June 18th, 2016
‘Put all things to the test and keep what is good’
St. Paul gave the above advice to the church of Thessalonica in the first century. This article describes cancer(1) related discoveries, which put cancer research itself to the test.
Cancer is a huge health problem. The World Health Organization (WHO) reported that in 2012 approximately 32,6 million people are living with cancer worldwide (and were diagnosed less than five years ago) and that a massive amount of more than 8 million people died from cancer in 2012. Fortunately, the American Cancer Society, which is a big organization that supports cancer research, granted about an impressive amount of 427 million dollars for cancer research this year.
How can this money be used to improve cancer research?
Currently, the most common cancer treatments are traditional cancer treatments, namely surgery, chemotherapy and radiotherapy. These treatments aim to cure or to slow down cancers by cutting away (tumor) tissue, by killing rapidly dividing (tumor) cells or by killing (tumor) cells of the patient at specific sites. These therapies can be used solitary, but to improve the outcome, they are often combined with each other or with newer treatments, including immunotherapy.
Plenty research is done on immunotherapy, which might be the most promising therapy against cancer. Antitumor immunotherapy aims to support the subjects’ own immune defense in roughly two ways:
Comfortable lab mice
To better investigate these treatments and disease mechanisms in patients, lab animals – mostly mice – are being used as models. Their treatment results and disease mechanisms should be similar to the ones of human subjects. Therefore, it is very important that the housing of laboratory animals is comfortable and not too boring for the animals. To achieve this, official regulations for working with mice are being used, which include:
Here we see laboratory mice in a cage, which is the size of a large shoebox. The brown chunks are pieces of nutritious food and the flask next to the food is the water supply. Notice the ventilation holes to improve the air quality, the yellow hay for convenient walking and chewing and the movable red box to manipulate the environment.
Recently, Kokolus and colleagues discovered how different ambient temperatures influence the development of a tumor in laboratory mice. The researchers compared mice in a standard laboratory with a temperature of 22-23˚C (ST) to mice in a so-called thermoneutral temperature of 30-31˚C (TT).
It turns out that mice maintained at TT show a decreased tumor growth in four tumor models of skin tumors, breast tumors, colon tumors or pancreatic tumors. Furthermore, mice at TT develop less metastatic lesions. It is important to note that the benefits of an increased ambient temperature are not present in mouse models with a dysfunctional immune system.
These findings can partly be explained by so called CD8 T cells or CD8 T lymphocytes, which are members of the adaptive immune system and target cells that express specific molecules on the cell surface. In tumors of TT mice, more of these lymphocytes were present in the tumor. They were also more tumor cell specific and more activated to combat tumors. Their higher activation is indicated by a higher expression of surface molecules CD69 and GLUT-1 and an increased production of tumor repressing molecule IFN-ɣ. Importantly, tumor growth in TT mice and ST mice were similar when CD8 cells were depleted, proving the pivotal role of these lymphocytes in the battle against tumors.
Another important finding refers to immunosuppressive FoxP3 T cells, that inhibit CD8 T cell function and contribute to tumor growth. These suppressive cells were less present in tumors of mice housed at TT.
Interestingly, tumor-bearing mice at ST were unable to maintain body temperature at 37ᵒC. Accordingly, these and other tumor bearing mice revealed increased heat seeking behavior, preferring 38˚C (the warmest option of the experiment) over TT, whereas tumor free mice preferred TT.
In summary, replacing the standard housing temperature for thermoneutral temperature increased the immune reaction of the mice against tumors. This effect seems to depend on the presence of CD8 T cells. Moreover, the decreased body temperature in mice housed at ST highly suggests that this ambient temperature causes cold stress in mice. Investigators found that in order to retain a suitable body temperature, a whole-body response induces higher levels of stress (neuro)hormones, such as catecholamines. These stress increasing factors contribute to an impaired immune function, strongly suggesting that cold stress inhibits the immune defense against tumors.
This study therefore suggests that the standard housing temperature is not suitable for investigating the immune system. The importance of changing the housing conditions is also illustrated by a study of Seok et al. that describes that mouse models with inflammatory diseases relatively poorly resemble the same diseases in human subjects. Preventing cold stress in laboratory mice is important to further humanize the model, so the rodents should be able to reach thermoneutral ambient temperatures. One way to accomplish this, is increasing the housing temperature to TT. A more creative way would be top put clothes on mice, however, research of Lodhi and Semenkovich reveals this wouldn’t be a wise solution.
Moreover, because this study shows that CD8 T cells are essential for the delayed growth of several tumors, the results support earlier research, like a study of Zou for example, that focused on CD8 T cell immunotherapy. It underscores that immunotherapies in mice are improved after depletion of immunosuppressive T cells.
Following St. Paul’s suggestions researchers should ask the following questions in the future:
Put all things to the test
1. What is the effect of 38ᵒC as ambient temperature on tumor growth and metastasis in mice?
2. How does cold stress influence the immune defense against tumors?
3. What is the effect of TT on the antitumor activity of other major immune cells which are frequently used in immunotherapies, like CD4 T cells and dendritic cells?
4. What is the influence of various degrees of cold stress on immunotherapies?
And keep what is good
5. What is the most cost-effective, mouse friendly and ethical acceptable way to further humanize the mouse model?
In conclusion, mice at thermoneutrality have a better immune defense against tumors, highly suggesting improved housing of mice is necessary for improved cancer research.
Footnote 1: A tumor emerges when genetically damaged cells multiply without any constraints like programmed cell death (apoptosis). Apoptosis normally removes unnecessary or malfunctioning cells from a tissue. A patient gets cancer when a tumor becomes malignant by actively invading nearby and distant tissues.
Photo: Flickr, viridovipera
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cancer, temperature, treatment, mice, therapy, tumor, immunotherapy