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

gle CD4 + T cells. Short-term culture of these cell suspensions in medium supplemented
with human serum, and recombinant IL-2 and IL-7 leads to dramatic
changes of the cellular composition. In about two-thirds of the cultured tumor cell
suspensions there is marked lymphocyte proliferation that peaks between days 14
and 21. Tumor cells rapidly decline because of both dilution and death in the culture
dish. Proliferation of T lymphocytes does not preserve the original CD4/CD8 ratio.
In fact, the dominant expanding population is CD3 + CD8 + . Monitoring of the expansion
at the antigen-specific level is possible using tetramers. For Melan-A/MART-1
tetramers, a 2000-fold expansion has been measured in the period of 21days. Since
the size of the initial population could be determined with tetramers, it was possible
to make a minimal estimate of 10±11 cell divisions during the culture period [71].
Thus, two conclusions can be drawn from these observations. On one hand, the
sheer numerical inferiority of Melan-A-reactive T cells accumulated in metastases
may in itself account for the apparent lack of efficient antitumor activity. No additional
defects may be invoked. Rapid tumor growth rates together with the lack of appropriate
lymphocyte growth support signals in the tumor environment may suffice
to explain the failure of T cells to expand at the same or a faster pace than that of tumor
cells. Eventually, the tumor would escape CTL control. On the other hand,
Melan-A-specific T cells do not seem to bear major functional defects. They can proliferate
vigorously in the presence of cytokines and residual tumor cells. The expanded
population exhibits potent lytic activity against tumors and can release IFN-g
specifically upon challenge with antigen-bearing tumors.
Fig. 4.2 Dramatic changes in cellular composition
of TILNs upon culture in the presence of
cytokines. This cartoon summarizes the outcomes
after in vitro culture of metastatic lymph
node cell suspensions from melanoma patients
in our laboratory. Culture in medium supplemented
with fetal calf serum but devoid of cytokines
favors the outgrowth of melanoma cell lines in
close to 40% of cases. In contrast, culture in
4.4 Monitoring the Spontaneous CTL Responses to Tumor Antigens
medium supplemented with human serum, rIL-2
and rIL-7 leads to dramatic expansions of T lymphocytes
in about 60±70% of cases. The CD4/
CD8 composition of these expanding cells also
changes during expansion often resulting in
large proportions of CD8 + T lymphocytes. Similar
findings can be observed with TILs from dissociated
metastatic melanoma tumors [105].
Further details are explained in the text.
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