Dual Effect of Immune Cells within Tumour Microenvironment: Pro- and Anti-Tumour Effects and Their Triggers
Department of Biochemistry and Molecular Biology-A, University of Murcia, 30120 Murcia, Spain
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Author to whom correspondence should be addressed.
Cancers 2022, 14(7), 1681; https://doi.org/10.3390/cancers14071681
Submission received: 25 February 2022
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Revised: 21 March 2022
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Accepted: 23 March 2022
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Published: 25 March 2022
(This article belongs to the Special Issue Immune Microenvironment and Cancer Progression)
Simple Summary
The relationship between the immune system and tumours is currently one of the most studied topics in the field of cancer. Previously, it was thought that a tumour could be malignant on its own; nonetheless, nowadays, we know that it needs the support of different cells and factors, namely, the tumour microenvironment (TME). Among the components that constitute the TME, we find immune cells responsible for supporting the tumour, which play a key role in this tumoural milieu. Although immune cells, under normal conditions, can identify and destroy nascent tumour cells in a process named cancer immunosurveillance, they can be influenced by different factors in the presence of the tumour in a process termed cancer immunoediting. The fact that immune cells can behave as guardians (anti-tumour immunity) or as bystanders or supporters of the tumour (pro-tumour immunity) makes them a “double-edged sword” in the TME.
Abstract
Our body is constantly exposed to pathogens or external threats, but with the immune response that our body can develop, we can fight off and defeat possible attacks or infections. Nevertheless, sometimes this threat comes from an internal factor. Situations such as the existence of a tumour also cause our immune system (IS) to be put on alert. Indeed, the link between immunology and cancer is evident these days, with IS being used as one of the important targets for treating cancer. Our IS is able to eliminate those abnormal or damaged cells found in our body, preventing the uncontrolled proliferation of tumour cells that can lead to cancer. However, in several cases, tumour cells can escape from the IS. It has been observed that immune cells, the extracellular matrix, blood vessels, fat cells and various molecules could support tumour growth and development. Thus, the developing tumour receives structural support, irrigation and energy, among other resources, making its survival and progression possible. All these components that accompany and help the tumour to survive and to grow are called the tumour microenvironment (TME). Given the importance of its presence in the tumour development process, this review will focus on one of the components of the TME: immune cells. Immune cells can support anti-tumour immune response protecting us against tumour cells; nevertheless, they can also behave as pro-tumoural cells, thus promoting tumour progression and survival. In this review, the anti-tumour and pro-tumour immunity of several immune cells will be discussed. In addition, the TME influence on this dual effect will be also analysed.
