Establishment of K-19⁺ myeloma cell clones. (A) Schematic representation of the mammalian expression vectors pCI-CD19 and pCI-▵19. CMV, cytomegalovirus immediate early enhancer/promoter; Int, chimeric intron; ED, TM, and CD, extracellular, transmembrane, and cytoplasmic domains of CD19, respectively; Poly(A), SV40 late polyadenylation signal; the arrows indicate the positions of pCI-neo specific primers pCIF and pCIR. (B) Single color flow cytometric analysis with PE-labeled mouse antihuman IgG as a negative control (control IgG) and PE-labeled CD19 antibody showing the expression level of the CD19 transgene on different clones. (C) RT-PCR amplification of mRNA from K-19⁺ and K-▵19 clones using full-length CD19F1 and CD19R1 primers (top) or truncated form CD19 F1 and CD19R2 primers (middle). (D) PCR amplification of genomic DNA from the parental cell line, KMS-5, and neo-control clones (M nos. 1, 2, and 3).