Assessment of Immunological Markers as Mediators of Graft Vasculopathy Development in Heart Transplantation

Proinflammatory and cytotoxic CD38 + HLA-DR + effector memory CD8 + T cells are peripherally expanded in human cardiac allograft vasculopathy

Background

T cell mediated immunity is reported to play a pathogenic role in cardiac allograft vasculopathy (CAV) in heart transplant (HTx) patients. However, peripheral blood CD8 + T cells have not been previously characterized in CAV. This study aimed to identify potentially pathogenic circulating CD8 + T cell populations in high grade CAV patients using cellular indexing of transcriptomes and epitopes by sequencing (CITE-seq).

Methods

Peripheral blood mononuclear cells (PBMC) collected from International Society for Heart and Lung Transplant (ISHLT) grade 2 or 3 CAV (high grade CAV; n=6) and normal HTx (n=12) patients were analyzed using CITE-seq and VDJ-seq. Key findings were validated by flow cytometry in an independent patient cohort of age-matched CAV (n=11) patients, normal HTx (n=12) patients and healthy donor subjects (n=11).

Results

Among the seven peripheral CD8 + T cell clusters, high grade CAV patients demonstrated a significantly higher proportion of the CD38 + HLA-DR + CD8 + effector memory T (Tem) cell cluster compared to normal HTx patients (median 6.2% vs 2.9%, p=0.01). CD38 + HLA-DR + CD8 + Tem cells showed clonal expansion, activated interferon-γ (IFNG) signaling and enhanced cytotoxicity with granzyme B (GZMB) and perforin (PRF) overexpression. Significantly higher proportion of the proinflammatory and cytotoxic CD38 + HLA-DR + CD8 + Tem cell cluster in high grade CAV compared to normal HTx patients was validated by flow cytometry. There was significantly increased clonal expansion of peripheral CD8 + T cells in high grade CAV compared to normal HTx patients (median Shannon index = 4.4 vs 6.1, p=0.03). CITE-seq identified LAIR2 as a potential biomarker for identifying high grade CAV patients as increased expression was found in CD38 + HLA-DR + CD8 + Tem cells. Plasma LAIR2 was significantly elevated in the high grade CAV (n=20) compared to normal HTx patients (n=20; 16.0 pg/mL vs 70.3 pg/mL, p=0.02).

Conclusions

We discovered and validated circulating CD38 + HLA-DR + CD8 + Tem cells to be significantly increased in high grade CAV compared to normal HTx patients. The proinflammatory and cytotoxic phenotype of this CD8 + T cell cluster suggest its potential pathogenic role in human CAV.

Clinical Perspective

What is new?: This is the first study to identify clonal expansion of circulating CD38 + HLA-DR + effector memory CD8 + T cells in human cardiac allograft vasculopathy. CD38 + HLA-DR + effector memory CD8 + T cells possess both proinflammatory and cytotoxic characteristics, suggesting their potential pathogenic role in human cardiac allograft vasculopathy. LAIR2 is a potential signature gene of CD38 + HLA-DR + effector memory CD8 + T cells. What are the clinical implications?: Circulating CD38 + HLA-DR + effector memory CD8 + T cells and plasma LAIR2 protein are potential early biomarkers of cardiac allograft vasculopathy. Evaluation of CD38 + HLA-DR + effector memory CD8 + T cells in longitudinal studies may reveal how this T cell cluster contributes to the development of human cardiac allograft vasculopathy. Inhibiting the expansion of CD38 + HLA-DR + effector memory CD8 + T cells and/or the LAIR2 pathway may become important therapeutic targets for prevention and treatment of human cardiac allograft vasculopathy.

The Presence of a Marked Imbalance Between Regulatory T Cells and Effector T Cells Reveals That Tolerance Mechanisms Could Be Compromised in Heart Transplant Children

Regulatory T cells (Treg) are crucial for the induction and maintenance of graft tolerance. In pediatric heart transplant procedures, the thymus is routinely excised, removing the primary source of T-cell replenishment. Consequently, thymectomy joined to the effects of immunosuppression on the T-cell compartment may have a detrimental impact on Treg values, compromising the intrinsic tolerance mechanisms and the protective role of Treg preventing graft rejection in heart transplant children.

Basiliximab impairs regulatory T cell (TREG) function and could affect the short-term graft acceptance in children with heart transplantation

CD25, the alpha chain of the IL-2 receptor, is expressed on activated effector T cells that mediate immune graft damage. Induction immunosuppression is commonly used in solid organ transplantation and can include antibodies blocking CD25. However, regulatory T cells (Tregs) also rely on CD25 for their proliferation, survival, and regulatory function. Therefore, CD25-blockade may compromise Treg protective role against rejection. We analysed in vitro the effect of basiliximab (BXM) on the viability, phenotype, proliferation and cytokine production of Treg cells. We also evaluated in vivo the effect of BXM on Treg in thymectomized heart transplant children receiving BXM in comparison to patients not receiving induction therapy. Our results show that BXM reduces Treg counts and function in vitro by affecting their proliferation, Foxp3 expression, and IL-10 secretion capacity. In pediatric heart-transplant patients, we observed decreased Treg counts and a diminished Treg/Teff ratio in BXM-treated patients up to 6-month after treatment, recovering baseline values at the end of the 12-month follow up period. These results reveal that the use of BXM could produce detrimental effects on Tregs, and support the evidence suggesting that BXM induction could impair the protective role of Tregs in the period of highest incidence of acute graft rejection.

The role of immunological biomarkers in cardiac rejection

PURPOSE OF REVIEW

To summarize the promises and limitations of candidate noninvasive immunological biomarkers in cardiac rejection, with a special focus on the chemokine CXCL10, as a pretransplant predictive marker of early heart acute rejection. Potential issues for transfer from research to the clinic are addressed.

RECENT FINDINGS

Early changes of immune biomolecules in peripheral blood, reflecting graft or heart recipient's immune status, are candidate biomarkers able to diagnose or predict cardiac rejection, ideally giving an opportunity to intervene before heart failure occurs. The support of robust analytical methodologies is necessary for the transition from biomarker discovery to clinical implementation.

SUMMARY

Cardiac rejection represents the main problem after heart transplantation. Endomyocardial biopsy, although invasive and not risk free, is the gold-standard procedure for rejection monitoring. Noninvasive heart damage biomarkers manifest substantially after rejection occurrence. The goal is to detect graft injury at the earliest possible stage in disease initiation. Some biomolecules associated with the early immune response to cardiac allograft retain the power to be diagnostic and, even better, predictive of acute rejection, as in the case of pretransplant CXCL10 serum level. Multicenter studies for assay validation and standardization, integrated analysis of multiple biomarkers, and cost-effectiveness evaluation are mandatory efforts.

Correlations of lymphocyte subset infiltrates with donor-specific antibodies and acute antibody-mediated rejection in endomyocardial biopsies

BACKGROUND

Acute antibody-mediated rejection (AMR) is a major complication after heart transplantation, posing a significant risk for allograft failure, cardiac allograft vasculopathy, and poor survival. While the inflammatory milieu of cellular rejection and Quilty lesions is well known, the immunologic components of AMR are not well understood. Our aim was to better define the immunophenotype of infiltrating lymphocytes in biopsies with AMR, specifically in relation to donor-specific antibodies to human leukocyte antigen (HLA) class I, II, or both.

METHOD

We performed a retrospective analysis of cardiac transplant patients with concurrent endomyocardial biopsies (EMB), donor-specific antibody (DSA) measurements, and immunofluorescence for C4d at our institution (2005-2011). DSA was evaluated against HLA class I and class II specificities pre- and posttransplant using flow cytometry and/or Luminex bead assays. Acute cellular rejection (ACR) and pathologic AMR (pAMR) were based on the International Society for Heart and Lung Transplantation 2005/2013 reports. Immunohistochemical analysis for CD3, CD4, CD8, and CD79a was performed using standard immunohistochemical protocols on one formalin-fixed, paraffin-embedded EMB from each patient. The number of lymphocytes expressing each protein was enumerated microscopically at 400×. Ratios of T:B cells and CD4:CD8 T cells were then calculated for each EMB.

RESULTS

Seventy-nine cardiac transplant patients who had pre- and posttransplant DSA measurements were analyzed. Of these 79 patients, 37 had DSA against HLA class I, HLA class II, or both. Of patients with DSA, the average CD4:CD8 ratio in the EMB was 0.80, while those with only ACR had a CD4:CD8 ratio of 1.49. Interestingly, the T:B cell ratio in patients with and without DSA was 5.7 and 5.5, respectively.

CONCLUSION

Cardiac transplant patients with DSA against HLA have more CD8 cytotoxic T cells than CD4 helper T cells in the EMB lymphocytic infiltrate compared with patients without DSA against HLA. The inflammatory infiltrate T:B cell ratio was similar in patients both with and without DSA. The relative increase of cytotoxic T cells in EMB while the patient has DSA suggests a possible pathogenic role of these cells and may aid in the diagnosis and treatment of AMR.

Simultaneous diagnosis and gene therapy of immuno-rejection in rat allogeneic heart transplantation model using a T-cell-targeted theranostic nanosystem

As the final life-saving treatment option for patients with terminal organ failure, organ transplantation is far from an ideal solution. The concomitant allograft rejection, which is hardly detectable especially in the early acute rejection (AR) period characterized by an intense cellular and humoral attack on donor tissue, greatly affects the graft survival and results in rapid graft loss. Based on a magnetic resonance imaging (MRI)-visible and T-cell-targeted multifunctional polymeric nanocarrier developed in our lab, effective co-delivery of pDNA and superparamagnetic iron oxide nanoparticles into primary T cells expressing CD3 molecular biomarker was confirmed in vitro. In the heart transplanted rat model, this multifunctional nanocarrier showed not only a high efficiency in detecting post-transplantation acute rejection but also a great ability to mediate gene transfection in T cells. Upon intravenous injection of this MRI-visible polyplex of nanocarrier and pDNA, T-cell gathering was detected at the endocardium of the transplanted heart as linear strongly hypointense areas on the MRI T(2)*-weighted images on the third day after cardiac transplantation. Systematic histological and molecular biology studies demonstrated that the immune response in heart transplanted rats was significantly suppressed upon gene therapy using the polyplex bearing the DGKα gene. More excitingly, the therapeutic efficacy was readily monitored by noninvasive MRI during the treatment process. Our results revealed the great potential of the multifunctional nanocarrier as a highly effective imaging tool for real-time and noninvasive monitoring and a powerful nanomedicine platform for gene therapy of AR with high efficiency.

Flow cytometry: a flexible tool for biomarker research

Flow cytometry is increasingly recognized as an invaluable technology in biomarker research. Owing to its multiparametric nature it can provide highly detailed information on any single cell in a heterogeneous population. Its versatility means it can be conducted in both the preclinical and clinical setting, generating biomarker data that can drive decisions pertaining to dose selection in clinical trials, treatment options for cancer sufferers and even suitability of patients to receive transplants. Most tissue types can be utilized by the flow cytometrist, allowing the technology to be applied to many fields of research, yet consensus still needs to be reached on standardization, regulation and validation of multiparametric flow cytometry assays. In parallel, continual innovation in analysis software to manage the huge datasets that can be generated is also needed. Nevertheless, the flexibility of flow cytometry means that it remains at the forefront of both routine and exploratory biomarker studies.