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

Fig. 16.4 Kaplan±Meier Plot
depicting survival of mice
bearing hepatic melanoma
metastases. C57BL/6 mice
were injected intrasplenically
with 2.5 × 10 6 murine melanoma
cells. After 1 week, animals
received i.v. injections of
either PBS (solid line), 8 mg
ch14.18 + 24000 IU IL-2
(dashed line) or 8 mgof
ch14.18±IL-2 (dotted line) for 7
consecutive days. Surviving animals
were sacrificed on day 122.
16.5 Melanoma
and non-treated control mice. Taken together, these data indicated that such clonotypic
T cells are activated and expanded by IL-2 in the tumor microenvironment, and
subsequently are capable of controlling tumor growth [63]. Alternatively, GD2-positive
B78-D14 murine melanoma tumors and GD2-negative wild-type B16 melanoma
tumors were induced by separate s.c. injection of these respective tumor cells on the
left and the right side of the animal, resulting in individual tumors either expressing
or lacking the GD2 target antigen of the IL-2 immunocytokine. Boosting the immune
response by targeting IL-2 to one localized tumor proved sufficient to promote
a powerful response against non-targeted tumors. This experimental design definitely
excluded the possibility that the curative response against the wild-type B16 tumor
was a bystander effect of the response against the B78-D14 cells. This finding is
also highly significant for future clinical trials, since heterogeneity of gene expression
is a characteristic of many tumors and their subsequent metastases. In fact, loss
of antigen was suggested to be a major mechanism of immune escape in melanoma
[64]. The eradication of tumor masses achieved despite the lack of targeting due to
lack of the GD2 antigen expression strongly emphasizes the curative potential of this
therapy in a clinical setting.
Since T cells are the main effector cells induced by the IL-2 immunocytokine in our
animal model, the eradication of distant wild-type B16 tumors strongly indicated a
systemic involvement of this T cell response. Thus, T cells were activated either at the
tumor site which was targeted by ch14.18±IL-2 or at the lymph node draining the tumor
[65] where T cells entered the periphery and migrated to the GD2-negative wildtype
B16 tumors. Importantly, analyses of T cell infiltrates by quantitative RT-PCR indicated
the presence of highly expressed TCR Vb regions in both tumor variants.
TCR clonotype mapping revealed the high expression of these regions to be caused
by clonal expansion and also indicated that these specific clonotype TCR transcripts
were identical in both tumors. Taken together, these data suggested that T cell clones,
activated locally by targeted IL-2 therapy actually recirculate and mediate the eradication
of distant tumor sites not subjected to in situ immunocytokine therapy [66].
Treatment of melanoma with the ch14.18±IL-2 immunocytokine induced a Tcell-dependent
immune response, followed by a long-lasting protective tumor immunity
331