Engraftment of B-cell tumors requires CD4⁺tumor-associated cells. A representative experiment using tumor W (MZL) is shown. Qualitatively similar results were also obtained using tumors M (MZL) and J (FL; data not 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; each panel is a representative section from one of 3 mice in each experimental group. The images show representative sections for each graft that 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; examples of uninvolved omentum are marked with blue arrows. (A) Robust engraftment of a tumor that has undergone mock depletion (beads without antibody). After mock depletion and before injection, T cells make up 11% of the specimen with a CD4:CD8 ratio of 1.7, B cells make up 76% of the specimen, and viability was 91%. Next, 1 × 10⁷ cells were injected i.p., and mice were necropsied at 14 days. The grafts of this tumor contains a mixture of B and T cells (Figure 5). (B) Removal of non-B cells from the specimen ablated engraftment (viability after depletion of B cells was 94%; cell number for injection, 7 × 10⁶, was matched to the B-cell number injected in A). (C) CD8⁺ cells are not required for engraftment. CD8⁺ cells were depleted by a factor of at least 20-fold. For CD8⁺ cells (viability after depletion was 79%; cell number for injection was 1 × 10⁷), there was no discernable effect on the tumor volume or B-cell composition (D) CD4⁺ cells are required for engraftment. The high-power inset shows that the omental areas consist entirely of adipose tissue with a few small vessels, and no tumor is present. Viability at the time of implementation was 83%. (Original magnification ×12.5 and ×400 (insets); the CD4 depletions were assessed with 3 mice each for tumors W, M, and J; the CD8 depletions were performed with 3 mice each on tumors W and M; the various treatments showed essentially indistinguishable results with the various source tumors.)