A. Rootsweiss et al., THE EFFICIENCY OF TUMOR-CELL PURGING USING IMMUNOMAGNETIC CD34(-SEPARATION SYSTEMS() CELL), Bone marrow transplantation, 19(12), 1997, pp. 1239-1246
Immunomagnetic separation with anti-CD34 monoclonal antibodies and par
amagnetic microbeads has been used to enrich hematopoietic stem cells
from human bone marrow (BM) or mobilized peripheral blood mononuclear
cells (PBMNC). The introduction of this technique also constitutes a n
ew principle of tumor cell purging, The efficiency in terms of purging
tumor cells from PBMNC was evaluated in seven different experiments.
Mobilized (chemotherapy and G-CSF) PBMNC were collected from patients
with solid tumors (n = 6) and multiple myeloma (n = 1) by leukapheresi
s using an automated MNC separation system and contaminated with 1% (n
= 5) or 10% (n = 2) tumor cells from different epithelial cell lines
being CD34-negative. The cell mixture was sensitized with anti-CD34 (9
C5) antibodies and sheep anti-mouse IgG1 paramagnetic microspheres and
enriched for CD34(+) cells using an Isolex 50 magnetic separator. Pur
ity of CD34(+) cells was studied by flow cytometry (FACScan) and tumor
cell depletion was evaluated by comparative human tumor cloning assay
s (HTCA) containing methylcellulose and agar. We achieved a median pur
ity of CD34(+) cells of 85.9% (range 69.8-92.9%) and a median yield of
48.1% (range 21.0-85.2%). From these data in each case the estimated
log depletion of tumor cells was calculated and compared with the expe
rimentally achieved (HTCA) log depletion (log Delta depletion = log ex
perimental depletion - log calculated depletion). In our experiments w
e achieved a median depletion of 2.75 log (range 1.55-3.69 log). When
corrected for CD34(+) cell yield of each experiment we observed a medi
an 'yield corrected depletion' of 2.38 log (range 1.48-3.15 log), The
following Delta depletion values were obtained: +0.32 log (HTB 129, br
east), +0.21 log (HTB 26, breast), +0.04 log (HTB 26) for experiments
with higher experimental depletion, and -0.23 log (HTB 26), -0.9 log (
HTB 26, PBMNC from patient with multiple myeloma), -0.82 log (HTB 131,
breast) and -1.66 log (HTB 131) for lower depletion efficacy than cal
culated, These data suggest that depletion mag depend on specific cell
surface characteristics of tumor cells. Moreover, plasma factors leg
paraprotein) may also have some impact. In summary, the Isolex 50 prov
ides a high purity of CD34(+) cells and depletion of tumor cells was e
fficient. However, calculated and experimental purging efficiencies ar
e not necessarily identical.