Unusual Inclusions Occurring in the Blasts of Four Patients With Acute Leukemia and Down’s Syndrome

The blast cells from four patients with acute leukemia and Down’s syndrome were found to contain unusual inclusions which manifested similar morphologic and cytochemical characteristics. Ultrastructure studies of the blasts from one of these patients revealed the inclusions to be single membrane-bound structures containing electron-dense amorphous debris, membranous substance, and virus-like particles.