The Value of Single-cell Technologies in Solid Organ Transplantation Studies

Abstract

Single-cell technologies open up new opportunities to explore the behavior of cells at the individual level. For solid organ transplantation, single-cell technologies can provide in-depth insights into the underlying mechanisms of the immunological processes involved in alloimmune responses after transplantation by investigating the role of individual cells in tolerance and rejection. Here, we review the value of single-cell technologies, including cytometry by time-of-flight and single-cell RNA sequencing, in the context of solid organ transplantation research. Various applications of single-cell technologies are addressed, such as the characterization and identification of immune cell subsets involved in rejection or tolerance. In addition, we explore the opportunities for analyzing specific alloreactive T-or B-cell clones by linking phenotype data to T-or B-cell receptor data, and for distinguishing donor-from recipient-derived immune cells. Moreover, we discuss the use of single-cell technologies in biomarker identification and risk stratification, as well as the remaining challenges. Together, this review highlights that single-cell approaches contribute to a better understanding of underlying immunological mechanisms of rejection and tolerance, thereby potentially accelerating the development of new or improved therapies to avoid allograft rejection.

When the Guest Meets the Host: Assessing the Immune Reconstitution of the Liver Graft One Cell at a Time

“…Clinically relevant therapeutic targets through high-resolution scRNA-seq are being adopted for personalized treatment options with improved graft and patient survival. 2 However, single-cell analyses in LT are in their infancy. A human liver cell atlas has been generated by performing scRNA-seq of ~10 000 cells from livers with normal function.…”

“…Whole tissue RNA sequencing provides an average readout of RNA content and is significantly influenced by cell-type abundance. 2 This approach cannot be used to study rare cell populations, cellular heterogeneity, and cell-specific pathways. 2 In the era of precision medicine, single-cell RNA-seq (scRNA-seq) enabled characterization of heterogeneous tissue and complex conditions such as LT in human and murine models.…”

“…2 This approach cannot be used to study rare cell populations, cellular heterogeneity, and cell-specific pathways. 2 In the era of precision medicine, single-cell RNA-seq (scRNA-seq) enabled characterization of heterogeneous tissue and complex conditions such as LT in human and murine models. Clinically relevant therapeutic targets through high-resolution scRNA-seq are being adopted for personalized treatment options with improved graft and patient survival.…”

“…Liver grafts suffer multiple and repeated injury events associated with procurement, storage, and surgical factors (early stressors), followed by alloimmunity and long-term exposure to immunosuppressive therapy. 1,2 Known as a master regulator of lipid, protein, and carbohydrate metabolism, the liver also has tolerogenic properties. 1 Critically, >80% of the liver's blood supply comes as venous blood from the gut, rich in nutrients, and microbial degradation products.…”

“…Importantly, graft-derived immune cells considerably decreased from 96.0% to 7.0%, whereas recipient-derived cells increased from 3.04% to 92.7% within 2 h post-LT. CD49a+CD49b− NK and tissue-resident CD206+MerTK+ macrophages represented the exemption, where populations were divided almost evenly between graft-recipient origins by the stable phase (Figure 1A), expanding our current knowledge about immune reconstitution timelines. Deconvolution of donor and recipient cells in grafts has led to mixed results because of differences in technology 2,7 (eg, scRNA-seq of SNP variants, HLA typing, and X-Y chromosome profiling), low cell number, or marker specificity. Huang et al 4 overcame this challenge by validating immune profiles longitudinally with CyTOF and donor cells expressing enhanced green fluorescent protein cells.…”