Gene transfer of the S24F regulated on activation normal T-cell expressed and secreted-chemokine ligand 5 variant attenuates cardiac allograft rejection

Immune Regulation of the Liver Through the PCSK9/CD36 Pathway During Heart Transplant Rejection

BACKGROUND

PCSK9 (proprotein convertase subtilisin/kexin 9), which is mainly secreted by the liver, is not only a therapeutic target for hyperlipidemia and cardiovascular disease, but also has been implicated in the immune regulation of infections and tumors. However, the role of PCSK9 and the liver in heart transplant rejection (HTR) and the underlying mechanisms remain unclear.

METHODS

We assessed serum PCSK9 expression in both murine and human recipients during HTR and investigated the effect of PCSK9 ablation on HTR by using global knockout mice and a neutralizing antibody. Moreover, we performed multiorgan histological and transcriptome analyses, and multiomics and single-cell RNA-sequencing studies of the liver during HTR, as well. We further used hepatocyte-specific Pcsk9 knockout mice to investigate whether the liver regulated HTR through PCSK9. Last, we explored the regulatory effect of the PCSK9/CD36 pathway on the phenotype and function of macrophages in vitro and in vivo.

RESULTS

Here, we report that murine and human recipients have high serum PCSK9 levels during HTR. PCSK9 ablation prolonged cardiac allograft survival and attenuated the infiltration of inflammatory cells in the graft and the expansion of alloreactive T cells in the spleen. Next, we demonstrated that PCSK9 was mainly produced and significantly upregulated in the recipient liver, which also showed a series of signaling changes, including changes in the TNF-α (tumor necrosis factor α) and IFN-γ (interferon γ) signaling pathways and the bile acid and fatty acid metabolism pathways. We found mechanistically that TNF-α and IFN-γ synergistically promoted PCSK9 expression in hepatocytes through the transcription factor SREBP2 (sterol regulatory element binding protein 2). Moreover, in vitro and in vivo studies indicated that PCSK9 inhibited CD36 expression and fatty acid uptake by macrophages and strengthened the proinflammatory phenotype, which facilitated their ability to promote proliferation and IFN-γ production by donor-reactive T cells. Last, we found that the protective effect of PCSK9 ablation against HTR is dependent on the CD36 pathway in the recipient.

CONCLUSIONS

This study reveals a novel mechanism for immune regulation by the liver through the PCSK9/CD36 pathway during HTR, which influences the phenotype and function of macrophages and suggests that the modulation of this pathway may be a potential therapeutic target to prevent HTR.

Virus-Derived Chemokine Modulating Protein Pre-Treatment Blocks Chemokine–Glycosaminoglycan Interactions and Significantly Reduces Transplant Immune Damage

Immune cell invasion after the transplantation of solid organs is directed by chemokines binding to glycosaminoglycans (GAGs), creating gradients that guide immune cell infiltration. Renal transplant is the preferred treatment for end stage renal failure, but organ supply is limited and allografts are often injured during transport, surgery or by cytokine storm in deceased donors. While treatment for adaptive immune responses during rejection is excellent, treatment for early inflammatory damage is less effective. Viruses have developed highly active chemokine inhibitors as a means to evade host responses. The myxoma virus-derived M-T7 protein blocks chemokine: GAG binding. We have investigated M-T7 and also antisense (ASO) as pre-treatments to modify chemokine: GAG interactions to reduce donor organ damage. Immediate pre-treatment of donor kidneys with M-T7 to block chemokine: GAG binding significantly reduced the inflammation and scarring in subcapsular and subcutaneous allografts. Antisense to N-deacetylase N-sulfotransferase1 (ASONdst1) that modifies heparan sulfate, was less effective with immediate pre-treatment, but reduced scarring and C4d staining with donor pre-treatment for 7 days before transplantation. Grafts with conditional Ndst1 deficiency had reduced inflammation. Local inhibition of chemokine: GAG binding in donor organs immediately prior to transplant provides a new approach to reduce transplant damage and graft loss.

HLA-DQ alloantibodies directly activate the endothelium and compromise differentiation of FoxP3high regulatory T lymphocytes

Development of donor-specific antibodies is associated with reduced allograft survival in renal transplantation. Recent clinical studies highlight the prevalence of human leukocyte antigen (HLA)-DQ antibodies amongst de novo donor-specific antibodies (DSAs), yet the specific contribution of these DSAs to rejection has not been examined. Antibody-mediated rejection primarily targets the microvasculature, so this study explored how patient HLA-DQ alloantibodies can modulate endothelial activation and so immunoregulation. HLA-DQ antibodies phosphorylated Akt and S6 kinase in microvascular endothelial cells. This activation prior to culture with alloreactive lymphocytes increased IL-6 and RANTES secretion. The antibody-mediated upregulation of IL-6 was indeed Akt-dependent. The binding of HLA-DQ antibodies to endothelial cells selectively reduced T cell alloproliferation and FoxP3^high Treg differentiation. In clinical studies, detection of HLA-DQ DSAs with other DSAs is associated with worse graft survival than either alone. Endothelial cells stimulated with HLA-DR and HLA-DQ antibodies showed a synergistic increase in pro-inflammatory cytokine secretion and a decrease in Treg expansion. HLA-DQ antibodies strongly promote pro-inflammatory responses in isolation and in combination with other HLA antibodies. Thus, our data give new insights into the pathogenicity of HLA-DQ DSAs.

CXCR4 Antagonist Reduced the Incidence of Acute Rejection and Controlled Cardiac Allograft Vasculopathy in a Swine Heart Transplant Model Receiving a Mycophenolate-based Immunosuppressive Regimen

BACKGROUND

CXC motif chemokine receptor 4 (CXCR4) blockade is pursued as an alternative to mesenchymal stem cell treatment in transplantation based on our previous report that burixafor, through CXCR4 antagonism, mobilizes immunomodulatory mesenchymal stem cells. Here, we explored the efficacy of combining mycophenolate mofetil (MMF)-based immunosuppressants with repetitive burixafor administration.

METHODS

Swine heterotopic cardiac allograft recipients received MMF and corticosteroids (control, n = 10) combined with burixafor as a 2-dose (burixafor2D, n = 7) or 2-dose plus booster injections (burixafor2D + B, n = 5) regimen. The efficacy endpoints were graft survival, freedom from first acute rejection, and the severity of intimal hyperplasia. Each specimen was sacrificed either at its first graft arrest or after 150 days.

RESULTS

After 150 days, all specimens in the control group had died, but 28.5% of the burixafor2D group survived, and 60% of the burixafor2D + B group survived (P = 0.0088). Although the control group demonstrated acute rejection at a median of 33.5 days, the burixafor2D + B group survived without acute rejection for a median of 136 days (P = 0.0209). Burixafor administration significantly attenuated the incidence rate of acute rejection (P = 0.002) and the severity of intimal hyperplasia (P = 0.0097) at end point relative to the controls. These findings were associated with reduced cell infiltrates in the allografts, and modulation of C-reactive protein profiles in the circulation.

CONCLUSIONS

The augmentation of conventional MMF plus corticosteroids with a CXCR4 antagonist is potentially effective in improving outcomes after heart transplantation in minipigs. Future studies are warranted into optimizing the therapeutic regimens for humans.