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

16.2 Treatment of Tumor Metastases with Immunocytokines
Tab. 16.2 Boost of tumor-protective immunity after tumor challenge of mice cured of established
pulmonary colon cancer metastases
Initial Treatment Interval Tumor Boost Metastatic Lung
tumor (weaks) challenge score weight (g)
CT26-KSA huKS1/4±IL-2 6 CT26-KSA ± 0,0,0,0,1,1,2,3 0.28+0.1
CT26-KSA huKS1/4±IL-2 6 CT26-KSA huKS1/4±IL 2 a 0,0,0,0,0,0,0,0 0.19+0.01
None none none CT26-KSA PBS 2,2,2,3,3,3,3,3 0.51+0.11
None none none CT26-KSA huKS1/4±IL-2 a 2,2,3,3,3,3,3,3 0.62+0.10
a
A boost of tumor-protective immunity was attempted 4 days after tumor challenge by two i. v. injections
of 5 mg huKS1/4±IL-2 each on days 4 and 6.
BALB/c mice (n = 8) that had been tumor free for 6 weeks after treatment with
huKS1/4±IL-2 were challenged at this time point with CT26-KSA, followed after
4 days with two non-curative doses of huKS1/4±IL-2 fusion protein. Thus, 4 weeks
after this boost, all eight mice completely rejected the tumor cell challenge. In contrast,
a control group of mice (n = 8) that was challenged with CT26-KSA tumor cells
after 6 weeks, but received PBS instead of the huKS1/4±IL-2 fusion protein, exhibited
metastases in all eight mice, 4 weeks after tumor cell challenge [12].
The finding of a long-lasting tumor-protective immunity was always consistent with
the appearance of CD8 + memory Tcells in secondary lymphoid organs as determined
by flow cytometry. Furthermore, mice with established pulmonary metastases successfully
treated with huKS1/4±IL-2 immunocytokine showed a 10% increase in
CD44 hi , Ly-6C hi , CD45RB lo and CD62L lo CD8 + Tcells in contrast to naive mice 6 weeks
after tumor inoculation. This represents a well-accepted memory phenotype [15, 16].
T cell memory was further analyzed by assessing CTL precursor (pCTL) frequency
by limiting dilutions. In this case, the huKS1/4±IL-2 immunocytokine-treated mice
revealed an approximately 30-fold increase in pCTL frequency over PBS controls,
which further documented the development of a CD8 + T cell memory immune response
[15]. Significantly, this memory immune response was maintained in the absence
of tumor antigen. This was demonstrated by using CD8 + T cells from huKS1/
4±IL-2-treated animals which were horizontally transferred into syngeneic scid/scid
mice. These CD8 + T cells were literally parked for 6 weeks in these immune-deficient
mice, lacking mature T and B lymphocytes, to allow activated CD8 + T cells to apoptose
and CD8 + memory T cells to survive. In fact, there was a continuous decrease in
the number of CD8 + T cells, until 5 weeks later less than 5% of CD8 + T cells were detectable
by FACS analysis, suggesting that the majority of these T effector cells apoptosed.
Thus, the continuous presence of tumor antigen or naive T cells was not required
to maintain a long-lived CD8 + T cell memory among CD8 + T cells that were
adoptively transferred into syngeneic mice and left there for 6 weeks. In fact, when
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