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

tivation of naive T cells requires two independent signals. First, binding of the peptide/MHC
complex by the TCR which transmits signals to T cells indicating antigen
recognition and second, ligation of CD28 with B7±1 or B7±2 which produces a second
signal and thereby initiates T cell responses and production of armed effector T
cells [37, 38].
A marked increase over controls observed in expression of CD25, i. e. the high-affinity
IL-2 receptor a chain, and CD69, an early T cell activation antigen, indicated that
T cell activation took place in secondary lymphoid tissues following vaccination and
tumor cell challenge. Furthermore, we observed a specific and decisive elevation in
the production of pro-inflammatory cytokines, interferon (IFN)-g and IL-12 by such
T cells as shown in Fig. 16.1 which is known to be a key feature of their activation
[17]. The notion that secondary lymphoid tissue of mice that exhibited protective tumor
immunity contained tumor-specific CD8 + T cells was further supported by the
finding that splenocytes isolated from such mice specifically lysed MC38-CEA-KSA
tumor target cells in vitro in an MHC class I antigen-restricted manner. In contrast,
splenocytes isolated from mice in all control groups failed to lyse these tumor target
cells.
As mentioned above, the rationale for using small boosts with huKS1/4±IL-2 fusion
protein to improve tumor-protective immune responses induced by our CEA-based
DNA vaccine was based on results of our prior work where this approach completely
eradicated CT26 lung tumor metastases in 100% of syngeneic BALB/c mice [11, 12].
In fact, injection of small, non-curative doses of huKS1/4±IL-2 fusion protein shortly
Fig. 16.1 Induction of pro-inflammatory
cytokines. C57BL/6J mice transgenic
for CEA were immunized, challenged
with MC38-CEA-KSA tumor cells
and boosted with huKS1/4±IL-2 fusion
protein. Splenocytes were obtained 1
week after tumor cell challenge and cells
were plated in the presence of irradiated
MC38 cells; cultured supernatants were
harvested after 24 h and either analyzed
for release of IFN-g (A) or IL-12 (B) by a
solid-phase sandwich ELISA. Each value
represents the mean for four animals;
bars, SD.
16.2 Treatment of Tumor Metastases with Immunocytokines
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