What's the target of the antibody rituximab?
CREATE TABLE "cancer_immunotherapy_monoclonal_antibodi" (
  "antibody" text,
  "brand_name" text,
  "approval_date" real,
  "type" text,
  "target" text
);
SELECT "target" FROM "cancer_immunotherapy_monoclonal_antibodi" WHERE "antibody"='rituximab';