NGF and mastocytosis: To investigate the role of TRKA signaling in the pathogenesis of mastocytosis and acute leukemia, 19 C57BL/6J mice were transplanted with retrovially gene-modified primary hematopoietic stem/progenitor cells (TRKA/NGF = 7, TRKA = 6, NGF = 6) in two independent experiments (Figure 1A).