Authors: Akwasi Afrane Bediako & Raymond Ohene Gyan
Affiliation: Faculty of Biosciences, University For Development Studies, Ghana
Date: 28/03/2025
The human immune system consists of tissues, cells, and molecules that work together to defend against harmful foreign substances, known as pathogens, which can cause diseases. By utilizing innate and adaptive mechanisms, the immune system protects the human body and promotes overall well-being.
The innate immune system is a network of physical and chemical barriers such as skin and mucous membranes that serve as a first line of defense. The adaptive immune system, which is also responsible for generating antibodies and immune cells plays a crucial role in recognizing and eliminating specific pathogens in the human body, thus exhibiting a higher level of complexity and specificity in its functionality (Martínez-Lostao et al., 2015).
Cancer, a genetic disorder, is an umbrella term for diseases resulting from abnormal cell division. Cell division is when a cell duplicates its genetic and cell contents and cleaves into two identical cells. Normal cells in the body know when to divide and when to stop dividing (Parkin et al., 2001).
Cancer cells do not have that control ability. They divide without limit, resist death, and have the potential to invade other organs and tissues for their survivability, with disastrous consequences for the human system (Bediako et al., 2024).
Cancer and the Immune System
Cancer is not one disease, but many. There are different types of cancer, classified according to where they occur in the body, the specific cell type from which they arise, and, increasingly, the specific genetic mutations found within the cancer cells. Cancers that arise in the epithelium, the layer of cells covering the surface of the body and lining the internal organs and glands, are called carcinomas. Carcinomas can form in organs such as the lung, breast, colon, and stomach, or glands such as the ovary and prostate.
Sarcomas are cancers of the supporting tissues of the body, such as bone, muscle, and blood vessels. Cancers of the white blood cells and the lymph glands are called leukaemia and lymphomas, respectively. Melanomas arise from darkly pigmented cells, called melanocytes, located in the skin.
The immune system plays a pivotal role in recognizing and eliminating anomalous cells. The capacity of the immune system to recognize and eliminate malignant cells is commonly referred to as immune surveillance. The immune system comprises an intricate assembly of cellular tissues and organs, which function in collaboration to provide protective immunity against pathogenic agents and abnormal cell division.
The immune system plays a crucial role in preventing cancer cells by inhibiting their development. Through immune surveillance, cytotoxic T cells and natural killer cells primarily eliminate emerging and existing abnormal proliferating cells, while macrophages contribute to the process by phagocytosis and antigen presentation.
Components of the Immune System Involved in Cancer Defense
Innate immunity contributes to cancer defense through the immediate, nonspecific action of natural killer (NK) cells, which target and destroy cancer cells lacking major histocompatibility complex (MHC) class I molecules. Macrophages also participate in tumor cell destruction, though their role can be complex. Dendritic cells, vital for immune responses, capture and process tumor antigens, then present them to T cells, thereby activating the adaptive immune system to target and eliminate tumor cells (Martínez-Lostao et al., 2015).
Cytotoxic T lymphocytes (CTLs) primarily target and destroy tumor cells presenting tumor-associated antigens on MHC class I molecules. Helper T cells, through the secretion of cytokines, play a crucial role in coordinating and amplifying the immune response against cancer cells and pathogens. These cytokines can enhance the activity of other immune cells, including CTLs and NK cells.
The CTLs and NK cells utilize granzyme A and granzyme B to induce apoptosis in target cells, including cancer cells. These granzymes are delivered into the target cell, triggering both caspase-dependent and caspase-independent pathways that lead to cellular self-destruction. In addition to granzymes, granule-associated molecules like granulysin also contribute to cancer cell elimination, although their precise mechanisms and relative importance are still being investigated. A deeper understanding of these cytotoxic mechanisms is crucial for developing more effective immunotherapies that enhance the immune system’s capacity to recognize and eliminate cancer cells (Garg et al., 2024).
How Cancer Cell Evades the Immune System
A significant challenge in cancer immunotherapy is that cancer cells frequently downregulate MHC class I expression to evade detection and destruction by CTLs, which rely on MHC class I presentation of tumor-associated antigens. While this loss of MHC class I renders cancer cells less susceptible to CTL-mediated killing, they may become more vulnerable to NK cell-mediated destruction. This mechanism of immune evasion is commonly observed in aggressive cancers, including lung and breast cancer (Ribas et al., 2015).
Cancer Immunotherapy
Cancers present significant treatment challenges, including comprehensive immune escape mechanisms to continuous cell proliferation, late-stage diagnosis, and limited therapeutic options. Current immunotherapeutic approaches, such as immune checkpoint inhibitors, have shown promising clinical efficacy among some cancer patients (Kumar and Amankwaa, 2017, Garg et al., 2024). However, there is an urgent need for more effective treatment strategies utilizing immunotherapy approaches due to cancer cell resistance.
It is proposed that future research focus on developing combinatorial immunotherapies that enhance immune cell activation while targeting evading cancer cells. Research efforts should also gear toward biomarker discovery for early cancer detection and improving high targeting of cancer cells without depending on the MHC protein (Showalter et al., 2017).
Conclusion
The human immune system plays a crucial role in recognizing and eliminating cancer cells through cytotoxic mechanisms, primarily mediated by T cells and NK cells, which release cytotoxic proteins. Immunotherapy has transformed cancer treatment by leveraging these immune responses, with cancer vaccines and adoptive T-cell therapy demonstrating significant promise. However, challenges such as tumor immune evasion and therapeutic resistance remain.
Future research should focus on optimizing combination immunotherapies, identifying predictive biomarkers for early cancer detection, and personalizing treatment strategies to overcome resistance and improve patient outcomes. A deeper understanding of tumor-immune interactions will facilitate the development of novel cancer vaccines and other targeted therapies to enhance the immune system’s ability to effectively combat cancer..
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