References
MACROPHAGE
MDSC
PMID:20414655, PMID:2880923, PMID:3115975, PMID:20028852
Macrophages import cystine through their x c ??? transporter, reduce it to cysteine and then export the cysteine through their ASC neutral amino acid transporter.
PMID:20028852
MDSCs express the cystine transporter but lack cystathionase and the ASC neutral amino acid transporter
Therefore, macrophages, DCs, and MDSCs can import cystine; however, unlike macrophages and DCs, MDSCs are unable to export cysteine.
MDSC sequester cystine and prevent T cells from obtaining cysteine which is important for Tcell activation.