Figure 4. Tumor cell elimination mediated by the novel scBsTaFv CD8-PSCA(MB1).
To analyze killing properties of the novel CD8-engaging single-chain bsAb standard chromium release assays were performed. A, to compare the anti-tumor effect of the novel scBsTaFv CD8-PSCA(MB1) with the conventional bsAb CD3-PSCA(MB1), [51Cr]-labeled PC3-PSCA cells and either pre-activated PBMCs (left panel), isolated pre-activated CD8+ T cells (middle panel) or freshly isolated CD8+ T cells (right panel) were cultivated in the presence or absence of 30 pmol/ml of recombinant bsAbs for 22 h. Mean of specific lysis ± SD of one representative donor is shown. BI, summary of (A, left panel) seven different donors is shown. Statistical significance was determined with one-way ANOVA and Bonferroni Multiple Comparison test (***p<0.001 with respect to control: no Ab; *p<0.05 significant difference between the conventional anti-CD3 bsAb and the novel anti-CD8 bsAb). BII, In order to estimate the ratio of CD8+ to CD4+ T cells, the pre-activated PBMC preparations of all seven donors were stained for CD8+ and CD4+ T cells and analyzed by FACS.