BL22 is a type of protein that scientists have created to interact with certain cancer cells. Experiments have shown that BL22 can bind with cancer cells that have a particular kind of protein (called CD22 ) on their surface, and can kill those cells. CD22 is present on certain types of hairy cell leukemia (HCL) cancer cells, and researchers have been working on treatments that will use BL22 and other related proteins to interact with and kill these kinds of cancer cells. The primary purpose of this study will be to provide access to and treatment with BL22 for patients who have HCL in order to determine their response to the treatment. In addition, the study will assess potential side effects of BL22 and examine why some patients respond better than others to treatment with BL22 and related therapies.