Vector-encoded proteins are the target antigens of the GMC-specific immune response: identification of an immunodominant HSV-TK epitope. (A) LCLs from patient 2 were transduced with retroviral vectors encoding single components of the SFCMM2 vector and used as target in a standard chromium release assay at the indicated E/T ratios. LCLs expressing the TN fusion protein (●), the wild-type HSV-TK (■), or the neo gene (▴) were recognized and killed at a similar level. Untransduced LCLs (○) and LCLs expressing the ΔLNGFr cell-surface marker¹⁵  (□) were not recognized. (B) HLA-B*0701⁺ LCLs (LCL-B7) were incubated with 10 μM peptide TK._279-288 and used as stimulator cells in an IFN-γ release assay. An unrelated peptide (UR pep) able to bind HLA-B*0701 molecule was used as control for specificity.