Radioresistant pseudo-colony formation in the PHA-leukocyte feeder colony assay

In the PHA-leukocyte feeder colony assay — a fluid assay on top of an agar underlayer — colonies might not be the product of clonogenic cells but rather from aggregates, as was already shown for hairy cell leukemia ( Leukemia Res., 11, 911 (1987)). To study the role of aggregation in this colony assay in other B-cell malignancies, we irradiated cells from B-chronic lymphocytic leukemia, B-non-Hodgkin's lymphoma and multiple myeloma. In nearly all cases, viable “colonies” were seen after irradiation, albeit in lower numbers. These data indicate that in the PHA-leukocyte feeder colony assay, a considerable percentage of colonies from a large variety of B-cell malignancies originate from aggregating rather than from proliferating cells.