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

6
Immune Cells in the Tumor Microenvironment
Theresa L. Whiteside
6.1
Introduction
Tumors create a unique microenvironment, in which all cells appear to be devoted to
one purpose, i. e. that of supporting and promoting tumor progression. Although
immune and inflammatory cells are frequently a component of this microenvironment,
their functional status appears to be different from that of leukocytes infiltrating
inflammatory sites in non-malignant tissues. Also, effects of the tumor microenvironment
seem to extend beyond the tumor and systemic changes in the immune
cell responses have been observed in tumor-bearing hosts. Over the years, speculations
about the role of tumor-infiltrating immune cells in promoting or controlling
tumor growth have been replaced by more solid information based on results of increasingly
sophisticated in situ analyses. In this chapter, recent progress in our understanding
of the immune cell interactions with the tumor will be reviewed. The
complexity of these interactions and the existence of multiple ingenious ways in
which tumors manage to disarm the host immune system indicate that novel approaches
are necessary to immune therapies targeting human cancer.
6.2
The Immune System and Tumor Progression
Cancer Immune Therapie: Current and Future Strategies
Edited by G. Stuhler and P. Walden
Copyright # 2002 Wiley-VCH Verlag GmbH & Co. KGaA
ISBNs: 3-527-30441-X (Hardback); 3-527-60079-5
(Electronic)
In man, tumor development from a single transformed cell to a clone of malignant
cells forming a tumor is a multi-step process [1]. It involves multiple genetic changes,
which occur in the progeny of the transformed cell over many years, accumulate and
result in the establishment of the malignant phenotype characterized by uncontrolled
growth [1]. The cumulative effect of these changes is to assure survival of the tumor at
the expense of surrounding normal tissue cells. Thus, the tumor microenvironment
within a tissue becomes modified in the course of tumor development, largely to meet
its requirements and sustain its growth. Among the tissue cells surrounding the tumor
and forming a scaffold supporting its expansion, cells of the hematopoietic system,
lymphocytes, macrophages and granulocytes are frequently found. While the presence
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