The microscopic anatomy of experimental rat CC531 colon tumour metastases:Consequences for immunotherapy?

The colon adenocarcinoma cell line CC531 was adopted as a model for immunot herapeutical treatment of experimental colorectal metastases in a syngeneic rat model. We studied the presence and localization of T and natural kille r cells, vessels and matrix proteins in in vivo growing CC531 tumours by im munohistochemistry. CC531 tumours were induced either in the lungs by injec ting CC531 tumour cells into a tail vein or in the liver by injection of CC 531 tumour cells under the liver capsule or into a mesenteric vein. All 3 t umour types were composed of islets of tightly apposed tumour cells surroun ded by abundantly present tumour-stroma which contained tumour vessels and matrix proteins. Some of these matrix proteins, especially laminin and coll agen IV formed a basal membrane-like structure around the tumour nodules. T his structure was most pronounced in mesenteric vein-induced liver tumours and less prominent in subcapsular-induced liver tumours and tail vein-induc ed lung tumours. Tumour-infiltrating lymphocytes of both T and natural kill er cell origin were found in the tumours, but predominantly in the tumour s troma, separated from the islets of tumour cells by the basal membrane-like structure. We hypothesize that the matrix proteins of these tumours play a n ambivalent role: they may provide a substratum for migration of effector cells into the tumour stroma but may also provide a barrier preventing dire ct contact between tumour target cells and immune effector cells.