Recent experiments using fetal thymus organ culture (FTOC) systems der
ived from class I deficient mice have provided evidence supporting the
view that specific recognition of class I MHC plus peptide complexes
is required for the positive selection of CD8(+)T cells. The addition
of class I binding peptides to FTOC systems derived from beta 2-microg
lobulin and TAP 1 deficient mice induced the positive selection of CD8
(+)T cells in a peptide specific manner The specific recognition of pe
ptide during positive selection implies that the repertoire of specifi
city's exhibited by CD8(+)T cells is at least in part determined by th
e repertoire of self-peptides presented by class I MHC in the thymus.