Serum levels of IL-7 in bone marrow transplant recipients: relationship toclinical characteristics and lymphocyte count

IL-7 is produced by stromal cells and is the major lympho- and thymopoietic cytokine, IL-7 induces proliferation and differentiation of immature thymo cytes, and protects thymocytes from apoptosis by induction of bcl-2 express ion. The regulation of IL-7 production is poorly characterized, although do wn-regulation by transforming growth factor-beta (TGF-beta) has been descri bed. We measured the serum levels of IL-7 before and after bone marrow tran splant (BMT) in 32 children undergoing BMT for genetic diseases (severe com bined immune deficiency (SCID) and thalassemia), aplastic anemia, and acute lymphoblastic and non-lymphoblastic leukemia (ALL and ANLL), Prior to BMT, the highest IL-7 levels were observed in patients with SCID and ALL, ie th ose patients with genetic or acquired lymphopenia, Patients with thalassemi a and ANLL had normal levels of IL-7, Over the 8 weeks following BMT, the I L-7 levels of patients with SCID and ALL fell as the absolute lymphocyte co unt (ALC) increased. No detectable change in IL-7 levels was observed in th e patients with thalassemia and ANLL, Levels of IL-7 were highest in the yo ung infants with SCID compared to the age-matched controls. Together, the d ata demonstrate that serum levels of IL-7 in lymphopenic patients are inver sely related to patient age and the absolute lymphocyte count (ALC), The in verse relationship to ALC suggests that there is either direct regulation o f stromal production or more likely, binding of secreted IL-7 to lymphocyte s expressing IL-7 receptors.