Mixed signature of activation and dysfunction allows human decidual CD8+ T cells to provide both tolerance and immunity

Abstract

Understanding how decidual CD8+ T cell (CD8+ dT) cytotoxicity is regulated and how these cells integrate the competing needs for maternal-fetal tolerance and immunity to infection is an important research and clinical goal. Gene-expression analysis of effector-memory CD8+ dT demonstrated a mixed transcriptional signature of T cell dysfunction, activation, and effector function. High protein expression of coinhibitory molecules PD1, CTLA4, and LAG3, accompanied by low expression of cytolytic molecules suggests that the decidual microenvironment reduces CD8+ dT effector responses to maintain tolerance to fetal antigens. However, CD8+ dT degranulated, proliferated, and produced IFN-γ, TNF-α, perforin, and granzymes upon in vitro stimulation, demonstrating that CD8+ dT are not permanently suppressed and retain the capacity to respond to proinflammatory events, such as infections. The balance between transient dysfunction of CD8+ dT that are permissive of placental and fetal development, and reversal of this dysfunctional state, is crucial in understanding the etiology of pregnancy complications and prevention of congenital infections.

Keywords: T cell exhaustion; cytotoxicity; placenta; pregnancy; trophoblast.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.

Transcriptional signatures of CD8+ EM dT dysfunction, activation, and effector function are coupled. (A) Unsupervised PCA analysis, using all 54,715 probes, of first trimester (dT 6–12 wk) and term pregnancy (dT > 37 wk) CD8+ EM dT and EM pT. (B) GSEA performed with assorted immunological signatures, showing positive correlation for an in vitro CD8+ activation signature, an effector signature, and a CD8+ viral exhaustion signature (MSigDB). (C) GSEA comparing first trimester CD8+ EM dT to gene modules of dysfunction, activation, and activation coupled to dysfunction (16).

Fig. 2.

Stimulation of CD8+ EM dT generates signatures of T cell activation. (A) A MaSigPro time-course analysis of ∼2,000 immunological relevant genes preselected based on the Immune System Process GO terms expressed by first trimester CD8+ EM dT stimulated with anti-CD3/CD28 in the presence of 50 U/mL IL-2 for 0, 12, or 72 h. Five clusters of temporally sensitive genes were identified. (B) K-Cluster analysis highlighting select genes in clusters 3–5.

Fig. 3.

CD8+ dT are functional upon activation. (A) FACS plots (Left) and percentages (Right) of CD107a+CD8+ pT and dT after stimulation with PMA/Ionomycin (1 μg/mL) for 6 h. Percentage CD107a+ cells are depicted within total CD8+ T cells and the four CD8+ T cell subpopulations (as percentage of total CD8). (B) Representative histograms (Left) and percentage divided cells (Right) of CFSE-labeled total CD8+ T cells at days 3, 4, 5, and 6 after stimulation with anti-CD3/28 (2 μL/mL) and 50 U/mL IL-2. (C) FACS plots (Left) and percentages (Right) of expression of intracellular IFN-γ, TNF-α, and IL-2 in total CD8+ pT and dT stimulated with PMA/Ionomycin (1 μg/mL) for 6 h. Bars represent the median with interquartile range; data are representative of three to six independent experiments; *P ≤ 0.05, **P ≤ 0.01.

Fig. 4.

Decidual CD8+CD28− T cells increase PRF and GZMB upon activation. Histograms of intracellular PRF (A) and GZMB (B) expression in CD8+CD28− pT and dT cultured for 6 d in the presence of IL-2 (50 U/mL), TNF-α (20 ng), IL-12 (20 ng), anti-CD3/28 (2 μL/mL), or a combination of anti-CD3/28 and IL-12. The vertical line signifies the PRF and GZMB mean fluorescence intensity (MFI) after addition of a nonactivating concentration of IL-2.

Fig. 5.

PRF, but not GZMB, is suppressed in HCMV-specific CD8+CD28− dT. Histograms and MFI of PRF (A and B) and GZMB (C and D) expression in tetramer-positive CD8+CD28− pT and dT, directly ex vivo and after in vitro expansion. Bars depict the median with interquartile range; *P ≤ 0.05, **P ≤ 0.01.