Study Comparing Inotuzumab Ozogamicin In Combination With Rituximab Versus Defined Investigator's Choice In Follicular Non-Hodgkin's Lymphoma (NHL)

Inclusion Criteria:

* Subjects with a diagnosis of CD20 and CD22-positive, follicular lymphoma, who have received 1 or 2 prior regimens, at least 1 of which should have contained administration of rituximab (either as a single agent or in combination).
* Age 18 years or older.
* ECOG performance status \<= 2.
* ANC \>= 1.5 x 10\^9/L (1500/mL) and platelets \>= 75 x 10\^9/L (75,000/mL), serum creatinine \<= 1.5 x ULN and urine protein to creatinine ratio of \<= 0.5, total bilirubin \<= 1.5 x ULN, AST and ALT \<= 2.5 x ULN.
* At least 1 measurable disease lesion that is \>= 1.5 cm x 1.5 cm by CT or MRI, in an area of no prior radiation therapy, or documented progression in an area that was previously irradiated.

Exclusion Criteria:

* Subjects with clinical evidence of transformation to a more aggressive subtype of lymphoma or grade 3b follicular lymphoma.
* Subjects whose disease is rituximab refractory, meaning that they did not have a CR or PR, or that they experienced disease progression within 6 months from the initiation of the rituximab or rituximab containing treatment regimen administered immediately preceding study enrollment.