But it misses these, because they look perfectly normal. This similarity also makes the infected cells almost impossible to kill with any kind of targeted drugs. There is simply no easy way to sort out the good from the bad. Siliciano has been counting these cells in his Baltimore volunteers for five years. Siliciano favors the first theory.
Immunological memory lasts forever.
This is why someone who catches measles in childhood will remain immune to the disease into old age. Memory cells may die over time, but they also make replacements by cell division. And every time a memory cell divides, it faithfully reproduces the HIV that is stitched into its genes. However, the Diamond Center's Ho prefers the second theory. Actually, memory cells are much shorter-lived, he believes.