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Kaipe, H. Cancer-Associated Fibroblasts and T Cells. Encyclopedia. Available online: (accessed on 24 June 2024).
Kaipe H. Cancer-Associated Fibroblasts and T Cells. Encyclopedia. Available at: Accessed June 24, 2024.
Kaipe, Helen. "Cancer-Associated Fibroblasts and T Cells" Encyclopedia, (accessed June 24, 2024).
Kaipe, H. (2021, June 29). Cancer-Associated Fibroblasts and T Cells. In Encyclopedia.
Kaipe, Helen. "Cancer-Associated Fibroblasts and T Cells." Encyclopedia. Web. 29 June, 2021.
Cancer-Associated Fibroblasts and T Cells

CAFs release a number of different factors, including chemokines, cytokines, and growth factors, that promote immunosuppression through recruitment of immunosuppressive cells such as T regulatory cells (Tregs) and myeloid cells, upregulation of immune checkpoint molecules on T cells, and regulation of T-cell migration.

pancreatic ductal adenocarcinoma (PDAC) cancer-associated fibroblasts (CAFs) T cells tumor microenvironment immune checkpoint inhibitors chemokines

1. Introduction

Pancreatic cancer is projected to be the second leading cause of cancer-related deaths in 2030 as a result of the lack of an effective treatment and the increasing incidence rate [1]. The only potential cure for pancreatic cancer is surgery, but due to its late detection only 15–20% of the diagnosed patients present with resectable tumors, and with surgery alone, less than 10% survive 5 years or more. Resection followed by chemotherapy increases the 5-year overall survival to only 16–20% [2][3]. The standard treatment for unresectable tumors is chemotherapy but the median overall survival is at best 16 months [4].

Although cancer immunotherapy has been shown to be effective against a variety of cancers during the last decade, there is very little progress in pancreatic cancer [5]. The majority of pancreatic tumors are defined as pancreatic ductal adenocarcinoma (PDAC), which is characterized by a dense stroma surrounding the cancer cells [6]. Release of extracellular matrix components by CAFs triggers fibrosis which obstructs the intra-tumoral vessels and prevents therapy delivery and infiltration of tumor-reactive immune cells. Therefore, it is likely that immunotherapy combined with other treatments targeting the stromal barrier could be promising for pancreatic cancer patients.

CAFs release a number of different factors, including chemokines, cytokines, and growth factors, that promote immunosuppression through recruitment of immunosuppressive cells such as T regulatory cells (Tregs) and myeloid cells, upregulation of immune checkpoint molecules on T cells, and regulation of T-cell migration. It is still not well understood which factors are involved in regulating T-cell exhaustion and migration. However, several recent studies and subsequent clinical trials support that reprogramming of the suppressive microenvironment by blocking certain chemokine/chemokine receptor axes can improve immunotherapy outcomes in pancreatic cancer patients.

2. Therapeutic Treatments to Target CAF-Derived Immunosuppressive Factors

Several clinical trials have evaluated the benefit of targeting immunosuppressive factors in pancreatic cancer patients measured by clinical outcomes. However, to our knowledge, there are no studies investigating the effects on the immune profile after therapy. Table 1 includes a summary of the completed and active clinical trials targeting CAF-derived immunosuppressive factors in pancreatic cancer.

Table 1. Immunosuppressive targets in the pancreatic tumor microenvironment used in preclinical models and clinical trials with the reported observations on the effects on immune cells and the primary end point of the clinical trial.
Target Observations in Preclinical Models [ref] CLINICAL TRIALS
NCT Treatment Phase Condition Status Primary Endpoint//
Observations [ref]
    NCT00841191 Siltuximab I/II Unresectable Completed CBR//
No benefit
=inflammatory cytokines
=Angiogenesis markers
↓pSTAT3 [67]
NCT02767557 Tocilizumab
II Unresectable Recruiting OS
IL-6 + ICI
  ↓Tumor growth
↑T-cell infiltration [68]
NCT04258150 Nivolumab
II Unresectable Active ORR
NCT04191421 Siltuximab
I/II Unresectable Recruiting Determine dose
    NCT00176813 Celecoxib
II Unresectable Completed OS//
No benefit [69]
II Unresectable Completed DFS/OS/tolerability//
No benefit
↓VEGF [70]
II Unresectable Completed Toxicity/ORR//
↓CA19.9 [71]
II Unresectable Completed Toxicity/ORR//
↓CA19.9 [72]
NCT03838029 Etodolac
II Resectable Recruiting DFS/biomarkers in blood
NCT03498326 Celecoxib
II Resectable Recruiting DFS
COX-2 + ICI            
  ↓Tumor growth
↑CD8+ T-cell infiltration [73]
NCT03878524 Multiple drugs including Celecoxib
II Unresectable Recruiting Find the best combination of drugs
    NCT00844064 AP 12009 I Unresectable Completed MTD//
NCT04624217 SHR-1701 I/II Unresectable Recruiting RP2D/ORR
NCT03666832 TEW-7197 I/II Unresectable Recruiting DFS
NCT03685591 PF-06952229
I Unresectable Recruiting DLT
TGF-β + ICI            
  ↓Tumor growth
↑T-cell infiltration
↑CD8+ T-cell cytotoxicity [74,75]
NCT02734160 Galunisertib
I Unresectable Completed DLT//
Limited effects [76]
NCT04429542 BCA101
I Unresectable Recruiting Safety/tolerability/DLT
NCT02947165 NIS793
I Unresectable Active DLT
ref, reference; ICI, immune checkpoint inhibitor; NCT, identifier; CBR, clinical benefit response; OS, overall survival; ORR, objective response rate; DSF, disease-free survival; MTD, maximum tolerated dose; RPD2, recommended phase 2 dose; DLT, dose-limiting toxicities; CA19.9, carbohydrate antigen; =, no changes; ↓, decrease; ↑, increase; //, separation between primary endpoint and observations.

A phase I/II clinical trial (NCT00841191) assessing the safety and efficacy of anti-IL-6, siltuximab, administered as a monotherapy to patients with pancreatic cancer, showed a good tolerance, but did not detect any clinical benefit [7]. The efficacy of anti-IL-6 combined with immune checkpoint inhibitors or with chemotherapy is currently being studied in several clinical trials (NCT04258150, NCT04191421).

The benefits of the COX-2 inhibitor, celecoxib, administered in combination with standard chemotherapy treatment, have been studied in several phase II clinical trials [8][9][10][11]. The treatment was well tolerated by the patients in all the studies but with varying clinical effects. Another study showed a 4-fold increase in one-year overall survival for patients treated with combination therapy compared to chemotherapy alone [11]. The benefits of COX-2 inhibitors are being further investigated in several clinical trials (NCT03838029, NCT03498326, NCT03878524).

A phase I clinical trial (NCT02734160) evaluating anti-TGF-β-R1 combined with anti-PD-L1 in metastatic pancreatic cancer patients showed limited clinical effects with an objective response rate of only 3% and a median overall survival of 5 months [12]. The synergistic effect of anti-TGF-β and immune checkpoint inhibitors is being evaluated in different ongoing clinical trials (NCT04624217, NCT04429542, NCT02947165). Furthermore, a phase I/II clinical trial (NCT00844064) with advanced pancreatic cancer patients who received the TGF-β2 anti-sense oligonucleotide, OT-101, followed by subsequent chemotherapy, showed an improved overall survival [13]. Further clinical trials with anti-TGF-β are ongoing (NCT03666832, NCT03685591).

3. Therapeutic Treatments to Target Chemokines

T-cell infiltration into the tumor nest is crucial for a good prognosis in pancreatic cancer patients. As described above, many antagonists have been tested in preclinical animal models. However, only a few are currently being evaluated in clinical trials to treat pancreatic cancer patients. These include blocking of CCR2, CCR5, CXCR2, and CXCR4.Table 2 includes a summary of the completed and active clinical trials targeting chemokine receptors in pancreatic cancer.

Table 2. Inhibitors of chemokines used in preclinical models and clinical trials with the reported observations on the effects on immune cells and the primary endpoint of the clinical trials.
Target Observations in Preclinical Models [ref] CLINICAL TRIALS
NCT Treatment Phase Condition Status Primary Endpoint//
Observations [ref]
  + CXCR2 target:
↓ MDSC infiltration [113]
NCT01413022 PF-04136309
Ib Unresectable Completed Optimal dose and toxicity//
↑CD8+ and CD4+ T-cell infiltration [114]
NCT02732938 PF-04136309
Ib/II Unresectable Completed DLT//
No benefit
Pulmonary toxicity [115]
CCR5 + ICI          
    NCT04721301 Maraviroc
I Unresectable Active Safety and tolerability
CCR2 + CCR5 + ICI            
    NCT03184870 Multiple drugs including BMS813160
I/II Unresectable Active Toxicity/Tregs numbers/ORR/PFS
CXCR1/2 + ICI          
  ↑ CD4+ and CD8+ T-cell infiltration [116,117]
↑ CD4+ and CD8+ T-cell cytotoxicity [116]
↓Neutrophils [116]
↓Tregs [117]
NCT04477343 SX-682
I Unresectable Recruiting MTD
CXCL12/CXCR4 axis            
    NCT02179970 AMD3100 I Unresectable Completed Safety//
↑ T-cell, NK-cell infiltration and activation
↑ B-cell activation
↓CXCL8 [118]
CXCL12/CXCR4 axis + ICI            
  ↑CD8+ T-cell infiltration and cytotoxicity [51] NCT03168139 NOX-A12
I/II Unresectable Completed Safety//
Stable disease
↑Th1 cytokines [119]
NCT02826486 BL-0840
IIa Unresectable Completed ORR//
↑CD8+ T-cell infiltration
↓Tregs [120]
NCT04177810 AMD3100
II Unresectable Recruiting ORR
NCT02907099 BL-0840
II Unresectable Active ORR
NCT04543071 BL-0840
II Unresectable Recruiting ORR
ref, reference; NCT, identifier; ↓, decrease; ↑, increase; MDSC, myeloid-derived suppressor cells; TAM, tumor-associated macrophages; ICI, immune checkpoint inhibitor; NK, natural killer cells; Th1, T helper type 1 cells; OS, overall survival; DLT, dose-limiting toxicities; ORR, objective response rate; PFS, progression-free survival; MTD, maximum tolerated dose; // separation between primary endpoint and observations.

The safety and the efficacy of CCR2 blockade with PF-04136309, in combination with chemotherapy (folfirinox), has been shown in a phase Ib clinical trial in pancreatic cancer patients with advanced or borderline resectable tumors [14]. Blockade of the CCL2/CCR2 chemokine axis was well tolerated by the patients, which also showed a partial response. Combination treatment with chemotherapy resulted in a reduction in tumor-associated macrophages and an increased number of CD8+and CD4+T cells in the primary tumor compared to chemotherapy alone [14]. However, another safety and pharmacokinetics/pharmacodynamics phase Ib study which combined PF-04136309 and chemotherapy (gemcitabine/nab-paclitaxel) in patients with metastatic PDAC showed no significant improvement compared to chemotherapy alone but showed possible toxic effects in the lungs [15].

Preclinical models in pancreatic cancer have shown that inhibition of the CCL5/CCR5 axis with maraviroc leads to tumor cell apoptosis and growth arrest [16]. Clinical trials in colorectal cancer with this drug (NCT01736813, NCT03274804) have shown promising results [17][18], with reduced proliferation of tumor cells and a shift towards M1 macrophages in one of the trials [17]. After these encouraging results, clinical trials with maraviroc combined with immune checkpoint inhibitors are currently ongoing for metastatic pancreatic cancer (NCT04721301). To boost the specific and encouraging effects of CCR2 and CCR5 antagonists, a phase Ib/II clinical trial with dual blockade of CCR2 and CCR5 with BMS 813160 as a monotherapy or in combination with chemotherapy or immunotherapy is currently ongoing for advanced pancreatic cancer patients (NCT03184870)

Another chemokine antagonist that has been shown to alter the tumor immune environment is the CXCR1/2 antagonist SX-682. The main function of CXCR2 is to regulate the recruitment and migration of neutrophils and MDSCs. SX-682 has been shown to enhance Th1 immune response in several animal models including melanoma, breast, lung, and prostate cancer [19][20][21]. This inhibitor is currently undergoing a safety evaluation in a phase I clinical trial for pancreatic cancer patients in combination with anti-PD-1 treatment (NCT04477343).

The CXCL12/CXCR4 axis excludes effector T cells from the tumor nests, impacting the efficacy of immune checkpoint inhibitors. The administration of the CXCR4 antagonist AMD3100 induced CD8+T cells infiltration and promoted a rapid activation and response of intratumoral T cells, natural killer cells, and B cells in a phase I clinical trial for metastatic PDAC [22]. The safety and clinical benefit of AMD3100 combined with anti-PD-1 treatment is being assessed in a phase II clinical trial (NCT04177810). A phase

4. Conclusions

Pancreatic CAFs have emerged as important regulators of the tumor microenvironment, both as restrainers of tumor growth but also as suppressors of tumor-reactive immunity. The recent discoveries about the diverse functions of different CAF subpopulations have significantly increased our understanding of the complex pancreatic stroma, but many questions still remain. The low mutational burden and the suppressive milieu in pancreatic cancer have been suggested to contribute to the lack of response to immune checkpoint inhibitors, but a key issue may be to assist T cells to efficiently come within close proximity of the malignant cells. Several lines of evidence suggest that chemokines and their cognate ligands play an important role in promoting T-cell exclusion from the tumor and further preclinical and clinical studies evaluating the role of chemokines are necessary to take full advantage of immune checkpoint therapeutics.


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