Cytokines and cell surface markers in prediction of cardiac allograft rejection

Lymphocyte surface molecules as immune activation biomarkers

Immunosuppression is mandatory after solid organ transplantation between HLA mismatched individuals. It is a lifelong therapy that needs to be closely monitored to avoid under- and over-immunosuppression. For many drugs, pharmacokinetic monitoring has been proven to be beneficial. However, the therapeutic ranges are statistically derived surrogate markers for the effects that cannot predict the individual response of single patients. Better tailored immunosuppression biomarkers are needed that indicate immune activation. T cells are critically involved in organ rejection, and the means to assess their activation state may be promising to individualize immunosuppressive therapies. Activated T cells can be monitored with flow cytometry based on surface molecules that are typically up regulated or with molecules that are cleaved off the cell surface. Among these molecules are the interleukin-2 receptor (CD25); transferrin receptor (CD71); the T cell co-stimulatory molecules CD28, CD69, and CD154 and sCD30, which is a member of the TNF-alpha family. The effect of immunosuppressive drugs on T cell activation can be recorded with indirect cell function assays or by directly monitoring activated T cells in whole blood. Soluble proteins can be measured with immunoassays. This review provides a summary of the experimental and clinical studies investigating the potential of surface molecules as a tool for immune monitoring. It critically discusses the obstacles and shortcomings from an analytical and diagnostic perspective that are currently preventing their use in multicenter trials and clinical routine monitoring of transplant patients.

Surface markers of lymphocyte activation and markers of cell proliferation

The individualization of immunosuppression is an approach for preventing rejection in the early phase after transplantation and for avoiding the long-term side effects of over immunosuppression. Pharmacodynamic markers, either specific or nonspecific, have been proposed as complementary tools to drug monitoring of immunosuppressive drugs. A key event in graft rejection is the activation and proliferation of the recipient's lymphocytes, particularly T cells. Activated T cells express surface receptors, such as CD25 (the IL-2 receptor) and CD71 (the transferrin receptor), or co-stimulatory molecules (CD26, CD27, CD28, CD30, CD154 or CD40L, and CD134). Both surface marker expression and cell proliferation are predominately assessed by flow cytometry. Protocols have been established and utilized for both in vitro and ex vivo investigations with either isolated lymphocytes or whole blood. This article reviews the current body of research regarding the use of lymphocyte proliferation and surface activation markers with an emphasis on T cells. Experimental and clinical results related to these markers, as well as methodological issues and open questions, are addressed.

Review: Pharmacodynamic monitoring of immunosuppression in kidney transplantation

Advances in immunosuppressive therapies have improved kidney transplant outcomes. However, immunosuppressant drug-induced toxicities continue to reduce tolerability and impact patient and graft survival. A major ongoing challenge in kidney transplantation is to establish ways of tailoring immunosuppressant therapy so as to maintain efficacy while minimizing toxicity. Pharmacodynamic monitoring by direct measurement of immune cell function has the potential to personalize immunosuppression. The purpose of this review is to provide the clinician with an overview of the methodology and use of immune function monitoring in the field of kidney transplantation.

Expansion and tissue infiltration of an allospecific CD4+CD25+CD45RO+IL-7Ralphahigh cell population in solid organ transplant recipients

It has been recently shown (Seddiki, N., B. Santner-Nanan, J. Martinson, J. Zaunders, S. Sasson, A. Landay, M. Solomon, W. Selby, S.I. Alexander, R. Nanan, et al. 2006. J. Exp. Med. 203:1693–1700.) that the expression of interleukin (IL) 7 receptor (R) α discriminates between two distinct CD4 T cell populations, both characterized by the expression of CD25, i.e. CD4 regulatory T (T reg) cells and activated CD4 T cells. T reg cells express low levels of IL-7Rα, whereas activated CD4 T cells are characterized by the expression of IL-7Rα^high. We have investigated the distribution of these two CD4 T cell populations in 36 subjects after liver and kidney transplantation and in 45 healthy subjects. According to a previous study (Demirkiran, A., A. Kok, J. Kwekkeboom, H.J. Metselaar, H.W. Tilanus, and L.J. van der Laan. 2005. Transplant. Proc. 37:1194–1196.), we observed that the T reg CD25⁺CD45RO⁺IL-7Rα^low cell population was reduced in transplant recipients (P < 0.00001). Interestingly, the CD4⁺CD25⁺CD45RO⁺IL-7Rα^high cell population was significantly increased in stable transplant recipients compared with healthy subjects (P < 0.00001), and the expansion of this cell population was even greater in patients with documented humoral chronic rejection compared with stable transplant recipients (P < 0.0001). The expanded CD4⁺CD25⁺CD45RO⁺IL-7Rα^high cell population contained allospecific CD4 T cells and secreted effector cytokines such as tumor necrosis factor α and interferon γ, thus potentially contributing to the mechanisms of chronic rejection. More importantly, CD4⁺IL-7Rα⁺and CD25⁺IL-7Rα⁺ cells were part of the T cell population infiltrating the allograft of patients with a documented diagnosis of chronic humoral rejection. These results indicate that the CD4⁺CD25⁺IL-7Rα⁺ cell population may represent a valuable, sensitive, and specific marker to monitor allospecific CD4 T cell responses both in blood and in tissues after organ transplantation.

Pharmacodynamics of T-cell function for monitoring immunosuppression

OBJECTIVES

Recent studies show that measuring pharmacodynamic (PD) effects offers a unique possibility to predict immunosuppression. Thus, in this study we have monitored the PD properties of immunosuppressants on diverse T-cell functions in heart transplant (HTx) recipients.

MATERIALS

PDs and blood concentrations (PK) of three different basis-immunosuppressive drugs were studied: cyclosporin A (CsA); tacrolimus (TRL) and sirolimus (SRL). T-cell function was analysed by expression of proliferating cell nuclear antigen (PCNA) labelling, expression of cytokines (IL-2, IFN-gamma) and surface antigen (for example, CD25) by FACS analysis.

RESULTS

In group I, at time points C0 and C2, increased CsA-PK significantly inhibited expression of IL-2, IFN-gamma, PCNA and CD25 (P < 0.05). Correlations (r(2)) at C2 between inhibition of T-cell functions (PD) with PK and with drug doses were: CsA-PK: 0.71-0.91 and CsA-dose: 0.73-0.87. In group II, increased TRL-PK over time did not further inhibit expression of CD25, but inhibited PCNA expression more on day 3, and IL-2 and IFN-gamma expression was significantly higher on days 2 and 3 compared to PD effects of CsA (P < 0.05). Blood SRL concentrations in C0 group III, increased on day 1 and remained stable at days 3 and 4. Expression of PCNA was not altered in the SRL-PK category, whereas expression of CD25 was higher and expression of cytokines was lower than PD effects of CsA.

CONCLUSIONS

Our results show that PD effects on T-cell function can be used to monitor immunosuppression bringing potential to increase the efficacy and safety of immunosuppressive therapy after HTx.

Cytokine analysis to predict immunosuppression

BACKGROUND

Recently, it has been realized that TH1/TH2 cytokine production offer the unique possibility to predict drug efficacy. However, there is still an incessant need to explore assay conditions and techniques of analyzing cytokines, which are specific and reliable for monitoring drug efficacy.

METHODS

In this study we used the multiplex bead array technique to detect cytokines of TH1/TH2 cells in whole blood of heart transplanted (HTx) recipients.

RESULTS

We found significantly different levels of cytokine expression in HTx recipients compared with cytokine levels in patients prior to HTx. Furthermore, particular cytokine levels were significantly decreased 2 h after drug dosing, compared with cytokine levels before dosing in mitogen-stimulated whole blood.

CONCLUSIONS

Cytokine analysis with the multiplex array technique in mitogen-stimulated whole blood provides the possibility to predict immunosuppression.

Local bioactive tumour necrosis factor (TNF) in corneal allotransplantation

The aim of this study was to examine the kinetic profile of bioactive TNF levels in aqueous humour of rabbit eyes undergoing corneal allograft rejection and to investigate the effect of locally blocking TNF activity after corneal transplantation. In a rabbit corneal transplantation, endothelial allograft rejection was identified and correlated with increase in central graft thickness. Samples of aqueous humour obtained on alternate days following transplantation were tested for TNF mRNA and bioactive TNF protein. To investigate the effect of locally blocking TNF activity in allograft recipients, the fusion protein TNFR-Ig was administered by injections into the anterior chamber after transplantation. Pulsatile increases in levels of this cytokine were found in 14 of 15 allograft recipients. Peaks of TNF bioactivity preceded by varying intervals the observed onset of rejection in allograft recipients. TNF levels were not elevated in aqueous humour from corneal autograft recipient controls or in serum of allografted animals. mRNA levels were elevated before onset of and during clinically observed allograft rejection. In three of seven animals receiving TNFR-Ig injections on alternate days from day 8 to day 16 post-transplant, clear prolongation of corneal allograft survival was demonstrated. Bioactive TNF is present in aqueous humour following rabbit corneal allotransplantation. Rather than correlating directly with endothelial rejection onset, pulsatile peak levels of TNF precede and follow the observed onset of endothelial rejection. Blockade of TNF activity prolongs corneal allograft survival in some animals, indicating that this cytokine may be a suitable target in local therapy of corneal allograft rejection.

Donor-derived soluble HLA plasma levels can not be used to monitor graft rejection in heart transplant recipients

OBJECTIVE

Increased levels of both donor- and recipient-derived HLA class I molecules (sHLA-I) can be found in serum or plasma of transplanted patients during rejection. Earlier data indicate that levels of donor-derived sHLA-I (dsHLA-I) correlate better with graft rejection than total sHLA Class I (Zavazava N, Kraatz E, Gassel AM, Muller-Ruchholtz W. Plasma MHC class I expression in cardiac graft patients: donor-specific soluble antigen in a pre-sensitized graft patient. Transplant Proc 1991;23:2258-2260; Claas FHJ, Jankowska-Gan E, DeVito LD, et al. Monitoring of heart transplant rejection using a donor-specific soluble HLA class I ELISA. Hum Immunol 1993;37:121). Therefore, quantifying donor-derived soluble counterparts of HLA Class I (sHLA-I) in the plasma of the recipient may offer a new possibility for non-invasive monitoring of rejection after organ transplantation.

METHODS

In an extended study with 34 heart transplant recipients, we used sHLA-I specific ELISAs to monitor donor-derived soluble sHLA-A2, -A3, -A9, -B7, -B12 and B51.

RESULTS

The assays were sensitive enough to detect dsHLA Class I in plasma of the recipients. However, the levels of sHLA were not found to be a useful tool for monitoring rejection. Rejection was often associated with low levels of donor sHLA. The recent finding that antibodies can inhibit the detection of sHLA molecules might explain this discrepancy. In order to test this hypothesis, patient sera were screened for the presence of anti-HLA antibodies and the results were related to the donor-derived sHLA levels. Only in four out of 34 patients HLA Class I specific antibodies could explain the low sHLA levels during rejection.

CONCLUSIONS

In heart transplantation increased donor-derived sHLA levels are not a suitable marker for rejection and that antibody formation can not explain these results. Therefore, monitoring rejection episodes on the basis of donor-derived soluble HLA molecules is not a realistic approach to decrease the number of biopsies after heart transplantation.

Cell surface markers and circulating cytokines in graft versus host disease

Graft versus host disease (GVHD) remains the major obstacle to the widespread application of allogeneic bone marrow transplantation (BMT) despite improvement in drug prophylaxis. T cells in the donor bone marrow recognize and react against host alloantigens and thereby initiate GVHD, but the precise mechanisms by which host tissues are damaged remain unclear. In the current study, we determined the cytokine secretion, cell population distribution, and cell surface markers expression by ELISA and flow cytometer, to understand further the pathophysiology of GVHD. Our results demonstrated that there was no significant change in the cell ratio of B-and T- lymphocytes, and helper/suppressor cells during GVHD development when compared to the condition before transplantation. Furthermore, the percentage of natural killer cells, the interleukin-2 receptor (IL-2R) or the HLA-DR antigen on both CD4 and CD8 positive cells presented no significant difference between pre-transplantation and during GVHD. The serum cytokine secretion of IL-1, TNF-alpha, IL-2, ICAM-1, endothelin, TGF-beta showed no difference before BMT and during GVHD. However, when patients in the developing of GVHD, there was significant difference in the serum levels of soluble IL-2R (slL-2R), epidermal growth factor (EGF), and platelet derived growth factor (PDGF). In addition, with patients who develop GVHD, the mixed lymphocyte reaction also presented a significant difference. This study indicated that some serum cytokines such as sIL-2R, growth factors, and the mixed lymphocyte reaction may be used as parameters for the early detection of the development of GVHD.

Donor-specific stimulation of peripheral blood mononuclear cells from recipients of orthotopic liver transplants is associated, in the absence of rejection, with type-2 cytokine production

In this study, we examined the cytokine production by human peripheral blood mononuclear cells (PBM) from recipients of orthotopic liver transplants which had been stimulated by donor-specific alloantigen. Levels of interleukin (IL)-2, IL-4, interferon (IFN)-gamma, IL-10 and transforming growth factor (TGF)-beta produced in vitro from PBM of 15 transplant recipients at 5-7 months post transplantation were analysed after donor-specific, third-party, or non-specific stimulation. Mononuclear cell proliferation in response to stimulation and cytokine mRNA from the cell cultures were assayed. Donor-specific antigen was obtained from donor spleen cells which had been obtained and frozen in liquid nitrogen at the time of organ retrieval. Third-party restimulation used equivalent numbers of spleen cells pooled from the other 14 organ donors. Cytokine production was correlated with the clinical condition of the patient, including biopsy results when available, and biochemical data. The data show a highly significant correlation between the donor-specific- and third-party- stimulated IL-4 and IL-10 production from recipient PBM with stable liver graft function as assessed by histopathology and/or biochemistry. This correlation was independent of level of immunosuppression. These data strongly support a role for IL-4 and/or IL-10 in the induction and/or maintenance of tolerance to human liver allografts. Measurement of the levels of these cytokines from recipient PBM after donor-specific antigen stimulation in vitro may be a useful test for monitoring for acute allograft rejection.

The application of human monoclonal antibodies for monitoring donor derived soluble HLA class I molecules in the serum of heart transplant recipients

Increased levels of both donor and recipient derived HLA molecules can be found in serum and plasma of transplanted patients during rejection. Recent data suggest that levels of donor specific soluble HLA Class I (sHLA-1) correlate better with graft rejection than total sHLA Class I [1, 2]. Therefore, quantification of donor specific soluble counterparts of HLA Class I in the serum of the recipient may be a new way for non-invasive monitoring of rejection after organ transplantation. Up to now, only a limited number of mouse monoclonal antibodies (alpha HLA-A2, and alpha HLA-B7) has been used in enzyme linked immunosorbent assays (ELISAs) to detect donor specific HLA molecules in the plasma of transplant recipients. To monitor other donor-recipient combinations, we tested some of our HLA Class I specific human monoclonal antibodies, routinely used in complement dependent cytotoxicity, for their suitability in ELISA based assays. In the present model system, we used alpha HLA-A9 (BvK5C4) or alpha HLA-A3 (OK2F3) hybridoma-supernatant to set up a sHLA-A9 and sHLA-A3 specific ELISA. In a pilot study we show that these assays were sensitive enough to detect an increase of donor specific sHLA-I during rejection in the plasma of two heart transplant recipients. Use of a large set of human hybridoma's will enable monitoring most recipient/donor combinations in the near future.