Figure 1.

CD20 expression in a diffuse large B-cell lymphoma sample taken at relapse containing a 4 base pair deletion at nucleotide position 353–356. (A) Representation of the amino acid sequence coding for the trans-membrane portion of the CD20 protein (adapted from Binder et al.)⁵ Light blue amino acids are contained within the sequenced region of exon 5 of the MS4A1 gene and dark blue amino acids represent the rituximab epitope brought together by a disulfide bond at two cysteine residues. The red arrow represents the location of the 4 base pair deletion leading to premature termination at amino acid 121 (highlighted with a star). (B) Bright CD20 protein expression by flow cytometry in the mutated sample; inset: CD20 expression of a non-mutated diffuse large B-cell lymphoma sample analyzed during the same time frame demonstrating CD20 fluorescent intensity of benign non-B cells (CD20 negative) and tumor cells (CD20 positive) within the sample. (C) Bright CD20 protein expression by immunohistochemistry in the mutated sample (L26 antibody).