02 BOOK OF ABSTRACTS .indd

The humoral and cellular mechanisms effective
for killing tumor cells in vitro
Vladimir Kotnik 1 , Katarina Jordan 1 , Katarina Pirc 1 , Srdjan Novakovi} 2
1
Institute of Microbiology and Immunology, Medical Faculty, University of Ljubljana,
Korytkova 2, 1000 Ljubljana, Slovenia, 2 Institute of Oncology Ljubljana, Zalo{ka 2, 1000
Ljubljana, Slovenia
Aim of the presentation is to discus different humoral and cellular mechanisms of
surveillance and defense against tumors.
Material and methods: Rabbit antibodies directed against membrane antigens of
K562 cells were produced and used to make K562 – anti K562 antibodies immune
complexes. Guinea pig complement finally diluted 1:10 was used to trigger the
apoptosis and the cell death of target cells. Apoptosis and cell death were detected
by the flow cytometry employing Annexin V test. The same kind of experiment was
used on CD20+ Raji cells. Anti CD20 humanized monoclonal antibodies were used
to make immune complexes. Human complement finally diluted 1:5 was added to
induce apoptosis and cell killing. Effect was detected by Annexin V test also. The
same target cells were used to asses effects of nonprimed fresh human PBMC. The
Annexin test was used to detect a possible synergistic action of complement and
PBMC induced cell death.
Results: Clear proapoptotic and cytotoxic activity of complement was detected in
both models. PBMC were cytotoxic also, but in a lesser degree than complement.
Synergistic effect of both ways of cytotoxicity was not observed.
Discussion: Tumor cells induced immune response and the production of specific
antibodies directed against selected tumor antigens. These antibodies together with
34l19
complement induce apoptosis and cell cytotoxicity of antibody specific tumor cells.
Tumor cells labeled with specific antibodies activate nonprimed PBMC obviously
via ADCC mechanisms resulting in apoptosis and cell death. However, the tested
mechanisms were functional and very effective in described models, several
investigators reported, that tumor cells are able to escape from destruction using
distinctive strategies, like changing or shedding of specific antigens, developing
inhibitory regulatory molecules able to stop functioning of killer cells or complement
activation, making tolerogenic surfaces etc.