Investigation of the Mechanism and the Effect of Cryoimmunology in the Copenhagen Rat

This study examined the potential for “cryoimmunology” to increase the destruction of the Dunning AT-1 prostate tumor after cryosurgery. Two possible mechanisms explaining the cryoimmunologic response were studied. The first was that an antitumor antibody is produced after cryosurgery. The second was that freezing induces an immunostimulatory signal that creates a T-cell response to the tumor. Six groups of animals (three experimental groups and three control groups) were treated once per week for 4 weeks with different therapies designed to investigate these mechanisms. Three types of immune response were measured: (1) the anti-AT-1 tumor immune titer (Ab response) by serum ELISA, (2) the effect on secondary tumor growth after challenge with live AT-1 cells (size and weight of the secondary tumor over time), and (3) the nature of the immunologic infiltrate into the secondary tumors by immunoperoxidase stain. ELISA showed that immune titers were present in the experimental groups after therapy, but the presence of an immune titer did not have a significant effect on tumor propagation. Histology showed the immunologic infiltrate was similar in all groups. These results showed that an immune response to AT-1 tumor was measurable by serum antibody, but it did not significantly limit secondary tumor growth or affect tumor histology. This suggests that the growth of AT-1 tumors is not inhibited by a cryoimmunological response. Thus, the effect of in vivo cryosurgery in the AT-1 tumor system would likely be limited to cellular and vascular changes.