The immune system declines and malfunctions with age, but researchers are making strides towards methods of reprogramming that might restore an age-damaged immune system to better operation: researchers have "identified a protein that could serve as a target for reprogramming immune system cells exhausted by exposure to chronic viral infection into more effective "soldiers" against certain viruses like HIV, hepatitis C, and hepatitis B, as well as some cancers, such as melanoma. ... the protein Blimp-1 (B-lymphocyte-induced maturation protein 1) represses the normal differentiation of CD8 T cells into memory T cells, which recognize disease-causing agents from previous infections and enable the body to mount faster, stronger immune responses. The team also reports that Blimp-1 causes exhausted CD8 T cells to express inhibitory receptors, which prevent recognition of specific antigens, further weakening immune response. The researchers describe how complete deletion of Blimp-1, which is overexpressed in CD8 T cells during chronic viral infection, reversed these aspects of T cell exhaustion." Note that one important cause of immune system aging is chronic infection by cytomegalovirus - this work probably has relevance to aging.