The phenomenon of hormesis, whereby small amounts of seemingly harmful or stressful agents can be beneficial for the health and lifespan of laboratory animals has been reported in literature. In particular, there is accumulating evidence that daily brief cold stress can increase both numbers and activity of peripheral cytotoxic T lymphocytes and natural killer cells, the major effectors of adaptive and innate tumor immunity, respectively. This type of regimen (for 8 days) has been shown to improve survival of mice infected with intracellular parasite Toxoplasma gondii, which would also be consistent with enhanced cell-mediated immunity.
Presentation of the hypothesis
This paper hypothesizes that brief cold-water stress repeated daily over many months could enhance anti-tumor immunity and improve survival rate of a non-lymphoid cancer. The possible mechanism of the non-specific stimulation of cellular immunity by repeated cold stress appears to involve transient activation of the sympathetic nervous system, hypothalamic-pituitary-adrenal and hypothalamic-pituitary-thyroid axes, as described in more detail in the text. Daily moderate cold hydrotherapy is known to reduce pain and does not appear to have noticeable adverse effects on normal test subjects, although some studies have shown that it can cause transient arrhythmias in patients with heart problems and can also inhibit humoral immunity. Sudden immersion in ice-cold water can cause transient pulmonary edema and increase permeability of the blood-brain barrier, thereby increasing mortality of neurovirulent infections.
Testing the hypothesis
The proposed procedure is an adapted cold swim (5–7 minutes at 20 degrees Celsius, includes gradual adaptation) to be tested on a mouse tumor model. Mortality, tumor size, and measurements of cellular immunity (numbers and activity of peripheral CD8+ T lymphocytes and natural killer cells) of the cold-exposed group would be compared to those of control groups (warm swim and no treatment). Cold-water stress would be administered twice a day for the duration of several months.
Implications of the hypothesis
If the hypothesis is supported by empirical studies and the method is shown to be safe, this could lead to the development of an adjunctive immunotherapy for some (non-lymphoid) cancers, including those caused by viral infections.