Minor histocompatibility antigens in man and their role in transplantation

Matching of the minor histocompatibility antigen HLA-A1/H-Y may improve prognosis in corneal transplantation

BACKGROUND

Minor histocompatibility (H) antigens are peptides of allelic intracellular proteins that play an important role in human leukocyte antigen (HLA) matched transplantations. In an animal model of keratoplasty, minor H antigens have even been reported to exceed the immunogenicity of major H antigens (MHC). This investigation is to assess any benefit of matching the broadly expressed gender (H-Y) and HA-3 antigens in HLA-A1 donor positive human keratoplasty.

METHODS

A total of 229 HLA-A1 donor positive keratoplasties were analyzed. A Cox proportional hazards model and Kaplan-Meier analysis were applied to estimate the effect of H-Y or HA-3 mismatches on rejection-free graft survival.

RESULTS

Eighty-one cases were mismatched for H-Y (male donor to female recipient). A mean follow up of two years showed graft survival as high as 88% in the H-Y compatible group compared to only 77% in the H-Y mismatched group (P = 0.02). Eight out of 62 cases were mismatched for HA-3. No statistically significant influence of HA-3 matching on rejection-free graft survival was observed (85% vs. 73%, P=0.52).

CONCLUSION

HLA-A1/H-Y matching and matching for other broadly expressed minor H antigens may further improve prognosis in keratoplasty.

Minor histocompatibility antigens – big in tumour therapy

Technical advances combined with the deciphering of the human genome have facilitated the identification of the molecular nature of human minor histocompatibility (H) antigens. To date, it is believed that minor H antigens result from just any polymorphic protein, regardless of their functional properties. A closer look at the first series of autosomally encoded human minor H proteins reveals a striking functional relationship. Here, we propose that T cells generated after HLA-identical stem cell transplantation (SCT) for malignancies are likely to be directed towards peptides derived from minor H proteins involved in tumourigenesis. This novel insight has important consequences in the search for, and the use of, minor H antigens as immunotherapeutics in stem-cell-based immunotherapy of haematological malignancies and solid tumours.

The minor histocompatibility antigen HA-3 arises from differential proteasome-mediated cleavage of the lymphoid blast crisis (Lbc) oncoprotein

Minor histocompatibility (H) antigens crucially affect the outcome of human leukocyte antigen (HLA)-identical allogeneic stem cell transplantation (SCT). To understand the basis of alloimmune responses against minor H antigens, identification of minor H peptides and their antigenicity-determining mechanisms is essential. Here we report the identification of HA-3 and its encoding gene. The HA-3 peptide, VTEPGTAQY (HA-3T), is encoded by the lymphoid blast crisis (Lbc) oncogene. We thus show for the first time that a leukemia-associated oncogene can give rise to immunogenic T-cell epitopes that may have participated in antihost and antileukemic alloimmune responses. Genotypic analysis of HA-3- individuals revealed the allelic counterpart VMEPGTAQY (HA-3M). Despite the lack of T-cell recognition of HA-3- cells, the Thr-->Met substitution had only a modest effect on peptide binding to HLA-A1 and a minimal impact on recognition by T cells when added exogenously to target cells. This substitution did not influence transporter associated with antigen processing (TAP) transport, but, in contrast to the HA-3T peptide, HA-3M is destroyed by proteasome-mediated digestion. Thus, the immunogenicity of minor H antigens can result from proteasome-mediated destruction of the negative allelic peptide.

Induction of HA-1-specific cytotoxic T-cell clones parallels the therapeutic effect of donor lymphocyte infusion

Donor lymphocyte infusions (DLI) can induce a graft-versus-leukaemia (GvL) reaction in patients with relapsed disease. However, the mechanisms involved in remission induction are not completely known. A patient with chemotherapy-refractory relapse 1 year after human leucocyte antigen (HLA)-identical, unrelated stem cell transplantation (SCT) for bcr/abl-positive common acute lymphoblastic leukaemia (ALL) received a DLI from the original donor, and achieved complete cytogenetic and molecular remission concomitantly with extensive graft-versus-host disease (GvHD). Seven CD8+, donor-derived, alloreactive T-cell clones were generated by stimulating post-DLI remission cells with the patient's pretransplant mature dendritic cells. The minor histocompatibility antigen (mHag) recognized by these T-cell clones was identified as HA-1, a mHag associated with acute GvHD after SCT. Our finding provides evidence of HA-1-associated GvL effects after DLI that paralleled the eradication of full-blown, chemotherapy-refractory ALL relapse after allogeneic SCT.

Generation of helper and cytotoxic CD4+T cell clones specific for the minor histocompatibility antigen H-Y, after in vitro priming of human T cells by HLA-identical monocyte-derived dendritic cells

BACKGROUND

There is now convincing evidence that minor histocompatibility antigens (mHag) may play a significant role in the pathogenesis of graft-versus-host disease after HLA-identical bone marrow transplantation. Indeed, in this clinical situation, T cells specific for mHag have been isolated. Here, we addressed whether one can generate mHag-specific T cells in vitro, without any in vivo immunization, among healthy blood donors.

METHODS

We used monocyte-derived dendritic cells (Mo-DCs) as antigen presenting cells to induce primary responses between healthy HLA-identical siblings, in mixed lymphocyte dendritic cell reactions (MLDCRs).

RESULTS

We show that CD4+ T-cell clones, specific for the mHag H-Y, can be generated in vitro. These clones were derived from a gender-mismatched positive MLDCR pair of HLA-identical siblings and were restricted by the HLA DQB1*0502 molecule. In addition, these CD4+ T clones were also able to lyse allogeneic targets with the same pattern of restriction and specificity than helper function. Finally, acute myeloid leukemia (AML) blast cells were susceptible to lysis by these clones.

CONCLUSIONS

Altogether, these results predict that Mo-DCs could help to generate class II-associated, mHag-specific, T-cell lines or clones in vitro, between healthy blood donors, without any need of transplantation-mediated immunization.

Positivity in a modified mixed leukocyte reaction test correlates with molecular HLA-C disparity in prediction of unrelated bone marrow transplantation outcome

The modified mixed leukocyte reaction (MMLR) test consists of the standard MLR (SMLR) test to which interleukin-4 (IL-4) has been added. It is a sensitive procedure capable of detecting alloreactivity not detected by the SMLR. In the present study we applied the MMLR test to unrelated bone marrow transplantation (BMT) in an attempt to predict graft versus host disease (GVHD) and graft rejection (GR) by detecting alloreactivity between recipient/donor pairs otherwise found to be fully matched (HLA class I A and B tested by serology; class II DRB1 and DQB1 by sequence specific oligonucleotide probes [SSOP]) and by studying the relationship of MMLR alloreactivity and HLA-C disparity in the prediction of transplant related complications. Thirty-five patients transplanted from unrelated donors were included in the study. The MMLR test was seen to correlate with the incidence of transplant related complications, as of the 19 positive, cases 12 (63%) developed acute GVHD and 7 (37%) GR, while of the 16 negative cases only 5 (31%) developed GVHD (4 acute, 1 chronic) (p = 0.0001) and 2 (12.5%) GR. No such correlation was seen between the SMLR and the incidence of transplant related complications: the SMLR test was positive in only 4 (11%) cases (all of which developed GVHD or GR) but of the 31 negative cases 22 (71%) also developed GVHD or GR. Reactivity in the MMLR also correlated with molecular HLA-C disparity (p = 0.015): While of the 19 positive cases 10 (53%) had molecular HLA-C disparity, of the 16 cases with negative MMLR, 14 (87.5%) were matched for molecular HLA-C. Two-way analysis confirmed that patients with positive MMLR transplanted from HLA-C mismatched donors were more likely to develop post BMT complications, including GVHD and GR, than patients with negative MMLR transplanted from HLA-C matched donors (r = +0.70) (p = 0.001). We conclude that the MMLR test may be a useful tool in the prediction of transplant related complications such as GVHD and GR, post unrelated BMT. Moreover, the MMLR test, in conjunction with molecular HLA-C typing, may improve unrelated donor selection.

Analysis of graft-versus-host disease (GVHD) and graft rejection using MHC class I-deficient mice

GVHD is a major complication in allogeneic bone marrow transplantation (BMT). MHC class I mismatching increases GVHD, but in MHC-matched BMT minor histocompatibility antigens (mH) presented by MHC class I result in significant GVHD. To examine the modification of GVHD in the absence of cell surface MHC class I molecules, beta2-microglobulin-deficient mice (beta2m(-/-)) were used as allogeneic BMT recipients in MHC- and mH-mismatched transplants. Beta2m(-/-) mice accepted MHC class I-expressing BM grafts and developed significant GVHD. MHC (H-2)-mismatched recipients developed acute lethal GVHD. In contrast, animals transplanted across mH barriers developed indolent chronic disease that was eventually fatal. Engrafted splenic T cells in all beta2m(-/-) recipients were predominantly CD3+alphabetaTCR+CD4+ cells (15-20% of all splenocytes). In contrast, CD8+ cells engrafted in very small numbers (1-5%) irrespective of the degree of MHC mismatching. T cells proliferated against recipient strain antigens and recognized recipient strain targets in cytolytic assays. Cytolysis was blocked by anti-MHC class II but not anti-CD8 or anti-MHC class I monoclonal antibodies (MoAbs). Cytolytic CD4+ T cells induced and maintained GVHD in mH-mismatched beta2m(-/-) mice, supporting endogenous mH presentation solely by MHC class II. Conversely, haematopoietic beta2m(-/-) cells were unable to engraft in normal MHC-matched recipients, presumably due to natural killer (NK)-mediated rejection of class I-negative cells. Donor-derived lymphokine-activated killer cells (LAK) were unable to overcome graft rejection (GR) and support engraftment.

The allogeneic CD4+ T-cell-mediated graft-versus-leukemia effect

CD4+ T-cells have emerged as important cells in the initiation and delivery of the GVL response. Nevertheless it seems likely that they act in concert with other T-cells and NK cell effectors to produce the full in vivo effect of GVL. How they interact with other effectors is yet to be determined. Furthermore it is very likely that different hematological malignancies have different susceptibility to attack by various lymphocyte subsets, depending upon their MHC expression, nature of the antigens presented and other properties not yet defined. Here we specifically focus on the role of CD4+ T-cells in mediating GVL, particularly in chronic myeloid leukemia. Candidate antigens recognised by CD4+ cells are described and new approaches to GVL modulation in clinical bone marrow transplantation are discussed.

Predictive value of host-specific donor helper T-cell precursor frequency for acute graft-versus-host disease and relapse in HLA-identical siblings receiving allogeneic bone marrow transplantation for hematological malignancies

BACKGROUND

Acute graft-versus-host disease (aGVHD) is still one of the main causes of morbidity and mortality after allogeneic bone marrow transplantation. Attempts to avoid GVHD are associated with an increased risk of relapse, probably because the graft-versus-leukemia effect is also abrogated. It was recently suggested that a high frequency of host-specific donor helper T cell precursors (HTLp) might be predictive of significant aGVHD (grade > or = II).

METHODS

We retrospectively studied the frequency of HTLp by means of simplified limiting-dilution analysis to determine its predictive value for aGVHD and relapse. Pre-bone marrow transplantation, host-specific donor HLTp frequencies were analyzed in 32 patients who had received marrow from HLA-identical siblings for hematological malignancies, in terms of aGVHD and relapse.

RESULTS

HTLp frequencies were significantly higher in patients who had aGVHD > or = grade II (n=14) than in those without aGVHD (n=18) (P=0.007). Patients who relapsed (n=13) had significantly lower HTLp frequencies than those who did not relapse (n=19) (P<0.0001). The probabilities of relapse (Kaplan-Meier method) when the HTLp frequency was higher and lower than 1/200,000 were 0% and 88%, respectively (P<0.0001).

CONCLUSIONS

The definition of HTLp cut-off values predictive of aGVHD and relapse should contribute to donor selection and could open the way to protocols adapting immunomodulation to the likely risk of aGVHD and relapse.

Donor helper T-cell frequencies as predictors of acute graft-versus-host disease in bone marrow transplantation between HLA-identical siblings

BACKGROUND

Despite the current level of sophistication of molecular typing for class I and class II alleles, a significant proportion (20-40%) of recipients of HLA-identical sibling marrow develop severe, acute graft-versus-host disease (GVHD) after bone marrow transplantation. It has been suggested that the frequency of patient-specific helper T lymphocyte precursors (HTLp) detected in the HLA-identical sibling donor correlates with the incidence and severity of acute GVHD after transplantation.

METHODS

This study group consisted of 42 patients who all received bone marrow from HLA-identical sibling donors from January 1990 to December 1996. Using a limiting dilution analysis, donor HTLp frequencies were determined on samples collected before transplantation. The HTLp assay used the cytotoxic T-cell line, CTLL-2, which proliferates in the presence of interleukin-2. The reliability and reproducibility of this assay was established by using cryopreserved batches of CTLL-2 cells of known sensitivity.

RESULTS

The recipient-directed HTLp frequencies detected in the donor before transplantation were correlated with the incidence and severity of acute GVHD experienced by the recipient after transplantation. Statistical analysis revealed an extremely significant correlation between donor precursor frequencies and the development of acute GVHD in the patient after transplantation (P<0.0001).

CONCLUSIONS

This study suggests that together with molecular typing the HTLp frequency should be considered when selecting the most suitable sibling donor for bone marrow transplantation.

Graft-versus-leukaemia

The high relapse rate after T-cell depleted bone marrow transplantation (BMT) for chronic myeloid leukaemia (CML) and the ability of donor lymphocyte transfusions to induce stable remission in patients relapsing after BMT has emphasized the importance of alloreacting donor T-lymphocytes in the graft-versus-leukaemia (GVL) effect in this disease. The mechanisms underlying the GVL response and its relationship with graft-versus-host disease are becoming better defined. There is accumulating evidence that the CD4+ T-cell plays a central role in the GVL response. The prominent role of GVL in the cure of CML after BMT may be associated with the fact that CML cells are strongly immunogenic. New transplant strategies are being devised to separate GVL from graft-versus-host reactions. Future developments focus on the identification of leukaemia-specific antigens and the amplification of T-cell responses against them.

HLA and graft-versus-host disease: a population-based study of HLA phenotypes of Jewish and Arabic bone marrow transplanted patients in Israel

The relationship between the incidence of graft-versus-host disease (GVHD) and human leukocyte antigens (HLA) was analyzed in HLA-identical sibling bone marrow transplantation donor/recipient pairs from the two major populations in Israel: Jewish and Arabic. HLA phenotypes were significantly different, in both groups, between patients and healthy controls. Among Jews, a higher incidence of GVHD was found with A28, CW3, CW6 of class I and DR7, DQ2 of class II; a lower incidence was found with A2, A26, B14. Among Arabs, a higher incidence of GVHD was found with B41, CW7 of class I, and DR2, DR13 of class II. The development of GVHD is apparently associated with HLA phenotypes specific to each population.

Mechanisms of the graft-versus-leukemia reaction

It is now clear that the graft-versus-leukemia (GVL) effect which accompanies allogeneic bone marrow transplantation for hematological malignancies is a powerful therapeutic weapon which, if harnessed, could improve our ability to treat refractory malignant disorders. Advances in the understanding of the alloimmune response now provide a clearer picture of the mechanisms involved in the GVL reaction: the CD4+ T cell plays a central role in the orchestration of leukemia cell killing. The immunogenicity of the leukemia is also a major factor determining the effectiveness of the GVL response. The characterization of antigens restricted to leukemia and hematopoietic tissues should make it eventually possible to produce specific and powerful antileukemic alloresponses in donor lymphocytes by adoptive immunotherapy or by vaccines.

Functional expression of minor histocompatibility antigens on human peripheral blood dendritic cells and epidermal Langerhans cells

Adequate presentation and cell surface expression of foreign minor histocompatibility antigens (mHag) to allogeneic T cells can lead to graft versus-host disease (GvHD) after HLA matched bone marrow transplantation (BMT). Cells of the dendritic cell (DC) lineage, including epidermal Langerhans cells (LC), are the most potent inducers of primary alloreactive T cell responses in vivo and in vitro. To explore the possible role of peripheral blood DC and of skin derived LC in the induction of alloimmune responses against mHag, we analysed the functional expression of mHag on these professional antigen-presenting cells (APC). To this end, cytotoxic T cell (CTL) clones specific for mHag H-Y and HA-1 to HA-4 were used to demonstrate the presence of these antigens on highly purified DC and LC. Our results demonstrate that, like other cells of the hematopoietic lineage, DC and LC express all the mHag tested for. The functional expression of mHag on these potent APC suggests their involvement in the induction of mHag specific GvH directed T cell responses after allogeneic BMT.

Frequency of donor cytotoxic T cell precursors does not correlate with occurrence of acute graft-versus-host disease in children transplanted using unrelated donors

Bone marrow transplantation (BMT) from unrelated volunteers is frequently associated with both increased incidence and increased severity of acute graft-versus-host disease (GVHD). In the last years, it has been suggested that the analysis of the frequency of cytotoxic T lymphocyte precursors (CTLp) of unrelated HLA-matched donors can be used to detect disparity for HLA class I antigens and as a predictive test for development of severe GVHD. In this report, we summarized our experience regarding 20 pediatric patients affected by various hematological disorders, receiving allogeneic BMT from unrelated donors. HLA class I and II antigens of donor/recipient pairs were determined by means of serological typing, whereas molecular typing of HLA-class II antigens of patients and their potential donors was performed using PCR-SSP and PCR-fingerprinting techniques. CTLp values, estimated using limiting dilution analysis, were high (range, 1:7000-1:40,000) in 9 of 20 patients, while the other 11 children had low or undetectable levels (< 1:100,000) of CTL precursors. CTLp frequency was compared with the incidence and severity of GVHD observed after BMT. Our data demonstrate that the frequency of donor CTLp does not statistically correlate either with the occurrence of clinically significant acute GVHD or with disparity for HLA-class II molecular typing between donor and recipient. In particular, 4 of the 10 evaluable patients with an undetectable CTLp frequency developed grade IV, III, II, and IV acute GVHD, respectively. Although the limited number of subjects studied does not allow us to draw any firm conclusion, our data suggest a certain caution in considering this test suitable for the selection of potential donors.

Mismatches of minor histocompatibility antigens between HLA-identical donors and recipients and the development of graft-versus-host disease after bone marrow transplantation

BACKGROUND

Graft-versus-host disease (GVHD) can be a major complication of allogeneic bone marrow transplantation even when the donor and recipient are siblings and share identical major histocompatibility antigens. The explanation may be a mismatch of minor histocompatibility antigens. We previously characterized five minor histocompatibility antigens, HA-1, 2, 3, 4, and 5, that are recognized by T cells in association with the major histocompatibility antigens HLA-A1 an A2.

METHODS

We collected peripheral-blood leukocytes from 148 bone marrow recipients and their sibling donors, who were genotypically HLA identical. Fifty pairs were positive for HLA-A1, 117 were positive for HLA-A2, and 19 were positive for both. The pairs were typed with cytotoxic-T-cell clones specific for minor histocompatibility antigens HA-1, 2, 3, 4, and 5.

RESULTS

Mismatches of HA-3 were equally distributed among recipients in whom GVHD developed and those in whom it did not. By contrast, a mismatch of only HA-1 was significantly correlated with GVHD of grade II or higher (odds ratio, infinity; P = 0.02) in adults. One or more mismatches of HA-1, 2, 4, and 5 were also significantly associated with GVHD (odds ratio, infinity; P = 0.006) in adults. These associations were not observed in children.

CONCLUSIONS

A mismatch of minor histocompatibility antigen HA-1 can cause GVHD in adult recipients of allogeneic bone marrow from HLA-identical donors. Prospective HA-1 typing may improve donor selection and identify recipients who are at high risk for GVHD.

Human H-Y: a male-specific histocompatibility antigen derived from the SMCY protein

H-Y is a transplantation antigen that can lead to rejection of male organ and bone marrow grafts by female recipients, even if the donor and recipient match at the major histocompatibility locus of humans, the HLA (human leukocyte antigen) locus. However, the origin and function of H-Y antigens has eluded researchers for 40 years. One human H-Y antigen presented by HLA-B7 was identified as an 11-residue peptide derived from SMCY, an evolutionarily conserved protein encoded on the Y chromosome. The protein from the homologous gene on the X chromosome, SMCX, differs by two amino acid residues in the same region. The identification of H-Y may aid in transplantation prognosis, prenatal diagnosis, and fertilization strategies.

Identification of a graft versus host disease-associated human minor histocompatibility antigen

Minor histocompatibility antigen disparities between human leukocyte antigen (HLA)-matched bone marrow donors and recipients are a major risk factor for graft versus host disease (GVHD). An HLA-A2.1-restricted cytotoxic T cell clone that recognized the minor histocompatibility antigen HA-2 was previously isolated from a patient with severe GVHD after HLA-identical bone marrow transplantation. The HLA-A2.1-bound peptide representing HA-2 has now been identified. This peptide appears to originate from a member of the non-filament-forming class I myosin family. Because HA-2 has a phenotype frequency of 95 percent in the HLA-A2.1-positive population, it is a candidate for immunotherapeutic intervention in bone marrow transplantation.

The immunogenetics of bone marrow transplantation

It is now clear that it is not necessary to use an HLA genotypically identical donor to have a successful marrow transplant. However, it is equally clear that the likelihood of complications increases with each increment in histoincompatibility. The implication is that histocompatibility testing must be of the highest possible precision to choose the optimal donor, and to predict the risk of adverse alloreactivity. Most clinicians would seriously consider transplantation from a one locus-mismatched relative or an HLA-matched unrelated donor in virtually any situation in which transplantation from a matched sibling would be felt to be the standard of care. More thought would need to go into transplantation from a two or three locus-mismatched relative or a mismatched unrelated donor.

Immunological characterization of the tumor-specific bcr/abl junction of Philadelphia chromosome positive chronic myeloid leukemia

Recent developments in the understanding of the process of antigen presentation by major histocompatibility complex (MHC) molecules and their recognition by T-lymphocytes has led investigators to speculate that the hybrid bcr/abl fusion protein P210 present in chronic myeloid leukemia (CML) cells may generate leukemia-specific antigens recognized by T-cells. We used synthetic peptides representing the fusion region of P210 to study MHC class I and class II pathways of antigen recognition in normal subjects and patients with CML. We found that most normal individuals have a low proliferative response to 18mer fusion peptides representing the two alternative splicing variants b2a2 and b3a2, and a T-lymphocyte precursor frequency (HTLPf) characteristic of unprimed responders. No increase in HTLPf was found in CML patients after bone marrow transplantation (BMT), suggesting that peptide recognition does not form part of the graft-versus-leukemia process. In contrast, untransplanted patients with CML had very high HTLPf, suggesting an autologous but immunologically ineffective recognition of leukemia-specific peptides through HLA class II. Preliminary studies using the T2 cell line (which expresses HLA class I only in the presence of peptides binding to HLA-A2) indicate that nonapeptides spanning the breakpoint of the b2a2 and b3a2 variants of P210 do not bind to this particular class I molecule and are therefore unlikely to initiate class I mediated lymphocyte responses.

Multiple minor histocompatibility antigen disparities between a recipient and four HLA-identical potential sibling donors for bone marrow transplantation

A patient with acute leukemia and her family including four HLA-identical siblings were analyzed to select a donor who was not only HLA- but also minor histocompatibility (mH) antigen compatible for allogeneic bone marrow transplantation (BMT). The HLA-A2 restricted mH antigen-specific HA-1, -2, -4, and -5 cytotoxic T-lymphocyte (CTL) clones were used to type the family members for expression of these mH antigens. The patient and one HLA-identical sibling were compatible for these mH antigens. This sibling was selected as the bone marrow donor. The patient engrafted promptly but developed acute and chronic graft-versus-host disease. To study the presence of other mH antigen disparities between recipient and donor, host-versus-graft CTL lines and clones were generated by stimulation of recipient peripheral blood lymphocytes (PBLs) with donor bone marrow cells, and graft-versus-host CTL lines were generated after BMT by stimulation of PBLs of donor origin with recipient bone marrow cells. These CTL lines were cytotoxic to cells from the bone marrow donor and from the recipient, respectively, and to cells from several other family members. T-cell lines, generated from the patient after BMT by stimulation of recipient-derived PBLs with donor bone marrow cells, exhibited no specific cytotoxicity to donor or recipient cells. Chimerism studies after BMT revealed that the PBLs and T-cell lines generated after BMT were of donor origin.(ABSTRACT TRUNCATED AT 250 WORDS)

Gender-related influences on the development of chronic graft-versus-host disease-induced experimental lupus nephritis

Autoimmune diseases are far more common in women than in men. In the incidence of systemic lupus erythematosus (SLE), the female-to-male ratio is as high as 10:1. This suggests that sex hormones may play a fundamental role in determining the susceptibility to these diseases. In order to investigate the sex-related differences in the inducibility of chronic graft-versus-host disease-related experimental lupus nephritis, lymphocytes from female DBA/2 donor mice were administered to either male or female (C57BL10 x DBA/2)F1 recipients. An additional group of male recipients received lymphocytes from male DBA/2 donors. After four cell transfers, female recipients developed a significantly higher albuminuria than both male groups. Serum concentrations of autoantibodies against glomerular basement membrane (GBM), collagen IV, and laminin were significantly higher in females 2-4 weeks after induction. Levels of circulating autoantibodies against renal tubular epithelial antigens (RTE) and nuclear antigens were not different between the sexes. In transfer studies, the necessity of the presence of anti-GBM and anti-RTE autoantibodies for the development of glomerulonephritis was confirmed. These findings indicate that: (i) in this model of lupus nephritis, susceptibility to glomerulonephritis is strongly influenced by sex-related genes; and (ii) among the variety of autoantibodies occurring in this model of SLE, both anti-GBM and anti-RTE autoantibodies play a key role in the pathogenesis of glomerulonephritis.

Isolation of an HLA-A2.1 extracted human minor histocompatibility peptide

Purified HLA-A2.1 molecules obtained by affinity chromatography of 6 x 10(10) Epstein Barr virus (EBV)-transformed B lymphocytes were used in an attempt to isolate the human HLA-A2.1-restricted minor histocompatibility (H) peptides H-Y and HA-2. Fraction 18 of the high-performance liquid chromatography (HPLC)-separated HLA-A2.1 peptide pool was found to contain the natural HA-2 peptide. An HA-2-specific, HLA-A2.1-restricted cytotoxic T lymphocyte clone lysed HLA-A2.1+ HA-2- EBV-transformed B lymphocyte cell lines reproducibly and in a concentration-dependent fashion in the presence of fraction 18, but not in the presence of other HPLC fractions. By contrast, H-Y sensitizing activity was not found in any fraction. Amino acid sequencing of peptide fraction 18 revealed a mixture of peptides with maximal length of nine amino acids, in which the presence of Leu at positions 2 and 9 was dominant. Surprisingly, the HA-2 peptide could not be mimicked by any of the peptide mixtures synthesized according to the amino acid sequences found in fraction 18. Our failure to obtain the actual amino acid sequence of the human minor H peptide HA-2 from a peptide pool with the established pattern for binding to HLA-A2.1 may indicate that this CTL defined minor H peptide does not represent an abundant HLA-A2.1 binding peptide.

Proteasome subunits encoded by the major histocompatibility complex are not essential for antigen presentation

Major histocompatibility complex (MHC) class I molecules bind and deliver peptides derived from endogenously synthesized proteins to the cell surface for survey by cytotoxic T lymphocytes. It is believed that endogenous antigens are generally degraded in the cytosol, the resulting peptides being translocated into the endoplasmic reticulum where they bind to MHC class I molecules. Transporters containing an ATP-binding cassette encoded by the MHC class II region seem to be responsible for this transport. Genes coding for two subunits of the '20S' proteasome (a multicatalytic proteinase) have been found in the vicinity of the two transporter genes in the MHC class II region, indicating that the proteasome could be the unknown proteolytic entity in the cytosol involved in the generation of MHC class I-binding peptides. By introducing rat genes encoding the MHC-linked transporters into a human cell line lacking both transporter and proteasome subunit genes, we show here that the MHC-encoded proteasome subunit are not essential for stable MHC class I surface expression, or for processing and presentation of antigenic peptides from influenza virus and an intracellular protein.

Minor histocompatibility antigens, defined by graft-vs.-host disease-derived cytotoxic T lymphocytes, show variable expression on human skin cells

Little is known on the effector mechanisms inducing the cutaneous lesions observed during acute graft-vs.-host disease (aGvHD) after allogeneic bone marrow transplantation (BMT). Histological findings have indicated that infiltrating CD8+ lymphocytes probably play a role. We addressed the question of whether host minor histocompatibility (mH) antigen-reactive cytotoxic T lymphocytes (CTL) could account for this phenomenon via direct lysis of the epidermal cell layer. Six CTL clones, obtained from peripheral blood lymphocytes of patients suffering from aGvHD, each recognizing a well-characterized MHC class I-restricted mH antigen epitope, were tested on cultured keratinocytes of nine MHC and mH antigen-typed donors. Four of six mH antigen-specific CTL clones lysed unstimulated MHC class I-expressing, as well as recombinant interferon-gamma (rIFN-gamma)-activated, ICAM-1, MHC class I- and II-expressing keratinocytes. Two strongly cytolytic CTL clones showed no recognition of keratinocytes of donors whose phytohemagglutinin-activated T cell lines were readily lysed. With respect to a GvHD, the results imply that some class I-restricted CTL obtained from peripheral blood lymphocytes of a GvHD patients have the in vitro potential to destroy resting as well as IFN-gamma-activated epidermal cells, whereas others do not. In other words, CTL-defined human mH antigens vary with respect to their expression in the skin. It is intriguing that those minor H antigens which cannot be detected on human keratinocytes in vitro are those known to be associated with the occurrence of GvHD.

Oligonucleotide typing is a perfect tool to identify antigens stimulatory in the mixed lymphocyte culture

An important criterion for the selection of donors for bone marrow transplantation is the grade of matching for HLA between donor and recipient. For patients that lack an HLA-identical sibling, an extending pool of unrelated volunteers for bone marrow donation is available. From these donors the best matched candidate can be selected by serological typing, followed by a mixed lymphocyte culture (MLC). Oligonucleotide genotyping for HLA class II antigens is considered to be valuable for the prediction of MLC reactivity. We investigated whether this typing method, in combination with serological typing, would cover the recognition of all MLC stimulatory determinants. One hundred thirty-six combinations of HLA-A, -B, and -DR serologically identical individuals were tested in the MLC. Additional typing for HLA-DRB and HLA-DPB by oligonucleotide genotyping made it possible to evaluate the influence of these genes on MLC reactivity. Combinations that were matched for HLA-DRB gave significantly lower responses than those that were mismatched. Nevertheless, in the matched combinations responses were observed to 94% relative response index. These responses could all be attributed to HLA-DP, since all combinations that were identical by HLA-DPB genotyping were negative in the MLC. In conclusion, with the combined use of serology and oligonucleotide genotyping, responder-stimulator combinations can be selected that are identical for all MLC stimulatory determinants.

Minor histocompatibility antigens

Immune responses against foreign tissue or organs can be directed against alloantigenic differences between donor and host encoded by genes of the major histocompatibility complex (MHC; HLA in man and H-2 in mouse). However, when MHC antigens are matched, as in HLA-identical siblings, or between different mouse strains sharing the same H-2 haplotype, graft rejection still occurs and is then directed against alloantigenic differences termed minor histocompatibility (H) antigens. Their molecular nature is not yet determined but they are recognised by T cells in an MHC-restricted manner, so are assumed to be derived from molecules co-expressed with MHC class I or II glycoproteins, possibly as peptides or as "super-antigens". The genes encoding them are scattered throughout the genome, including the Y chromosome, on which the H-Y antigen gene has been mapped in both man and mouse. One striking feature of minor H antigens is their recognition by T cells but not by antibodies. This made work with them, before our ability to generate T cell responses and maintain T cell clones in vitro, very slow but currently the use of MHC-restricted T cell clones has enabled detailed mapping studies and should eventually allow for their molecular characterisation.

Pretransfused patients with severe aplastic anaemia exhibit high numbers of cytotoxic T lymphocyte precursors probably directed at non-HLA antigens

Patients with severe aplastic anaemia (SAA) have a relatively high risk of graft rejection after transplantation of bone marrow from HLA-identical siblings compared with patients transplanted for leukaemia. This is presumed to be due to pretransplant blood transfusions which sensitize the recipient's immune system to non-HLA antigens expressed on donor marrow cells. To test this hypothesis, we estimated in the peripheral blood of 18 SAA patients, the frequencies of alloreactive cytotoxic T lymphocyte precursors (CTL-p) directed against mononuclear cells from syngeneic twins, HLA-identical siblings or HLA-matched unrelated individuals. The results were compared with the frequencies of CTL-p in 13 healthy subjects or leukaemia patients who had not been transfused. Pretransfused patients with SAA had significantly higher frequencies of CTL-p directed against HLA-identical siblings (P = 0.002), and against HLA-matched unrelated individuals (P = 0.004), than did untransfused individuals. In contrast, the frequency of CTL-p in two pretransfused patients against syngeneic mononuclear cells was very low. We propose that the increased numbers of CTL-p in the blood of pretransfused SAA patients are directed against non-HLA antigens on target cells and may be the result of prior blood transfusion.

Induction of minor histocompatibility antigen-specific T-helper but not T-cytotoxic response is dependent on the source of antigen-presenting cell

We studied the accessory cell requirements for triggering in vivo primed human major histocompatibility complex class I- and class II-restricted T cells specific for minor histocompatibility antigens. We compared the antigen-presenting capacities of peripheral blood lymphocytes (PBLs) and Epstein-Barr virus-transformed lymphoblastoid cell lines (EBV-LCLs), both derived from the same donor, to induce minor histocompatibility antigen-specific cytotoxic and proliferative T cells. PBLs and EBV-LCLs were equally effective as antigen-presenting cells to trigger cytotoxic-T-cell responses specific for minor histocompatibility antigens, some of which were reactive with B cells only. In contrast, a clear difference was found between the capacities of the two antigen-presenting cell types to induce minor histocompatibility antigen-specific T-helper-cell responses. PBLs as antigen-presenting cells could induce T-helper-cell lines reactive against minor histocompatibility antigens presented on PBLs, on EBV-LCLs, or on both cell types as stimulator cells. Unexpectedly, however, EBV-LCLs as antigen-presenting cells in all instances failed to induce T-helper-cell responses specific for minor histocompatibility antigens presented on PBLs or on both PBLs and EBV-LCLs as stimulator cells and could only trigger T-helper cells directed against B-cell-specific minor histocompatibility antigens. Our findings indicate a dichotomy in the capacity of EBV-LCLs to present minor histocompatibility antigens in the induction versus the effector phse of the in vitro T-helper-cell response. Furthermore, the results show different in vitro accessory cell requirements for major histocompatibility complex class I- and class II-restricted T-cell responses specific for human minor histocompatibility antigens.