Engraftment of B-cell tumors requires tumor-associated non-B cells. A representative experiment using tumor J (FL; 68% B cells in the thawed aliquot of tumor tissue) is shown. The flow cytometry shows the cellular composition at the time of injection. The omentum with associated mesentery and organs was harvested at 14 days postinjection; each panel is a representative section from 1 of 3 mice in each experimental group. Qualitatively similar results were obtained using tumor W (MZL; data not shown). The images show representative sections for each graft, which include the omentum (black outline), spleen (yellow), and pancreas (orange). Several examples of the lymphoid tumor within the omental areas are marked with green arrows. (A) Robust engraftment of a tumor that has undergone mock depletion (beads without antibody). After mock depletion and before injection, T cells made up 28% of the specimen, B cells and other cell types made up 72% of the specimen, and viability was higher than 80%. Next, 1 × 10⁷ cells were injected i.p., and mice were necropsied at 14 days. (B) Removal of non-B cells from the specimen ablated engraftment (cell number for injection, 7 × 10⁶ with 94% viability was matched to the B-cell number injected in A). The high-power inset shows that the omental areas consist entirely of adipose tissue with a few small vessels, and no tumor is present. (C) The nonneoplastic T-cell fraction of the B-cell tumor can engraft despite removal of the B cells (cell number for injection, 3 × 10⁶ [85% viable], was matched to the number of non-B cells injected in A). Note that although tumor volume is clearly decreased compared with the mock-depleted specimen (A), there are definitive foci of lymphoid tumor marked by the green arrows (immunohistochemical studies indicate that these foci are >90% T cells, with no evidence of B cells; data not shown). (D) The non-B-cell fraction rescues engraftment of the B-cell fraction. The fractions used in B and C were mixed in appropriate proportions to recapitulate the composition of the mock-depleted specimen (cell number for injection, 1 × 10 ⁷ [91% viable] was matched to the number injected in A). The reconstitution suggests that the failure of B cells to engraft in B is a result of loss of a cellular component in the non-B-cell fraction as opposed to any other nonspecific effect of the bead-based manipulation. (Original magnification ×12.5 and ×400 (insets); each treatment with each tumor was assessed with 3 mice; the entire set of studies using tumor J was conducted twice, and the studies of tumor W were conducted once, all with essentially indistinguishable results.)