Long-Term Bone Marrow Cultures Provide Access to Early Lymphoid Progenitors

Long-term bone marrow cultures provide defined systems for studying and manipulating hematopoietic progenitors. Myeloid bone marrow cultures harbor early lymphoid progenitors; however, the nature and phenotype of these progenitors has not been investigated. Phenotypic and molecular markers associated with lymphopoiesis were used to characterize the lymphoid population maintained in these cultures. Cells within myeloid cultures expressed genes associated with lymphopoiesis but did not express the B cell-specific lambda5 gene. Flow cytometry demonstrated that cultures lacked cells expressing markers associated with B cell development. Furthermore, rearrangements of immunoglobulin heavy chain diversity (D) and joining (J(H)) gene segments were not detected in the myeloid cultures suggesting that these conditions support early B cell progenitors. Transferring myeloid cultures to conditions optimal for lymphopoiesis resulted in B cell development that temporally recapitulated events in the bone marrow. We also demonstrate that these lymphoid progenitors are targets for retroviral transduction. This study suggests that long-term cultures provide a useful system to access early lymphoid progenitors and study the events that regulate their differentiation.