UVB-irradiated apoptotic cells induce accelerated growth of co-implanted viable tumor cells in immune competent mice

The presence of a solid tumor is the result of a complex balance between rejection, tolerance and regeneration in which the interactions of tumor cells with cells of the host immune system contribute strongly to the final outcome. Here we report on a model where lethally UVB-irradiated cells cause accelerated growth of viable tumor cells in vitro and in allogeneic immune competent mice. UVB-irradiated tumor cells alone did not form tumors and failed to induce tolerance for a second challenge with the same allogeneic tumor. Our data show an important role for dying cells in promoting accelerated tumor cell growth of a small number of viable tumor cells in a large inoculum of UVB-irradiated tumor cells. This occurs when viable and dying/dead tumor cells are in close proximity, suggesting that mobile factors contribute to growth promotion. The anti-inflammatory and growth promoting properties of apoptotic cells are based on several independent effects. UVB-irradiated apoptotic cells directly release a growth...