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

16.3Non-small Cell Lung Carcinoma
Effective vaccination was demonstrated in a prophylactic setting when immunization
with the pW-CEA vaccine, followed by a lethal challenge with LLC-CEA-KSA
cells, reduced s.c. tumor growth to about 25% of that observed in control animals injected
only with PBS. Control vaccinations with attenuated S. typhimurium carrying
only the control expression vector pER-CEA which was anchored in the ER did not
inhibit s.c. tumor growth [43]. These findings have several implications. First, attenuated
S. typhimurium per se failed to induce tumor-protective immunity in our animal
model. Second, using this carrier with the pW-CEA vaccine accomplished targeting
to secondary lymphoid tissue since this attenuated strain of S. typhimurium was
reported previously to serve as a useful oral carrier which effectively transported
DNA through the gastrointestinal tract and then through the M cells into the Peyer's
patches of the small intestine [44±46]. From there, the attenuated bacteria enter
APCs such as macrophages and DCs, where they die because of their mutation rendering
then unable to synthesize aromatic amino acids, thereby liberating multiple
copies of DNA inside the phagocytes. Third, aside from providing a ªdanger signalº
that stimulates the innate immune system by producing IL-12 and NO [44±46], the
attenuated bacteria carrier provided for an intralymphatic vaccination with naked
DNA [47±49] which was recently reported to be far more effective than either intramuscular,
intradermal, s.c. or intrasplenical routes of vaccination [50]. Importantly,
the pER-CEA vaccine provided an important negative control because it lacked both
the endogenous leader and C-terminal anchor sequences, while also containing an
ER targeting and an ER-retention signal, SEKDEL, thus causing its complete retention
in the ER. Thus, this truncated molecule could not enter the cytoplasm to be
processed in the proteasome. Consequently this prevented suitable peptide epitopes
from combining with MHC class I molecules for transport to the cell surface. However,
this very same sequence of antigen processing and presentation worked very
well indeed in our tumor model as indicated by the effective protective immunity induced
by the pW-CEA vaccine encoding the intact CEA gene that ultimately achieved
expression of CEA epitopes on the cell surface [43].
Significantly, our results indicated that the pW-CEA vaccine elicited an effective
MHC class I antigen-restricted and T cell-mediated, tumor-protective immune response.
This resulted in a 75% reduction of s.c. tumor growth and completely prevented
the dissemination of experimental pulmonary metastases in two of eight
CEA-transgenic mice. Importantly, however, i.v. boosts with non-curative doses of
huKS1/4±IL-2 immunocytokine (5 × 5 mg) completely eradicated s.c. tumor growth
in 100% of experimental animals and prevented dissemination of pulmonary metastases
in 75% of these mice. In contrast, in a control experiment, an equal dose of the
huKS1/4±IL-2 immunocytokine used to boost the control vaccine pER-CEA proved
ineffective. The results of our experiment preventing experimental pulmonary metastases
of Lewis lung carcinoma are depicted in Fig. 16.3.
Significantly, our results suggested some of the immunological mechanisms responsible
for the effective vaccination with the pW-CEA vaccine. Thus, marked activation
of both T cells and DCs was indicated by a decisive up-regulation in expression of
the T cell integrin LFA-2 (CD2) on CD8 + T cells and the CD48 adhesion molecule on
DCs. These two molecules are known to synergize in the binding of T lymphocytes
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