title: Resolving the daratumumab interference with blood compatibility testing.
abstract: BACKGROUND
  Daratumumab (DARA), a promising novel therapy for multiple myeloma, is an IgG1κ monoclonal antibody that recognizes CD38 on myeloma cells. During routine compatibility testing, we observed that the plasma of five of five DARA-treated patients demonstrated a positive antibody screen and panreactivity on red blood cell (RBC) panel testing. We hypothesized that the observed panreactivity reflected DARA binding to CD38 on reagent RBCs, and we investigated methods to prevent this binding.
  
  
  METHODS
  DARA binding to CD38+ or CD38- HL60 cells was assessed by flow cytometry. To remove cell surface CD38, cells were incubated with dithiothreitol (DTT) or trypsin. Soluble CD38 or anti-DARA was used to neutralize DARA in solution. Routine blood bank serologic methods were used to test samples from DARA-treated patients and normal plasma samples spiked with DARA and/or alloantibodies.
  
  
  RESULTS
  Normal plasma samples spiked with DARA (0.1-10 µg/mL) and incubated with reagent RBCs recapitulated the interference observed with samples from DARA-treated patients. Flow cytometry experiments confirmed DARA binding to CD38+ HL60 cells, but not to CD38- controls. DTT treatment of CD38+ HL60 cells reduced DARA binding by 92% by denaturing cell surface CD38. Treating DARA-containing plasma with soluble CD38 or anti-DARA idiotype also inhibited DARA binding.
  
  
  CONCLUSIONS
  DARA causes panreactivity in vitro by binding to CD38 on reagent RBCs. Treating reagent RBCs with DTT is a robust method to negate the DARA interference, enabling the safe provision of blood to DARA-treated patients. Because DTT denatures Kell antigens, K- units are provided to these patients.
authors.affiliation: Blood Bank, Department of Pathology, Brigham and Women's Hospital.
authors.forename: Claudia I
authors.initials: CI
authors.lastname: Chapuy
authors.affiliation: Blood Bank, Department of Pathology, Brigham and Women's Hospital.
authors.forename: Rachel T
authors.initials: RT
authors.lastname: Nicholson
authors.affiliation: Blood Bank, Department of Pathology, Brigham and Women's Hospital.
authors.forename: Maria D
authors.initials: MD
authors.lastname: Aguad
authors.affiliation: Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts.
authors.forename: Bjoern
authors.initials: B
authors.lastname: Chapuy
authors.affiliation: Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts.
authors.forename: Jacob P
authors.initials: JP
authors.lastname: Laubach
authors.affiliation: Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts.
authors.forename: Paul G
authors.initials: PG
authors.lastname: Richardson
authors.affiliation: Janssen R&D, Spring House, Pennsylvania.
authors.forename: Parul
authors.initials: P
authors.lastname: Doshi
authors.affiliation: Blood Bank, Department of Pathology, Brigham and Women's Hospital.
authors.forename: Richard M
authors.initials: RM
authors.lastname: Kaufman
mesh_terms: D051997:ADP-ribosyl Cyclase 1 / Q000235:genetics / Q000378:metabolism; D000911:Antibodies, Monoclonal / Q000276:immunology* / Q000627:therapeutic use; D001788:Blood Grouping and Crossmatching; D003429:Cross Reactions / Q000187:drug effects; D004229:Dithiothreitol / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004912:Erythrocytes / Q000187:drug effects / Q000276:immunology* / Q000378:metabolism; D005434:Flow Cytometry; D018922:HL-60 Cells; D006801:Humans; D009101:Multiple Myeloma / Q000276:immunology / Q000628:therapy; D012698:Serologic Tests; D014162:Transfection
chemical_list: D000911:Antibodies, Monoclonal; C556306:daratumumab; D051997:ADP-ribosyl Cyclase 1; D004229:Dithiothreitol