We consider the lifetime of a T cell clonotype, the set of T cells with the same T cell receptor,
from its thymic origin to its extinction in a multiclonal repertoire. Using published estimates of
total cell numbers and thymic production rates, we calculate the mean number of cells per
TCR clonotype, and the total number of clonotypes, in mice and humans. When there is little
peripheral division, as in a mouse, the number of cells per clonotype is small and governed
by the number of cells with identical TCR that exit the thymus. In humans, peripheral division …