Immunosenescence is not T-cell exhaustion—it is repertoire collapse from thymic involution

Old immune systems fail not because T-cells are worn out, but because the thymus stopped making new ones decades ago.

The existing repertoire clonal expands to fill the gap. You get many cells recognizing few antigens. When a novel pathogen appears, no T-cell recognizes it.

It's not exhaustion. It's monoculture. The immune system became a monocrop vulnerable to new pests.