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

334 16 Immunocytokines: Versatile Molecules for Biotherapy of Malignant Disease
jection was not coupled to the presence of higher numbers of clonotypic T cells [71].
Moreover the last tumor samples for TCR clonotype mapping were obtained at day
21, a time when the progressive growth of the tumor just started to level off; thus,
the presence of clonally expanded T cells was at least not caused by tumor necrosis
but rather was a therapy-induced immune response.
The finding that almost no clones were discovered in the draining lymph nodes
further suggested that priming occurred in the tumor and not in the lymph node.
Furthermore, even when we were able to detect an occasional clonal expansion
within these lymph nodes, none of these were identical to those present in the tumor.
The induction of lymphoid tissues at the tumor site will overcome two of the
major obstacles to prolonged immune responses to weakly immunogenic tumors,
i. e. clonal anergy and clonal exhaustion [72]. Thus it may avoid T cell anergy by providing
a suitable cytokine and cellular environment together with a high antigen
load. Clonal exhaustion may also be prevented, since naive T cells can be continuously
primed. Actually, immunocytokine LT-a-dependent lymphoid neogenesis may
improve antitumor responses in several ways and the possibility that naive T cells
can be primed next to the tumor by a tertiary lymphoid organ has several advantages
for immunotherapy. First, a larger number of primed tumor-specific T cells will become
available since tumor-specific antigens predominate [73]. Second, a reduction
will occur in the time between priming and expansion thus decreasing the risk of
primed T cells not reaching the tumor. Third, ongoing T cell responses will react
more readily and quickly to changes in the antigen expression profile of the tumor.
In addition, this may stop lymphocytes from leaving the tumor microenvironment,
which is beneficial since effective immunotherapy depends more on sustaining an
immune response at the appropriate location than on its initiation [74]. Taken together,
our results suggested that the effectiveness of tumor-targeted LT-a therapy
was due to direct clonal expansion of tumor-specific T cells through the formation of
peritumoral lymphoid tissue [69].
16.5.3
ch14.18±IL-2 Immunocytokine Boosts Protective Immunity Induced by an Autologous
Oral DNAVaccine against Murine Melanoma
Initial experiments designed to develop an autologous oral DNA vaccine protecting
against murine melanoma indicated that peripheral tolerance toward melanoma selfantigens
gp100 and TRP-2 could be broken by such a vaccine in CD57BL/6J mice.
Specifically, this was accomplished by a DNA vaccine containing the murine ubiquitin
gene fused to minigenes encoding peptide epitopes gp100 25±33 and TRP-2 181±188.
Characteristically, these epitopes contained dominant anchor residues for MHC class I
antigen alleles H-2D b and H-2K b , respectively. Delivery of this vaccine was by oral gavage
using an attenuated strain of S. typhimurium as carrier that delivered the DNA to
a secondary lymphoid tissues, i. e. the Peyer's patch. Three vaccinations with 10 8 bacteria
at 2-week intervals induced effective tumor-protective immunity in a prophylactic
setting since a lethal s.c. challenge of wild-type B16 melanoma cells 1 week after the
last vaccination, resulted in complete tumor rejection in 25% of experimental mice.