4). The two populations were individually labeled with CellTrace and then co-cultured at the original ratio (one Treg to nine effector cells), combining either labeled Treg with unlabeled T-effector cells, or conversely labeled T-effector cells with unlabeled Treg cells. These experiments demonstrate that a very low frequency of Foxp3+ T cells arise from the labeled effector T-cell population, cultured alone or with labeled Treg cells, in the absence or presence of 1α25VitD3 (<2% at day 14; data not shown). These data suggest that 1α25VitD3 is not acting to enhance adaptive/activation-dependent

Foxp3 expression. Furthermore, across a dose titration of 1α25VitD3, Treg cell proliferation was only reduced at 10−6 M 1α25VitD3, whereas at all other concentrations proliferation Seliciclib mw was unaffected or even enhanced (Fig. 6C and D). In contrast, proliferation of labeled effector T cells in co-culture was reduced at all concentrations of 1α25VitD3 PI3K inhibitor tested (10−9–10−6 M 1α25VitD3; Fig. 6C and D).

These data imply that culture of T cells with 1α25VitD3 preferentially expands Treg over T-effector cells. Our earlier studies demonstrated that 1α25VitD3 enhances IL-10 expression by CD4+ T cells not only in culture, but also following ingestion of standard formulary doses of 1α25VitD3 by both steroid refractory asthma patients and healthy subjects [12, 14]. Subsequent work has demonstrated that no parallel increase in Foxp3 gene expression occurred in the same peripheral blood CD3+CD4+ T cells, analyzed directly ex vivo pre- and post-1α25VitD3 ingestion (data not shown). To investigate whether vitamin D might influence Foxp3 expression in the tissues, we analyzed the frequency of CD4+Foxp3+ cells in bronchoalveolar lavage (BAL) samples available from a pediatric severe asthma cohort under study, where serum 25-hydroxyvitamin D3 status was also being assessed (Supporting Information Table 1) [21]. Strikingly the majority of these patients showed a vitamin D status reflecting insufficiency (<75nmol/L) or deficiency (<50 nmol/L) [22]. A statistically significant correlation between serum vitamin

D status, and the frequency of CD4+Foxp3+ T cells in the BAL was observed (r = 0.71, p = 0.02), suggesting an in vivo correlate of our in vitro observations on the capacity of 1α25VitD3 to influence Foxp3+ Treg cell prevalence mafosfamide (Fig. 7 and Supporting Information Fig. 5). Interest in enhancing Treg cells in patients is clearly driven by the therapeutic potential of these cells. An attractive approach would be the use of pharmacological agents such as 1α25VitD3, or vitamin D supplementation, to induce the expansion and/or maintenance of Treg cells. This approach is especially suited to ongoing chronic diseases such as asthma that occur at high prevalence, where a simple treatment such as vitamin D supplementation would be relatively safe, acceptable to patients, and cost effective.