88 - Secretion of indoleamine 2-3 deoxygenase by adipose derived mesenchymal stromal cells as a biomarker for immune suppressive capacity

Abstract

Mesenchymal Stem Cells (MSC) have demonstrated significant therapeutic utility in a number of indications. The multi-functional nature of these cells includes significant capacity to suppress immune responses. Little is known regarding the mechanisms that induce or maintain the immune suppressive phenotype desired for some clinical applications. Two suggested methods for enhancing the immune suppressive function of MSC is to pre-incubate the cells with IFN-gamma or to change or alter media supplement to reduce fibrinogen in the culture. For any altered method of culture, a release test is needed to assure consistency in therapeutic function prior to initiating clinical trials. Indoleamine 2-3 deoxygenase (IDO) catalyzes the catabolism of tryptophan modulating T cell function and enhancing peripheral tolerance. It is secreted and can be easily measured with an ELISA with a large dynamic range. As such IDO measurement has the elements to be a valuable rapid and sensitive release assay. We have measured IDO secretion in normal healthy donor MSC with low to no detectable levels, 0.81ng/ml sensitivity IDO assay. IFN-g induces IDO expression depending on the time of exposure, the amount of IFN-g used to induce the exposure, and media supplement used to culture the MSC (Media supplements tested PLTMax, PLT-Gold, Fibrinogen-Depleted, FBS). Doubling the activation time from 24–48 hours approximately doubles the IDO expression. After 48 hour exposure and wash out of IFN-g, subsequent culture in base supplemented mediums, IDO levels peak at 48 hour and plateaued for up to 4 days of culture. We observed substantial donor to donor variation in IDO expression that was dependent on the underlying media supplement. Fibrinogen depletion alone was not the factor in increasing IDO expression as a fibrinogen containing media supplement (PLT-Gold) was the media supplement that induced the highest level of IDO secretion across all donors tested. Together, this data suggests that measurement of IDO secretion is a sensitive and rapid test that may be useful for release testing, that IFN-g can be used to enhance the secretion of IDO, and that there may be substantial variability in the level of IDO secretion due to donor and the media supplements used to grow the MSC.