FITC-conjugated allopeptides enable visualization of alloreactive CTLs.

Anti–HLA-B7 CTLs HNB7.1 were incubated with FITC-conjugated P11 or control peptide P21 at 4°C, and fluorescence was measured by flow cytometry. CTLs were successfully labeled by P11, but not by P21. To rule out peptide binding to the MHC alleles on the surfaces of CTLs rather than to the TCR, 2 CTL lines against A2 and B7, respectively, were raised from the same individual. P11 successfully labeled anti-B7 UWB7, whereas P21 labeled anti-A2 CTL only, indicating allospecific binding by the peptides.