Changing manifestations of a chronic feline haematopoietic proliferative disease during immunotherapy with staphylococcal protein A.

A cat with feline leukaemia virus-associated malignant disease was treated by ex vivo immunoadsorption using staphylococcal protein A coated filters. During the 12-week course of treatment, the morphological manifestations of the haematopoietic disease showed a progressive transition from erythroid to myeloerythroid to myeloid predominance, and the disease was preceded by and associated initially and terminally with a blast transformation of lymphoblastic morphology. Necropsy revealed massive meningo-cerebral, as well as hepatic, renal, myeloid, lymphoid, peritoneal and pelvic infiltrations largely consisting of lymphoblastic cells. Evidence of myeloid and erythroid differentiation was present in all the infiltrates. The several possible bases for this shift of morphological expression are considered.