Abstract
Spontaneous regression (SR) of tumours is a rare phenomenon not yet fully understood. The aim of this study was to investigate immune cells infiltrating progressive and SR tumours in a Lewis rat sarcoma model. Rats were subcutaneously inoculated with rat sarcoma R5-28 (clone C4) cells. Developing tumours were obtained on day 42 and cryosections were immunohistochemically processed for detection of immune cells. A high density of granulocytes was found in the necrotic areas of both progressive and SR tumours. CD4+ cells and CD8+ cells were rare and sparsely dispersed in the tumour tissue without clear difference between the two types of tumours. On the contrary, CD161+ cells were abundant and evenly distributed in SR tumours, but these cells were very rare in progressive tumours. Based on the differences in number and distribution of the immune cell subpopulations, we believe that natural killer (CD161+) cells play a major role in the destruction of cancer cells during SR of tumours in this Lewis rat model.
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