The α-interferon (α-IFN) has been shown efficacious in controlling thrombocytosis
in chronic myeloproliferative disorders. In order to better understand the mechanisms
by which this effect is produced, the main parameters of thrombopoiesis have been
evaluated in 8 patients with Essential Thrombocythaemia (ET)just before and at the
end of induction therapy with α-IFN. The patients, 2 males and 6 females, 17-54 years
old, at diagnosis or at least 3 months off cytotoxic drugs, received α-IFN (Roferon
A-Roche) s.c. at a daily dose of 3 × 106 IU for 6-13 weeks. The baseline platelet count of 993±266×109/1 fell, after treatment, to a value of 377±96×109 /1. The histological analysis of the bone marrow showed that the number of megakaryocytes
(MK), initially 5-15 times the normal value (N), decreased to a value of 3-6 × N,
while the MK volume resulted always high. The "in vitro" study of megakaryocytopoiesis,
by the plasma-clot culture technique, documented a significant decrease of the number
of MK colonies (from 73±18 to 29±15; p <0.0001). The half life-span of autologous
platelets labelled withulIn-oxine remained unchanged (97±22 and 101±25 hours before
and after therapy, respectively), while the platelet function abnormalities (hypo-aggregation,
storage pool deficiency, etc) appeared less severe after treatment.
It is concluded that in ET the α-IFN therapy is able to normalize the platelet count
mainly or exclusively by a decrease of platelet production.
The work was supported in part by grant of National Research Council (CNR), special
Project Oncology No 85.02200.44.
