T cells can be activated by peptides that are unrelated in sequence to their selecting peptide.
Ignatowicz L, Rees W, Pacholczyk R, Ignatowicz H, Kushnir E, Kappler J, Marrack P. T cells can be activated by peptides that are unrelated in sequence to their selecting peptide. Immunity. 1997 Aug; 7(2):179-86.