Leukemia cell derived factor (LDF) induces hematopoiesis.

A leukemic cell line, A1, derived from a child with acute lymphoblastic leukemia was observed to have early B-cell lineage. When irradiated A1 cells were cultured with normal bone marrow cells in presence of recombinant erythropoietin (rhEPO), it stimulated burst forming unit erythroid (BFU-E). In order to determine if other leukemia cells or cell lines also induce similar stimulation, we used different leukemic cell lines and fresh B-cells from patients with chronic lymphocytic leukemia in bone marrow bioassay. Our results suggest that not all leukemic cells induce BFU-Es. To further identify the leukemia cell derived factor (LDF), A1 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 collected and used in the bioassay, it also stimulated BFU-E, suggesting LDFs may be shed from plasma membrane. To further identify LDF, A1 plasma membrane associated proteins were separated by ion-exchange FPLC. Protein fractions were collected and were used in the bioassay to identify the fraction that induced BFU-Es.