- Phase I: Patients receive CTX IV followed by pentostatin IV on day 1 of course 1. Patients also receive filgrastim (G-CSF) subcutaneously once daily beginning on day 3 and continuing until blood counts recover. During the second and subsequent courses, patients receive CTX IV, pentostatin IV, and rituximab IV on day 1. Patients also receive G-CSF as in course 1. Treatment repeats every 3 weeks for 3 courses in the absence of disease progression or unacceptable toxicity. Patients with at least a partial response after the third course receive an additional 3 courses.