Inclusion Criteria:

- Subjects who have been previously diagnosed with CD22-positive, B-cell NHL, according
to WHO classification, which has progressed after at least 2 prior therapies of
probable clinical benefit

- At the expanded cohort, part 2 of the study, subjects must have one of the following:

- Follicular lymphoma previously treated with at least one dose of rituximab, but have
not received radioimmunotherapy

- Diffuse large B-cell lymphoma

- Age 18 years or older

Exclusion Criteria:

- Candidate for potentially curative therapies in the opinion of the investigator

- Chronic lymphocytic leukemia

- Burkitt's lymphoma, primary effusion lymphoma, and precursor B-cell lymphoblastic
lymphoma