Recombinant Bispecific Monoclonal Antibody (bsMAb) Against CD20 and CD22 Active In Vitro and In Vivo Against B-Cell Lymphomas.

Background: Preclinical and clinical results suggest improved anti-lymphoma activity of combining anti-CD20 and anti-CD22 MAbs. Our aim was to develop a recombinant bispecific MAb against CD20 and CD22 antigens, and to evaluate its anti-tumor potency compared to the parental MAbs.

Methods: Tetravalent anti-CD20/CD22 bsMAb in the form of anti-CD20 IgG linked to two anti-CD22 scFv’s was prepared recombinantly. The ability of the bsMAb to inhibit cell growth and mediate CDC and ADCC was evaluated by cell-based assays. Phosphorylation and distribution of CD22 in B-lymphoma cells treated with the bsMAb were studied by immunoblotting. The extension of survival of disseminated Daudi lymphoma cells in SCID mice also was evalauted.

Results: In contrast to the parental anti-CD22 MAb, epratuzumab, the bsMAb did not internalize in Ramos cells. In CDC tests, the bsMAb showed no cytotoxic effects, similar to epratuzumab, although it did bind C1q complement protein, unlike epratuzumab. In ADCC, the bsMAb was as potent as the parental humanized anti-CD20 Mab, hA20, in inducing target-cell lysis. The anti-CD20/CD22 bsMAb has distinct effects on NHL B-cell lines compared to each parental monospecific MAb or in combination:

1. <10 nM bsMAb causes cells to aggregate;

2. in the soluble, non-crosslinked form, while none of the parental MAbs alone or mixed had significant anti-proliferative activity, the recombinant bsMAb was strongly anti-proliferative;

3. the anti-proliferation activities induced by an anti-IgM Ab and the bsMAb were synergistic; and

4. the bsMAb resulted in rapid redistribution of CD22 into detergent-resistant membrane microdomains on the cell surface.

Initial animal studies show that the bsMab significantly extended survival over control SCID mice.

Conclusion: The recombinantly fused anti-CD20/CD22 bsMAb has new properties compared to the parental monospecific MAbs, and may represent a new class of potential therapeutic agents that could replace binary combinations of antibodies.