Soluble c‐kit molecule in serum from healthy individuals and patients with haemopoietic disorders

Summary The proto‐oncogeae, c‐kit, encodes a transmembrane tyrosine kinase receptor (KIT) and plays an important role in haemopoiesis. We have identified a 95kD soluble form of KIT (S‐KIT) in culture supernatant of human megakaryoblastic cell line, CMK. To study the physiological significance of S‐KIT, we have established a sensitive sandwich ELISA system. Serum samples from healthy individuals contained detectable amounts of S‐KIT. Next, we determined a total of 220 samples from 134 patients with haemopoietic disorders. A considerable number of patients with acute myeloid leukaemia (AML), especially those with more immature phenotypes (MO, Ml or M2) had elevated levels of serum S‐KIT. Those levels decreased to the normal range after effective chemotherapy. In chronic myeloid leukaemia, patients with myeloid blastic crisis showed markedly elevated levels of serum S‐KIT. In contrast, S‐KIT levels decreased in cases with either acute or chronic lymphoid leukaemia. There was a tendency for patients with severe aplastic anaemia to show decreased levels, but it was not significant. In myelodysplastic syndrome, S‐KIT levels appeared to vary by subsets, with higher concentration in more advanced forms of the disease. Although the functional role of S‐KIT is not yet elucidated, these results suggest that the serum S‐KIT levels may reflect the pathological states of various haematological disorders.