PURGING OF MAMMARY-CARCINOMA CELLS DURING EX-VIVO CULTURE OF CD34(+) HEMATOPOIETIC PROGENITOR CELLS WITH RECOMBINANT IMMUNOTOXINS

Tumor cells have been found in autologous hematopoietic cell transplan ts used after high-dose chemotherapy. To specifically eliminate contam inating mammary tumor cells during ex vivo expansion of CD34(+) hemato poietic progenitor cells, we used recombinant immunotoxins (ITs) direc ted against cell-surface antigens expressed on mammary carcinoma cells . ITs were expressed from fusion cDNAs combining a single-chain antibo dy fragment (scFv) directed against the Erb-B2 or epidermal growth fac tor (EGF) receptors with a truncated Pseudomonas exotoxin A fragment d evoid of its cell-binding domain. CD34(+) hematopoietic progenitor cel ls did not express Erb-B2 and EGF receptors as detected by Western blo tting. Ex vivo expansion of total hematopoietic cells or of colony-for ming cells from CD34(+) progenitors in the presence of stem-cell facto r (SCF), interleukin-1 (IL-1), IL-3, IL-6, and erythropoietin (Epo) wa s not affected when ITs were added to the cultures. In contrast, MDA-M B 453 and MCF-7 mammary carcinoma cells were depleted in a dose-and ti me-dependent manner by more than 3 log in coculture with CD34(+) cells over a period of 7 days in the presence of 100 to 1,000 ng/mL of anti -Erb-B2 IT. this included elimination of the subpopulations with regro wth potential. Similarly, addition of either anti-Erb-B2 or anti-EGF r eceptor ITs to primary breast cancer cells isolated from patients with metastatic disease resulted in elimination of cytokeratin-positive ce lls in seven of seven samples. ITs are highly efficient and convenient to use for the depletion of mammary tumor cells during ex vivo expans ion of hematopoietic progenitor-cell autografts. (C) 1998 by The Ameri can Society of Hematology.