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

392 Glossary
T bodies are being tested for their antitumor activities in clinical trials with renal cell
carcinoma patients.
Telomerase, telomerase reverse transcriptase (hTERT)
A ribonucleoprotein (larger than 100 kDa) with reverse transcriptase activity that, in
concert with other molecules, adds multiple short telemetric DNA repeats to the 3'
end of chromosomes (telomeres) to preserve their structural integrity. Without telomerase
activity cells progressively loose their terminal sequence with each cell cycle.
Telomerase is expressed in self-replicating stem cells and in more than 85% of all tumors
but rarely in normal cells. Telomerase expression is thought to be among the
essential factors in tumorigenesis and therefore is considered as a potential universal
tumor-associated antigen.
T helper 1 (T h1)/T helper 2 (T h2) dichotomy
Th1/Th2 dichotomy of the regulatory T lymphocyte responses where the immune
reaction is polarized towards cellular or humoral immune responses. These different
directions of the immune responses might, in some situations, be mutually suppressive.
The polarity of the immune response is usually correlated to the cytokine profiles
with interleukin (IL)-2, interferon (IFN)-g and tumor necrosis factor-a being indicative
of a Th1 response, and IL-4, -5 and -10 indicative of a Th2 response. Selective
activation of Th1 cells is mediated by IFN-g and IL-12, and inhibited by IL-4 and -10,
whereas IL-4 is essential for growth and differentiation of Th2 cells.
Toll-like receptor (TLR)
Highly conserved cell surface receptors expressed preferentially on leukocytes but
also on epithelial cells in lung, ovary or prostate. They are human homologs of the
Drosophila Toll gene that is involved in dorsal/ventral differentiation. TLRs are important
receptors in innate immunity. They bind microbial lipoproteins, DNA (see
GpG motif) or lipopolysaccharide, and induce a range of cellular activities including
proliferation and cytokine secretion. At least 10 TLRs have been identified to date
that share a Toll/interleukin-1 receptor motif in the cytoplasmic domain and multiple
copies of leucine-rich repeats in the extracellular domain. Activation of TLRs results
in signaling via nuclear factor (NF)-kB, MyD88 and IRAK TRAF6 molecules.
Different types of monocytes express different spectra of the TLRs (pathogen-associated
molecular pattern recognition profiles) which translate into differences in cytokine
production depending on the nature of pathogens and, thus, in a polarization
of the resulting adaptive immune response (see Adaptive immunity).
Tumor antigen, tumor-associated antigen (TAA), tumor rejection antigen
An antigen expressed exclusively or predominantly by tumor cells. Since the majority
of the antigens described so far for various different tumors are not tumor-specific
but expressed in non-malignant cells as well, the more cautious term TAA is usually
preferred. TAA can be differentiation antigens shared with non-transformed cells of
the tumor histotype, over-expressed proteins, embryonic antigens, antigens of the tumor-testis
type, viral antigens in cases of tumor-associated viruses or mutations.