Decreased percentage of CD4+FoxP3+ cells in bronchoalveolar lavage from lung transplant recipients correlates with development of bronchiolitis obliterans syndrome. Transplantation. 2010;90:540-546. [PMID: 20628341 DOI: 10.1097/tp.0b013e3181e8dabe]

Rejection and regulation: a tight balance

PURPOSE OF REVIEW

Achieving allograft tolerance is the holy grail of transplantation. However, tolerance and rejection are two extreme ends of a scale that can be tipped in either direction. We review the novel effector and regulatory mechanisms involved and factors that tip the balance in favor of rejection or regulation.

RECENT FINDINGS

It is increasingly recognized that established T-cell phenotypes could change their commitments. New data point to the plasticity of Th17 cells in vivo with a reciprocal balance of Th17 cells and regulatory T cells (Tregs) driven by the local cytokine environment. Treg-cell profiles have been linked to acute and chronic allograft outcomes, and emerging data also indicate a novel role of a regulatory B-cell population. Current research efforts are looking into factors that tip the balance toward allograft tolerance by targeting cytokines, novel costimulatory pathways such as T-cell immunoglobulin mucin molecules, and components of innate immunity, particularly dendritic cells.

SUMMARY

The balance of effector and regulatory mechanisms contributing to allograft outcome is very complex. It is likely that targeting multiple pathways will be required to achieve tolerance. Further studies are warranted to define this balance and identify optimal combination of therapeutic interventions.

Bronchoalveolar lavage as a tool to predict, diagnose and understand bronchiolitis obliterans syndrome

Bronchiolitis obliterans syndrome (BOS), a condition of irreversible small airway fibrosis, is the principal factor limiting long-term survival after lung transplantation. Bronchoscopy and bronchoalveolar lavage (BAL), techniques central to lung transplant clinical practice, provide a unique opportunity to interrogate the lung allograft during BOS development and identify potential disease mechanisms or biomarkers. Over the past 20 years, numerous studies have evaluated the BAL cellular composition, cytokine profiles and protein constituents in lung transplant recipients with BOS. To date, however, no summative evaluation of this literature has been reported. We developed and applied objective criteria to qualitatively rank the strength of associations between BAL parameters and BOS in order to provide a comprehensive and systematic assessment of the literature. Our analysis indicates that several BAL parameters, including neutrophil count, interleukin-8, alpha defensins and MMP-9, demonstrate highly replicable associations with BOS. Additionally, we suggest that considerable opportunity exists to increase the knowledge gained from BAL analyses in BOS through increased sample sizes, covariant adjustment and standardization of the BAL technique. Further efforts to leverage analysis of BAL constituents in BOS may offer great potential to provide additional in-depth and mechanistic insights into the pathogenesis of this complex disease.

ICOS-expressing lymphocytes promote resolution of CD8-mediated lung injury in a mouse model of lung rejection

Acute rejection, a common complication of lung transplantation, may promote obliterative bronchiolitis leading to graft failure in lung transplant recipients. During acute rejection episodes, CD8(+) T cells can contribute to lung epithelial injury but the mechanisms promoting and controlling CD8-mediated injury in the lung are not well understood. To study the mechanisms regulating CD8(+) T cell-mediated lung rejection, we used a transgenic model in which adoptively transferred ovalbumin (OVA)-specific cytotoxic T lymphocytes (CTL) induce lung injury in mice expressing an ovalbumin transgene in the small airway epithelium of the lungs (CC10-OVA mice). The lung pathology is similar to findings in humans with acute lung transplant. In the presence of an intact immune response the inflammation resolves by day 30. Using CC10-OVA.RAG(-/-) mice, we found that CD4(+) T cells and ICOS(+/+) T cells were required for protection against lethal lung injury, while neutrophil depletion was not protective. In addition, CD4(+)Foxp3 (+) ICOS(+) T cells were enriched in the lungs of animals surviving lung injury and ICOS(+/+) Tregs promoted survival in animals that received ICOS(-/-) T cells. Direct comparison of ICOS(-/-) Tregs to ICOS(+/+) Tregs found defects in vitro but no differences in the ability of ICOS(-/-) Tregs to protect from lethal lung injury. These data suggest that ICOS affects Treg development but is not necessarily required for Treg effector function.

The role of autoimmunity in obliterative bronchiolitis after lung transplantation

First performed in the 1960s with long-term successes achieved in the 1980s, lung transplantation remains the only definitive treatment option for end-stage lung disease. Chronic lung rejection, pathologically classified as obliterative bronchiolitis (OB) with its clinical correlate referred to as bronchiolitis obliterans syndrome, is the limiting factor than keeps 5-yr survival rates for lung transplant significantly worse than for other solid organ transplants. Initially, OB was largely attributed to immune responses to donor antigens, alloimmunity. However, more recent work has demonstrated the role of autoimmunity in the process of lung transplant rejection. IL-17 and autoantigens such as collagen type V and K-α1 tubulin have been implicated in the development of chronic rejection. Ultimately, this translational review discusses the role that autoimmunity plays in the development of OB and lung transplant rejection and then discusses options for therapeutic intervention.

Enrichment of regulatory T cells in acutely rejected human liver allografts

Acute cellular rejection (ACR) occurs frequently after liver transplantation and can usually be controlled. Triggering of allospecific immune responses and lack of immunoregulation are currently suggested as a cause of ACR, but there are no investigations of intrahepatic immune responses during ACR. Therefore we prospectively analyzed the intrahepatic T cell infiltration pattern in correlation to the severity of ACR in a cohort of patients with graft hepatitis (n = 151). While CD4(+) cells dominated the portal infiltrates in mild-moderate ACR, CD8(+) cells prevailed in severe ACR. Furthermore portal CD8(+) and not CD4(+) infiltration correlated with serum transaminases and with the likelihood of subsequent ACRs. Surprisingly, the rise of portal effector T cells density during ACR was surpassed by the increase in portal infiltration of regulatory T cells by a factor of two. Thus ACRs rather showed an increase and not a lack of regulation, as was suggested by analysis of peripheral blood mononuclear cells. Despite the pattern of enhanced immunoregulation, patients with severe ACR had a higher risk for subsequent rejections and showed a trend to a reduced survival. Thus, patients with severe rejections might need a modification of their immunosuppression to improve prognosis.

Vitamin D deficiency in lung transplant patients: is it important?

BACKGROUND

Vitamin D deficiency has been reported in different chronic pulmonary diseases like asthma and chronic obstructive pulmonary disease, but little is known in lung transplant recipients.

METHODS

Serum 25-hydroxyvitamin D (25-OHD) levels and pulmonary function (forced expiratory volume in 1 sec [FEV(1)] %predicted) were measured in 131 lung transplant patients during their yearly posttransplant check-up hospital stay, and the total number of infections and perivascular/peribronchiolar rejections were assessed from transplantation on.

RESULTS

Vitamin D deficiency (<30 ng/mL) occurred in 62 of 131 patients (47.3%), of whom 26 (19.8%) were severely deficient (<20 ng/mL). The FEV(1) was significantly lower in the deficient group compared with the group with normal levels (P=0.019). Moreover, we could find an association between FEV(1) and 25-OHD levels in univariate analysis (P=0.018), which remained significant in multivariate analysis (P=0.012). The same holds true for the association between 25-OHD levels and the peak postoperative FEV(1) (P=0.021 in multivariate analysis). We also identified significantly more patients with moderate to severe B-grade rejections in the deficient group (P=0.0038).

CONCLUSION

Vitamin D deficiency is present in 47% of our lung transplant patients and seems independently associated with a lower FEV(1) and more severe B-grade rejections. This study raises the potential need for additional vitamin D treatment in lung transplantation and clearly indicates the role of a randomized placebo-controlled trial with vitamin D supplementation, which is ongoing in our center.

Lung transplantation affects expression of the chemokine receptor type 4 on specific T cell subsets

Alloreactive T cells that infiltrate the graft after lung transplantation (LTx) play a role in chronic rejection. Chemokines such as thymus and activation-regulated chemokine (TARC), macrophage-derived chemokine (MDC) and monocyte chemotactic protein-1 (MCP-1) are produced locally in the lung and attract T cells via chemokine receptor 4 (CCR4). In a TARC gradient, cells expressing CCR4(++) migrate more efficiently than CCR4(+) -expressing cells. In this study, we compared the CCR4 expression of T cells in blood from 20 lung transplant recipients to healthy controls. We then examined whether CCR4 expression is associated with the occurrence of chronic rejection. The CCR4(++) expression was decreased on CD4 T cells from LTx patients (P < 0·0001) when compared to healthy controls. The analysis of CD4 T cell subsets showed that this decrease was present on central memory, effector memory and terminally differentiated T cells (P = 0·0007, P < 0·0001 and P = 0·05, respectively), while a trend was found for naive CD4 T cells (P = 0·06). Also, the expression of CCR4(+) on regulatory T cells (T(regs) ) was decreased in LTx patients when compared to healthy controls (P = 0·02). Interestingly, the CCR4(++) expression on CD4 effector memory T cells was decreased in patients developing chronic rejection sometimes more than a year before the clinical diagnosis when compared to patients who did not (P = 0·04). The analysis of CD8 T cell subsets only showed the CCR4(+) expression to be increased significantly on effector memory and terminally differentiated CD8 T cells (P = 0·02, P = 0·03, respectively) in LTx patients, but no relation was found in chronic rejection. In conclusion, the expression of CCR4 on T cell subsets was altered after LTx and appears to be related to chronic rejection.

Do CD4+ Foxp3+ Treg cells correlate with transplant outcomes: a systematic review on recipients of solid organ transplantation

Regulatory T cells (Tregs) are considered to be critical for the induction of transplant tolerance. Tregs counts were measured in blood, biopsy and urine sample after transplantation in many studies. Although not unanimous, some studies have suggested that Tregs is associated with better outcome and can also serve as an immune marker to predict the individual risk of rejection and identify tolerant patients. In this study, we systematically reviewed the correlation between Tregs and transplant outcomes, identifying if Tregs can predict transplant rejection and tolerance. A total of 22 articles were included and assessed, the results showed that Tregs in recipients are helpful to maintain a stable graft function, reduce acute/chronic rejection rate. And the Tregs in graft and urine, rather than in PBL, may have a better diagnostic value for transplant outcomes. However, since the low quality of included studies, results may be influenced by bias. More high quality studies with bigger sample size are still needed in future.