As shown in

Fig. 6A, as expected, we found that the primary Th17 clones (E0) had potent effector cell function promoting naïve CD4+ T-cell proliferation in the presence of OKT3, which is consistent with the results shown in Fig. 1E using CFSE dilution assays. Furthermore, we found that Th17 clones derived from the first and the second round of expansion also significantly increased the proliferation of naïve T cells, indicating that these Th17-cells retained immune-enhancing function. However, after the third cycle of stimulation, all the three clones (E3) strongly suppressed find more the proliferation of naïve CD4+ T cells, suggesting that these cells had become functional Tregs. Th1-C1, a CD4+ Th1-cell line serving as an effector T-cell control, increased the proliferation of naïve CD4+ T cells. In contrast, the naturally occurring CD4+CD25+ Treg line, serving as a suppressive T-cell control, strongly inhibited the proliferation of naïve CD4+ T cells. We further extended this finding to the other additional Th17 clones. We observed that some Th17 clones were changed to suppressive cells

until Cyclopamine the fourth cycle of stimulation (E4) and some clones had suppressive activity starting from the second cycle of stimulation (E2) (data not shown). In addition, we determined whether the expanded Th0 cells from different expansion cycles following the same protocol used to expand Th17 cells could suppress the proliferation of naïve CD4+ T cells. As shown in Supporting IMP dehydrogenase Information

Fig. 4, we found that all Th0 cells (expanded and unexpanded) promoted the proliferation of another responding naïve CD4+ T cell in the presence of OKT3. These results indicate that Th17 clones can be converted into functional Tregs induced by TCR stimulation and expansion. To examine the mechanism by which expanded Th17 clones suppressed naïve CD4+ T cells through soluble factors or cell–cell contact manner, we next performed Transwell experiments 28. As shown in Fig. 6B, each of the three times expanded Th17 clones (E3), when cultured in the inner wells containing medium with OKT3 and purified APCs, failed to proliferate by themselves. Furthermore, only one of the E3-Th17 clones (E3-CTh17-18) partially inhibited the proliferative activity of naïve CD4+ T cells cultured in the outer wells containing OKT3 and purified APCs, whereas the remaining two clones did not exhibit this suppressive function. In addition, control Th1-C1 cells proliferated in the inner wells, whereas CD4+CD25+ naturally occurring Tregs did not proliferate. However, neither of these two controls inhibited the proliferation of naive CD4+ T cells in the outer wells separated by Transwell inserts. These results indicate that the suppressive activities of the Th17 cells after expansion are mediated through cell–cell contact dependent as well as soluble factor(s)-mediated mechanisms.