Final Report Summary - PANCREATIC CANCER (Pancreatic stellate cells - sentinels for tissue damage?)
Final report
Grant agreement number: 237667
'Pancreatic stellate cells - sentinels for tissue damage?'
Christine Feig, Cambridge research institute, United Kingdom
Pancreatic cancer is a highly aggressive disease for which currently no curative therapies exist. Every year about 70000 people are diagnosed with pancreatic cancer in the European Union (EU) and most will die within six to 12 months after diagnosis. Pancreatic cancer has one of the lowest five-year survival rates of less than 5 %. It is the cancer with the highest mortality to incidence ratio. This dismal prognosis is a result of the late presentation of clinical symptoms, the lack of biomarkers allowing early screening, the early metastatic dissemination and ultimately the resistance to conventional therapy.
Past research has focused on understanding the biology of the tumour cells and designing therapies to kill them. It has now become recognised that tumours are composed of more than just cancer cells and that those additional components are supporting tumour growth and inhibiting successful therapy. The sum of these additional tumour components is called stroma. This project was designed to study the contribution of a particular stromal cell called pancreatic stellate cell (PSC) to tumour development. It was proposed that this cell crosstalks to the cells of the immune system to instruct them not to attack the tumour cells. Furthermore, it was hypothesised that because PSCs exists even in the healthy pancreas that this function is a default programme to prevent autoimmunity. Therefore, cancer development may be a consequence of actively inducing ignorance of the immune system against its own tissues even if they have become cancerous in a balancing act to avoid autoimmunity.
The proposal was structured in two aims, of which the first was to isolate these cells from the pancreas of mice and study their responses to certain stimuli in culture dishes. While all points of this aim were addressed we could not obtain any results supporting our hypothesis that PSCs are tolerogenic antigen-presenting cells. Interestingly, similar results were published by another group studying the closely related hepatic stellate cell. Therefore, we entirely focused on aim two, which has more immediate relevance because it investigated the function of PSC in a developing tumour in a live animal.
In aim two we proposed to eliminate PSCs from a growing tumour and investigate the consequences of that action. PSCs are a very abundant component of pancreatic tumours and were shown to support tumour cell growth and metastasis. However, we postulated that PSCs possess yet another function, which is to suppress the immune response to pancreatic tumours. To address that we chose a system whereby these cells can be specifically killed in a mouse by administration of diphtheria toxin. Mice are very resistant to this toxin unless the receptor, to which the toxin binds is expressed by the cell type to be targeted. This can be achieved by genetic manipulation of mice. We have therefore bred a diphtheria toxin receptor transgenic mouse specific for PSC to a mouse that develops pancreas cancer. This pancreas cancer model is based on the expression of an oncogenic mutant of Kras and a mutant of the tumour suppressor gene p53 in the pancreas. These mice develop tumours as they naturally age, which closely resemble the human disease including co-morbidities such as jaundice, ascites and cachexia. The onset can be anytime between two and six months of age, which requires a rigorous screening to detect developing tumours. This involves palpating the mice' abdomen weekly and ultrasound screening to confirm that hard masses within the abdomen are indeed tumours. Once a tumour of a certain size is confirmed we injected diphtheria toxin and continued to measure the tumour size by ultrasound and compared the growth curves to control treated mice. As expected tumours depended on the presence of PSC, as tumours in mice treated with diphtheria toxin slowed their growth significantly. Furthermore, we could show that PSC have an immunosuppressive role as this tumour growth arrest following PSC elimination was dependent on T cells. We could show that by depleting CD4 and CD8 T cells concurrently with DTx treatment, which reversed the tumour stasis effect. These findings also imply that an effective anti-tumour immune response occurs in these mice during the establishment of pancreatic cancer but due to the presence of PSC in the tumour microenvironment the immune system is blocked from attacking the tumour. This is a very important finding as much of the literature claims that tumours loose the proteins that the immune system recognises so that they become invisible to the immune system. If this were the case all efforts to develop tumour vaccination strategies would be pointless. Indeed, cancer vaccination trials have largely been unsuccessful but not due to a failure to prime an immune response but rather a lack of efficacy. Our data could explain these results because PSC build a 'wall' around the tumour, which does not allow the immune cells to attack. In other words: PSC establish a veil of invisibility to immune cells to protect the tumour. Once the veil was removed the immune system immediately rushed in and attacked tumour cells causing tumour growth arrest.
Further implications are that targeting the PSC is a promising strategy to allow the body's own cytotoxic T cells to attack tumour cells. Because cytotoxic T cells are highly selective 'killers' cancer therapy based on them should have far fewer side effects than radical chemotherapy, which targets not just tumour cells but essentially any dividing cell. Currently, we are investigating in more detail how the PSC establishes this immunosuppressive environment. We are following the hypothesis that PSC instruct the blood vessel cells in the tumour to not allow the entry of immune cells. Preliminary experiments in this direction are promising. We are planning to submit the work for publication in the next few months.
Grant agreement number: 237667
'Pancreatic stellate cells - sentinels for tissue damage?'
Christine Feig, Cambridge research institute, United Kingdom
Pancreatic cancer is a highly aggressive disease for which currently no curative therapies exist. Every year about 70000 people are diagnosed with pancreatic cancer in the European Union (EU) and most will die within six to 12 months after diagnosis. Pancreatic cancer has one of the lowest five-year survival rates of less than 5 %. It is the cancer with the highest mortality to incidence ratio. This dismal prognosis is a result of the late presentation of clinical symptoms, the lack of biomarkers allowing early screening, the early metastatic dissemination and ultimately the resistance to conventional therapy.
Past research has focused on understanding the biology of the tumour cells and designing therapies to kill them. It has now become recognised that tumours are composed of more than just cancer cells and that those additional components are supporting tumour growth and inhibiting successful therapy. The sum of these additional tumour components is called stroma. This project was designed to study the contribution of a particular stromal cell called pancreatic stellate cell (PSC) to tumour development. It was proposed that this cell crosstalks to the cells of the immune system to instruct them not to attack the tumour cells. Furthermore, it was hypothesised that because PSCs exists even in the healthy pancreas that this function is a default programme to prevent autoimmunity. Therefore, cancer development may be a consequence of actively inducing ignorance of the immune system against its own tissues even if they have become cancerous in a balancing act to avoid autoimmunity.
The proposal was structured in two aims, of which the first was to isolate these cells from the pancreas of mice and study their responses to certain stimuli in culture dishes. While all points of this aim were addressed we could not obtain any results supporting our hypothesis that PSCs are tolerogenic antigen-presenting cells. Interestingly, similar results were published by another group studying the closely related hepatic stellate cell. Therefore, we entirely focused on aim two, which has more immediate relevance because it investigated the function of PSC in a developing tumour in a live animal.
In aim two we proposed to eliminate PSCs from a growing tumour and investigate the consequences of that action. PSCs are a very abundant component of pancreatic tumours and were shown to support tumour cell growth and metastasis. However, we postulated that PSCs possess yet another function, which is to suppress the immune response to pancreatic tumours. To address that we chose a system whereby these cells can be specifically killed in a mouse by administration of diphtheria toxin. Mice are very resistant to this toxin unless the receptor, to which the toxin binds is expressed by the cell type to be targeted. This can be achieved by genetic manipulation of mice. We have therefore bred a diphtheria toxin receptor transgenic mouse specific for PSC to a mouse that develops pancreas cancer. This pancreas cancer model is based on the expression of an oncogenic mutant of Kras and a mutant of the tumour suppressor gene p53 in the pancreas. These mice develop tumours as they naturally age, which closely resemble the human disease including co-morbidities such as jaundice, ascites and cachexia. The onset can be anytime between two and six months of age, which requires a rigorous screening to detect developing tumours. This involves palpating the mice' abdomen weekly and ultrasound screening to confirm that hard masses within the abdomen are indeed tumours. Once a tumour of a certain size is confirmed we injected diphtheria toxin and continued to measure the tumour size by ultrasound and compared the growth curves to control treated mice. As expected tumours depended on the presence of PSC, as tumours in mice treated with diphtheria toxin slowed their growth significantly. Furthermore, we could show that PSC have an immunosuppressive role as this tumour growth arrest following PSC elimination was dependent on T cells. We could show that by depleting CD4 and CD8 T cells concurrently with DTx treatment, which reversed the tumour stasis effect. These findings also imply that an effective anti-tumour immune response occurs in these mice during the establishment of pancreatic cancer but due to the presence of PSC in the tumour microenvironment the immune system is blocked from attacking the tumour. This is a very important finding as much of the literature claims that tumours loose the proteins that the immune system recognises so that they become invisible to the immune system. If this were the case all efforts to develop tumour vaccination strategies would be pointless. Indeed, cancer vaccination trials have largely been unsuccessful but not due to a failure to prime an immune response but rather a lack of efficacy. Our data could explain these results because PSC build a 'wall' around the tumour, which does not allow the immune cells to attack. In other words: PSC establish a veil of invisibility to immune cells to protect the tumour. Once the veil was removed the immune system immediately rushed in and attacked tumour cells causing tumour growth arrest.
Further implications are that targeting the PSC is a promising strategy to allow the body's own cytotoxic T cells to attack tumour cells. Because cytotoxic T cells are highly selective 'killers' cancer therapy based on them should have far fewer side effects than radical chemotherapy, which targets not just tumour cells but essentially any dividing cell. Currently, we are investigating in more detail how the PSC establishes this immunosuppressive environment. We are following the hypothesis that PSC instruct the blood vessel cells in the tumour to not allow the entry of immune cells. Preliminary experiments in this direction are promising. We are planning to submit the work for publication in the next few months.