Myeloid-Derived Suppressor Cells (MDSC) expressing Arginase (ARG) 1 are potent inhibitors of T cell function in cancer. MDSC deplete L-Arginine (L-Arg) in serum and the tumor microenvironment, severely impairing antitumor responses. Work done in the preceding five years identified the mechanisms by which MDSC deplete LArg and has started to identify the molecular mechanisms by which L-Arg depletion causes T cell anergy. We found that MDSC expressing ARG 1 infiltrate tumors and deplete L-Arg by rapid incorporation through CAT transporters. This L-Arg-depleted environment causes a T cell cycle arrest by inhibiting cyclin D3 and cdk4 (but not cyclin D2 or cdk6), inhibits the production of IFNg (but not IL2), and blocks the expression of the T cell receptor z chain (CD3z), severely impairing T cell function. Inhibition of ARG 1 re-establishes proliferation, IFNg production, and CD3z expression, and triggers an anti-tumor response. These mechanisms were found in mice and patients with cancer. Our results therefore suggest that L-Arg depletion triggers the selective inhibition of specific genes important for effector functions of T cells, and not a generalized decrease in protein synthesis from nutrient starvation. The data also suggest that this phenomenon is caused by the activation of a checkpoint that mediates the inhibition of these effector mechanisms. Therefore, blocking this checkpoint may make T cells resistant to the anergizing/tolerizing effect of MDSC. The proposed research will identify the molecular mechanisms triggered by L-Arg depletion that inhibit the expression of genes and proteins necessary for T cell effector functions. We will demonstrate the importance of these mechanisms in tumorbearing mice and cancer patients, and will design and test novel therapeutic approaches that combine the inhibition of MDSC with the protection of T cells from the tolerizing tumor microenvironment.

Agency
National Institute of Health (NIH)
Institute
National Cancer Institute (NCI)
Type
Research Project (R01)
Project #
3R01CA082689-08S1
Application #
7417307
Study Section
Experimental Therapeutics Subcommittee 1 (ET)
Program Officer
Mccarthy, Susan A
Project Start
1999-08-01
Project End
2008-07-31
Budget Start
2007-08-01
Budget End
2008-07-31
Support Year
8
Fiscal Year
2007
Total Cost
$201,658
Indirect Cost
Name
Louisiana State Univ Hsc New Orleans
Department
Pediatrics
Type
Schools of Medicine
DUNS #
782627814
City
New Orleans
State
LA
Country
United States
Zip Code
70112
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