Cutting Edge: Immunosuppressant as Adjuvant for Tolerogenic Immunization

Kang Y, Xu L, Wang B, Chen A, Zheng G . J Immunol . 2008;180(8):5172–5176 PURPOSE OF THE STUDY. Immunosuppressive agents are used frequently for the treatment of allergy, autoimmune disease, and transplant rejection but are thought to provide only temporary benefit. The authors of this study sought to determine if dexamethasone, a glucocorticoid with potent immunosuppressive properties, could promote long-term antigen-specific tolerance when administered with a peptide immunogen. METHODS. The authors used a model of delayed-type hypersensitivity (DTH) to hen ovalbumin by subcutaneously injecting ovalbumin twice during a 2-week interval into BALB/c mice. Mice with established DTH to ovalbumin were then immunized with an ovalbumin-derived MHCII-restricted peptide in the presence or absence of dexamethasone. All mice were retested for DTH at 2-week and 4- to 5-month time points after completion of immunization by injecting ovalbumin into the footpad and measuring the increase in footpad thickness. Blood-derived CD4 + CD25 + Foxp3 + regulatory T cells (Tregs) were quantitated by labeling peripheral white blood cells with carboxyfluorescein diacetate succinimidyl ester (CFSE), stimulating the cultures with ovalbumin peptide, and analyzing for CFSE dilution (indicating cell division). Dendritic cells (DCs) in draining lymph nodes (LNs) were assessed for maturity by staining for CD11c, CD83, and CD86, as well as interleukin 10 (IL-10) in some experiments. Transgenic mice containing large numbers of ovalbumin-specific CD4 + T cells were studied also. A similar set of experiments was performed with nonobese-diabetic mice, a mouse model of autoimmune diabetes, by using dexamethasone and an insulin-derived MHCII-restricted peptide. Primary outcomes measured were median time to development of diabetes (as defined by glycosuria) and measurement of Treg numbers and antigen-specific proliferation. RESULTS. Treatment with dexamethasone induced long-term desensitization (as long as 4–5 months) in mice with preestablished DTH to hen ovalbumin as evidenced by a decrease in foot-pad swelling after ovalbumin challenge. This finding was accompanied by an expansion of CD4 + CD25 + Foxp3 + Tregs, which largely had specificity for ovalbumin. Dexamethasone, in the presence of ovalbumin, seemed to block DC maturation in draining LNs and facilitated differentiation of IL-10 + DCs. Furthermore, treatment of nonobese-diabetic mice with dexamethasone hindered development of spontaneous diabetes and was associated with the development of long-term antigen-specific persistent Tregs. CONCLUSIONS. Dexamethasone, when applied together with peptide, can promote long-term tolerance. The underlying mechanism may involve dexamethasone9s effect on inhibiting DC maturation and promoting development of persistent antigen-specific Tregs. REVIEWER COMMENTS. Development of long-term tolerance, as opposed to transient desensitization, is the end goal of immunotherapy protocols, and this study suggests that glucocorticoids may be effective adjuvants in achieving this goal. The authors of this article speculated that other small-molecule immunosuppressant drugs, including cyclosporine and FK506, may also be effective for this purpose, but there is some evidence that these agents may actually promote development of allergic disease in children after solid organ transplantation.