For many years the primary regulator of blood platelet production had a name, thrombopoietin, but the putative protein was never purified nor the gene cloned, so many doubted its very existence. Based on the identification of a previously undescribed proto-oncogene termed c-Mpl, predicted to encode a novel cytokine receptor, we and two other groups nearly simultaneously cloned the thrombopoietin gene.
As predicted, thrombopoietin is the primary regulator of platelet production, its levels being inversely related to platelet levels in the blood. The availability of recombinant thrombopoietin has enabled many studies of its biology. The hormone engages a number of common and unique biological signaling systems, and its use in animal models of thrombocytopenia predicted it would be very useful clinically.
Despite an initial setback in clinical development related to the use of a highly engineered, non-natural version of the hormone in normal individuals donating platelets for transfusion, thrombopoeitin mimic drugs have now been developed and FDA-approved for use in patients with immune thrombocytopenia.
Numerous other clinical indicators are also under active investigation, including chemotherapy-induced thrombocytopenia.