Bispecific antibodies effectively purge cancer cells from peripheral blood stem cell collections without affecting colony forming units.

Peripheral blood stem cell collections (PBSC) are increasingly being used for hematopoietic reconstitution after high dose chemotherapy However, PBSC are often contaminated by tumor cells contributing to a later relapse as demonstrated by several investigators. Elimination of tumor cells, e.g., by immunomagnetic techniques can improve the situation but have certain disadvantages like high costs, complicated technology and restriction to the ex vivo situation. Therefore, we developed an immunological approach using T-cell redirecting, quadroma-derived, intact bispecific antibodies with specificities anti-CD3 X anti-ep-cam (BiUII) and antiCD3 X anti-c-erb-B2 (BiZ) to eliminate tumor cells from PBSC. The main advantage of this approach is that besides T-cells also Fcreceptor I positive cells such as monocytes, macrophages, dendritic cells or activated neutrophiles are recruited and activated by intact Fc-beanng bispecific antibodies. Probably, as a result of this concentrated attack of different immune cells, in vitro growth inhibition experiments demonstrate a log 3-5 reduction of tumor cells contaminating PBSC from cancer patients (with a defined 0.1%0.2% or 1% tumor cell contamination). Conferring the purging protocol to an animal model, we received between 67-100% survival by injecting initially tumor-contaminated (1 2x10e6 HCT-8 cells/mouse) and subsequently bispecific antibodypurged PBMC in SCID mice compared to 0% survival of unpurged samples. Varying the temperature, incubation time, antibody and cell concentration we were able to define optimal conditions for tumor cell destruction while sparing normal cells. Colony-forming units were not adversely affected under conditions found to be optimal, with a mean recovery of 105% as compared with the control