Preferential Regulatory T-Cell Generation from Memory CD4+ T-Cells Is Deficient During Acute Exacerbation of Multiple Sclerosis

Multiple sclerosis (MS) is an immune-mediated disease with reported defects in thymic T-cell output. Thymically-derived natural regulatory T-cells (nTregs) play a vital role in suppressing autoimmune responses. We have previously shown that, in humans, all activated T-cells attain transient FOXP3 expression that correlates with suppressive ability. In fact, peripheral generation of induced Tregs (iTregs) is likely the dominant source of regulatory cells in healthy adults and even more so in MS patients. Through the use of a sensitive flow-based suppression assay, we observed that memory and naïve CD4+CD25-FOXP3- T-cells both developed regulatory ability subsequent to a variety of activating stimuli. This suppressive ability was greater than that observed in nTregs and not explained by exhaustion of nutrients or competition for APCs. While blockade of activation using anti-IL-2, CTLA-4 Ig, anti-TGF-β, indomethacin or cyclosporin A did not affect iTreg generation, methotrexate preempted the induction of regulatory ability. Moreover, irradiation of iTregs also abrogated regulatory function. Interestingly, memory-derived CD25+ iTregs displayed significantly greater activation-induced FOXP3 induction compared to naïve counterparts, and exhibited significantly enhanced suppressive function per cell. Furthermore, the CD25- fraction of activated memory-derived iTregs also demonstrated regulatory function not observed in naïve counterparts. In particular, this induced regulatory population was present in both healthy controls and quiescent MS patients, but deficient during MS acute exacerbation. These studies suggest that iTreg development and function may vary dependent on precursor origin, and that clinical recovery from exacerbation to ix quiescence in MS is associated with a restoration of function in memory-derived CD4+CD25-FOXP3- Tregs.