Figure 8.

Expression of CD38 and complement regulatory proteins impact susceptibility to isatuximab-induced CDC. (A) C3b deposition was quantified by flow cytometry on the surface of MM and DLBCL cell lines, either with natural CD38 RD >250,000 molecules/cell, or for cell lines with parental cell line CD38 RD <250,000 molecules/cell with and without engineering to overexpress CD38 above this threshold. ⋆ indicates CDC sensitive cell lines. (B) Cell surface expression levels of CD38 and the complement regulatory proteins CD46, CD55, and CD59 were determined for MM and DLBCL cell lines by flow cytometry. (C) Complement regulatory protein expression was not affected by overexpression of CD38 in MM and DLBCL cell lines resistant to isatuximab-mediated CDC, for parental cell lines expressing high levels of complement regulatory proteins. (D) Isatuximab-triggered CDC lysis of resistant MM cell lines required increased CD38 expression (>250,000 molecules/cell) and functional inhibition of complement regulatory proteins such as CD59. Experiments were repeated at least twice, with each treatment analyzed in duplicate. Results are mean (SD). Ab, antibody; CDC, complement-dependent cytotoxicity; DLBCL, diffuse large B-cell lymphoma; hIgG1, human immunoglobulin G1; MM, multiple myeloma; RFU, relative fluorescence units; SD, standard deviation.