02 BOOK OF ABSTRACTS .indd

Classical tumor vaccine potently stimulates dendritic cells
for the activation of naive T lymphocytes and forming
of memory cell pool
Srdjan Novakovi} 1 , Vida Stegel 1 , Andreja Kopitar 2 , Alojz Ihan 2 ,
Barbara Jezer{ek Novakovi} 1
1
Institute of Oncology Ljubljana, Zalo{ka 2, 1000 Ljubljana, Slovenia; 2 Institute of
Microbiology and Immunology, Medical Faculty, Korytnikova 2, 1000 Ljubljana, Slovenia
Background: The dendritic cells - DC represent a small subpopulation of bone
marrow-derived leukocytes that have a primary role in antigen presentation. They
appear to be required for the initial activation of naive T-cells. DC exist in two
stages of maturation. Immature (non-activated) DC expressing a low level of
co-stimulatory molecules and mature DC displaying increased levels of the cell
surface co-stimulatory molecules (CD40, CD80, CD86, CD83) as well as HLA-DR
molecules. The maturation of DC is primed through different stimuli (cytokines,
microbial products) and consequently results in antigen presentation and T cell
activation. In reply to antigen recognition, the responding T cells secrete growth
promoting cytokines (e.g. IL2, IL4, IFNγ) and express cell surface molecules CD25
(IL-2-receptor), and CD69 (activation marker). After the interaction of CD4+ T helper
cell (Th) with an antigen presenting cell, Th differentiate to effector Th1 – producing
predominately IFNγ and TNFγ, and/or Th2 - producing IL4, IL5, IL9, IL10, IL13.
Aim: Since it has been clearly presented that DC could be stimulated in different
ways, we considered that irradiated tumor cells combined with the nonspecific
immunomodulator might be quite useful for their activation. The aim of this study
was thus to determine the capability of DC stimulated through the irradiated tumour
cells and MVE-2 to induce the activation of T cells.
Materials and Methods: For the activation of DC, irradiated B16F1 melanoma cells
and nonspecific immunomodulator MVE-2 were used. The activation of T cells was
assessed by the determination of expression of T-cell specific activation markers -
CD25, CD69. Using the cytotoxicity assay, the cytotoxic activity of MNC co-incubated
with DC was determined.
Results: Activated DC significantly increased the proportion of CD25+ and CD69+
cells among CD3+ T lymphocytes; at the same time a significant increase of cytotoxic
capacity was determined in MNC co-incubated with DC that have been previously
stimulated with the tumor vaccine. With the results of in vivo experiments, the
phagocytic cells (including DC) were proved to be essential for establishing an
active protection against tumor cells (tumor development), but more importantly,
also for the formation of memory cell pool.
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Conclusion: The tumor vaccine composed of irradiated tumor cells and a nonspecific
immunomodulator provides an efficient stimulus to DC making them competent
activators of T lymphocytes.