State of the art reviewCell-free DNA beyond a biomarker for rejection: Biological trigger of tissue injury and potential therapeutics
Section snippets
Cell-free DNA tissue source and characteristics is linked to disease pathogenesis
Advances in genome sequencing now permit the identification of the tissue source of cfDNA. Prior technologies in stem cell transplant used HLA haplotypes differences between donor and recipient and identified hematopoietic cells as a major contributor of cfDNA.6 The novel genome sequencing approaches leverage DNA methylation7,8 or histone footprints,9 markers that are tissue-specific, to map the tissue source of cfDNA in transplant and non-transplant conditions. In our own experiments, the
The potential roles of cell-free DNA in cell/tissue injury
In addition to its diagnostic role discussed above, existing research focusing on the pathogenic roles of cfDNA has proceeded rapidly and in several directions (Figure 2). cfDNA plays a direct role in thrombosis, a complication that is frequent in transplantation.13 cfDNA is also a damage-associated molecular pattern (DAMP) that is recognized by pattern recognition receptors (PRRs), which activate innate immune signaling or cell death pathways that either provoke or prevent disease progression.
How does extracellular DNA interact with intracellular DNA sensors?
Protein binding is often a necessary step to internalize cfDNA. For example, purified naked DNA is endocytosed35 when bound to proteins such as LL37,36 C1q,37 anti-dsDNA antibodies,38 and histones.39 cfDNA complexed with nucleosomes requires binding to HMGB1 with RAGE40 before it is taken up by phagocytic cells,40 or binding to anti-dsDNA for uptake by Fc or other unidentified receptors.41 Nucleosome- HMGB1 complex can also bind TLR2 on macrophages, resulting in direct signaling into the cell (
Sepsis
Circulating cfDNA is associated with poor outcomes in patients with severe sepsis. 48 DNA-sequence analyses show the majority of cfDNA from sepsis patients is from the host and not from the infecting bacteria.48 Circulating cell-free mitochondrial DNA (cf-mtDNA) released with sepsis activates TLR9 and contributes to cytokine production, splenic apoptosis, and kidney injury with overproduction of mitochondrial ROS .49 Inhibition of TLR9 or MyD-88 attenuates septic acute kidney injury (AKI) and
Biological role of cfDNA in Transplantation
The accompanying review (page xx) discusses donor-derived cfDNA (dd-cfDNA) as a potential surrogate marker for heart transplant rejection. Similarly findings have been reported in lung transplantation.79, 80, 81 Nolan et al. suggested a Q-score consisting of six urinary biomarkers, including urinary dd-cfDNA, that could distinguish quiescent no rejection from acute rejection of kidney transplantation, reducing the need for kidney biopsy.82 However, few studies have investigated the role of
Future prospective of cfDNA-targeted therapy
In recent years, various types of cfDNA- targeted drugs have been studied (Table 1). Only recombinant human DNase (rhDNase), dornase alpha (Plumozyme®) is approved by FDA, used as an adjunct therapy in the treatment of cystic fibrosis by inhalation, which digests increased cfDNA in the airway followed by improving lung function and reducing the risk of pulmonary exacerbations.87 However, some clinical trials have shown the benefit of rhDNase in other diseases and some trials using rhDNase for
Conclusion and perspective
Cell-free DNA as a non-specific marker for allograft injury. However, growing evidence in transplant and non-transplant conditions indicates that cfDNA is biologically active. For example, the tissue source and characteristics of cfDNA are intrinsically linked to it the underlying disease pathogenesis. These show distinctive features in antibody-mediated rejection versus acute cellular rejection,12 potentially increasing the specificity of the cfDNA test. This would be welcome news in thoracic
References (96)
- et al.
Circulating cell-free DNA as a biomarker of tissue injury: assessment in a cardiac xenotransplantation model
J Heart Lung Transplant
(2018) - et al.
Genomewide bisulfite sequencing reveals the origin and time-dependent fragmentation of urinary cfDNA
Clin Biochem
(2017) - et al.
Cell-free DNA comprises an in vivo nucleosome footprint that informs its tissues-of-origin
Cell
(2016) - et al.
Innate immune detection of microbial nucleic acids
Trends Microbiol
(2013) - et al.
IRF-8/interferon (IFN) consensus sequence-binding protein is involved in Toll-like receptor (TLR) signaling and contributes to the cross-talk between TLR and IFN-gamma signaling pathways
J Biol Chem
(2006) - et al.
Recognition of cytosolic DNA activates an IRF3-dependent innate immune response
Immunity
(2006) - et al.
The alarmin properties of DNA and DNA-associated nuclear proteins
Clin Ther
(2016) - et al.
Nucleosomes and DNA bind to specific cell-surface molecules on murine cells and induce cytokine production
Clin Immunol Immunopathol
(1992) - et al.
Oxidized mitochondrial DNA activates the NLRP3 inflammasome during apoptosis
Immunity
(2012) - et al.
Transmembrane mutations in toll-like receptor 9 bypass the requirement for ectodomain proteolysis and induce fatal inflammation
Immunity
(2011)