LEUKEMIA-CELL DERIVED FACTOR (LDF) INDUCES HEMATOPOIESIS

A leukemic cell line, A(1), derived from a child with acute lymphoblas tic leukemia was observed to have early B-cell irradiated A(1) cells w ere cultured with marrow cells in presence of recombinant erythropoiet in (rhEPO), it stimulated burst forming unit erythroid (BFU-E). In ord er to determine if other leukemia cells or cell lines also induce simi lar stimulation, we used different leukemic cell lines and fresh B-cel ls from patients with chronic lymphocytic leukemia in bone marrow bioa ssay. Our results suggest that not all leukemic cells induce BFU-Es. T o further identify the leukemia cell derived factor (LDF), A(1) cells were lysed and differentially centrifuged to separate plasma membrane protein from cytosolic and nuclear proteins. Only membrane associated protein were shown to induce BFU-E. However, when spent medium was col lected and used In the bioassay, it also stimulated BFU-E, suggesting LDFs may be shed from plasma membrane. To further identify LDF, A(1) p lasma membrane associated proteins were separated by ion-exchange FPLC . Protein fractions were collected and were used in the bioassay to id entify the fraction that induced BFU-Es.