Explain the mechanism by which immunosuppression increases an individual's susceptibility to developing oral cancer.

The human immune system constantly performs a vital process called immune surveillance, which involves continuously monitoring the body for abnormal cells, including those that are pre-cancerous or have undergone malignant transformation. Specialized immune cells, primarily cytotoxic T-lymphocytes, also known as killer T-cells, and natural killer (NK) cells, are crucial in recognizing and eliminating these potentially harmful cells before they can develop into overt tumors. Immunosuppression refers to the weakening or deliberate suppression of this immune system, often induced by medications given to organ transplant recipients to prevent rejection, or for individuals with autoimmune diseases, or as a consequence of certain medical conditions like HIV/AIDS. When the immune system is suppressed, its ability to carry out this essential immune surveillance is severely compromised, directly increasing an individual's susceptibility to developing various cancers, including oral cancer. Oral cancer is predominantly oral squamous cell carcinoma, which arises from the flat cells lining the mouth.
This increased susceptibility to oral cancer under immunosuppression occurs through several direct mechanisms. First, the suppressed immune system fails to effectively control oncogenic, or cancer-causing, viruses. For example, certain high-risk strains of human papillomavirus (HPV) are strongly linked to oral cancers, particularly those affecting the oropharynx, which includes the back of the throat, base of the tongue, and tonsils. In an individual with a healthy immune system, these viral infections are typically cleared naturally. However, immunosuppression prevents the immune system from effectively controlling HPV replication and persistence. The prolonged presence and activity of HPV allow its viral proteins to interfere with normal cellular growth and division mechanisms, directly promoting the malignant transformation of oral cells into cancer.
Second, immunosuppression directly impairs the immune system's ability to identify and eliminate cells that have undergone spontaneous genetic mutations or have otherwise transformed into malignant cells. Cells in the body frequently acquire genetic mutations. While most are harmless, some can lead to abnormal cell behavior or even the development of pre-cancerous conditions. Under normal circumstances, immune cells like cytotoxic T-lymphocytes and NK cells recognize these mutated or pre-cancerous oral cells by detecting abnormal proteins or signals on their surface. These immune cells then efficiently destroy the abnormal cells, preventing them from proliferating and forming a tumor. Immunosuppression significantly reduces the number, function, and coordinated activity of these critical immune cells. This diminished immune response means that nascent oral cancer cells, which would otherwise be identified and eliminated, can evade detection, survive, and multiply unchecked, ultimately leading to the growth of a clinically detectable oral cancer.