Target specificity (matched targets). AAV/HM1.24 generated a CTL response against various HM1.24-positive and -negative HLA-matched targets. The key shows the 8 target cells used in the experiments displayed in panels A-D. Stack of CTL experiments from each of 3 donors (panels A-C, each experiment performed in quadruplicate) and a compilation of the 3 experiments (D), as indicated. Of the target cells used, only autologous PBMCs and K562 cells were HM1.24 negative. All others displayed some level of HM1.24 expression by RT-PCR analysis (data not shown). Note that the 4 primary MM (HM1.24-positive) and both MM cell lines were killed by the HM1.24-stimulated CTLs. However, also note that HM1.24-negative PBMCs and K562 cells were not killed, indicating strong antigen specificity of the CTLs generated by AAV/HM1.24 loading.