T cell-NF-κB activation is required for tumor control in vivo

Abstract

Background: T cells have the capacity to eliminate tumors but the signaling pathways by which they do so are incompletely understood. T cell priming requires activation of the transcription factors AP-1, NFAT and NF-κB downstream of the TCR, but whether activation of T cell-NF-κB in vivo is required for tumor control has not been addressed. In humans and mice with progressively growing tumors, the activity of T cell-intrinsic NF-κB is often reduced. However, it is not clear if this is causal for an inability to reject transformed cells, or if it is a consequence of tumor growth. T cell-NF-κB is important for T cell survival and effector differentiation and plays an important role in enabling T cells to reject cardiac and islet allografts, suggesting the possibility that it may also be required for tumor elimination. In this study, we tested whether normal T cell-NF-κB activation is necessary for the rejection of tumors whose growth is normally controlled by the immune system.

Methods: Mice with genetically impaired T cell-NF-κB activity were subcutaneously injected with MC57-SIY tumor cells. Tumor growth was measured over time, and the anti-tumor immune response was evaluated using flow cytometry and cytokine detection assays.

Results: Mice with impaired T cell-NF-κB activity were unable to reject tumors that were otherwise eliminated by wildtype mice, despite equal accumulation of tumor-reactive T cells. In addition, specific impairment of NF-κB signaling downstream of the TCR was sufficient to prevent tumor rejection. Tumor antigen-specific T cell-IFN-γ and TNF-α production, as well as cytotoxic ability, were all reduced in mice with impaired T cell-NF-κB, suggesting an important role for this transcription factor in the effector differentiation of tumor-specific effector T cells.

Conclusions: Our results have identified the NF-κB pathway as an important signaling axis in T cells, required for the elimination of growing tumors in vivo. Maintaining or enhancing T cell-NF-κB activity may be a promising avenue for anti-tumor immunotherapy.

Keywords: Cytokine production; Cytotoxicity; Effector function; NF-κB; Priming; T cell; Tumor rejection.

Figure 1

IKKβ expression in T cells is required for MC57-SIY tumor rejection. a) One million MC57-SIY tumor cells were subcutaneously injected into CD4-cre x IKKβ^fl/fl mice, and tumor growth was measured over time. b) Fully mismatched skin from wildtype BALB/c mice (H-2^d) was transplanted into CD4-cre x IKKβ^fl/fl mice (H-2^b). Results are representative of at least 2 experiments. ***p < 0.001.

Figure 2

Normal T cell priming in CD4-cre x IKKβ ^fl/fl mice. CD4-cre x IKKβ^fl/fl mice were subcutaneously injected with 10⁶ MC57-SIY tumor cells, were sacrificed on day 7 and splenocytes were prepared for flow cytometry. Graphical representation (a and c) and absolute numbers (b and d) of SYI:Kb⁺ tumor-specific CD8⁺ T cells (a and b) and of Ki67⁺ proliferating CD8⁺CD44^hi cells (c and d). Results are representative of at least 2 independent experiments. NS = not significant.

Figure 3

T cell-IKKβ activity is required for anti-tumor effector function. CD4-cre x IKKβ^fl/fl and littermate control mice were subcutaneously injected with 10⁶ MC57-SIY tumor cells and sacrificed 7 days later. a) Splenocytes were restimulated in vitro with γ-irradiated MC57-SIY tumor cells, and frequency of tumor-specific IFN-γ-secreting cells was determined by ELISpot. b) Mean spot size (from a) was used to evaluate amount of IFN-γ secretion on a per-cell basis. Results are representative of 2 experiments. c) Quantification of soluble IFN-γ and TNF-α from CD8⁺ splenocytes restimulated in vitro with γ-irradiated MC57-SIY tumor cells or PMA + ionomycin, as assessed by cytokine bead array. d) Mice bearing MC57-SIY tumors for 7 days were injected with a 1:1 ratio of CFSE-labeled cells loaded with (CFSE^low) or without (CFSE^high) SIY peptide. Eighteen hours later, mice were sacrificed and the presence of the target cells was assessed by flow cytometry. Results are representative of at least 2 experiments. e) Specific lysis of SIY-specific cells was calculated using the ratio of the transferred populations as described in Materials and Methods. Results combine 2 independent experiments. *p < 0.05, **p < 0.01.

Figure 4

Rejection of the MC57-SIY tumor is dependent on CARMA1 but not MyD88 expression. One million MC57-SIY tumor cells were subcutaneously injected into either MyD88-KO (a) or CARMA1-KO (b) mice, and tumor growth was measured over time. c) Wildtype and CARMA1-KO mice were subcutaneously injected with 10⁶ MC57-SIY tumor cells and sacrificed 7 days later. Enriched splenic CD8⁺ T cells were restimulated with γ-irradiated MC57-SIY cells and an ELISpot was used to measure the frequency of cells secreting IFN-γ. The experiment was repeated 3 times with 3–5 mice per group/experiment. **p < 0.01, ***p < 0.001.