT cells and T cells. IVB MAIT cells also responded more vigorously with expression of IFN-γ, granzyme B, and perforin in response to Escherichia coli stimulation compared to PB. MR1 was not expressed in syncytiotrophoblasts, but in placental villous and decidual macrophages. These data indicate that maternal MAIT cells accumulate in the intervillous space of the placenta and that they are highly armed to quickly respond if bacteria are encountered at the foetal-maternal interface.