We report two preliminary trials of antibody treatment of
B-cell lymphoma. Advanced
lymphoma was treated with chimeric FabFc2, in which mouse Fab' gamma is linked to two human Fc gamma 1 fragments so as to recruit natural effectors to
tumor targets. Terminal
lymphoma was treated with bispecific antibody (BsAb) which recruits the
ribosome-inactivating protein saporin. These different mechanisms led to interesting differences in patterns of
tumor clearance. Eight patients were treated with chimeric antibody of two specificities, each at 12 mg/kg: anti-CD37, plus either anti-CD38 or anti-CD19 according to
tumor phenotype. On completion of the 3-wk treatment, residual plasma antibody had a half-life exceeding 10 d.
Tumor cells in blood disappeared rapidly. However significant reductions in solid masses occurred in only three patients, becoming apparent 3-4 wk after beginning treatment and then continuing slowly. Five patients were treated with preformed
immune complexes of
saporin and F(ab' gamma)2 BsAb. Although doses of
saporin reached 10 mg weekly, contact with the
tumor can only have been fleeting: plasma antibody was undetectable (< 0.5 micrograms/mL) 48 h after infusion, whereas the
saporin disappeared even faster and was undetectable (< 4 ng/mL) at 24 h.
Tumor cells disappeared from the blood more slowly than occurred with chimeric antibody. In contrast shrinkage of extravascular
tumor was more rapid, and occurred in all patients, but proved less durable.