We describe the state of the immune system at the late stage of 1,2-dimethylhydrazine (DMH)-induced colon cancer and after administration of placenta-derived multipotent cells (PDMCs). The spleen and thymus indices did not differ among the groups of intact and DMH-treated rats and were not affected by the administration of placenta-derived multipotent cells following the DMH treatment. Moreover, no difference in spontaneous or stimulated phagocytic activity of peritoneal macrophages was observed between healthy rats or the animals with DMH-induced colon cancer (with or without the administration of PDMCs). However, the proliferation of the T cells in the spleen was lower in rats with colon cancer regardless of the administration of PDMCs. Similarly, no changes were observed in the cell cycle distribution of proliferating spleen cells after stimulation by lipopolysaccharide.
Conclusion. Our data demonstrate the absence of the active reaction by peritoneal macrophages and spleen cells to a colon cancer at mid/late stage. Additionally, the administration of PDMCs does not result in a measurable anti-tumor immune response.