Purging of epithelial tumor cells from peripheral blood stem cells by means of the bispecific antibody BIS-1

Peripheral blood stem cell (PBSC) support in breast cancer patients allows high-dose chemotherapy, but tumor cell contamination of the PBSCs is a pote ntial source of relapse. Specific carcinoma cell killing can be obtained by retargeting activated T cells with bispecific antibody BIS-1, directed aga inst epithelial glycoprotein-2 and CD3, To purge epithelial tumor cells fro m the PBSCs of breast cancer patients, activation of T cells in PBSCs and T -cell retargeting by BIS-1 was studied, PBSCs, obtained by leukapheresis af ter chemotherapy and recombinant human granulocyte colony-stimulating facto r, were cultured in the presence of PBS, interleukin-2, OKT3, or interleuki n-2/OKT3 for induction of T-cell activation. Subsequently, lysis of epithel ial tumor cell lines by activated T cells of PBSCs in the presence or absen ce of BIS-1 was assessed with the Cr-51-release assay or immunocytochemical staining. The effect on PBSC hematopoietic colony formation (HCF) was eval uated by the granulocyte macrophage colony-stimulating units assay. Prior t o activation, PBSCs front breast cancer patients contained higher levels of CD8+ T cells than peripheral blood from healthy volunteers (P < 0.05). The potential of PBSCs to sustain tumor cell lysis was increased after all pri or activations and was further enhanced by BIS-1, Maximal BIS-1 effect was observed after OKT3 activation of PBSCs for 72 h (P < 0.0005), inducing a > 3 log depletion of tumor cells. HCF was not affected by prior OKT3 activati on and/or BIS-1, In conclusion, specific tumor cell lysis by PBSCs can be o btained in vitro by OKT3 activation and BIS-1 retargeting of T cells, witho ut affecting BCP. At present, studies are evaluating this format for future clinical application.