A Method for the Elution of Anti-CD20 With an EDTA/Glycine Acid Solution for Accurate Immunophenotyping of B Lymphocytes Sensitized With Rituximab.

OBJECTIVES

To assess the efficacy of a method to circumvent CD20-positive antigen masking by rituximab for flow cytometry analysis of B-cell malignancies in hematology patients.

METHODS

Mononuclear cells (MNCs) from 10 healthy individuals and 5 untreated patients with B-cell malignancies were sensitized with rituximab. Patients' diagnoses included chronic lymphocytic leukemia, hairy cell leukemia, and follicular lymphoma. MNCs were isolated by gradient density centrifugation. An EDTA/glycine acid (EGA) elution method was used to dissociate CD20-rituximab complexes; afterwards, CD20-positive immunoreactivity was assessed by flow cytometry. A saturation curve was built based on serial dilutions of rituximab. Median fluorescent intensities of CD20-positive signals were obtained before sensitization with rituximab and after its elution with EGA.

RESULTS

CD20-positive signals were not detectable by flow cytometry after rituximab sensitization of B cells. CD20-sensitized vs CD20-unsensitized, CD20-sensitized vs CD20-eluted, and CD20-eluted vs CD20-negative control (NC) MNC populations exhibited statistical differences (P = .001), while CD20-sensitized vs CD20-NC populations did not (P = .499), confirming CD20 antigen masking by rituximab.

CONCLUSIONS

Rituximab interfered with the flow cytometry protocol for CD20 determination on normal and neoplastic B cells. The EGA method efficiently eluted rituximab, allowing for accurate identification of CD20-positive B cells.