CD19 mRNA quantification improves rituximab treatment-to-target approach: A proof of concept study

•Treatment-to-target approach for RTX monitors CD19 + B cells by flow cytometry (FC).•Relapses occur despite the CD19 antigen remaining under the detection limit of FC.•CD19 mRNA quantification is more sensitive than FC in detecting CD19 + B cells.•CD19 mRNA quantification can be applied to other antibodies against CD20 + B cells.

We compared pre-amplification (PA) RT-PCR blood CD19 mRNA quantification with flow cytometry (FC), to personalize rituximab re-treatment in neuromyelitis optica spectrum disorders (NMOSDs) patients. 47 blood samples from 3 NMOSDs patients were studied. PA-RT-PCR quantified CD19 in all samples, and a positivity threshold was defined, whereas CD19 + B cells were under threshold in 31/47 samples by FC. In all samples where CD19 + B cells were above FC threshold, they resulted above the PA-RT-PCR threshold. CD19 mRNA was above threshold in 8 other samples, resulted negative by FC, and preceded the FC positivity in 7/8 samples by 1-3 months, showing major sensitivity.