Inhibition of alloreactive cytotoxic T lymphocytes by peptides from the alpha 2 domain of HLA-A2

Soluble HLA-I-mediated secretion of TGF-beta1 by human NK cells and consequent down-regulation of anti-tumor cytolytic activity

Soluble HLA class I (sHLA-I) molecules can regulate survival of NK cells and their anti-tumor killing activity. Herein, we have analysed whether interaction of sHLA-I with CD8 and/or different isoforms of killer Ig-like receptors (KIR) induced secretion of transforming growth factor (TGF)-beta1. CD8+KIR- NK cell clones secreted TGF-beta1 upon the interaction of sHLA-I with CD8 molecule. sHLA-Cw4 or sHLA-Cw3 alleles engaging inhibitory isoforms of KIR, namely KIR2DL1 or KIR2DL2, strongly downregulated TGF-beta1 production elicited through CD8. On the other hand, sHLA-Cw4 or sHLA-Cw3 alleles induced secretion of TGF-beta1 by ligation of stimulatory KIR2DS1 or KIR2DS2 isoforms. TGF-beta1 strongly reduced NK cell-mediated tumor cell lysis and production of pro-inflammatory cytokines such as TNF-alpha and IFN-gamma. Also, TGF-beta1 inhibited NK cell cytolysis induced by the engagement of stimulatory receptors including NKG2D, DNAM1, 2B4, CD69, NKp30, NKp44 and NKp46. The IL-2-dependent surface upregulation of some of these receptors was prevented by TGF-beta1. Furthermore, TGF-beta1 hampered IL-2-induced NK cell proliferation but not IL-2-mediated rescue from apoptosis of NK cells. Depletion of TGF-beta1 restored all the NK cell-mediated functional activities analysed. Taken together these findings suggest that sHLA-I antigens may downregulate the NK cell-mediated innate response by inducing TGF-beta1 release.

Behavior of serum human major histocompatibility complex class I antigen levels in human immunodeficiency virus-infected patients during antiretroviral therapy: correlation with clinical outcome

Human major histocompatibility complex class I antigens (HLA-A, -B, and -C) are heterodimeric molecules composed of a alpha heavy chain noncovalently associated with an invariant protein known as beta(2)-microglobulin. Beside being expressed on the membrane of the large majority of nucleated cells, HLA class I antigens are evident in serum (sHLA-I). We have previously detected a significant increase in the serum level of beta(2)-microglobulin-associated HLA-I antigens in human immunodeficiency virus (HIV)-infected patients compared with HIV-negative controls. The introduction of highly active antiretroviral therapy (HAART) modified the clinical course of the disease and decreased the acquired immunodeficiency syndrome-related morbidity and mortality. Therefore, we measured the levels of sHLA-I antigens in 64 HIV-infected patients before and during HAART treatment and correlated them with the immunological and virological response to antiretroviral treatment. Serum sHLA-I antigen level was elevated in all HIV-infected patients before and significantly decreased after 36 months of HAART treatment, correlating with the decrease of plasma HIV-RNA level and with the increase of CD4+ T-lymphocyte number. These results suggest that the measurement of sHLA-I antigens serum level might represent a useful surrogate marker to monitor HIV-positive patients undergoing HAART treatment.

Impact of culture conditions on the proliferative lifespan of human T cells in vitro

BACKGROUND

In human T cells, telomerase is transiently expressed upon activation and stimulation and, as shown previously, telomerase levels are able to control the lifespan of T cells. To improve T-cell expansion it is of critical importance to understand the effects of culture parameters on telomerase activity and lifespan.

METHODS

We investigated the influence of culture condition (FCS, human AB serum and autologous serum) and stimulation (PHA/feeder cells, anti-CD3/CD28 beads) on the lifespan, clonogenicity (number of positive wells), cell cycle, telomerase activity and telomere length of T cells in vitro.

RESULTS

The proliferative lifespan of T cells expanded with PHA/feeder cells and autologous serum from different donors was doubled compared with stimulation with PHA/feeder cells and AB serum. No or only a small difference was found for T cells expanded with anti-CD3/CD28 beads and autologous or AB serum. The use of autologous serum also increased the clonogenicity to about three-fold compared with the use of AB serum or FCS, without any signs of differences in the fractions of cycling cells. Interestingly, T cells cultured with autologous serum exhibited a significantly higher telomerase activity at day 6 after stimulation and a reduced decline of telomerase activity compared with cultures with AB serum.

DISCUSSION

The use of autologous serum combined with PHA stimulation and feeder cells remarkably extends the proliferative lifespan and clonogenicity and increases the telomerase activity of human T cells in vitro. This might be useful for applications where large numbers of specific T cells are required.

Apoptosis of antigen-specific T lymphocytes upon the engagement of CD8 by soluble HLA class I molecules is Fas ligand/Fas mediated: evidence for the involvement of p56lck, calcium calmodulin kinase II, and Calcium-independent protein kinase C signaling pathways and for NF-kappaB and NF-AT nuclear translocation

The binding of soluble HLA class I (sHLA-I) molecules to CD8 on EBV-specific CTL induced up-regulation of Fas ligand (FasL) mRNA and consequent sFasL protein secretion. This, in turn, triggered CTL apoptosis by FasL/Fas interaction. Molecular analysis of the biochemical pathways responsible for FasL up-regulation showed that sHLA-I/CD8 interaction firstly induced the recruitment of src-like p56(lck) and syk-like Zap-70 protein tyrosine kinases (PTK). Interestingly, p59(fyn) was activated upon the engagement of CD3/TCR complex but not upon the interaction of sHLA-I with CD8. In addition, sHLA-I/CD8 interaction, which is different from signaling through the CD3/TCR complex, did not induce nuclear translocation of AP-1 protein complex. These findings suggest that CD8- and CD3/TCR-mediated activating stimuli can recruit different PTK and transcription factors. Indeed, the engagement of CD8 by sHLA-I led to the activation of Ca2+ calmodulin kinase II pathway, which eventually was responsible for the NF-AT nuclear translocation. In addition, we found that the ligation of sHLA-I to CD8 recruited protein kinase C, leading to NF-kappaB activation. Both NF-AT and NF-kappaB were responsible for the induction of FasL mRNA and consequent CTL apoptosis. Moreover, FasL up-regulation and CTL apoptotic death were down-regulated by pharmacological specific inhibitors of Ca2+/calmodulin/calcineurin and Ca2+-independent protein kinase C signaling pathways. These findings clarify the intracellular signaling pathways triggering FasL up-regulation and apoptosis in CTL upon sHLA-I/CD8 ligation and suggest that sHLA-I molecules can be proposed as therapeutic tools to modulate immune responses.

DQ 65–79, A Peptide Derived from HLA Class II, Mimics p21 to Block T Cell Proliferation

DQ 65-79, a peptide derived from residues 65-79 of the alpha-chain HLA class II molecule DQA03011, blocks T cell proliferation and induces T cell apoptosis. Using a yeast two-hybrid assay, we previously identified proliferating cell nuclear Ag (PCNA) as an intracellular ligand for DQ 65-79. In this study, we show that three regions of PCNA, residues 81-100, 121-140, and 241-261, interact with DQ 65-79. Residues 241-261 of PCNA also interact with the C terminus (residues 139-160) of the cell cycle regulator, p21, suggesting that DQ 65-79 and p21 might function similarly. We show here that DQ 65-79 competitively inhibits binding of p21 to PCNA and that both DQ 65-79 and p21 139-160 induce T cell apoptosis, suggesting that DQ 65-79 and p21 act similarly to inhibit cell growth.

Peripheral blood lymphocytes immunophenotype and serum concentration of soluble HLA class I in burn patients

The level of the soluble form of histocompatibility class I antigens, associated with beta(2)-microglobulin (sHLA-I) has been determined by an ELISA sandwich method in serum from burned patients (n=42) and healthy volunteers (n=30). The sHLA-I level was insignificantly increased in burn patients at the stage of burn shock (1284+/-324U/ml, mean+/-S.E.M.) and after day 28 postburn (1368+/-258U/ml) compared to volunteers (1150+/-90U/ml). At the same time a decrease of sHLA-I levels between 4 and 14 days (638+/-178U/ml) was determined (P<0.05). Increased levels of sHLA, though not significant, were detected in patients with TBSAB >70% in comparison to patients with TBSAB from 30 to 70% during burn shock (1493+/-528 and 1075+/-339U/ml, respectively). Expression of membranous HLA class I antigens (mHLA-I) in peripheral blood lymphocytes (PBLs) was assayed simultaneously by indirect immunofluorescence. The number of CD3(+), CD4(+), CD8(+), CD25(+), CD71(+) and CD26(+) lymphocytes was also evaluated. The expression of mHLA-I in PBLs was increased significantly in patients with TBSAB <70% at early postburn period. Daily monitoring showed that the relative numbers of CD25(+) and CD71(+) lymphocytes in patients varied greatly within short intervals of time during burn shock. The data obtained suggest that mHLA-I expression can reflect postburn lymphocyte activation. The serum content of sHLA-I does not depend on lymphocyte number or activated lymphocyte number in peripheral blood at burned patients.

HLA-B7 beta-pleated sheet-derived synthetic peptides are immunodominant T-cell epitopes regulating alloresponses

Chronic rejection of transplanted allografts is the major cause of graft loss after clinical solid organ transplantation. Recent data link the indirect presentation of allopeptides to chronic graft loss; thus, identification of immunodominant epitopes on major histocompatibility complex (MHC) antigens could significantly contribute to establishing novel ways for monitoring and managing chronic rejection. Here, we show that synthetic allo-MHC-derived peptides covering the polymorphic region 56 to 120 of HLA-B7 modulate alloresponses. In particular, the 2 beta-pleated sheet-derived peptides covering residues 91 to 105 and 96 to 120, respectively, but not sequences from the alpha1 helix, were presented by autologous peripheral blood lymphocytes to induce T-cell proliferation. In addition, the 2 beta-pleated sheet-derived peptides and the alpha1-derived peptide residues 60 to 75 abrogated lysis of HLA-B7 target cells by anti-HLA-B7 cytotoxic T lymphocytes (CTLs). Although most residues between 91 and 120 are normally not directly accessible to T cells, our results indicate that peptides derived from the lower surface of the peptide-binding groove of HLA-B7 are immunodominant in HLA-B7 alloresponses. To characterize the binding and stability of allopeptides to T cells, the 62-70 peptide-derived from the 60-75 allopeptide that blocked cytotoxicity of anti-HLA-B7 CTL-was synthesized and coupled with fluorescein isothiocyanate. The peptide specifically labeled anti-B7 CTL, but not anti-HLA-A2 CTL as measured by flow cytometry. Peptide binding to CTL was specific at 4 degrees C and remained stable for 12 hours, whereas it remained stable for less than 2 hours at 37 degrees C. These studies allow the identification of HLA-B7 T-cell epitopes and reveal for the first time a novel, previously unrecognized application of synthetic HLA-derived allopeptides to visualize alloreactive T cells.

DQ 65-79, a peptide derived from HLA class II, induces I kappa B expression

A synthetic peptide corresponding to residues 65-79 of the alpha helix of the alpha-chain of the class II HLA molecule DQA03011 (DQ 65-79) inhibits the proliferation of human T lymphocytes in an allele nonrestricted manner. By using microarray technology, we found that expression of 29 genes was increased or decreased in a human CTL cell line after treatment with DQ 65-79. This study focuses on one of these genes, IkappaB-alpha, whose expression is increased by DQ 65-79. IkappaB proteins, including IkappaB-alpha and IkappaB-beta, are increased in T cells treated with DQ 65-79. Nuclear translocation of the NF-kappaB subunits p65 and p50 is decreased in T cells after treatment with DQ 65-79, while elevated levels of p65 and p50 are present in cytosol. DQ 65-79 inhibits the degradation of IkappaB-alpha mRNA and inhibits the activity of IkappaB kinase. These findings indicate that the DQ 65-79 peptide increases the level of IkappaB proteins, thereby preventing nuclear translocation of the transcription factor, NF-kappaB, and inhibiting T cell proliferation.

Allochimeric class I MHC molecules prevent chronic rejection and attenuate alloantibody responses

BACKGROUND

We have shown that treatment with molecularly engineered, allochimeric [alpha1 hl/u]-RT1.Aa class I MHC antigens bearing donor-type Wistar-Furth (WF, RT1.Au) amino acid substitutions for host-type ACI (RTI.Aa) sequences in the alpha1-helical region induces donor-specific tolerance to cardiac allografts in rat recipients. This study examined the effect of allochimeric molecules on the development of chronic rejection.

METHODS

Allochimeric [alpha1 hl/u]-RT1.Aa class I MHC antigenic extracts (1 mg) were administered via the portal vein into ACI recipients of WF hearts on the day of transplantation in conjunction with subtherapeutic oral cyclosporine (CsA, 10 mg/kg/day, days 0-2). Control groups included recipients of syngeneic grafts and ACI recipients of WF heart allografts treated with high-dose CsA (10 mg/kg/day, days 0-6).

RESULTS

WF hearts in ACI rats receiving 7 days of CsA exhibited myocardial fibrosis, perivascular inflammation, and intimal hyperplasia at day 80. At day 120, these grafts displayed severe chronic rejection with global architectural disorganization, ventricular fibrosis, intimal hyperplasia, and progressive luminal narrowing. In contrast, WF hearts in rats treated with [alpha1 hl/u]-RT1.Aa molecules revealed only mild perivascular fibrosis, minimal intimal thickening, and preserved myocardial architecture. Alloantibody analysis demonstrated no IgM alloantibodies in all groups. An attenuated, but detectable, anti-WF IgG response was present in recipients receiving allochimeric molecules, with IgG1 and IgG2a subclasses predominating. Immunohistochemical analysis of allografts demonstrated minimal T cell infiltration and IgG binding to vascular endothelium.

CONCLUSION

Treatment with allochimeric molecules prevents the development of chronic rejection. Such effect may be in part caused by deviation of host alloantibody responses.

In vitro immunosuppressive activity of soluble HLA class I and Fas ligand molecules: do they play a role in autologous blood transfusion?

BACKGROUND

The immunomodulatory effects of allogeneic blood transfusion may contribute to a poor prognosis in patients with cancer who are undergoing surgery, and clinical trials have been carried out to investigate whether these patients would benefit from autologous blood donation. As the immunomodulatory effects of allogeneic blood transfusion have been related to soluble molecules released from residual WBCs during storage, the in vitro immunomodulatory activity of soluble molecules detected in supernatants from stored autologous blood was evaluated.

STUDY DESIGN AND METHODS

Blood was donated by four healthy volunteers. Packed WBC-reduced RBCs were obtained and stored for 30 days, and supernatants were collected. FFP and serum were also obtained. The concentration of soluble molecules was determined by immunoenzymatic assays. The in vitro immunomodulatory activity of undiluted blood component supernatant was assessed by antigen-specific cytotoxic T-cell activity and mixed lymphocyte reactions in autologous combinations and by apoptosis induction in Fas+ cells.

RESULTS

The concentrations of soluble Fas-ligand and HLA class I molecules were higher in packed RBCs than in WBC-reduced RBCs, FFP, and serum. Undiluted supernatants of packed RBCs strongly inhibited functional assays and induced apoptosis in Fas+ cells. The immunomodulatory effects were correlated with the amount of soluble Fas ligand and HLA class I molecules.

CONCLUSION

The results of the present study are comparable with those already reported in allogeneic blood components, and they indicate that undiluted supernatants of autologous blood components may exert immunosuppressive effects in vitro.

Soluble HLA class I/CD8 ligation triggers apoptosis in EBV-specific CD8+ cytotoxic T lymphocytes by Fas/Fas-ligand interaction

In the present study, we report that allogeneic soluble HLA class I (sHLA-I) molecules isolated from serum induce apoptosis on EBV-specific CD8(+) Fas(+) cytotoxic T lymphocytes (CTL). CTL apoptosis is induced by the binding of sHLA-I molecules to CD8 and its extent depends on the time of incubation with sHLA-I molecules. Apoptosis is triggered by the interaction of Fas(+) CTL with soluble Fas-ligand, which is released following the binding of sHLA-I antigens to CD8 molecules. These results suggest that sHLA-I molecules may regulate immune responses by inducing apoptosis in virus-specific CTL.

Soluble HLA class I and Fas ligand molecules in blood components and their role in the immunomodulatory effects of blood transfusions

It has been known for many years that blood transfusions may have immunomodulatory effects, however an ultimate explanation of this phenomenon is lacking. In the present paper we report that the concentrations of soluble HLA class I (sHLA-I) and soluble Fas ligand (sFasL) molecules in supernatants of blood components which contain elevated numbers of residual donor leukocytes, like red blood cells and random-donor platelets, are significantly higher than in other blood components. Elevated amounts of sFasL molecules are also found in some commercial immunoglobulin preparations. sHLA-I and sFasL molecules in blood components and in immunoglobulin preparations are biologically active in vitro as they inhibit mixed lymphocyte responses and cytotoxic T cell activity in allogeneic and autologous combinations and induce apoptosis in Fas-positive cells. If these results are paralleled in vivo the amount of sHLA-I and sFasL molecules should be taken into account in clinical practice in order to select the blood component and the immunoglobulin preparation which could induce the desired immunomodulatory effect in the recipient.

An immunosuppressive and anti-inflammatory HLA class I-derived peptide binds vascular cell adhesion molecule-1

BACKGROUND

A synthetic peptide corresponding to residues 75-84 of HLA-B2702 modulates immune responses in rodents and humans both in vitro and in vivo.

METHODS

We used a yeast two-hybrid screening, an in vitro biochemical method, and an in vivo animal model.

RESULTS

Two cellular receptors for this novel immunomodulatory peptide were identified using a yeast two-hybrid screen: immunoglobulin binding protein (BiP), a member of the heat shock protein 70 family, and vascular cell adhesion molecule (VCAM)-1. Identification of BiP as a ligand for this peptide confirms earlier biochemical findings, while the interaction with VCAM-1 suggests an alternative mechanism of action. Binding to the B2702 peptide but not to closely related variants was confirmed by ligand Western blot analysis and correlated with immunomodulatory activity of each peptide. In mice, an ovalbumin-induced allergic pulmonary response was blocked by in vivo administration of either the B2702 peptide or anti-VLA-4 antibody.

CONCLUSIONS

We propose that the immunomodulatory effect of the B2702 peptide is caused, in part, by binding to VCAM-1, which then prevents the normal interaction of VCAM-1 with VLA-4.

Proliferating cell nuclear antigen as the cell cycle sensor for an HLA-derived peptide blocking T cell proliferation

Synthetic peptides corresponding to structural regions of HLA molecules are novel immunosuppressive agents. A peptide corresponding to residues 65-79 of the alpha-chain of HLA-DQA03011 (DQ65-79) blocks cell cycle progression from early G1 to the G1 restriction point, which inhibits cyclin-dependent kinase-2 activity and phosphorylation of the retinoblastoma protein. A yeast two-hybrid screen identified proliferating cell nuclear Ag (PCNA) as a cellular ligand for this peptide, whose interaction with PCNA was further confirmed by in vitro biochemistry. Electron microscopy demonstrates that the DQ65-79 peptide enters the cell and colocalizes with PCNA in the T cell nucleus in vivo. Binding of the DQ65-79 peptide to PCNA did not block polymerase delta (pol delta)-dependent DNA replication in vitro. These findings support a key role for PCNA as a sensor of cell cycle progression and reveal an unanticipated function for conserved regions of HLA molecules.

Thymic dendritic cells express inducible nitric oxide synthase and generate nitric oxide in response to self- and alloantigens

Thymocytes maturing in the thymus undergo clonal deletion/apoptosis when they encounter self- or allo-Ags presented by dendritic cells (DCs). How this occurs is a matter of debate, but NO may play a role given its ability of inducing apoptosis of these cells. APC (a mixed population of macrophages (Mphi) and DCs) from rat thymus expressed high levels of inducible NO synthase (iNOS) and produced large amounts of NO in basal conditions whereas iNOS expression and NO production were very low in thymocytes. Analysis by FACS and by double labeling of cytocentrifuged preparations showed that DCs and MPhi both express iNOS within APC. Analysis of a purified preparation of DCs confirmed that these cells express high levels of iNOS and produce large amounts of NO in basal conditions. The capacity of DCs to generate NO was enhanced by exposure to rat albumin, a self-protein, and required a fully expressed process of Ag internalization, processing, and presentation. Peptides derived from portions of class II MHC molecules up-regulate iNOS expression and NO production by DCs as well, both in self and allogeneic combinations, suggesting a role of NO in both self and acquired tolerance. We also found that NO induced apoptosis of rat double-positive thymocytes, the effect being more evident in anti-CD3-stimulated cells. Altogether, the present findings might suggest that DC-derived NO is at least one of the soluble factors regulating events, in the thymus, that follow recognition of self- and allo-Ags.

Recent advances in immunosuppressants

In recent years, a large number of structurally diverse immunosuppressants have been discovered that are effective for the treatment of organ transplantation. Some of them are undergoing clinical trials and may soon enter into routine clinical practice. These compounds are either chemical entities obtained from natural sources/synthetic means or biomaterials such as monoclonal antibodies/gene products/proteins. They have been found to interfere at different stages of T cell activation and proliferation, and can be identified as inhibitors of nucleotide synthesis, growth factor signal transduction and differentiation. Newer strategies involving combination of new agents with traditional immunosuppressants, monoclonal antibodies and gene therapy offer enormous potential, not only for the investigation of mechanisms pertaining to graft rejection, but also for its therapeutic prevention.

Prolongation of heart xenograft survival in a hamster-to-rat model after therapy with a rationally designed immunosuppressive peptide

BACKGROUND

Modification of the aminoacid sequence of peptides derived from the HLA class I heavy chain in combination with computer rational design resulted in the development of a peptide, RDP1258, with enhanced immunosuppressive activity.

METHODS

We evaluated the activity of this peptide, analyzing infiltrate by immunohistology and cytokine transcripts by reverse transcriptase-polymerase chain reaction method, in a hamster-to-rat xenograft model where recipients were treated with cobra venom factor (CVF) and peptide.

RESULTS

Although CVF or peptide alone had no effect, a combination of CVF/peptide RDP1258 resulted in a significant prolongation of graft survival (7.9+/-1 vs. 4.5+/-0 and 3.5+/-0 days, P<0.001). This effect was associated with an increased expression of heme oxygenase 1 (HO-1) in spleen, a significant reduced graft infiltrate, and a decrease of tumor necrosis factor-alpha mRNA transcripts (P<0.05) compared with CVF-treated recipients (1.6+/-0.07 vs. 3.3+/-0.3%, P=0.001) on day 3 after transplantation.

CONCLUSION

These observations are consistent with the observation that up-regulation of HO-1 results in inhibition of immune effector functions and suggest that the peptide acts, at least partially, through HO-1 regulation.

HLA-derived peptides as novel immunomodulatory therapeutics

A growing body of experimental evidence demonstrates that synthetic peptides corresponding to linear sequences of MHC (HLA in humans) proteins have immunomodulatory effects in vitro and in vivo in animal models and in humans. Although the original concept was that these peptides inhibited antigen recognition at the MHC-T cell receptor interface via physical blockade, it is now clear that the mechanisms responsible for the myriad of functional effects are more complex. Recent findings show that some peptides affect signal transduction and cell cycle progression. Fragments of MHC molecules can dampen or downregulate immune responses via a variety of mechanisms. Some soluble MHC molecules or synthetic peptides are capable of inducing and maintaining immunologic tolerance in animals. This information suggests that synthetic peptides themselves or drugs mimicking their effects may represent a new class of immunotherapeutics.

A novel method for measuring CTL and NK cell-mediated cytotoxicity using annexin V and two-color flow cytometry

An assay based on two-color flow cytometry has been developed to measure CTL and NK cell-mediated cytotoxicity. After effector/target cells are incubated together, CTL or NK populations are stained with an effector cell specific PE-conjugated mAb. Subsequently, annexin V-FITC binds to cells expressing phosphatidylserine (an early marker of apoptosis) on the cell surface. Target cells are gated upon as PE-negative and quantified with respect to their annexin V positivity. The shift from annexin Vneg to annexin Vhi is a discrete event such that all target cells fall within discernible populations with respect to annexin V. There is a strong correlation between cytotoxicity measured with our assay and a standard 51Cr release assay (r2 = 0.989). The PE/annexin V assay shows increased sensitivity at early timepoints after target/effector cell mixing. In addition, this method allows for analysis of target cells at the single cell level. Therefore, we have described a promising new technique to measure in vitro cell-mediated cytotoxicity. It avoids the potential difficulties of working with radioactive isotopes, and offers increased sensitivity and versatility.

Soluble HLA Class I, HLA Class II, and Fas Ligand in Blood Components: A Possible Key to Explain the Immunomodulatory Effects of Allogeneic Blood Transfusions

The immunomodulatory effect of allogeneic blood transfusions (ABT) has been known for many years. However, a complete understanding of the effects of ABT on the recipient’s immune system has remained elusive. Soluble HLA class I (sHLA-I), HLA class II (sHLA-II), and Fas ligand (sFasL) molecules may play immunoregulatory roles. We determined by double-determinant immunoenzymatic assay (DDIA) sHLA-I, sHLA-II, and sFasL concentrations in different blood components. sHLA-I and sFasL levels in red blood cells (RBCs) stored for up to 30 days and in random-donor platelets are significantly (P < .001) higher than in other blood components and their amount is proportionate to the number of residual donor leukocytes and to the length of storage. Blood components with high sHLA-I and sFasL levels play immunoregulatory roles in vitro as in allogeneic mixed lymphocyte responses (MLR) and antigen-specific cytotoxic T-cell (CTL) activity, and induce apoptosis in Fas-positive cells. These data suggest that soluble molecules in blood components are functional. If these results are paralleled in vivo, they should be taken into account in transfusion practice. Blood components that can cause immunosuppression should be chosen to induce transplantation tolerance, whereas blood components that lack immunosuppressive effects should be preferred to reduce the risk of postoperative complications and cancer recurrence.

Beta2-micro-free HLA class I heavy chain levels in sera of healthy individuals. Lack of association with beta2-micro-associated HLA class I heavy chain levels and HLA phenotype

We have applied a double-determinant immune assay (DDIA) to measure soluble beta2-microglobulin (beta2-micro)-free HLA class I heavy chains in serum. The mean concentration of beta2-micro-free HLA class I heavy chains in serum from 120 healthy subjects was 0.21+/-0.24 microg/ml. The individual serum levels of beta2-micro-free HLA class I heavy chains had a wide distribution, did not seem to be related with HLA phenotype, were stable over time and did not change with age. The serum levels of soluble beta2-micro-free HLA class I heavy chains did not correlate with those of soluble beta2-micro-associated HLA class I heavy chains, suggesting that their release is independently regulated. Three forms of soluble beta2-micro-free HLA class I heavy chains, with apparent molecular masses of 44, 39 and 37-35 kD, respectively, circulate in human serum. These results provide a useful background to assess the serum level of soluble beta2-micro-free HLA class I heavy chains in pathological conditions and to evaluate their putative immunoregulatory function.

Soluble HLA Class I, HLA Class II, and Fas Ligand in Blood Components: A Possible Key to Explain the Immunomodulatory Effects of Allogeneic Blood Transfusions

The immunomodulatory effect of allogeneic blood transfusions (ABT) has been known for many years. However, a complete understanding of the effects of ABT on the recipient’s immune system has remained elusive. Soluble HLA class I (sHLA-I), HLA class II (sHLA-II), and Fas ligand (sFasL) molecules may play immunoregulatory roles. We determined by double-determinant immunoenzymatic assay (DDIA) sHLA-I, sHLA-II, and sFasL concentrations in different blood components. sHLA-I and sFasL levels in red blood cells (RBCs) stored for up to 30 days and in random-donor platelets are significantly (P &lt; .001) higher than in other blood components and their amount is proportionate to the number of residual donor leukocytes and to the length of storage. Blood components with high sHLA-I and sFasL levels play immunoregulatory roles in vitro as in allogeneic mixed lymphocyte responses (MLR) and antigen-specific cytotoxic T-cell (CTL) activity, and induce apoptosis in Fas-positive cells. These data suggest that soluble molecules in blood components are functional. If these results are paralleled in vivo, they should be taken into account in transfusion practice. Blood components that can cause immunosuppression should be chosen to induce transplantation tolerance, whereas blood components that lack immunosuppressive effects should be preferred to reduce the risk of postoperative complications and cancer recurrence.

Purified truncated recombinant HLA-B7 molecules abrogate cell function in alloreactive cytotoxic T lymphocytes by apoptosis induction

BACKGROUND

Soluble MHC class I molecules are ubiquitous in human body fluids, including serum, urine, sweat, and cerebrospinal fluid. However, their biological function has remained unresolved. Membrane-derived human soluble MHC molecules (soluble human leukocyte antigen; sHLA) have been shown to induce apoptosis in alloreactive cytotoxic T lymphocytes (CTL). Here we report the efficacy of recombinant soluble HLA-B7 (rsHLA-B7) to modulate T-cell function.

METHODS

Primers of HLA-B7 were designed to allow amplification of a cDNA lacking the transmembrane and cytoplasmic domains yielding a truncated gene. rsHLA-B7 molecules were expressed in the human myeloma cell line 721.221 and purified by affinity chromatography using the BB7.7 mouse monoclonal antibody. CTL were generated from peripheral blood lymphocytes derived from healthy blood donors by stimulation with irradiated Epstein Barr virus-transformed HLA-B7-positive B cells. CTL were preincubated with rsHLA-B7, and cytotoxicity and apoptosis were tested according to standard procedure.

RESULTS

A total of 2 x 10(6) cells/ml secreted 10 microg/ml rsHLA-B7 as determined by a conformation-dependent ELISA, suggesting that rsHLA-B7 do not require the transmembrane and cytoplasmic regions for proper folding. After purification by affinity chromatography, rsHLA-B7 induced apoptosis in anti-HLA-B7 CTL, but not in anti-HLA-A2-specific, CTL. As a consequence, allorecognition of target cells by the CTL was significantly blocked.

CONCLUSION

Recombinant sHLA are sufficient binding cues for T cells, which efficiently induce apoptosis and block allorecognition of target cells by CTL. Thus, recombinant sHLA molecules may become a valuable new modality for specific immunological therapeutic intervention.

Expression of heat shock protein 70 blocks thymic differentiation of T cells in transgenic mice

Heat shock protein 70 (HSP70) is involved not only in protein folding, but also in processes of differentiation and cell-cycle progression. Recently, HSP70 has been implicated in mediation of functions of some immunosuppressive agents. To study the role of HSP70 in differentiation of haematopoietic cells, we generated transgenic mice using the human inducible hsp70 gene fused to the mouse H-2K promoter. These mice develop a T-cell deficiency that is characterized by thymic hypoplasia and a significant reduction in peripheral T cells. The total number of thymocytes is about 100-fold less than that in normal mice. The majority of the thymocytes are immature T cells that express neither CD4 nor CD8 molecules, indicating that T cells are affected at an early stage of thymic differentiation. Expression of the transgenic HSP70 was detected both in bone marrow cells and in thymocytes. Furthermore, injection of normal bone marrow cells into the T-cell deficient mice led to the generation of mature T cells indicating that the T-cell deficiency was caused by the action of HSP70 in T cells. The blockage of differentiation occurred only in T cells, both alphabeta- and gammadelta-T-cell receptor (TCR)-bearing cells, but not in B cells, granulocytes, and monocytes. The observations suggest that HSP70 may inhibit a cellular process that is essential for the differentiation of early stage T cells. Further experiments using this model system will widen our understanding of HSP70 and its function on a molecular level.

Inhibition of Cell Cycle Progression by a Synthetic Peptide Corresponding to Residues 65–79 of an HLA Class II Sequence: Functional Similarities but Mechanistic Differences with the Immunosuppressive Drug Rapamycin

A synthetic peptide corresponding to a region of the α1 α-helix of DQA03011 (DQ 65–79) inhibits the proliferation of human PBL and T cells in an allele-nonspecific manner. It blocks proliferation stimulated by anti-CD3 mAb, PHA-P, and alloantigen, but not by PMA and ionomycin. Substitution of each amino acid with serine shows that residues 66, 68, 69, 71–73, and 75–79 are critical for function. Inhibition of proliferation is long lasting and is not reversible with exogenous IL-2. The peptide can be added 24 to 48 h after stimulation and still block proliferation. The DQ 65–79 peptide does not affect expression of IL-2 or IL-2R; however, IL-2-stimulated proliferation is inhibited. Cell cycle progression is blocked at the G1/S transition, and the activity of cdk2 (cyclin-dependent kinase 2) kinase is impaired by the continued presence of p27. Although these results suggest a mechanism similar to that of rapamycin, the peptide inhibition is not reversed with FK-506, which indicates a distinct mechanism.

Characterization and biological significance of immunosuppressive peptide D2702.75-84(E --> V) binding protein. Isolation of heme oxygenase-1

This is the first report on peptidic inhibitors of heme oxygenase. Such peptides were originally developed from the immunomodulatory peptide 2702.75-84 which corresponds to amino acid residues 75 to 84 of the alpha1-helix of HLA-B2702 (2702.75-84) and has been shown to be immunosuppressive in vitro and in vivo. In vitro, 2702.75-84 inhibited cytotoxic T- and natural killer cell- mediated target cell lysis, and in vivo peptide therapy resulted in prolongation of heart and skin allograft survival in mice. The peptide was also shown to bind to heat shock protein 70. However, D-enantiomers of 2702.75-84 and derivatives thereof, while still being immunosuppressive, did not bind to heat shock protein 70. This study was designed to identify proteins binding to peptide D2702.75-84(E --> V) (rvnlrialry) consisting of D-amino acids. Compared with 2702.75-84 (RENLRIALRY), glutamic acid residue 76 (E) was replaced with valine (V). Affinity chromatography using immobilized D2702.75-84(E --> V) and mouse and human cell extracts, resulted in the isolation of heme oxygenase-1 (HO-1). Peptide D2702.75-84 inhibited HO activity in vitro in a dose dependent manner. Similar to what has been observed with other inhibitors of HO, administration of peptide into mice resulted in an up-regulation of HO-1 mRNA and protein, as well as enzyme activity in liver, spleen and kidney. Other peptides derived from 2702.75-84 with similar immunomodulatory activity displayed similar effects. In contrast, inactive derivatives of 2702.75-84 had no effect on HO activity. Therefore, the immunosuppressive effects of the described immunomodulatory peptides are similar to those of cobalt-protoporphyrin, a known up-regulator of HO-1. Our results suggest that HO-1 modulation may be a novel mechanism of immunomodulation.

Induction of tolerance in rodent cardiac allotransplantation using an MHC class I-derived peptide and cyclosporin A

BACKGROUND

The synthetic peptide corresponding to residues 75-84 of the human major histocompatibility complex class I molecule HLA-B7 (Allotrap 07) has been shown to inhibit differentiation of cytotoxic T lymphocyte precursors. Subsequent treatment of LEW-1A rats with this peptide was associated with a reduction in the level of cytotoxic activity directed to donor alloantigens. This study was undertaken to investigate the effect of Allotrap 07 on rodent heart allograft survival in LEW-1A recipients.

METHODS

Heart allografts from Lewis rats were heterotopically transplanted into the infrarenal abdominal aorta of ACI recipients. The treatment groups consisted of different regimens of short-term intravenous Allotrap 07 and oral cyclosporin A. All grafts were palpated daily, with rejection defined as the cessation of palpable contractions.

RESULTS

Cardiac allografts transplanted from Lewis to ACI rats survived indefinitely after administration of intravenous Allotrap 07 and oral cyclosporin A. Tolerance induction was donor-specific because third-party Brown-Norway, but not Lewis, grafts were rapidly rejected after implantation into ACI recipients.

CONCLUSIONS

Because donor-specific tolerance persisted long after cessation of peptide administration and did not occur when cyclosporin A was omitted from the immunosuppressive regimen, the mechanism may involve induction of clonal anergy.

Synchronous decline of serum-soluble HLA class I antigen and beta-cell function in insulin-dependent diabetes mellitus

Serum-soluble HLA class I molecules (sHLA) have immunomodulatory functions and their serum levels correlate with the HLA class I phenotype. We studied longitudinal changes of serum sHLA levels in insulin-dependent diabetes mellitus (IDDM). A total of 198 serum samples were obtained from 40 IDDM patients before and after IDDM onset. sHLA was assayed by a sandwich ELISA. sHLA levels in IDDM patients at the initiation of insulin therapy (IDDM onset) were markedly reduced compared with those in normal controls (334.2 +/- 26.3 ng/ml vs 492.4 +/- 55.5 ng/ml, mean +/- SEM, P = 0.0038). They fell sharply during 6 months before and after the onset of IDDM. The dynamic profile of sHLA and the time course of beta-cell loss were different between IDDM patients with and without HLA-A24. In those with HLA-A24, sHLA became significantly lower than normal controls with HLA-A24 at IDDM onset. Recovery of their sHLA values occurred at 3 years from IDDM onset. On the other hand, in those without HLA-A24, sHLA levels began to decrease since the onset of IDDM and became significantly lower than normal controls without HLA-A24 at 4 years after the onset. Recovery of sHLA occurred at more than 6 years from the onset. An early (within 18 months), complete loss of beta-cell function occurred in 5 of 13 IDDM patients with HLA-A24 compared with 1 of 14 of those without HLA-A24 (P = 0.077). A late (more than 36 months after the onset of IDDM), complete loss of beta-cell function occurred in 7 of 14 IDDM patients without HLA-A24 but in none of 13 of those with HLA-A24 (P = 0.0058). These results indicate that the decline of sHLA is synchronous with massive beta-cell destruction, and that these events occur during a short period in IDDM patients with HLA-A24, whereas they occur during a relatively long period in those without HLA-A24.

Immunosuppression by D-isomers of HLA class I heavy chain (amino acid 75 to 84)-derived peptides is independent of binding to HSC70

BACKGROUND

Peptides derived from the class I heavy chain were shown to modulate immune responses in vitro and in vivo. A peptide derived from HLA-B2702 (2702.75-84) inhibited differentiation of cytotoxic T cells as well as T cell and natural killer cell-mediated cytotoxicity in vitro. Peptide-mediated immunomodulation seemed to be independent of the MHC proteins expressed by responder and stimulator cells. In vivo studies in rodents demonstrated prolongation of heart and skin allograft survival after peptide therapy. Here, the correlation between the peptide's biological activity and its amino acid sequence was analyzed using peptides derived from amino acid 75-84 of several mouse, rat, and human MHC class I proteins as well as peptides with single amino acid substitutions in the 2702.75-84 sequence.

METHODS

Peptides consisting of both L- and D-amino acids were tested for inhibition of murine and human T cell-mediated and lymphokine-activated killer cell-mediated cytotoxicity, binding to hsc70, and prolongation of heart allograft survival in vivo.

RESULTS

Replacement of glutamic acid residue (E) at position 75 with valine (V) resulted in a peptide [2702.75-84(E>V)] with increased in vitro and in vivo activity but unchanged affinity for hsc70. Surprisingly, both L- and D-isomers of 2702.75-84 and 2702.75-84(E>V) inhibited cytotoxic cells in vitro and prolonged heart allograft survival in vivo. However, as expected, the peptides consisting of D-amino acids did not bind to hsc70.

CONCLUSION

Assuming that both D- and L-isomers modulate immune responses by similar mechanisms, these results suggest that the peptides' effect is independent of binding to hsc70.

Peptide-mediated immunosuppression

New insights into the mechanisms of allorecognition and the interactions of the TCR with the MHC molecule-peptide complex on antigen presenting cells have focused attention on developing novel biological strategies to modify the alloimmune response. Peptides derived from various regions of MHC class I and II molecules and structure-based peptides have demonstrated immunomodulatory effects both in vitro and in vivo. Their binding sites and mechanisms of action are under active investigation. Trials in human transplant recipients, with an MHC class I peptide have already begun.

Prevention of transplant rejection: current treatment guidelines and future developments

In the past 2 decades, progressive improvements in the results of organ transplantation as a therapeutic strategy for patients with end-stage organ disease have been achieved due to greater insight into the immunobiology of graft rejection and better measures for surgical and medical management. It is now known that T cells play a central role in the specific immune response of acute allograft rejection. Strategies to prevent T cell activation or effector function are thus all potentially useful for immunosuppression. Standard immunosuppressive therapy in renal transplantation consists of baseline therapy to prevent rejection and short courses of high-dose corticosteroids or monoclonal or polyclonal antibodies as treatment of ongoing rejection episodes. Triple-drug therapy with the combination of cyclosporin, corticosteroids and azathioprine is now the most frequently used immunosuppressive drug regimen in cadaveric kidney recipients. The continuing search for more selective and specific agents has become, in the past decade, one of the priorities for transplant medicine. Some of these compounds are now entering routine clinical practice: among them are tacrolimus (which has a mechanism of action similar to that of cyclosporin), mycophenolate mofetil and mizoribine (which selectively inhibit the enzyme inosine monophosphate dehydrogenase, the rate-limiting enzyme for de novo purine synthesis during cell division), and sirolimus (rapamycin) [which acts on and inhibits kinase homologues required for cell-cycle progression in response to growth factors, like interleukin-2 (IL-2)]. Other new pharmacological strategies and innovative approaches to organ transplantation are also under development. Application of this technology will offer enormous potential not only for the investigation of mechanisms and mediators of graft rejection but also for therapeutic intervention.

Survival of rat small bowel allografts treated with allotrap 07R

Previous reports from other investigators demonstrate prolongation of allogeneic heart graft survival and decrease in CTL responses in rats treated with a small synthetic peptide corresponding to residues 75-84 of the human HLA-B7-01 molecule (Allotrap 07R). We wished to determine the efficacy of these peptides in the highly immunogenic ACI > LEW and LEW > ACI small bowel transplant models. Animals were divided into treatment groups: I, none; II, Allotrap (20 mg/kg/day on Days 0-4); III, cyclosporine (CsA; 10 mg/kg/day on Days 0-4); IV, Allotrap + CsA (as in groups II and III); V, Allotrap (40 mg/kg/day every other day on Days -19 to 4); VI, Allotrap + CsA (as in groups III and V); VII, Allotrap + CsA (as in groups III and V, with Allotrap administered intragraft Days 0-4). The animals were sacrificed at the time of graft rejection (defined by dusky, necrotic stoma and increased stomal output). Peripheral blood, spleen, native bowel, and allograft intraepithelial and lamina propria lymphocytes were harvested and mixed lymphocyte culture (MLC) reactivity against self, donor, and third-party splenocytes was assessed. Statistical analysis was performed by ANOVA with Dunnett's t for multiple comparisons against a control as a post hoc test. We found a very slight, but significant prolongation of graft survival in with treatment protocol V for both strain combinations. In addition, MLC response of splenocytes to donor antigen was decreased with combined CsA and Allotrap, but not with Allotrap alone. We conclude that Allotrap decreases response to alloantigens, and slightly, but significantly prolongs graft survival in the hihgly immunogenic small bowel transplant model.

Synthetic MHC class I peptide prolongs cardiac survival and attenuates transplant arteriosclerosis in the Lewis-->Fischer 344 model of chronic allograft rejection

BACKGROUND

A synthetic peptide corresponding to residues 75-84 of the alpha1 domain of HLA-B7 molecule (HLA-B7.75-84 [Allotrap]) inhibits cytotoxic T cell function in vitro and, when combined with subtherapeutic doses of cyclosporine (CsA), prolongs allogeneic cardiac survival. We now report the effects of HLA-B7.75-84 in the Lewis --> Fischer 344 rat model of chronic cardiac allograft rejection.

METHODS

Animals were treated with CsA (5 mg/kg/day s.c.) alone or with CsA plus alternate-day HLA-B7.75-84 (20 mg/kg/day i.p.) for 30 days. Allografts harvested at day 100 were evaluated by histology and immunohistology.

RESULTS

HLA-B7.75-84 plus CsA prolonged allograft survival (75% of allografts survived >90 days) compared with CsA alone (27% of allografts survived >90 days) (P<0.05). Histologic examination of control allografts showed dense cellular infiltrates and moderate transplant arteriosclerosis (>75% of arteries showed 10-20% occlusion). Infiltrating leukocytes consisted of macrophages (>75% cells), T cells (10-20%), and rare natural killer cells (<5%). Cell activation was shown by expression of major histocompatibility complex class II antigens (>75%), interleukin (IL) 2 receptor (5-10%), and staining for IL-2 (approximately 5% of intragraft mononuclear cells), interferon-gamma (5-10%) and tumor necrosis factor-alpha (approximately 20%). Leukocytes and vessels also showed labeling for the fibrogenic cytokine, transforming growth factor-beta, and all vessels showed dense deposition of IgG (IgG2a, IgG2b) and C3. The addition of HLA-B7.75-84 decreased overall cellularity (P<0.01) without affecting the composition of the infiltrate, but completely prevented transplant arteriosclerosis, diminished myocardial injury, and abrogated expression of IL-2R, IL-2, interferon-gamma, tumor necrosis factor-alpha, and transforming growth factor-beta. HLA-B7.75-84 also blunted the humoral response, which resulted in a predominance of vascular deposition of the non-complement-fixing IgG2c isotype and a concomitant decrease in C3.

CONCLUSIONS

Therapy with synthetic class I major histocompatibility complex peptide (HLA-B7.75-84) attenuates key histologic features of graft arteriosclerosis, in association with inhibition of multiple cytokines and growth factors and modulation of host alloantibody responses in vivo, which is of interest since Allotrap is currently undergoing clinical trials.

Recent advances in graft-versus-host disease (GVHD) prevention

In the 1970s and 1980s, GVHD prevention approaches were limited in number. Recent advances in our understanding of the requirements for T-cell immune responses and for basic mechanism(s) involved in GVHD pathophysiology have led to exciting new strategies for GVHD prevention. This review focuses upon recent developments in GVHD prevention generated over the past 5 years. We have selected five different types of strategies to highlight including: 1) the in vivo targeting of GVHD-reactive T cells using either intact and F(ab')2 fragments of monoclonal antibodies directed against T-cell-surface determinants or immunotoxins which consist of antibodies linked to toxins, 2) a comparison of the in vivo immunosuppressive effects of FK506 and rapamycin on T-cell signaling, 3) the inhibition of T-cell activation through blockade of costimulatory or adhesogenic signals, 4) shifting the balance between acute GVHD-inducing T-helper-type 1 (Th1) T cells to anti-inflammatory T-helper-type 2 (Th2)-type T cells, and 5) the regulation of alloreactive T-cell activation by treatment with peptide analogs which affect either TCR/MHC, CD4/MHC class II, or CD8/MHC class I interactions. Collectively, these approaches are illustratrative of the progress made in extending our GVHD prevention armamentarium.

Biochemical and functional characterization of soluble multivalent MHC L(d)/Fc gamma 1 and L(d)/Fc mu chimeric proteins loaded with specific peptides

Central to the specificity of the immune system is the interaction between the T cell receptor and the major histocompatibility complex (MHC)-peptide ligand complex. To better understand the nature of this interaction, and to investigate possible avenues for specific therapeutic intervention, we have produced soluble recombinant molecules that can modulate antigen-specific T cells. Our approach involved the construction of recombinant murine genes composed of the MHC class I gene H-2L(d) and the Fc portion of immunoglobulin (Ig) heavy chain genes mu or gamma1. Stable transfectants of these L(d)/Fc gamma1 and L(d)/Fc mu genes generated correctly spliced transcripts and were capable of secreting chimeric protein. Immunoprecipitation analyses demonstrated the presence of chimeric L(d)/ Fc gamma1 and L(d)/Fc mu monomers of approximately 69 kDa and 90 kDa, respectively, as well as chimeric dimers under nonreducing conditions. The capacity of L(d)/Ig molecules to bind specific peptide ligands was demonstrated using radiolabeled peptides or with monoclonal reagents that specifically identify peptide-induced conformational changes in the L(d) ligand binding site. Soluble divalent L(d)/Fc gamma1 molecules were loaded with the murine cytomegalovirus-derived peptide and other L(d)-specific peptide ligands and subsequently isolated and purified. Peptide-loaded L(d)/Fc gamma1 molecules were capable of inhibiting the response of class I-restricted T cells in vitro in a peptide-specific fashion. The development of soluble multivalent chimeric proteins that possess unique properties of both the MHC class I and Ig molecules provides a valuable reagent for the study of potential mechanisms of in vitro and in vivo immune modulation.

Treatment with an HLA-peptide and cyclosporine A prolongs rat small bowel allograft survival

BACKGROUND

The ultimate treatment for severe short bowel syndrome is small bowel transplantation (SBT). Current immunosuppression for SBT is relatively ineffective and toxic. Peptides derived from residues 75-84 of the HLA-B7 molecule are immunomodulatory in vitro, and in rodents, when combined with subtherapeutic doses of cyclosporine (CsA), prolong cardiac and skin allograft survival without altering the recipient's rejection kinetics to third party allografts. We investigated the effects of HLA-B7 peptide fragment in a rat model of SBT.

METHODS

Heterotopic allogeneic SBT was performed in Dagouti (RT1a) to Lewis (RT1l) high-responder rat strain combination. B7.75-84 (40 mg/kg/d) and subtherapeutic CsA (10 mg/kg/d) were administered alone, or in combination, by gavage to allograft recipients on days 0 to 4 after SBT. Recipient pretreatment with B7.75-84 on days -14, -12, -10, and -7 followed by subtherapeutic CsA on days 0 to 4 after SBT was also carried out. Graft rejection was determined by the presence of a palpable abdominal mass on daily examination or by loss of more than 10% initial body weight.

RESULTS

Without immunosuppression allografts rejected at a median time of 6 days (range, 5 to 7; n = 7). This was not significantly altered with either CsA therapy alone (median 6 days; range, 6 to 7; n = 6) or B7.75-84 alone (median, 5 days; range, 5 to 6; n = 6). Recipient combination therapy with B7.75-84 and CsA after allografting significantly prolonged allograft survival (median, 11 days; range, 9 to 13; n = 9), as did recipient B7.75-84 pretransplant therapy (median, 10 days; range, 9 to 12; n = 6), when administered over a 2-week period before allografting.

CONCLUSION

Post-SBT recipient treatment with B7.75-84 produced statistically significant improvement in allograft survival only after combination with subtherapeutic CsA. Recipient pre-SBT treatment with B7.75-84 alone however, resulted in statistically significant improvement in allograft survival in combination with post-SBT subtherapeutic CsA. These synergistic effects may be valuable in achieving improved SBT survival clinically and warrant further exploration.

Indirect T-cell allorecognition: perspectives for peptide-based therapy in transplantation

Indirect allorecognition is an important component of allotransplant rejection. Although the initial indirect alloresponse is limited to a few dominant determinants on donor major histocompatibility complex (MHC) molecules, subsequent spreading to additional determinants on recipient and donor antigens is common. Gilles Benichou and colleagues discuss the mechanisms by which immunodominance is acquired or disrupted in indirect alloresponses, and examine the implications for the design of peptide-based selective immunotherapy in transplantation.

Presentation of HLA class I-derived peptides: potential involvement in allorecognition and HLA-B27-associated arthritis

Some 25 years ago, when purified HLA class I allotypes were first being analyzed, of major concern was that the papain used for solubilization might produce a mess of proteolytic fragments that would prove impossible to separate and sequence. Those fears proved unfounded (Parham et al. 1975), and the homogeneity of the preparations was sufficient to allow crystallization and determination of the three-dimensional structure (Bjorkman et al. 1987). Ironically the least ordered region of the electron density map provoked the most interest because it gave a first view of the diverse peptides bound by an MHC molecule. With this image a second chapter of HLA class I biochemistry began, its charge to determine the structures of bound peptides and their influence on the immune system. The extraordinary polymorphism of HLA class I heavy chains now seems quite manageable compared to the vast complexity of the peptides, and our present ignorance as to which ones are important for health and disease. The comparative weakness of most HLA class I associations with disease has made HLA-B27 an especially favored target for investigation, and more is known of the structure and peptide-presenting function of HLA-B27 than for any other HLA-B allotype (López de Castro 1994). Much of this information relates to the native HLA-B27 molecule and has been collected in the belief that disease is a direct consequence of its antigen-presenting function. If one subscribes to the relevance of the transgenic rodent models, this position has almost become untenable. For rats and mice 'non-functional' forms of HLA-B27 are the agents of disease, raising the possibility that B27-associated arthritis is induced by HLA class II presentation of a B27-derived peptide, a variant of the mechanism advanced for the classical HLA class II-associated diseases: type 1 diabetes, multiple sclerosis and rheumatoid arthritis (Gregersen et al. 1987, Roudier et al. 1989, Cucca & Todd 1996, Hall & Bowness 1996). Such speculation invites the obvious question as to whether other diseases associated with HLA class I and chronic inflammation, HLA-C and psoriasis for example (Tiilikainen et al. 1980, Yanagisawa et al. 1995), result from class II presentation of class I peptides.

Peptide specificity of alloreactive CD4 positive T lymphocytes directed against a major histocompatibility complex class I disparity

The mouse strains C57BL/6 (B6, H2b) and Kbm1 mutant bm1 have a defined difference of three amino acids at position 152, 155, and 156 in the MHC class I K molecule. This causes a change in the side and the bottom of the antigen presenting groove of the K molecule resulting in strong allogeneic responses in vitro and in vivo. Here we report on the peptide specificity of CD4+ T cells of B6 origin directed against the Kbm1 mutant and speculate on the peptide specificity of CD8+ bm1-specific T lymphocytes of B6 origin. Bm1-specific CD4+ T helper cells recognized a peptide derived from the Kbm1 molecule encompassing the three mutations, presented by MHC class II molecules on syngeneic cells. The ability of this peptide to bind to MHC class II resulted from amino acid mutations at positions 155 and 156. Furthermore, the recognition of the natural peptide derived from the Kbm1 molecule presented by MHC class II I-Ab molecules on cells of bml origin could be blocked by addition of an MHC class II I-Ab binding competitor peptide. Thus, due to the mutations in an MHC class I molecule, indirect presentation via MHC class II molecules and MHC class II-restricted recognition of a peptide derived from such a MHC class I molecule is demonstrable.

Induction of transplantation tolerance by chimeric donor/recipient class I RT1.Aa molecules

Donor-specific transplantation tolerance was induced by administration of chimeric antigens in which four donor immunogenic amino acids (a.a.) were substituted onto the host class I MHC protein. We constructed chimeric rat RT1.Aa cDNA molecules by substituting nucleotides in the alpha1 helical region that encode 10 Lewis (LEW; RT1.A1) a.a., namely Asp58, Arg62, Glu63, Gln65, Lys66, Gly69, Asn70, Asn73, Ser77, and Asn80 ([alpha(1h)1]-RT1.Aa). The chimeric [alpha(1h)1]-RT1.Aa cDNA sequence was verified before transfection into Buffalo (BUF; RT1b) hepatoma cells. Interestingly, the helical regions of LEW rats (alpha(1h)1) and Wistar Furth (WF; RT1u) rats (alpha(1h)u) share four a.a. (Arg62, Glu63, Gln65, and Gly69). Consequently, subcutaneous administration of [alpha(1)1]-RT1.Aa transfectants (20x10(6); day -7) immunized BUF rats to reject in rapid fashion either LEW heart allografts (mean survival time [MST] = 4.2+/-0.4 days vs. 5.6+/-0.5 days in controls; P<0.001) or WF heart allografts (MST=4.4+/-0.6 days vs. 6.0+/-0.0 days in controls; P<0.002). Subcutaneous immunization of ACI (RT1a) rats with [a(1)1]-RT1.Aa transfectants (bearing 10 LEW donor a.a.) accelerated the rejection of LEW hearts (MST=5.0+/-0.8 days vs. 8.2+/-0.4 days in controls; P<0.001). In contrast, the same [a(1)1]-RT1.Aa transfectants (bearing only four WF donor a.a.) injected subcutaneously into ACI rats modestly prolonged the survival of WF hearts to 14.0+/-10.3 days from 5.4+/-0.5 days in controls (P<0.001). Furthermore, ACI recipients were rendered tolerant to WF heart allografts by a single injection via the portal vein of soluble [a(1)1]-RT1.Aa (but not RT1.Aa, RT1.Au, or [a(2)1]-RT1.Aa) antigens in conjunction with brief oral gavage treatment with cyclosporine. Thus, selected donor immunogenic a.a. (Arg62, Glu63, Gln65, and Gly69) of class I MHC antigens become tolerogenic when flanked by host sequences.

Soluble HLA class I molecules induce apoptosis in alloreactive cytotoxic T lymphocytes

Soluble HLA class I molecules (sHLAs) have been identified in the serum of patients with inflammatory diseases, allografts and autoimmune diseases and in serum of healthy individuals. The biological significance of these molecules, particularly after allogeneic organ transplantation, has been enigmatic. Here we show that primary alloreactive CD8+ T cells interact with sHLA and undergo apoptosis in the absence of a second signal. Ligation of CD28 rescued T cells from death, implying that sHLAs induce apoptosis through selective stimulation of the T-cell receptor. CD95-L was upregulated after cytotoxic T lymphocytes were incubated with sHLAs, and cell death was blocked by a neutralizing anti-CD95-L antibody, suggesting that sHLAs induce endogenous mutual killing of activated T cells. These results provide a molecular basis for the capacity of sHLAs to downregulate T-cell responses, which may be especially relevant to organ transplantation.