T-lymphocyte subsets in renal allograft recipients treated with cyclosporine and azathioprine

Enhanced cardiac allograft survival by Vav1-Rac signaling blockade in a mouse model

BACKGROUND

Vav1-Rac signaling plays a pivotal role in TCR/antigen and CD28 signals for T cell activation. However, pharmacological interference of this signaling has not been tested in the prevention of alloimmune-mediated allograft rejection. It has been demonstrated that 6-thio-GTP, a metabolite of azathioprine, specifically inhibits Vav1-Rac activity in T lymphocytes. Here we show the immunosuppressive efficacy of 6-thio-GTP in the prevention of cardiac allograft rejection.

METHODS

T cell proliferations were measured by (3)H-thymidine uptake. The immunosuppressive activities of 6-thio-GTP were tested in the cardiac allograft model of C57BL/6 (H-2(b)) to Balb/c (H-2(d)) mice.

RESULTS

6-Thio-GTP inhibited TCR/alloantigen stimulated T cell proliferation and CD28-dependent T cell survival. Administration of 6-thio-GTP (0.5 mg/kg) prolonged graft survival to 13.8+/-2.39 days compared to 8.3+/-0.48 days in PBS controls (p<0.0001). Combination of 6-thio-GTP (0.5 mg/kg) with CsA (15 mg/kg) enhanced graft survival from 15.0+/-1.61 days in CsA treated recipients to 36.8+/-2.17 days in those received 20 days of combination therapy of CsA and 6-thio-GTP (p<0.0001), or to 42.7+/-16.63 days in the group treated with 20 days of CsA and 60 days of 6-thio-GTP (p<0.0001). Lymphocytes from 6-thio-GTP treated recipients with long-term surviving grafts (>60 days) displayed reduced proliferative response to alloantigen and higher frequencies of regulatory T cells (Treg).

CONCLUSION

Vav1-Rac inhibitor 6-thio-GTP prolongs allograft survival alone or in combination with CsA by suppression of alloreactive T cell activation. Our findings suggest the therapeutic potential of pharmacological interference of Vav1-Rac signaling for transplantation.

Persistent long-term changes in lymphocyte subsets induced by polyclonal antibodies

BACKGROUND

Clinicians are well aware of the short-term effects of immunosuppression by mono- or polyclonal antibodies. Little is known about long-term changes induced by these therapies.

METHODS

Forty-three renal allograft recipients were selected according to their initial postoperative immunosuppression: (1) BI group=basic immunosuppression with steroids and cyclosporine, n=16; (2) ATG group=basic immunosuppression plus polyclonal antibody antithymocyte globulin (ATG), n=11; and (3) OKT3 group=basic immunosuppression plus monoclonal antibody OKT3, n=16 patients. At intervals of 6 months, the following parameters were measured prospectively: lymphocyte surface antigens (HLA-DR, CD3, CD4, CD8, CD16, CD19, CD56, and CD57); serum and urine neopterin; serum amyloid A; and indirect and direct tests for herpes viruses.

RESULTS

The mean period of observation was 58.4 months. The most significant differences between the groups occurred for CD4+ and CD8+ T cells. The ratios of CD4+ to CD8+ cells (n=278 measurements) were significantly and persistently lower in the ATG group (P<0.001, Brown-Mood test). Five years after transplantation, the ATG group had a CD4+ to CD8+ cell ratio of x=0.6 versus x=1.7 in the OKT3 group and x=2.0 in the BI group. This inversion was due to a persistent depletion of the CD4+ cells and an increased regeneration of the CD8+ cells, in particular of the CD8+brightCD57+ subpopulation. Extent and duration of CD4+ depletion correlated with the cumulative ATG dose (r=0.7, P<0.05, Spearman rank correlation test).

CONCLUSION

Therapy with polyclonal antibody ATG induces dose-dependent long-term changes in T-cell lymphocyte subsets, which persist over a period of years.

Early diagnosis and successful treatment of acute cytomegalovirus encephalitis in a renal transplant recipient

We report the case of a 40-year-old male HIV-negative renal transplant patient with allograft rejection and immunosuppressive therapy who presented with acute cytomegalovirus (CMV) encephalitis. CT and MRI of the brain were normal but EEG showed diffuse slowing and dysrhythmia. In cerebrospinal fluid (CSF) initially 81 cells/microliters were found and immunocytochemistry showed a decreased CD4/CD8 ratio and increased values of activated lymphocytes, natural killer cells and immunoglobulin-containing cells. CMV-specific IgM antibodies in CSF and serum, immunostaining of CMV antigen in CSF cells and virus culture from CSF and urine were negative. During the first 3 weeks of illness no intrathecal production of immunoglobulins could be detected. Early diagnosis of CMV encephalitis was made by in situ hybridization (ISH) on CSF cell preparations and the polymerase chain reaction (PCR) which was positive in CSF and blood. On day 26 diagnosis was confirmed by detection of CMV-specific intrathecal IgG production. The patient was treated with ganciclovir, anti-CMV immunoglobulins and intrathecal beta interferon. He recovered completely after 2 months. Our data demonstrate the usefulness of ISH and PCR in the early diagnosis of CMV encephalitis and perhaps may encourage the use of intrathecal beta interferon in other patients with this disease.

Discriminating rejection from CMV infection in renal allograft recipients using flow cytometry

The ability to distinguish among rejection, cytomegalovirus (CMV) infection, and cyclosporin toxicity in the symptomatic renal allograft recipient remains one of the major issues in clinical transplantation. The practical application of immunologic monitoring of peripheral blood lymphocytes through the use of fluorescently labeled monoclonal antibodies and single-color flow cytometry has been limited by the inability to demonstrate significant correlations between the levels of specific T-cell subset populations and the cause of impaired renal function. In the present study using two-color analysis, we monitored the expression of interleukin-2 receptor (IL-2R) and HLA-DR antigen on the T-cells of a group of 51 renal cadaveric allograft recipients receiving cyclosporin, azathioprine, and prednisone for an average of 4 months after transplantation. We found that the proportion of CD3+ cells coexpressing IL-2R increased above baseline during 12 out of 14 rejection episodes that took place during the course of the study (P less than 10(-6)). Alternatively, we found that the proportion of cells coexpressing HLA-DR antigen on CD2+ cells increased above baseline during 11 out of 11 CMV infections (P less than 10(-6)). There was no correlation between the level of IL-2R+CD3+ cells and CMV infection or between the level of CD2+DR+ cells and rejection. These relationships showed a high degree of sensitivity and specificity when used to discriminate among possible etiologies for decreased renal function in the symptomatic patient.

Lymphocyte subpopulation with low membrane potential in the blood of cyclosporin- and prednisone-treated patients: in vivo selectivity for T4 subset

Previous work on the mode of action of CsA revealed that this drug shifts the membrane potential of human periferal blood lymphocytes in vitro. Recently we have analyzed lymphocytes of cyclosporin-treated transplant patients. Membrane potential analysis with the DIOC6(3) fluorescence dye indicates that all the studied patients have a subpopulation of lymphocytes with low membrane potential and that this population is made up predominently of OKT4+ cells. However there is no correlation between the clinical events and the percentage distribution of lymphocyte subpopulations as defined by the membrane potential and the T4/T8 ratio of the total lymphocyte population.

Detection of activated lymphocyte subsets by fluorescence and MTT staining

A double staining technique for simultaneously determinating cell surface phenotype and the degree of cell activation is described. As an activation marker, the tetrazolium dye MTT has been used. Cells were incubated for 30 min with MTT. Activated cells yielded a granular staining pattern. Upon termination of the reaction with sodium azide, a double-step immunofluorescence staining procedure using monoclonal antibodies specific for cell surface antigens was performed. The percentage of cells simultaneously displaying MTT formation and fluorescence was microscopically evaluated. Our results demonstrate that MTT staining is expressed concomitantly with the IL-2 receptor and the transferrin receptor. This method permits a simple characterization of activated T cell subsets and can be used clinically to analyse the T cell functions of patients being treated with immunosuppressive agents and patients with acquired immune deficiency syndrome.

Comparison of the staining of peripheral blood T lymphocytes by various anti-CD8 and HLA-DR monoclonal antibodies

T cell subset analysis with monoclonal antibodies is performed in variety of clinical situations, including the monitoring of transplant recipients. We compared the percentages CD8+ cells in the peripheral blood of ten normal volunteers and 26 renal transplant patients using fluorescein isothiocyanate (FITC)- or phycoerytrin (PE)-conjugated Leu2a and Leu2b monoclonal antibodies (mAb). Furthermore, the percentage of HLA-DR+ cells within this population was determined using two anti-HLA-DR antibodies of differing isotype (designated 203 and 243) and either an FITC or a PE label. For both controls and transplant recipients, the PE-conjugated Leu2a and Leu2b mAbs gave significantly higher percentages of positive cells than the FITC-conjugated antibodies (P less than 0.01). Furthermore, the percentage of Leu2b+ cells was higher than the percentage of Leu2a+ cells, irrespective of the fluorochrome used (P less than 0.01); this was particularly true for samples with less than or equal to 10% Leu2a+ cells. Cell sorting experiments indicated that up to 30% of the Leu2a- population were able to bind OKT8 or Leu2b mAb in blood samples with a low percentage of Leu2a+ cells. The percentage of Leu2+ cells that were stained with anti-HLA-DR mAb 203 or 243 varied considerably, depending on the fluorochrome and the isotype of the antibodies. We conclude that the analysis of peripheral blood T cells with mAbs that apparently have the same specificity may give significantly different results, depending on the patient population, the fluorochrome and the isotype of the antibodies.