Functional Plasticity of Gamma Delta T Cells and Breast Tumor Targets in Hypoxia.

ABSTRACT: Interactions between immune and tumor cells in the tumor microenvironment (TME) often impact patient outcome, yet remain poorly understood. In addition, the effects of biophysical features such as hypoxia [low oxygen (O₂)] on cells within the TME may lead to tumor evasion. Gamma delta T cells (??Tcs) naturally kill transformed cells and are therefore under development as immunotherapy for various cancers. Clinical trials have proven the safety of ??Tc immunotherapy and increased circulating ??Tc levels correlate with improved patient outcome. Yet, the function of ??Tc tumor infiltrating lymphocytes in human breast cancer remains controversial. Breast tumors can be highly hypoxic, thus therapy must be effective under low O₂ conditions. We have found increased infiltration of ??Tc in areas of hypoxia in a small cohort of breast tumors; considering their inherent plasticity, it is important to understand how hypoxia influences ??Tc function. In vitro, the cell density of expanded primary healthy donor blood-derived human ??Tc decreased in response to hypoxia (2% O₂) compared to normoxia (20% O₂). However, the secretion of macrophage inflammatory protein 1? (MIP1?)/MIP1?, regulated on activation, normal T cell expressed and secreted (RANTES), and CD40L by ??Tc were increased after 40?h in hypoxia compared to normoxia concomitant with the stabilization of hypoxia inducible factor 1-alpha protein. Mechanistically, we determined that natural killer group 2, member D (NKG2D) on ??Tc and the NKG2D ligand MHC class I polypeptide-related sequence A (MICA)/B on MCF-7 and T47D breast cancer cell lines are important for ??Tc cytotoxicity, but that MIP1?, RANTES, and CD40L do not play a direct role in cytotoxicity. Hypoxia appeared to enhance the cytotoxicity of ??Tc such that exposure for 48?h increased cytotoxicity of ??Tc against breast cancer cells that were maintained in normoxia; conversely, breast cancer lines incubated in hypoxia for 48?h prior to the assay were largely resistant to ??Tc cytotoxicity. MICA/B surface expression on both MCF-7 and T47D remained unchanged upon exposure to hypoxia; however, ELISAs revealed increased MICA shedding by MCF-7 under hypoxia, potentially explaining resistance to ??Tc cytotoxicity. Despite enhanced ??Tc cytotoxicity upon pre-incubation in hypoxia, these cells were unable to overcome hypoxia-induced resistance of MCF-7. Thus, such resistance mechanisms employed by breast cancer targets must be overcome to develop more effective ??Tc immunotherapies.

SUBMITTER: Siegers GM 

PROVIDER: S-EPMC6013583 | biostudies-literature | 2018

REPOSITORIES: biostudies-literature