Researchers here note that cytotoxic T cells undergo age-related changes in protein expression that make them more effective in the task of destroying cancer cells, an unusual example of a component of the immune system improving with age. Overall, an aged immune system is impaired in numerous ways, and is worse at protecting the individual against the onset of cancer. Identifying specific populations of immune cells that can effectively destroy cancer cells, if given direction and greater numbers, is relevant to the production of better immunotherapies, however.
The older someone is, the more likely they are to get cancer. This was thought to suggest that the human immune system becomes weaker with age and that the same must therefore be true of the killer T cells that play such a critical role in fighting off pathogens. The job of the T cell is to track down and kill virus-infected cells or tumour cells in the body. Up until now the accepted scientific view has been that T cells function less effectively as they age. However, researchers have now found the rather surprising result that the ability of cytotoxic CD8+ T cells to destroy tumour cells does not deteriorate but actually improves with age.
The reason why T cells are such effective killers has to do with the highly effective weapons that they have at their disposal. The production of the molecules perforin and granzyme is enhanced in older T cells. As its name suggests, the molecule perforin perforates the target cells making tiny pores in the cell membrane. Granzyme can then enter the cells and initiate apoptosis, a form of programmed cell death. In addition, older experienced T cells have an accurate picture of who they are supposed to be targeting. Cytotoxic CD8+ T cells have a good memory of who they have attacked and destroyed in the past. And as part of the adaptive immune system, they live and learn. T cells are able to form memory cells. If they come into contact with a pathogen that they are already acquainted with, they respond very quickly and very effectively.
This begs the question as to why older people are not better protected against tumour cells and viruses if their T cells are so powerful. "On the one hand we have age-related processes that occur naturally as the cell ages, but we also have to consider changes in cell function due to the ageing of the cell's environment. In the case of T cells, the evidence seems to suggest that the reason for the deteriorating immune response is not to be found in the T cells themselves but rather in the ageing environment."