Anti-HLA class II allele-specific immune reactivity in early post-dUCBT PB samples contributes to antileukemic cell reactivity. Post-dUCBT patient PBMC samples were propagated on HeLa cells transduced with mismatched HLA class II alleles of the nonengrafting CBU as specified in Figure 2A. T-cell cultures (n = 5) with proven HLA class II alloreactivity toward DRB1*08:01 (derived from patient 4), DRB1*15:01 (patient 11), DQB1*03:01 (patient 10), DQB1*04:02 (patient 4), and DQB1*05:01 (patient 2) were tested for reactivity toward the corresponding HLA class II molecule expressing HeLa and toward PLCs obtained from 6 patients, ie, patient 1 (DRB1*08:01, DQB1*04:02), patient 4 (DQB1*05:01), patient 6 (DRB1*08:01, DQB1*04:02), patient 9 (DQB1*03:01, DQB1*05:01), patient 10 (DRB1*15:01), and patient 11 (DRB1*11:01, DQB1*03:01). Complete HLA class II typing of the patients is presented in Table 3. x-axis: net % CD137 upregulation, ie, %CD137 upregulation on alloreactive CD4⁺ T cells following coculture with HLA class II–expressing HeLa cells or PLCs minus reactivity toward the empty HeLa cell (positive response: net CD137 upregulation >5%); y-axis: stimulator cells (Hela or PLC) per alloreactivity of the tested T-cell culture. Dark gray bar: positive control, HLA class II alloreactive T-cell culture with the corresponding HLA class II allele transduced HeLa cell; black bar: HLA class II alloreactive T-cell culture with PLCs expressing the corresponding HLA class II allele; light gray bar: HLA class II alloreactive T-cell culture with PLCs not expressing the corresponding HLA class II allele.