SP cells in DLBCL. (A) Hoechst 33342 staining detected an SP (as boxed) with low dye content in lymphoma cell lines both in vitro and in vivo after passaging by xenotransplantation in the mouse or egg, as indicated. Coincubation with verapamil (50 µg/mL) abrogated SP cell formation (lower middle panel); the proportions of SP cells are given in percentage of all nucleated cells. (B) The proportions of SP cells were characteristic for each cell line of ABC type (OCI Ly3 and U2932) and GCB type (Karpas 422, SuDHL4, OCI Ly1, and Balm-3; n = 10 per cell line; standard deviations indicated by errors bars). (C) SP cells were also detected in primary patient lymphoma cell specimen (example in C; mean value from 8 patient samples in B, separate column). (D) Identical monoclonal immunoglobulin heavy chain rearrangements were found in SP and non-SP cells, as shown for the representative patient sample of C. (E) Expression of CD19 and a low level of immunoglobulin κ light chain in SP and non-SP cells, compatible with an identical mature B-cell phenotype in both cell types. (F) Comparable transcript levels for the ABC transporter G2 in the cell lines OCI Ly1, OCI Ly3, U2932, and SuDHL4. (G) Cell-cycle analysis of non-SP vs SP cells of the cell lines Karpas 422, SuDHL4, OCI Ly1, and OCI Ly3 with significant enrichment of SP cells in the G₀/G₁ phase (2-way ANOVA G₀/G₁ non-SP vs SP all cell lines P < .0001, each cell line n = 3).