Yes, cytotoxicity is the ability to destroy cells. Most CD4 T cells are not cytotoxic, regardless of the host's age. In the Supercentenarians studied here, it was observed that the majority of their CD4 T cells were cytotoxic, which is a very surprising result.

Having more cytotoxic CD4 T's could give the immune system better ability to destroy invaders or cancer cells.

Even more surprising is that a large percentage of these mutant CD4 T's are clonal, all traceable back to one individual (T cell) that mutated.

It's been shown that supercentenarians enjoy resistance to disease over their entire lives. This research shows that may be due to their unique immune systems.