Hairy cell leukemia. Ultrastructural and cytochemical evaluation of leukemic colonies grown in a semi-solid medium

We examined the fine structure and enzymatic activity of cells composing colonies grown from blood and/or spleen of eight patients with hairy cell leukemia. Mononuclear cells (MNC) were plated over an agar layer in a medium containing methylcellulose and leukocyte-conditioned medium. After 7-10 days incubation colonies were harvested for cytologic study. Colony cells possessed a euchromatic nucleus with an occasional nucleolus. Their cytoplasm contained a prominent Golgi region, numerous mitochondria and small vesicles, many short strands of rough endoplasmic reticulum (RER) and an infrequent phagosome. Well-developed ribosome-lamella complexes and what may have been their intermediate forms appeared in colony cells from three patients. Strong activity for tartrate-resistant acid phosphatase, localized in the RER, nuclear envelope and some Golgi vesicles, was evident in 50-95% of all colony cells. Our results indicate that a high proportion of MNC forming colonies in this culture system maintain the characteristic morphology and cytochemical activity of hairy cells.