To analyze the effects of daratumumab and of nanobody-based hcAbs on the GDPR cyclase activity of living CD38-expressing tumor cells, we incubated CD38-transfected HEK cells or LP-1 cells with CD38-specific hcAbs, daratumumab, or araF-NAD, before addition of NGD+ (Figure 2). Here, CD38 is linked to neoplasm.