Comment on the loss of immunogenicity of tumor cells caused by freezing

Abstract

The freezing of cells to temperatures below about 1 3 0 ° C permits their extended storage in a state of "suspended animation" for decades if not longer. Such long-term storage of viable biological material offers potential benefits in a variety of research and clinical situations. The thesis advocated by Bartlett et al. (1977) is a good example. They suggest that the storage of human tumor tissue in the frozen state might permit its later use as an autologous vaccine in the immunotherapy of cancer. Unfortunately, the data of Bartlett et al., who used a model system of vaccines consisting of BCG and irradiated L10 hepatoma cells, seem to invalidate their own thesis. They reported that L10 cells that had been frozen and stored in liquid nitrogen (LN2) at --196 ° C possessed little or no capacity to prevent the progressive growth of challenge tumor cells, despite the fact that about 50% of the frozen-thawed cells excluded trypan blue. Bartlett et al. conclude that there was "clear evidence that tumor cells which were 'viable' after storage in LN 2 were significantly less immunogenic than cells used without prior freezing". A reasonable extension of that conclusion, if correct, would be that frozen-thawed cells are not suitable for immunotherapy. I believe there are reasons for suggesting that the conclusion of Bartlett et al., and its corollary, may be unduly pessimistic. Those authors have sought to use one of the major potential advantages of cryobiology, namely, the preservation of viable cells in the frozen state. I believe they have underestimated the present level of mechanistic understanding of low temperature biology, however. In this specific instance, this misreading of cryobiology might preclude its future application to a clinical situation in which freezing would be a requisite for the therapy.