CD20-selective inhibition of CD47-SIRPα “don't eat me” signaling with a bispecific antibody-derivative enhances the anticancer activity of daratumumab, alemtuzumab and obinutuzumab

ABSTRACT

Here, we report on a novel bispecific antibody-derivative, designated RTX-CD47, with unique capacity for CD20-directed inhibition of CD47-SIRPα “don't eat me” signaling. RTX-CD47 comprises a CD20-targeting scFv antibody fragment derived from rituximab fused in tandem to a CD47-blocking scFv. Single agent treatment with RTX-CD47 triggered significant phagocytic removal of CD20^pos/CD47^pos malignant B-cells, but not of CD20^neg/CD47^pos cells, and required no pro-phagocytic FcR-mediated signaling. Importantly, treatment with RTX-CD47 synergistically enhanced the phagocytic elimination of primary malignant B cells by autologous phagocytic effector cells as induced by therapeutic anticancer antibodies daratumumab (anti-CD38), alemtuzumab (anti-CD52) and obinutuzumab (anti-CD20). In conclusion, RTX-CD47 blocks CD47 “don't eat me” signaling by cancer cells in a CD20-directed manner with essentially no activity towards CD20^neg/CD47^pos cells and enhances the activity of therapeutic anticancer antibodies directed to B-cell malignancies.

KEYWORDS:

• bispecific antibody
• CD47
• phagocytosis
• rituximab
• SIRPα

Disclosure of potential conflicts of interest

No potential conflicts of interest were disclosed.

Acknowledgments

We would like to thank dr. Jeannette H.W. Leusen of the University Medical Center Utrecht, The Netherlands, for kindly providing the CEM and CEM.CD20 cells. We would like to thank Roche and dr. Christian Klein for provision of the anti-CD20 antibody obinutuzumab.

Financial support

This work was supported by Dutch Cancer Society grants RUG 2009–4355, RUG2011-5206, RUG2012-5541, RUG2013-6209, RUG2014-6986.