Therapeutic T cells induce tumor-directed chemotaxis of innate immune cells through tumor-specific secretion of chemokines and stimulation of B16BL6 melanoma to secrete chemokines

Background: The mechanisms by which tumor-specific T cells induce
regression of established metastases are not fully characterized.
In using the poorly immunogenic B16BL6-D5 (D5) melanoma model we
reported that T cell-mediated tumor regression can occur
independently of perforin, IFN-gamma or the combination of both.
Characterization of regressing pulmonary metastases identified
macrophages as a major component of the cells infiltrating the
tumor after adoptive transfer of effector T cells. This led us to
hypothesize that macrophages played a central role in tumor
regression following T-cell transfer. Here, we sought to determine
the factors responsible for the infiltration of macrophages at the
tumor site. Methods: These studies used the poorly immunogenic D5
melanoma model. Tumor-specific effector T cells, generated from
tumor vaccine-draining lymph nodes (TVDLN), were used for adoptive
immunotherapy and in vitro analysis of chemokine expression.
Cellular infiltrates into pulmonary metastases were determined by
immunohistochemistry. Chemokine expression by the D5 melanoma
following co-culture with T cells, IFN-gamma or TNF-alpha was
determined by RT-PCR and ELISA. Functional activity of chemokines
was confirmed using a macrophage migration assay. T cell activation
of macrophages to release nitric oxide (NO) was determined using
GRIES reagent. Results: We observed that tumor-specific T cells
with a type 1 cytokine profile also expressed message for and
secreted RANTES, MIP-1 alpha and MIP-1 beta following stimulation
with specific tumor. Unexpectedly, D5 melanoma cells cultured with
IFN-gamma or TNF-alpha, two type 1 cytokines expressed by
therapeutic T cells, secreted Keratinocyte Chemoattractant (KC),
MCP-1, IP-10 and RANTES and expressed mRNA for MIG. The chemokines
released by T cells and cytokine-stimulated tumor cells were
functional and induced migration of the DJ2PM macrophage cell line.
Additionally, tumor-specific stimulation of wt or
perforin-deficient (PKO) effector T cells induced macrophages to
secrete nitric oxide (NO), providing an additional effector
mechanism for T cell-mediated tumor regression. Conclusion: These
data suggest two possible sources for chemokine secretion that
stimulates macrophage recruitment to the site of tumor metastases.
Both appear to be initiated by T cell recognition of specific
antigen, but one is dependent on the tumor cells to produce the
chemokines that recruit macrophages.