Regulatory T cells (Tregs) are an immunosuppressive subgroup of CD4+ T cells which are identified by the expression of forkhead box protein P3 (Foxp3). The modulation capacity of these immune cells holds an important role in both transplantation and the development of autoimmune diseases. These cells are the main mediators of self-tolerance and are essential for avoiding excessive immune reactions. Tregs play a key role in the induction of peripheral tolerance that can prevent autoimmunity, by protecting self-reactive lymphocytes from the immune reaction. In contrast to autoimmune responses, tumor cells exploit Tregs in order to prevent immune cell recognition and anti-tumor immune response during the carcinogenesis process. Recently, numerous studies have focused on unraveling the biological functions and principles of Tregs and their primary suppressive mechanisms. Due to the promising and outstanding results, Tregs have been widely investigated as an alternative tool in preventing graft rejection and treating autoimmune diseases. On the other hand, targeting Tregs for the purpose of improving cancer immunotherapy is being intensively evaluated as a desirable and effective method. The purpose of this review is to point out the characteristic function and therapeutic potential of Tregs in regulatory immune mechanisms in transplantation tolerance, autoimmune diseases, cancer therapy, and also to discuss that how the manipulation of these mechanisms may increase the therapeutic options.

Inverse gas chromatography (IGC) was used to measure the infinite dilution diffusion coefficients of water in hydroxypropyl xylan (HPX) films containing sorbitol, a commonly used plasticizer, and cellulose nanocrystals (CNC) at temperatures above their glass transition temperatures (T g). HPX forms transparent but relatively rigid films and has the potential to be used for certain food-packaging applications. Sorbitol and CNC were added to HPX films to reduce T g and to reduce the water diffusivity, respectively. It was found that almost 40 wt % of sorbitol was needed to yield a HPX film to have the desired flexibility, as quantified by its T g, and that addition of a small amount of CNC (1–5 wt %) while maintaining the total concentration of sorbitol and CNC at 40 wt % (39–35 wt % of sorbitol) slightly increased the T g but significantly decreased the diffusivity of water. In particular, the infinite dilution diffusion coefficient of water for the HPX film with 35 wt % of sorbitol and 5 wt % CNC was comparable to that of the bare HPX film. The diffusion data suggest that effects of sorbitol and CNC on the water diffusivity follow the free volume theory.

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Inverse gas chromatography (IGC) was used to study the permeability of a series of aromas through neat hydroxypropyl xylan (HPX) film and HPX films containing sorbitol, a commonly used food grade plasticizer, and cellulose nanocrystal (CNC), a nanosized filler. The aroma used included methanol, ethanol, propanol, and butanol. Also, their solubility and diffusion coefficients at infinite dilution were measured over the temperature range 120−160 °C, and the corresponding permeability coefficients were calculated. It was observed that the alcohols exhibited lower solubility (3 orders of magnitude) and diffusivity (2−3 orders of magnitude) than those of water in the neat HPX film. Solubility coefficient showed a minimum over the range of the molecular weight of the aforementioned alcohols. However, the diffusion coefficient decreased monotonically with increasing the alcohol's molecular weight. Adding sorbitol (40 wt %) decreased solubility coefficients slightly but increased diffusion coefficients by about 1 order of magnitude. However, replacing 5 wt % of sorbitol by CNC while maintaining the total additive concentration at 40 wt % did not alter the solubility coefficients much but decreased diffusion coefficients by approximately half of the values of the HPX film containing 40 wt % sorbitol. Permeability, a quantity signifying the combined effect of solubility and diffusivity, was observed to decrease with increasing the alcohol's molecular weight. This implies that diffusivity controls the permeability of the alcohols at high molecular weights. As expected, sorbitol increases while CNC decreases permeability. However, effects of additives are stronger for methanol and ethanol than for propanol and butanol. Temperature also exerts stronger effects for methanol and ethanol than for propanol and butanol. The above observation is likely due to the differences in the abilities of the low and high molecular weight alcohols to form hydrogen bonds with HPX, sorbitol, and CNC.

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