Rationale: CD38 is a target for the
therapy of
multiple myeloma (MM) with
monoclonal antibodies such as
daratumumab and
isatuximab. Since MM patients exhibit a high rate of relapse, the development of new biologics targeting alternative CD38
epitopes is desirable. The discovery of
single-domain antibodies (
nanobodies) has opened the way for a new generation of antitumor
therapeutics. We report the generation of nanobody-based humanized
IgG1 heavy chain
antibodies (hcAbs) with a high specificity and affinity that recognize three different and non-overlapping
epitopes of CD38 and compare their cytotoxicity against CD38-expressing hematological
cancer cells in vitro, ex vivo and in vivo. Methods: We generated three humanized hcAbs (WF211-hcAb, MU1067-hcAb, JK36-hcAb) that recognize three different non-overlapping
epitopes (E1, E2, E3) of CD38 by fusion of llama-derived
nanobodies to the hinge- and Fc-domains of human
IgG1. WF211-hcAb shares the binding
epitope E1 with
daratumumab. We compared the capacity of these CD38-specific hcAbs and
daratumumab to induce CDC and ADCC in CD38-expressing tumor cell lines in vitro and in patient MM cells ex vivo as well as effects on xenograft
tumor growth and survival in vivo. Results: CD38-specific heavy chain
antibodies (WF211-hcAb, MU1067-hcAb, JK36-hcAb) potently induced antibody-dependent cellular cytotoxicity (ADCC) in CD38-expressing tumor cell lines and in primary patient MM cells, but only little if any
complement-dependent cytotoxicity (CDC). In vivo, CD38-specific heavy chain
antibodies significantly reduced the growth of systemic
lymphomas and prolonged survival of
tumor bearing SCID mice. Conclusions: CD38-specific nanobody-based humanized
IgG1 heavy chain
antibodies mediate cytotoxicity against CD38-expressing hematological
cancer cells in vitro, ex vivo and in vivo. These promising results of our study indicate that CD38-specific hcAbs warrant further clinical development as
therapeutics for
multiple myeloma and other
hematological malignancies.