Current paradigms of cancer-centric therapeutics are usually not sufficient to eradicate the malignancy, as the cancer stroma may prompt tumour relapse and therapeutic resistance. Among all the stromal cells that populate the tumour microenvironment, cancer-associated fibroblasts (CAFs) are the most abundant and are critically involved in cancer progression. CAFs regulate the biology of tumour cells and other stromal cells via cell–cell contact, releasing numerous regulatory factors and synthesizing and remodelling the extracellular matrix, and thus these cells affect cancer initiation and development. The recent characterization of CAFs based on specific cell surface markers not only deepens our insight into their phenotypic heterogeneity and functional diversity but also brings CAF-targeting therapies for cancer treatment onto the agenda. In this Review, we discuss the current knowledge of biological hallmarks, cellular origins, phenotypical plasticity and functional heterogeneity of CAFs and underscore their contribution to cancer progression. Moreover, we highlight relevant translational advances and potential therapeutic strategies that target CAFs for cancer treatment. Cancer-associated fibroblasts (CAFs) are often the most abundant cell type in the tumour microenvironment. Here, Song and colleagues discuss how to target or harness these cells for cancer therapy. They highlight the progress made to date and the remaining challenges in bringing CAF-targeted therapies to the clinic.

Turning foes to friends: targeting cancer-associated fibroblasts

Among all the stromal cells that present in the tumor microenvironment, cancer-associated fibroblasts (CAFs) are one of the most abundant and critical components of the tumor mesenchyme, which not only provide physical support for tumor cells but also play a key role in promoting and retarding tumorigenesis in a context-dependent manner. CAFs have also been involved in the modulation of many components of the immune system, and recent studies have revealed their roles in immune evasion and poor responses to cancer immunotherapy. In this review, we describe our current understanding of the tumorigenic significance, origin, and heterogeneity of CAFs, as well as the roles of different CAFs subtypes in distinct immune cell types. More importantly, we highlight potential therapeutic strategies that target CAFs to unleash the immune system against the tumor.

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Cancer-associated fibroblasts: an emerging target of anti-cancer immunotherapy.

Obstacles Posed by the Tumor Microenvironment to T cell Activity: A Case for Synergistic Therapies

Lactate has long been considered a “waste” by-product of cell metabolism, and it accumulates at sites of inflammation. Recent findings have identified lactate as an active metabolite in cell signalling, although its effects on immune cells during inflammation are largely unexplored. Here we ask whether lactate is responsible for T cells remaining entrapped in inflammatory sites, where they perpetuate the chronic inflammatory process. We show that lactate accumulates in the synovia of rheumatoid arthritis patients. Extracellular sodium lactate and lactic acid inhibit the motility of CD4+ and CD8+ T cells, respectively. This selective control of T cell motility is mediated via subtype-specific transporters (Slc5a12 and Slc16a1) that we find selectively expressed by CD4+ and CD8+ subsets, respectively. We further show both in vitro and in vivo that the sodium lactate-mediated inhibition of CD4+ T cell motility is due to an interference with glycolysis activated upon engagement of the chemokine receptor CXCR3 with the chemokine CXCL10. In contrast, we find the lactic acid effect on CD8+ T cell motility to be independent of glycolysis control. In CD4+ T helper cells, sodium lactate also induces a switch towards the Th17 subset that produces large amounts of the proinflammatory cytokine IL-17, whereas in CD8+ T cells, lactic acid causes the loss of their cytolytic function. We further show that the expression of lactate transporters correlates with the clinical T cell score in the synovia of rheumatoid arthritis patients. Finally, pharmacological or antibody-mediated blockade of subtype-specific lactate transporters on T cells results in their release from the inflammatory site in an in vivo model of peritonitis. By establishing a novel role of lactate in control of proinflammatory T cell motility and effector functions, our findings provide a potential molecular mechanism for T cell entrapment and functional changes in inflammatory sites that drive chronic inflammation and offer targeted therapeutic interventions for the treatment of chronic inflammatory disorders.

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Lactate Regulates Metabolic and Pro-inflammatory Circuits in Control of T Cell Migration and Effector Functions.

Pancreatic ductal adenocarcinoma (PDA) exhibits one of the poorest prognosis of all solid tumours and poses an unsolved problem in cancer medicine. Despite the recent success of two combination chemotherapies for palliative patients, the modest survival benefits are often traded against significant side effects and a compromised quality of life. Although the molecular events underlying the initiation and progression of PDA have been intensively studied and are increasingly understood, the reasons for the poor therapeutic response are hardly apprehended. One leading hypothesis over the last few years has been that the pronounced tumour microenvironment in PDA not only promotes carcinogenesis and tumour progression but also mediates therapeutic resistance. To this end, targeting of various stromal components and pathways was considered a promising strategy to biochemically and biophysically enhance therapeutic response. However, none of the efforts have yet led to efficacious and approved therapies in patients. Additionally, recent data have shown that tumour-associated fibroblasts may restrain rather than promote tumour growth, reinforcing the need to critically revisit the complexity and complicity of the tumour-stroma with translational implications for future therapy and clinical trial design.

/pdf/stromal-biology-and-therapy-in-pancreatic-cancer-a-changing-k8esnyy0o3.pdf

Stromal biology and therapy in pancreatic cancer: a changing paradigm

https://www.gastrojournal.org/article/S0016-5085(13)01076-7/pdf

Activated Pancreatic Stellate Cells Sequester CD8+ T Cells to Reduce Their Infiltration of the Juxtatumoral Compartment of Pancreatic Ductal Adenocarcinoma

Abasi Ene–Obong

Papers

Activated Pancreatic Stellate Cells Sequester CD8+ T Cells to Reduce Their Infiltration of the Juxtatumoral Compartment of Pancreatic Ductal Adenocarcinoma