Z Gastroenterol 2009; 47 - P357
DOI: 10.1055/s-0029-1241604

Tumor-specific regulatory T cells suppress lytic granule release of adoptively transferred cytotoxic effector T cells and inhibit tumor rejection

C Bauer 1, F Marangoni 1, T Murooka 1, N Elpak 1, TR Mempel 1
  • 1Massachusetts General Hospital, Center for Immunology and Inflammatory Diseases, Boston, United States

Aims: Regulatory T cells (Treg) interfere with the rejection of malignant tumors through cytotoxic T cells (CTL), but it is not well characterized at which levels of the T cell response:

(i) initial activation at the priming site,

(ii) trafficking to tumors,

(iii) survival and proliferation in the tumor stroma or

(iv) the execution of effector function, Treg-mediated suppression of CTL function predominantly occurs.

Here we investigated the local influence of Treg on CTL effector function in tumors and tumor-draining lymph nodes by combining intravital multiphoton microscopy and flow cytometry-based population assays.

Methods: Mice subcutaneously transplanted with hemagglutinin (HA)-expressing CT26 tumor cells (CT26-HA) received TCR transgenic HA-reactive Treg (HA-Treg, specific for HA107–119 in H2-IEd). At different time-points thereafter mice were adoptively transferred with HA-specific CTL generated in vitro from splenocytes of TCR transgenic CL4 mice (HA-CTL, specific for HA512–520 in H2-Kd). Phenotype and function of HA-CTL was analyzed at various time-points after transfer in the presence or absence of HA-Treg.

Results: Adoptive transfer of HA-CTL leads to rejection of CT26-HA, but not CT26 tumors. Transfer of HA-Treg inhibits rejection. Population measurements carried out on CTL derived from tumors, draining and remote LNs, as well as the spleen, demonstrate that transfer of HA-Treg cells significantly suppresses the ability of CTL to release their lytic granule contents upon encounter of cells presenting their cognate HA determinant.

Discussion: Our data indicate that Treg exert a suppressive effect on peripheral CTL by inhibiting effector functions, e.g. the release of lytic granules. The migratory and interactive behavior of HA-Treg and HA-CTL infiltrating CT26-HA tumor as well as their efficiency of degranulation is currently being investigated at the single-cell level by intravital multiphoton microscopy.