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

16.1.3
Binding and Cytokine Activity of IL-2 Immunocytokines
Evaluation of biological activities of IL-2 fusion proteins indicated that fusion of
rhIL-2 to the C-terminal of the immunoglobulin heavy chain did not reduce IL-2 activity
when measured in proliferation assays with IL-2-dependent mouse or human
T cell lines. In these assays the IL-2 activity of both constructs, ch14.18±IL-2 and
huKS1/4±IL-2, was compared to that of commercially available rhIL-2. These fusion
proteins proved remarkably stable throughout their purification and during subsequent
storage for over 4 years at ±20 8C or lyophilized. The effector functions of the
fusion proteins, i. e. their ability to mediate antibody-dependent cellular cytotoxicity
and complement-dependent cytotoxicity in vitro, were found to be maintained in a similar
range as those of the parental antibodies.
A comparison of the binding activity of the ch14.18±IL-2 fusion protein with that of
the ch14.18 antibody revealed essentially identical GD2 binding as determined by
both direct and competitive binding assays [6, 8]. Dissociation constants (Kd), calculated
from Scatchard analysis of saturation binding curves, were 18 and 24 nM for
ch14.18 and its IL-2 fusion protein, respectively. A Kd of 1.15 nM was determined for
the humanized KS1/4 antibody (huKS1/4), which was identical to that of the
huKS1/4±IL-2 fusion protein.
In summary, these findings indicated that these immunocytokines were biologically
functional and combine the unique targeting ability of antibodies with the immunomodulatory
properties of multi-functional cytokines. These data encouraged us to
critically evaluate the antitumor activity of these immunocytokines as tools to deliver
effective amounts of IL-2 to the tumor microenvironment capable of local activation
of suitable effector cells. The following sections are devoted exclusively to treatment
effects and mechanisms of immunocytokines in tumor models of colon carcinoma,
non-small cell lung carcinoma, prostate carcinoma, melanoma and neuroblastoma.
16.2
Treatment of Tumor Metastases with Immunocytokines
16.2.1
Colorectal Carcinoma
16.2 Treatment of Tumor Metastases with Immunocytokines
Colon carcinoma kills almost 55 000 people each year in the US [9]. Efforts were
made by Riethmçller et al. [10] to improve this situation by exploiting the over-expression
of the human epithelial cell adhesion molecule Ep-CAM/GA733±2 on the
surface of colon carcinoma cells recognized by the murine antibody 17±1A. In a randomized
clinical trial of 189 patients with minimal residual disease after complete
resection of Dukes' C colon carcinoma, a follow-up after 5 years indicated that treatment
with 17±1A reduced the death rate by 30 % and the recurrence rate by 27%.
A 7-year median follow-up confirmed these data and suggested that treatment with
17±1A may have actually cured colon carcinoma patients with no recurrence after
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