Winter, Hauke; van den Engel, Natasja K.; Poehlein, Christian H.; Hatz, Rudolf A.; Fox, Bernard A.; Hu, Hong-Ming:
Tumor-specific T cells signal tumor destruction via the lymphotoxin beta receptor.
In: Journal of Translational Medicine
Background: Previously, we reported that adoptively transferred perforin k/o (PKO), and IFN-gamma\k/o (GKO), or perforin/IFN-gamma double k/o (PKO/GKO) effector T cells mediated regression of B16BL6-D5 (D5) pulmonary metastases and showed that TNF receptor signaling played a critical role in mediating tumor regression. In this report we investigated the role of lymphotoxin-alpha (LT-alpha) as a potential effector molecules of tumor-specific effector T cells. Methods: Effector T cells were generated from tumor vaccine-draining lymph node (TVDLN) of wt, GKO, LT-alpha deficient (LKO), or PKO/GKO mice and tested for their ability to mediate regression of D5 pulmonary metastases in the presence or absence of LT-beta R-Fc fusion protein or anti-IFN-gamma antibody. Chemokine production by D5 tumor cells was determined by ELISA, RT-PCR and Chemotaxis assays. Results: Stimulated effector T cells from wt, GKO, or PKO/GKO mice expressed ligands for LT-beta receptor (LT-beta R). D5 tumor cells were found to constitutively express the LT-beta R. Administration of LT-beta R-Fc fusion protein completely abrogated the therapeutic efficacy of GKO or PKO/GKO but not wt effector T cells (p < 0.05). Consistent with this observation, therapeutic efficacy of effector T cells deficient in LT-alpha, was greatly reduced when IFN-gamma production was neutralized. While recombinant LT-alpha 1 beta 2 did not induce apoptosis of D5 tumor cells in vitro, it induced secretion of chemokines by D5 that promoted migration of macrophages. Conclusion: The contribution of LT-alpha expression by effector T cells to anti-tumor activity in vivo was not discernable when wt effector T cells were studied. However, the contribution of LT-beta R signaling was identified for GKO or PKO/GKO effector T cells. Since LT-alpha does not directly induce killing of D5 tumor cells in vitro, but does stimulate D5 tumor cells to secrete chemokines, these data suggest a model where LT-alpha expression by tumor-specific effector T cells interacts via cross-linking of the LT-beta R on tumor cells to induce secretion of chemokines that are chemotactic for macrophages. While the contribution of macrophages to tumor elimination in our system requires additional study, this model provides a possible explanation for the infiltration of inate effector cells that is seen coincident with tumor regression.