Human inherited PD-L1 deficiency is clinically and immunologically less severe than PD-1 deficiency

We previously reported two siblings with inherited PD-1 deficiency who died from autoimmune pneumonitis at 3 and 11 years of age after developing other autoimmune manifestations, including type 1 diabetes (T1D). We report here two siblings, aged 10 and 11 years, with neonatal-onset T1D (diagnosed at the ages of 1 day and 7 wk), who are homozygous for a splice-site variant of CD274 (encoding PD-L1). This variant results in the exclusive expression of an alternative, loss-of-function PD-L1 protein isoform in overexpression experiments and in the patients' primary leukocytes. Surprisingly, cytometric immunophenotyping and single-cell RNA sequencing analysis on blood leukocytes showed largely normal development and transcriptional profiles across lymphoid and myeloid subsets in the PD-L1-deficient siblings, contrasting with the extensive dysregulation of both lymphoid and myeloid leukocyte compartments in PD-1 deficiency. Our findings suggest that PD-1 and PD-L1 are essential for preventing early-onset T1D but that, unlike PD-1 deficiency, PD-L1 deficiency does not lead to fatal autoimmunity with extensive leukocytic dysregulation.

PD-1+ Tim3+ tumor-infiltrating CD8 T cells sustain the potential for IFN-γ production, but lose cytotoxic activity in ovarian cancer

Persistent exposure to tumor antigens results in exhausted tumor-infiltrating T cells (TILs) that express the immune checkpoint molecules, PD-1 and Tim3, and lack anti-tumor immunity. To examine the exhausted status of TILs in ovarian cancer, the potential for cytokine production, proliferation and cytotoxicity by purified PD-1+ Tim3+ CD8 TILs was assessed. The production of IFN-γ and TNF-α by PD-1+ Tim3+ CD8 TILs remained the same in an intracellular cytokine staining assay and was higher in a cytokine catch assay than that by PD-1- Tim3- and PD-1+ Tim3- CD8 TILs. %Ki67+ was higher in PD-1+ Tim3+ CD8 TILs than in PD-1- Tim3- CD8 TILs. However, patients with high PD-1+ Tim3+ CD8 TILs had a poor prognosis. The potential for cytotoxicity was then examined. %Perforin+ and %granzyme B+ were lower in PD-1+ Tim3+ CD8 TILs than in PD-1- Tim3- and PD-1+ Tim3- CD8 TILs. To observe the potential for direct cytotoxicity by T cells, a target cell line expressing membrane-bound anti-CD3scFv was newly established and a cytotoxic assay targeting these cells was performed. The cytotoxicity of PD-1+ Tim3+ CD8 TILs was significantly lower than that of PD-1- Tim3- and PD-1+ Tim3- CD8 TILs. Even though PD-1+ Tim3+ CD8 TILs in ovarian cancer showed a sustained potential for cytokine production and proliferation, cytotoxicity was markedly impaired, which may contribute to the poor prognosis of patients with ovarian cancer. Among the impaired functions of exhausted TILs, cytotoxicity may be an essential target for cancer immunotherapy.

Inhibition of immune checkpoints PD-1, CTLA-4, and IDO1 coordinately induces immune-mediated liver injury in mice

Cancer cells harness immune checkpoints such as cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), programmed cell death protein 1 (PD-1) and indoleamine 2,3-dioxygenase 1 (IDO1) to evade immune control. Checkpoint inhibitors have demonstrated durable anti-tumor efficacy in human and preclinical models. Liver toxicity is one of the common immune-related adverse events associated with checkpoint inhibitors (CPIs) and its frequency and severity often increase significantly during CPI combination therapies. We aim to develop a mouse model to elucidate the immune mechanisms of CPI-associated liver toxicity. Co-administration of CTLA-4 blocking antibody, 9D9, and/or an IDO1 inhibitor, epacadostat in wild-type and PD-1^-/- mice (to simulate the effect of PD1 blockade) synergistically induced liver injury and immune cell infiltration. Infiltrated cells were primarily composed of CD8+ T cells and positively associated with hepatocyte necrosis. Strikingly, sites of hepatocyte necrosis were frequently surrounded by clusters of mononuclear immune cells. CPI treatments resulted in increased expression of genes associated with hepatocyte cell death, leukocyte migration and T cell activation in the liver. In conclusion, blockade of immune checkpoints PD-1, CTLA-4, and IDO1 act synergistically to enhance T cell infiltration and activity in the liver, leading to hepatocyte death.

PD-1 deficiency is not sufficient to induce myeloid mobilization to the brain or alter the inflammatory profile during chronic neurodegeneration

Innate immune activation is a major driver of neurodegenerative disease and immune regulatory pathways could be potential targets for therapeutic intervention. Recently, Programmed cell death-1 (PD-1) immune checkpoint inhibition has been proposed to mount an IFN-γ-dependent systemic immune response, leading to the recruitment of peripheral myeloid cells to the brain and neuropathological and functional improvements in mice with Alzheimer's disease-like β-amyloid pathology. Here we investigate the impact of PD-1 deficiency on murine prion disease (ME7 strain), a model of chronic neurodegeneration. Although PD-1 was found to be increased in the brain of prion mice, the absence of PD-1 did not cause myeloid cell infiltration into the brain or major changes in the inflammatory profile. However, we observed a slight exacerbation of the behavioural phenotype of ME7 mice upon PD-1 deficiency. These results do not support the possibility of using immune checkpoint blockade as a therapeutic strategy in neurodegenerative disease.

Nitrosative damage during retrovirus infection-induced neuropathic pain

BACKGROUND

Peripheral neuropathy is currently the most common neurological complication in HIV-infected individuals, occurring in 35-50% of patients undergoing combination anti-retroviral therapy. Data have shown that distal symmetric polyneuropathy develops in mice by 6 weeks following infection with the LP-BM5 retrovirus mixture. Previous work from our laboratory has demonstrated that glial cells modulate antiviral T-cell effector responses through the programmed death (PD)-1: PD-L1 pathway, thereby limiting the deleterious consequences of unrestrained neuroinflammation.

METHODS

Using the MouseMet electronic von Frey system, we assessed hind-paw mechanical hypersensitivity in LP-BM5-infected wild-type (WT) and PD-1 KO animals. Using multi-color flow cytometry, we quantitatively assessed cellular infiltration and microglial activation. Using real-time RT-PCR, we assessed viral load, expression of IFN-γ, iNOS, and MHC class II. Using western blotting, we measured protein nitrosylation within the lumbar spinal cord (LSC) and dorsal root ganglion (DRG). Histochemical staining was performed to analyze the presence of CD3, ionized calcium binding adaptor molecule (Iba)-1, MHCII, nitrotyrosine, isolectin B4 (IB4) binding, and neurofilament 200 (NF200). Statistical analyses were carried out using graphpad prism.

RESULTS

Hind-paw mechanical hypersensitivity observed in LP-BM5-infected animals was associated with significantly increased lymphocyte infiltration into the spinal cord and DRG. We also observed elevated expression of IFN-γ (in LSC and DRG) and MHC II (on resident microglia in LSC). We detected elevated levels of 3-nitrotyrosine within the LSC and DRG of LP-BM5-infected animals, an indicator of nitric oxide (NO)-induced protein damage. Moreover, we observed 3-nitrotyrosine in both small (IB4+) and large (NF200+) DRG sensory neurons. Additionally, infected PD-1 KO animals displayed significantly greater mechanical hypersensitivity than WT or uninfected mice at 4 weeks post-infection (p.i.). Accelerated onset of hind-paw hypersensitivity in PD-1 KO animals was associated with significantly increased infiltration of CD4+ and CD8+ T lymphocytes, macrophages, and microglial activation at early time points. Importantly, we also observed elevated levels of 3-nitrotyrosine and iNOS in infected PD-1 KO animals when compared with WT animals.

CONCLUSIONS

Results reported here connect peripheral immune cell infiltration and reactive gliosis with nitrosative damage. These data may help elucidate how retroviral infection-induced neuroinflammatory networks contribute to nerve damage and neuropathic pain.

CRISPR-Cas9 mediated efficient PD-1 disruption on human primary T cells from cancer patients

Strategies that enhance the function of T cells are critical for immunotherapy. One negative regulator of T-cell activity is ligand PD-L1, which is expressed on dentritic cells (DCs) or some tumor cells, and functions through binding of programmed death-1 (PD-1) receptor on activated T cells. Here we described for the first time a non-viral mediated approach to reprogram primary human T cells by disruption of PD-1. We showed that the gene knockout of PD-1 by electroporation of plasmids encoding sgRNA and Cas9 was technically feasible. The disruption of inhibitory checkpoint gene PD-1 resulted in significant reduction of PD-1 expression but didn't affect the viability of primary human T cells during the prolonged in vitro culture. Cellular immune response of the gene modified T cells was characterized by up-regulated IFN-γ production and enhanced cytotoxicity. These results suggest that we have demonstrated an approach for efficient checkpoint inhibitor disruption in T cells, providing a new strategy for targeting checkpoint inhibitors, which could potentialy be useful to improve the efficacy of T-cell based adoptive therapies.

[Effect of PD-1 deficiency on atherogenic immune responses]

OBJECTIVE

To explore the functional changes of T lymphocyte from PD-1⁻/⁻ mice and the effects on atherogenic immune responses.

METHODS

PD-1⁻/⁻ mice were mated with ApoE⁻/⁻ mice to obtain PD-1⁻/⁻ApoE⁻/⁻mice. PD-1⁻/⁻ApoE⁻/⁻ mice were used as control. Both groups had a high-lipid diet for 12 weeks. Then the samples of aortic sinuses were harvested for oil-red and immunohistochemical stains. Samples of spleen and sera were obtained. Numbers of lymphocytes in spleen were evaluated by flow cytometry (FACS). And the cells of proliferation were also measured. The intracellular and serum cytokines were detected by enzyme-linked immunosorbent assay (ELISA).

RESULTS

After a 12-week high-lipid diet, aortic root revealed more lesions in PD-1⁻/⁻ApoE⁻/⁻ mice than in PD-1⁺/⁺ ApoE⁻/⁻ controls ((0.51 ± 0.08) vs (0.29 ± 0.06) mm², t = 2.36, P < 0.01)). There was a significant increase in CD3 T cells in the lesions of PD-1⁻/⁻ApoE⁻/⁻ mice ((154.88 ± 36.64)/mm² vs (59.38 ± 25.28)/mm², t = 2.14, P < 0.01). In PD-1⁻/⁻ApoE⁻/⁻ mice, the numbers of total cells ((8.59 ± 0.55)× 10⁷) and cells in CD4⁺ and CD8⁺ T lymphocyte subsets ((1.53 ± 0.18)× 10⁷ and (1.41 ± 0.15)×10⁷), increased significantly than those in control mice ((6.29 ± 0.39)×10⁷, (0.94 ± 0.10)×10⁷ and (0.70 ± 0.09)× 10⁷ respectively, t = 3.43, 2.88, 4.03, all P < 0.05). Same changes were detected in both CD3⁺ CD62L(-) and CD3⁺ CD25⁺ cells. PD-1 deficiency in both CD4⁺ and CD8⁺ T cells resulted in enhanced proliferation by either macrophages or dendritic cells as antigen presenting cells (APCs). The supernatant levels of interleukin-2 (IL-2) ((53.38 ± 5.94) pg/ml), interferon-γ (IFN-γ) ((114.50 ± 9.69) pg/ml) and tumor necrosis factor-α (TNF-α) ((326.00 ± 22.25) pg/ml ) from PD-1⁻/⁻ T cells co-cultured with CD3 were significantly higher than those of control T cells ((15.63 ± 2.23), (33.25 ± 4.16) and (64.50 ± 8.17) pg/ml respectively, t = 5.95, 7.70, 11.03, all P < 0.01). However, only the serum levels of TNF-α increased in PD-1⁻/⁻ApoE⁻/⁻mice compared with control.

CONCLUSIONS

PD-1 deficiency in T cells increase markedly immune responses. And it is one of the mechanisms in atherogenesis.

Programmed cell death-1 deficiency exacerbates T cell activation and atherogenesis despite expansion of regulatory T cells in atherosclerosis-prone mice

T cell activation represents a double-edged sword in atherogenesis, as it promotes both pro-inflammatory T cell activation and atheroprotective Foxp3⁺ regulatory T cell (Treg) responses. Here, we investigated the role of the co-inhibitory receptor programmed cell death-1 (PD-1) in T cell activation and CD4⁺ T cell polarization towards pro-atherogenic or atheroprotective responses in mice. Mice deficient for both low density lipoprotein receptor and PD-1 (Ldlr^−/−Pd1^−/−) displayed striking increases in systemic CD4⁺ and CD8⁺ T cell activation after 9 weeks of high fat diet feeding, associated with an expansion of both pro-atherogenic IFNγ-secreting T helper 1 cells and atheroprotective Foxp3⁺ Tregs. Importantly, PD-1 deficiency did not affect Treg suppressive function in vitro. Notably, PD-1 deficiency exacerbated atherosclerotic lesion growth and entailed a massive infiltration of T cells in atherosclerotic lesions. In addition, aggravated hypercholesterolemia was observed in Ldlr^−/−Pd1^−/− mice. In conclusion, we here demonstrate that although disruption of PD-1 signaling enhances both pro- and anti-atherogenic T cell responses in Ldlr^−/− mice, pro-inflammatory T cell activation prevails and enhances dyslipidemia, vascular inflammation and atherosclerosis.