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

16.5 Melanoma
16.5.2
Tumor Targeting of LT-a Induces a Peripheral Lymphoid-like Tissue Leading to an
Efficient Immune Response against Melanoma
Initial studies of a tumor-specific ch14.18±LT-a immunocytokine were performed in
a xenograft melanoma model where this treatment was effective in eliminating pulmonary
metastases [68]. Additional experiments in mice with different immune defects
demonstrated a dependence of the therapeutic effect on B lymphocytes and NK
cells. Based on these results, we further examined the effect of ch14.18±LT-a in an
autologous murine melanoma model and thereby scrutinized the working mechanisms
of directed LT-a therapy.
The LT-a immunocytokine-mediated therapy proved to be an effective treatment resulting
in the eradication of established pulmonary murine melanoma metastases
and s.c. tumors. Furthermore, our results suggested an improved T cell immune response,
which is most likely evoked by the induction of peripheral lymphoid tissue
at the tumor site. In fact, the functional significance of this tertiary lymphoid tissue
at tumor sites was confirmed by immunohistologic and electron microscopic analysis
of endothelial/lymphocyte interactions as well as TCR clonotype mapping, providing
evidence for the induction of new T cell clones among tumor-infiltrating lymphocytes
(TIL), which were shown to specifically lyse melanoma cells and to produce
IFN-g in response to a TRP-2180±188-derived peptide [69].
Importantly, the lymphoid-like tissue induced at the site of LT-a accumulation in the
tumor provided a prime environment for initiating T cell responses [70]. Consequently,
we determined whether this lymphoid tissue could promote the clonal expansion
of infiltrating T cells. In fact, analysis of the T cell clonality by RT-PCR/
DGGE (denaturing gradient gel electrophoresis) clonotype mapping revealed a specific
increase in the number of clones over the course of treatment. Comparative clonotype
analysis demonstrated that this increase in the number of clonally expanded
T cells was due to both the persistence as well as the occurrence of new clones. Significantly,
T cell clones detected in lymph nodes draining the tumor were never detected
recurrently in the tumor. This observation, together with the immunohistological
and electron microscopical evidence for the occurrence of high endothelial venules
and interaction of lymphocytes with the endothelia, provided strong presumptive
evidence that the therapy-induced tertiary lymphoid organ was functional and allowed
for priming of naive lymphocytes at the tumor site. Thus, the effects of
ch14.18±LT-a therapy differed substantially from the effects induced by the ch14.18±
IL-2 fusion protein therapy that only boosted a pre-existing T cell response [71].
Nevertheless, for both therapies the eradication of B78-D14 melanoma tumors was
mediated via clonally expanded tumor-specific T cells rather than a polyclonal, nonspecific
T cell population. As in the case of ch14.18±IL-2 treatment, targeted
ch14.18±LT-a therapy was closely linked to tumor regression, raising the question
whether the emergence of new clones was directly related to the treatment or a secondary
phenomenon reflecting the immunological rejection. However, separate analysis
of regressive and progressive parts of human melanoma lesions did not reveal
differences in the numbers of clonotypic T cells, indicating that immunological re-
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