Cancer Immune Therapy Edited by G. Stuhler and P. Walden ...

314 16 Immunocytokines: Versatile Molecules for Biotherapy of Malignant Disease
7 years. Mechanisms proposed for this antibody-induced antitumor effect were antibody-dependent
or complement-dependent cytotoxicity and phagocytosis [10].
Based on these encouraging clinical data we addressed the question whether an immunocytokine,
retaining all properties of another Ep-CAM-specific mAb with additional
immunostimulatory capabilities of IL-2, might be equally or more effective in
eliciting an antitumor response. For this purpose a huKS1/4±IL-2 immunocytokine
was constructed recognizing KSA, an Ep-CAM essentially identical in amino acid sequence
to that detected by the 17±1A antibody with only one amino acid difference
in the transmembrane portion of the protein antigen. This construct was used to determine
efficacy and mechanism of action of its antitumor activity in a syngeneic
mouse colon tumor model.
Because colon carcinoma is most likely to metastasize to liver in humans, an experimental
liver metastasis model was developed in BALB/c mice in order to establish efficacy
of immunocytokine therapy against the major metastatic site of this disease. This
was achieved by intrasplenic injection of CT26 colon carcinoma cells, which were
transduced with the gene encoding human KSA that served as a docking site for the
huKS1/4±IL-2 immunocytokine. Treatment of microscopically established hepatic micrometastases
resulted in a complete eradication of macroscopic liver metastases.
This was in contrast to controls that either received equivalent mixtures of antibody
and cytokine or a non-specific immunocytokine, such as ch14.18±IL-2, resulting in
both cases in the same massive tumor growth as in mice that received only PBS and
no other treatment. These findings are illustrated in Tab. 16.1. Proof of complete absence
of micrometastasis was extended beyond that commonly established for other
tumor models by establishing a highly sensitive detection system for CT26-KSA cells.
This was accomplished by RT-PCR of the human cDNA encoding the KS A expressed
only by CT26-KSA cells in contrast to naive murine hepatocytes. This assay detected
Tab. 16.1 Eradication of murine colorectal carcinoma liver and lung metastases by the huKS1/
4±IL2 fusion protein
Treatment a
Metastatic score Organ weight (g)
Liver metastasis
PBS 3333333 3.78+0.71
huKS1/4+IL-2 2233333 3.74+0.78
ch14.18±IL-2 2223333 3.11+0.55
huKS1/4±IL-2 0000000 1.07+0.07
Lung metastasis
PBS 333333 0.80+0.07
huKS1/4+IL-2 122233 0.58+0.18
huKS1/4±IL-2 000000 0.19+0.02
a Experimental liver and lung metastases were induced by intrasplenic injection of 3 610 4 or i.v. injection
of 5 610 4 CT26 KSA cells, respectively. Treatment was started 4 days thereafter, and consisted of
daily i.v. administration of PBS, 15 mg huKS1/4 and 45000 I. U. recombinant IL 2 or 15 mg of either
the non-specific fusion protein, ch14.18±IL 2, or the tumor-specific fusion protein, huKS1/4±IL 2, as
indicated for 7 consecutive days.