Background/Hypothesis: The mechanistic target of rapamycin (mTOR) is a kinase that functions in two complexes: rapamycin (RAPA)-sensitive mTORC1 and RAPA-insensitive mTORC2. These complexes play critical roles in essential cell functions; as such, there is strong interest in elucidating their immunometabolic function. To date, studies have been conducted using incomplete and/or non-specific pharmacological mTOR inhibitors; therefore, the precise and distinct function of these complexes remains unclear. We hypothesized that, in conventional DCs, mTORC1 deletion would diminish and mTORC2 deletion would augment immunometabolic and allostimulatory function.

Methods: The glycolytic and respiratory activity of wild-type (WT), mTORC1^DC-/-, and mTORC2^DC-/- DCs were analyzed using an extracellular flux analyzer. The role of mTORC1 and 2 in DC capacity to instigate immune responses was investigated in vivo using an H-Y mismatched C57BL/6 skin transplant model in which mTORC1 or mTORC2 was knocked out specifically in CD11c⁺ DCs of the donor graft.

Results: mTORC1^DC-/- and mTORC2^DC-/- DCs both exhibited increased glycolysis and respiration compared to WT; however, the ratio of glycolytic to spare respiratory capacity was reduced in mTORC1^DC-/-. Survival of skin allografts from mTORC1^DC-/- donors was prolonged and survival of mTORC2^DC-/- skin allografts was diminished. T cells from the draining LNs and spleen revealed that mice transplanted with mTORC1^DC-/- skin had diminished total CD4⁺, CD8⁺, and Treg in the spleen compared to controls whereas mice transplanted with mTORC2^DC-/- skin had increased total CD4⁺, CD8⁺, and Treg in the LNs.

Conclusions: These data reveal for the first time that both mTORC1 and 2 negatively regulate conventional DC metabolism. However, as mTORC1 deletion in donor DCs prolongs graft survival and diminishes alloimmunity and mTORC2 deletion reduces graft survival and augments alloimmunity, relative levels of glycolytic/respiratory function and not total function may be what dictate DC allostimulatory ability. Our studies suggest a link between DC metabolism and allograft outcome that may provide a basis for therapeutic targeting of DC metabolism to regulate alloimmunity.

CITATION INFORMATION: Watson A, Dai H, Menk A, Delgoffe G, Thomson A. mTORC1 and 2 Regulate Dendritic Cell (DC) Metabolism and Allostimulatory Function of Donor DCs in Skin Transplantation. Am J Transplant. 2017;17 (suppl 3).

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