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Background: We have previously developed and used limiting dilution analysis to measure frequencies of alloreactive cytotoxic T cell precursors (CTLp) and interleukin (IL)-2-producing T helper cells (IL-2/HTLp) to assess the risk of graft-versus-host disease in bone marrow transplantation (BMT). However, no test has been available to measure precursor frequencies of the important IL-4-secreting subset., Methods: We have now established a limiting dilution analysis to measure the frequency of IL-4-producing T helper cells (IL-4/HTLp) using the IL-4-responsive indicator cell line CT.h4S and have applied this assay to measure alloreactive IL-4/HTLp frequencies in BMT donor-recipient pairs. These frequencies were then analyzed in the context of clinical data to assess the relationship between the number of donor anti-recipient IL-4-secreting T cells and disease outcome., Results: Frequencies of IL-4/HTLp have been studied in HLA-identical siblings, HLA-"matched" unrelated, and HLA-mismatched combinations and found to range from approximately 1/500,000 in HLA-identical sibling pairs to -1/2,000 in HLA-DR-mismatched pairs. These frequencies were independent of those for IL-2/HTLp and showed a negative correlation with those for CTLp. Clinical follow-up of 30 patients showed that high IL-4/HTLp frequencies are associated with a reduced risk of severe graft-versus-host disease. High IL-4/HTLp frequencies may also indicate an increased risk of leukemia relapse., Conclusions: Our data suggest that measurement of IL-4/HTLp frequencies provides information distinct from that obtained with CTLp and IL-2/HTLp. This new assay provides a valuable additional method for optimizing donor selection in unrelated BMT.

Interferon-alpha therapy is effective in only approximately 20% of individuals with chronic HCV infection. A knowledge of the genetic and/or environmental factors that underlie this heterogeneity of response should provide useful predictors of clinical outcome. HCV infected patients and healthy subjects were selected from the expatriate Egyptian population living in Qatar, where chronic HCV infection poses a serious health problem. HCV infection was confirmed by ELISA and RT-PCR. Fifty five patients received interferon-alpha therapy for 6 months and their response was assessed by liver enzyme activity and histology of liver biopsies; the patient responses were followed during treatment and for 1 year afterwards. Twenty five patients were characterised as responders, and the remaining 30 as non-responders. All individuals in the study were typed for HLA class II alleles. Data were analysed by univariate and multivariate statistical methods. Expression of the HLA DR2 Major Histocompatibility class II allele is significantly associated with a beneficial response to interferon-alpha therapy in Egyptian patients (p < 0.005). This association is independent of cirrhosis, the absence of which also showed a significant association with response to therapy (p < 0.005). Our results therefore provide evidence that HLA DR2 is an important additional factor for predicting a long term response to interferon-alpha therapy in chronic HCV hepatitis.

Since lymphocytes continue to proliferate and divide in vivo, it is important to determine the fate of a radionulide following lymphocyte labelling. Using the mixed lymphocyte reaction (MLR), we induced indium-111 labelled lymphocytes from a specific in-bred rat strain (AS) to divide and then observed the subsequent 111In distribution between cells and supernatant. L10 and L12.4 cells, which are allospecific CD4+ T lymphocytes from the AS rat, were stimulated in the MLR by antigen-presenting cells from the August rat, a different strain. We labelled L10 or L12.4 lymphocytes on day 0, the first day of the stimulation cycle, and continued to culture the lymphocytes in vitro. The proliferation of the cells was estimated according to their increase in number. The distribution of 111In between cell and supernatant fractions and between viable and dead (but intact) cells was measured in the cell suspension each day after labelling. The metabolic activity of 111In-labelled lymphocytes was compared with control cells by measuring their uptake of fluorine-18 fluorodeoxyglucose ([18F]FDG). 111In-labelled lymphocytes showed a poor proliferative response compared with control cells 24-48 h after labelling but increased in number after this time. From 24 to 72 h, about 70% of 111In was in the supernatant but only about 5%-10% was associated with intact dead cells. These dead cells tended to retain their 111In, losing less than 30% per day, suggesting that 111In in the supernatant was the result of active elimination from viable cells. Moreover, 24 h after culture, considerably more 111In was associated with viable than with dead lymphocytes, although over the next few days this distribution reversed. 111In-labelled lymphocytes took up more [18F]FDG than control cells at 24 h but not at 0 or 72-96 h; the maximum [18F]FDG uptake coincided with the greatest reduction in cell number. Furthermore, [18F]FDG uptake correlated with the initial 111In burden in lymphocytes labelled with 111In 24 h previously. The results are consistent with active elimination of 111In by 111In-labelled lymphocytes. The energy requirements for this are diverted away from cell division, thereby increasing the probability of cell death. As lymphocytes become 111In deplete, they recover their capacity to proliferate and their risk of death decreases. These findings have important implications for 111In-labelled lymphocyte scintigraphy, suggesting that cells remaining viable immediately after labelling will either subsequently die or alternatively eliminate the label.

A newly developed, reliable, DNA-based method for typing for alleles of the HLA-C locus has been applied in the context of unrelated, volunteer donors for bone marrow transplantation. Some donors matched for HLA-A, -B, -DR, and -DQ have been found to generate in vitro high frequencies of CTL reactive with the recipient's cells. Here we demonstrate that there is a highly significant correlation of the frequencies of CTL precursors and incompatibility at the HLA-C locus. These data indicate that HLA-C locus incompatibility should be avoided in unrelated donor bone marrow transplantation.

We have used in vivo localization of radiolabeled antibodies in a rat renal transplant model to compare the level of induction of major histocompatibility complex (MHC) class I and class II molecules in grafts undergoing rejection with grafts in which rejection was modified by cyclosporine (CsA). MHC class II expression increased in rejecting grafts, peaking on day 4, whereas a later rise in CsA-treated grafts was noted. The use of donor-specific antibodies demonstrated that this was due, in part, to a rise in class II of donor origin. No major differences in MHC class I levels were noted between the two groups until after day 4, when very little antibody localization was seen in the rejecting group. Our results suggest that therapeutic doses of CsA may not prevent the upregulation of class II that occurs during rejection, and that levels of class II are not of prognostic value in kidney transplantation.

Between August 1985 and July 1994, we performed 115 volunteer unrelated donor (VUD) bone marrow transplants (BMT) for first chronic phase (n = 86) or advanced phase (n = 29) chronic myeloid leukemia (CML). Standard serologic HLA typing of potential donors and recipients was supplemented with one-dimensional isoelectric focusing (IEF) for class I proteins, allogenotyping for DR and DQ alleles using DNA restriction fragment length polymorphism (RFLP) analysis, and the measurement of antirecipient major histocompatibility complex (MHC) cytotoxic T-lymphocyte precursor cells in the donors' blood (CTLp assay). Recipients were conditioned for transplantation with a combination of high-dose chemotherapy and total body irradiation (n = 103) or high-dose chemotherapy alone (n = 12). Twenty eight recipients received ex vivo T-cell-depleted marrow, and 84 underwent some form of in vivo T-cell depletion. The probability of severe (grades III or IV) acute graft-versus-host disease (aGVHD) was 24%, and that of extensive chronic graft-versus-host disease (cGVHD), 38%. Proportional hazards regression analysis showed an association between low frequency CTLp and a reduced incidence of severe aGVHD (relative risk [RR], 0.28; P = .0035). The probability of relapse at 3 years was 23%, with first chronic phase disease being independently associated with a lower risk of relapse (RR, 0.71; P = .01). The overall leukemia-free survival (LFS) at 3 years was 37%; the LFS for the first chronic phase and advanced phase recipients was 41% and 26%, respectively. First chronic phase disease (RR, 0.56; P = .063) and the combination of recipient cytomegalovirus (CMV) seronegativity and an IEF-matched donor (RR, 0.48; P = .011) were both associated with improved LFS. The probabilities of survival and LFS for patients under 40 years of age transplanted in first chronic phase from an IEF-matched donor were 73% and 50%, respectively. We conclude that VUD BMT is a reasonable option for patients with CML; when using ex vivo or in vivo T-cell depletion, optimal results are achieved in patients transplanted in chronic phase with marrow from donors without demonstrable class I HLA mismatch and a low CTLp frequency.

Between May 1989 and February 1994, we performed 48 volunteer unrelated donor BMTs for first chronic phase chronic myeloid leukemia using in vivo T cell depletion for acute graft-versus-host disease (aGvHD) prophylaxis. In 40 cases, adequate material was available to measure the frequency of antirecipient MHC cytotoxic T lymphocyte precursor (CTLp) cells in the blood of potential donors. This supplemented standard serological typing, one-dimensional isoelectric focusing for class I proteins, and allogenotyping for DR and DQ alleles using DNA RFLP analysis in the donor selection process. All recipients were conditioned with cyclophosphamide 120 mg/kg, TBI 1320 cGy, and intravenous Campath 1G. GvHD prophylaxis consisted of CsA, short-course methotrexate, and intravenous Campath 1G. Minimum follow-up in all surviving recipients was 100 days. The development of aGvHD and the probability of leukemia-free survival were compared between the high frequency group (CTLp > 1 in 100,000) (n = 15) and the low frequency group (CTLp < 1 in 100,000) (n = 25). There was a trend for increasing grade of aGvHD, which was statistically significant in the high frequency group when compared with the low frequency group (P = 0.003). Both a high frequency of CTLp (relative risk [RR] = 9.0, P = 0.016) and HLA mismatch (RR = 6.7, P = 0.023) were predictors of severe aGvHD (grade III or IV). Multivariate analysis showed that CTLp group (RR = 3.4, P = 0.015) and CMV status (RR = 3.9, P = 0.008) were predictors of leukemia-free survival. Further investigation showed an interaction between the two, such that CMV seropositive recipients in the high frequency group had a relative risk of 9.4 (P = 0.0001) of treatment failure (death or relapse) when compared with other combinations. We conclude that with our present GvHD prophylaxis regimen, CTLp frequency analysis predicts post-BMT outcome and is a valuable aid in donor selection.

Donor/recipient histocompatibility antigen differences initiate acute graft-versus-host disease (GVHD) after bone marrow transplantation. Frequency analysis, using limiting dilution techniques, of functionally defined (helper or cytotoxic) antirecipient T lymphocyte precursors in the peripheral blood of the donor has been shown to be an accurate predictor for the development of moderate-to-severe acute GVHD. Here, we describe a sensitive assay for measuring alloreactive helper (IL-2-producing) T lymphocyte precursor (HTLp) frequencies, and compare the ability of this assay and the cytotoxic T lymphocyte precursor (CTLp) assay to detect HLA- class II and class I differences and to predict clinical outcome in a cohort of unrelated donor/recipient BMT pairs. Twenty-two pairs underwent unrelated donor BMT. Patients with high (> 1:100 x 10(3)) HTLp or CTLp frequencies had a higher incidence of moderate-to-severe (grades II-IV) acute GVHD (80% and 100%, respectively) than pairs with low (< 1:100 x 10(3)) frequencies (40% and 57%, respectively). Ten (45%) patients have died, but all patients with both a low HTLp and low CTLp frequency remain alive. The HTLp and CTLp assays provided similar predictive information for outcome. Given that the HTLp assay is more rapid and less labor intensive, it offers an additional or alternative functional method for donor selection in unrelated donor BMT.

The mechanism underlying the development of chronic infection with hepatitis B virus is not known. We have done two independent studies in Qatar, where such infection is common, to determine whether immunity to this virus is influenced by the HLA phenotype of an individual. The first study generated a hypothesis to test in the second. In both studies, there was a significant deficiency of HLA-DR2 and an excess of HLA-DR7 in patients with chronic persistent infection with hepatitis B virus. We conclude that HLA phenotype is one of the factors influencing the response to infection with this virus.

Objective: To compare the short- and medium-term complications (particularly infection) of bone marrow transplantation for chronic myeloid leukemia in patients with HLA-identical sibling donors or volunteer unrelated donors., Design: Retrospective review of two cohorts of patients., Setting: Tertiary referral center., Patients: One hundred three patients with chronic myeloid leukemia in first chronic phase., Intervention: Patients were treated with bone marrow transplantation using marrow from HLA-identical siblings (n = 57) and volunteer donors (n = 46)., Main Results: In total, 68 patients survived a median of 22 months from bone marrow transplant (range, 7 to 81 months). The actuarial probabilities of overall survival and leukemia-free survival at 2 years for the sibling donor group were 73% (95% CI, 60% to 86%) and 72% (CI, 60% to 84%), respectively, and for the volunteer donor group, 47% (CI, 31% to 63%) and 42% (CI, 26% to 58%) (P = 0.07 and 0.05, respectively). However, after adjustment for duration of disease, overall and disease-free survival in the two donor groups did not differ significantly. A major problem was an increased incidence of severe viral infection in the volunteer unrelated donor group (19 episodes in 16 of 46 patients compared with 7 episodes in 7 of 57 sibling donor patients, P = 0.01). The actuarial incidence of chronic graft-versus-host disease (GVHD) was higher in volunteer unrelated donor patients (77% [CI, 63% to 91%] compared with 49% [CI, 35% to 63%]; P = 0.02) but that of acute GVHD was not. The median performance status of the survivors in the volunteer donor group is similar to that in the sibling donor group. The incidence of hematologic relapse in both groups so far is low., Conclusion: Results appear to justify the continued use of volunteer donors in chronic-phase chronic myeloid leukemia, but infection and chronic GVHD are still major problems.

The main stimulus triggering early acute allograft rejection is known to be delivered by the allogeneic "passenger" leukocytes present within the grafts. Once these cells have been replaced by cells of recipient origin, subsequent rejection episodes are generally less frequent and less acutely destructive. How this replacement affects the cell populations responsible for allograft rejection is not known. Here we report that rat alloreactive non-cytotoxic AS (RT1I) anti-August (RT1c) CD4+ T cells, that were shown to be specific for RT1.Bc+ August spleen stimulators, were able to cause acute rejection of normal August kidney allografts transplanted into sublethally irradiated AS recipients. These cells, however, failed to reject passenger cell-depleted (PCD) August kidneys, despite the substantial expression of RT1.Bc+ products on the graft tubular epithelium. In experiments in vitro, August kidney tubular epithelial cells expressing RT1.Bc+ antigens were found to be unable to stimulate the alloreactive T cells to proliferate. Moreover, preincubation with class II-positive August kidney epithelial cells specifically abrogated the alloreactivity of the T cells. Adding recombinant interleukin-2, however, restored the response to alloantigens. These results are consistent with the hypothesis that T cell populations capable of mediating early acute allograft rejection are different from those mediating late rejection, when donor passenger leukocytes are no longer present. They also suggest clonal anergy as one of the mechanisms responsible for maintaining long-term transplantation tolerance.

A substantial proportion of patients undergoing allogeneic bone-marrow transplantation (BMT) develop moderate-to-severe acute graft-versus-host disease (GVHD). Anti-recipient helper (interleukin-2-producing) T-lymphocyte precursors (HTLp) have an important role in the control and amplification of the alloreactive immune response that initiates GVHD. We used a limiting dilution assay to measure the frequency of HTLp in the blood of marrow donors for 25 patients undergoing genotypically HLA-identical BMT for chronic myeloid leukaemia (n = 20), acute myeloid leukaemia (4), or thalassaemia (1). HTLp frequencies in donor blood ranged from 1 in 18 x 10(3) to less than 1 in 500 x 10(3); they were significantly higher (p = 0.02) in patients with grade II-IV acute GVHD than in those with grade 0-1 GVHD. The HTLp assay seems sufficiently sensitive to detect clinically significant minor histocompatibility antigen differences between the donor and recipient. The assay should prove valuable in selecting the best donor/recipient combination and could indicate the need to intensify GVHD prophylaxis when the only available donor has a high HTLp frequency.

It has been previously postulated that there are two pathways of sensitization of MHC-incompatible kidney allografts: a direct pathway in which the host responder T cells are activated by MHC-incompatible passenger dendritic cells of the graft, and an indirect pathway, in which graft alloantigens are processed like "nominal" T cell antigens by host accessory cells, and presented as self-MHC restricted moieties. We show here that a rat AS anti-August alloreactive CD4+ T cell line, and a presumptive clone, activated through the direct pathway are capable in an adoptive transfer model of initiating rejection of normal August kidney grafts. However, neither the T cell line nor the presumptive clone initiates rejection of passenger cell-depleted August kidneys. The results support the hypothesis that direct pathway--sensitized T cells play a dominant role in early acute rejection, but not in chronic rejection.

This study classified subgroups of learning disabled (LD) children while considering the effects of age. Specifically, scores on the Halstead-Reitan Neuropsychological Battery (HRNB) for older children, the Wechsler Intelligence Scale for Children-Revised (WISC-R), and Wide Range Achievement Test (WRAT) were clustered for a large sample of public school LD children at the age levels 9-10, 11-12, and 13-14 years old. Like clusters were then identified and collapsed across age groups. Discriminant analyses were performed at each age level, and for like clusters across ages as a measure of predictive validity. Results of this study suggested two distinct clusters at each age level; one showing diffuse deficits which varied little with age, and the other evidencing specific neuropsychological problems which may vary with age.

One explanation offered for the uniquely high precursor frequencies of T cells which recognize allogeneic major histocompatibility complex (MHC) molecules, and their lack of self-MHC restriction, is that the alloreactive cells are polyclonal populations the primary specificity of which is self-MHC plus peptide X1, X2, ... Xn. These are postulated to cross-react with allo-MHC plus peptides Y1, Y2, ... Yn. It has been further suggested that the structural basis for the crossreactivity between different MHC alleles is the similarity in amino acid sequence of that part of the molecule predicted to make contact with the T cell receptor (TcR). In order to test this concept, T cells were obtained with dual specificity for influenza haemagglutinin (HA), restricted by HLA-DR1Dw1, and for DR4Dw4/Dw14 expressed on allogeneic human B cell lines, and the specificity of one clone was studied in detail. The exposed, TcR-contacting surfaces of these two DR molecules are predicted to be identical. Although the HA-specific response was stimulated by DR1-expressing mouse DAP.3 transfectants, DAP.3 cells expressing the alloantigen DR4Dw4 were unable to stimulate, possibly because of a failure to present the necessary human peptide for anti-DR4 allorecognition. Therefore, the effects of pulsing the DR4Dw4-expressing DAP.3 cells with the HA peptide were examined. This peptide is known to bind to both DR1 and DR4. Addition of the HA peptide restored the anti-DR4Dw4 response. These data support the concept that allorecognition in some responder/stimulator combinations can be explained by cross-reactivity at the level of the MHC molecule and the peptide.

The ability of two HLA-DR-expressing human T cell clones to function as antigen-presenting cells (APC) was investigated using highly purified T cells. The results demonstrated that these T cell clones are unable to act as autonomous APC, and that recognition of nominal or alloantigens on the surface of T cells leads to a state of nonresponsiveness. The first observation was that a T cell clone with specificity for the 306-324 peptide of influenza hemagglutinin (HA), and raised from a DR1 responder, exhibited apparent degeneracy of major histocompatibility complex restriction when cultured with peptide in the presence of peripheral blood mononuclear cells (PBMC) expressing a wide variety of structurally unrelated DR types. However, when the PBMC were pulsed with peptide and washed before coculture with the clone, peptide was exclusively recognized with DR1Dw1. This implied that in the presence of soluble peptide the T cells were displaying ligand to each other, and that the third-party APC were providing costimulatory signals. To test the ability of T cells to act as autonomous APC, accessory cell-free preparations of two DR1-restricted clones were cultured with peptide in the presence or the absence of added B cell APC. T cell purity was established by the absence of proliferation in response to the mitogen phytohemagglutinin (PHA). PHA-nonresponsive T cells were completely unable to proliferate in response to peptide alone; furthermore, preculture of the HA-specific clone, in the complete absence of accessory cells, with the same concentration of peptide (1 microgram/ml) that induced optimal proliferation when presented by conventional APC, led to profound nonresponsiveness. The same phenomenon was also observed when two of three anti-DR1 alloreactive T cell clones were precultured with a DR1-expressing T cell clone. The ability of the DR1-expressing clone to induce nonresponsiveness in anti-DR1 clones correlated with recognition of the DR1 alloantigen on the DR1-expressing clone.

T lymphocyte responses to the MHC of an evolutionarily distant species are known to be weak compared with responses against allogeneic MHC products within a species. This fact was used to examine the regions of human MHC class II molecules required for the stimulation of strong primary immune responses against MHC alloantigens. A panel of mouse DAP.3 transfectants expressing the products of wild-type and recombinant DR1/H-2Ek MHC class II genes paired to either DR alpha or H-2E alpha genes was generated, and tested as stimulator cells for purified human T cells. A strong proliferative response to DAP.3 transfectants expressing allogeneic HLA-DR molecules was seen. In contrast, weak or absent responses were recorded against DAP.3 cells expressing H-2E molecules. Substitution of the DR1 beta chain with H-2E beta k led to a dramatic loss of recognition; alpha chain substitution had a less marked effect. Furthermore, replacement of the beta 2 domain of DR1 with H-2E sequence caused 90% inhibition, whereas introduction of the beta 2 domain of DR1 into H-2Ek led to a 10-fold increase in T cell response. These results are most readily explained if the beta 2 domain contributes to the interaction site for the CD4 molecule. Substitution of either half of the beta 1 domain led to a marked loss of response. This was more impressive following substitution of the TCR-contacting alpha-helical region of the domain.(ABSTRACT TRUNCATED AT 250 WORDS)

We previously demonstrated that multitransfused patients with severe aplastic anaemia (SAA) exhibit high numbers of alloreactive cytotoxic T lymphocyte precursors directed against their HLA identical siblings. In this study a group of patients who had received multiple blood transfusions for SAA, other haematological diseases or acute blood loss were tested for autocytotoxicity and the results compared with those of untransfused controls. These controls consisted of normal individuals, patients with chronic myeloid leukaemia (CML) or untransfused patients with SAA. There was a significantly higher degree of autocytotoxicity in multitransfused patients, than in the untransfused controls, including untransfused patients with SAA (P = 0.0001). These results suggest that blood transfusion is responsible for inducing autoreactivity. In one patient, in whom both alloreactive anti-non-MHC and autoreactive cytotoxic T lymphocytes (CTL) had been detected, it was demonstrated that there was no crossreactivity between the alloreactive and autoreactive CTL responses. Inhibition studies using monoclonal antibodies revealed the effector cells to be T lymphocytes and the restricting determinants to be both HLA class I and II molecules.

Umbilical cord blood has been used to effect hematological reconstitution and there are sufficient stem cells available in the cord blood obtainable from a single placenta to reconstitute an adult patient. Umbilical cord blood might therefore, have widespread potential use in the field of bone marrow transplantation. We compared alloreactivity of paired samples of adult and cord peripheral blood mononuclear cells, by measuring frequencies of both alloreactive T helper cells and cytotoxic T cell precursors (CTLp), using limiting dilution analysis. In addition we compared the phenotype of adult and neonatal PBMC, using monoclonal antibody staining. Cord PBMC in general showed higher frequencies of alloreactive Th than adult PBMC, with statistically significant differences in 6 out of 10 experiments. There was no statistically significant difference between adult and cord CTLp frequencies. Adult and cord PBMC surface phenotype was similar, except that cord blood contained fewer lymphocyte function-associated-3 (LFA-3) positive (memory) cells.

In this study we demonstrate that human T cell receptor (TcR) chains can be co-expressed with murine CD3 on the cell surface of a murine T cell hybridoma. Human TcR alpha and beta genes from the Jurkat leukaemic cell line were transfected into a TcR-negative mouse T cell hybridoma, TG40. The Jurkat TcR was successfully co-expressed at the cell surface with mouse CD3 components. Brightly staining transfectants were selected by fluorescence-activated cell sorting, and levels of expression comparable to a normal T cell line were achieved suggesting that the human TcR dimer assembled efficiently with the mouse CD3 complex. Northern blot analysis demonstrated similar levels of TcR messenger RNA to those found in the parental Jurkat line. Although we have not formally demonstrated surface expression of the Jurkat TcR alpha chain, the residual alpha gene transcript which is present in murine TG40 line is non-expressible. In order to test the signalling capacity of this human/mouse complex, the transfectants were stimulated with an anti-V beta 8 monoclonal antibody. This stimulus led to interleukin-2 production by the transfectants, demonstrating the delivery of a transmembrane signal. In addition, B10.A mice were immunised with the transfectants, and the antisera from these mice stained the transfectant and the Jurkat cell line, but not the parental T cell hybridoma. This interspecies transfection approach should now permit us to explore the requirements for T cell activation, the constraints on TcR alpha beta chain pairing, and creates ideal reagents for inducing a mouse anti-human TcR-specific response with a view to producing panels of anti-human TcR monoclonal antibodies.

Seventy-one patients with multiple sclerosis (MS) were classified into four subgroups according to the clinical pattern of their disease; their HLA-DR and DQ polymorphisms were defined by serological methods and analysis of Taq1 digestion fragments hybridizing with DRB, DQA, and DQB cDNA probes. The frequencies of the polymorphisms in the patients were compared with those of 100 control subjects. The frequencies of a 3.25-kb fragment from Mspl digests of genomic DNA which hybridized to DQA were also defined in the same groups of patients and control subjects. HLA-DR2 (DRw 15 subtype) and the associated HLA-DQw6 were observed in significant excess in the patients compared with the normal subjects (63% vs. 32% for DRw15; 65% vs. 42% for DQw6). There were no significant differences in the distribution of the DR or DQ alleles between the groups of patients showing different clinical patterns of disease, nor was there an excess in the patients of DQw8 and DQw9 which share hypervariable region sequences of the DQB chain in common with DQw6. The results argue against two recently proposed hypotheses of MS. First, they are not consistent with the proposal that susceptibility to MS is associated with expression of a hypervariable region of DQB shared by DQw6, 8, and 9. Second, they do not support the concept that primarily chronic progressive and relapsing/remitting MS are two immunogenetically distinct disease entities. Our evidence is consistent with the hypothesis that one of the true disease susceptibility genes for MS lies elsewhere within the HLA region and in Northern European populations is found in significant association with DRw15 and DQw6.

A segmental analysis of the key regions of HLA-DR1 that control T cell allorecognition was performed by using a series of transfected cell lines expressing the products of recombinant DRB/H-2Eb genes, paired with either DR alpha or H-2E alpha. Four of eight human T cell clones tolerated substitution of the H-2E alpha chain, but only one clone showed any response to the DR alpha/H-2E beta k dimer. Both the membrane-proximal and the membrane-distal domains of the beta-chain played an important part in stimulating these clones. The response of four of eight clones was markedly inhibited by substitution of the H-2E beta 2 for the DR beta 2 domain. This inhibition showed a complete correlation with the sensitivity of the clones to inhibition by anti-CD4 mAb. Taken together, these results suggest that the interaction site for CD4 may include residues on the beta 2-domain. Introduction of H-2Ek sequence into either half of the beta 1-domain led to a complete loss of response by all but two of the clones. This is consistent with these clones having dual specificity for exposed DR1-specific polymorphisms and for DR1-bound peptides. The pattern of response of one of the clones suggested that indirect conformational effects on the alpha 1-domain may also contribute to the influence of the amino-terminal half of the beta 1-domain on T cell recognition. In the presence of H-2E alpha, this clone responded more strongly when the amino-terminal half of the beta 1-domain was of H-2Ek rather than DR1 sequence. This implies that species matching of the floor of the beta 1-domain with the alpha-chain is more important than the presence of the alpha-chain of the parental species.

The separate contributions to allorecognition of peptide-binding and T cell receptor-contacting residues of an allogeneic HLA-DR molecule were investigated by site-directed mutagenesis. Alloreactive T cell clones were generated from a combination of responder (DR1Dw1,DR4Dw14) and stimulator (DR1Dw1, DR4Dw10) whose DR products differed at only three amino acid positions, two of which are predicted to interact with the T cell receptor (67 and 70), and one with bound peptide (71). Transfected murine DAP.3 cells expressing the wild type and mutated forms of DR4Dw10 in which the codons for residues 70 and/or 71 had been altered towards DR4Dw14 were used to stimulate a panel of anti-DR4Dw10 T cell clones. Substitutions at either position 70 or 71, or the combination of the two, led to loss of recognition by the alloreactive T cell clones. This implies that residues involved in peptide binding and residues involved in interaction with the T cell receptor are important for this panel of alloreactive T cell clones. The specificity of these alloreactive T cells for exposed polymorphic residues on the allogeneic MHC molecule was further demonstrated by the inhibitory effects of synthetic peptides, derived from the alpha-helix of the beta 1 domain of the DR4Dw10 molecule.

HLA 'matched' unrelated donor bone marrow transplantation (BMT) is associated with an increased incidence and severity of acute graft-versus-host disease (GVHD) in comparison with HLA-identical sibling transplants. Using a limiting dilution analysis system for quantitating frequencies of alloreactive cytotoxic T lymphocyte precursors (CTL-p), we previously demonstrated a correlation between CTL-p frequency and HLA disparity between responder and stimulator, and between CTL-p frequency and the incidence of acute GVHD following HLA A, B, DR matched unrelated donor BMT. In this study we assayed CTL-p frequencies in two HLA 'matched' unrelated donor/patient pairs, with single HLA antigenic mismatches detected by allogenotyping or isoelectric focusing but not by HLA serology, and demonstrated that the CTL-ps were specifically directed at the mismatched antigen. Both class I and class II antigens were detected. These data, and our previous work, suggest that high CTL-p frequencies in HLA 'matched' unrelated pairs are indicative of HLA antigenic variants undetected by serology but recognized by molecular typing, and that these are responsible for the value of the assay in predicting acute GVHD after BMT. We propose that this assay system be used in aiding final donor selection before unrelated or mismatched related donor BMT.

We describe the generation and characterization of a murine monoclonal antibody with broad anti-HLA-DR beta activity, but which does not recognize DRw11/Dw5. A BALB/c mouse was immunized with a human alloreactive T-cell clone, with the intention of generating monoclonal anti-T-cell-receptor antibodies. In the course of screening the resulting hybridomas, a clone was detected which secreted an antibody (MP2) with anti-HLA-DR activity. This was shown by flow cytometry as well as immunoprecipitation followed by gel electrophoresis. Flow cytometry experiments using transfectants bearing hybrid human/murine class II molecules demonstrated that MP2 binds to the DR beta chain. MP2 bound to a wide range of Epstein-Barr-Virus-transformed cell lines and transfectants expressing different DR beta 1 and DR beta 3 subtypes: the only exceptions were three transfectants expressing DRw11/Dw5. One of these (RGT1) was shown to be functionally normal in DRw11-restricted alloreactive and antigen-specific systems. The specificity of MP2 was confirmed in functional assays: it was able to inhibit the recognition of DR1 and DRw15 but not DRw11 by alloreactive T-cell clones. Previously reported sequence data show that the beta chain of DRw11 differs from all other DR and DQ beta chains at position 58 by a glutamic acid for alanine substitution. This may account for the inability of DRw11/Dw5 to be recognized by MP2. The data emphasize the value of transfectants in defining precisely the allelic and chain specificity of anti-major-histocompatibility-complex (MHC) antibodies, and illustrate the influence that inaccessible residues can have on the conformation of MHC molecules.

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.

The frequencies of HLA class II-specific cytotoxic T lymphocyte precursors (CTLp) were studied in number of unrelated individuals using a limiting dilution analysis system optimized for the detection of CD4+ CTLp. Peripheral blood mononuclear cells (PBMC) were enriched for CD4+ T cells by immunomagnetic depletion of CD8+ T cells. In some allogeneic combinations high CTLp frequencies were obtained with no significant difference between PBMC and CD4-enriched PBMC populations. In other combinations CTLp frequencies in CD4-enriched PBMC were found to be at least twentyfold lower than in the starting, unfractionated PBMC, suggesting a predominance in these pairs of CD8+ CTLp. In addition there was variation in CTLp frequencies against the same set of HLA class II gene products between individuals, and variation in CTLp frequencies against different HLA class II gene products within individuals. The HLA class II specificity of the assay system was demonstrated unequivocally with detection of CTLp against HLA-DR1 expressed on a murine L cell transfectant.

The strength of the immune response to foreign histocompatibility molecules has long puzzled immunologists. In this article Robert Lechler and colleagues propose that (1) allorecognition is structurally heterogeneous and varies according to the responder and stimulator MHC types, (2) in closely related combinations the focus of the alloreactive T cell may be on epitopes of endogenous peptides that are displayed by stimulator but not by responder MHC molecules, seen in a 'self-restricted' manner, and (3) in more disparate combinations the alloresponse may be directed primarily against residues on the allogeneic MHC molecule itself.

We investigated the Taq I digested DNA restriction fragment length polymorphism (RFLP) of the Major Histocompatibility Complex (MHC) class II genes: HLA-DRB, -DQA, and the class III genes: C4 and 21-hydroxylase(CYP21) in 56 caucasoid patients with systemic lupus erythematosus (SLE) and 62 control subjects in order to define the molecular variation of these genes and their association with SLE. The results showed that the gene frequencies of both HLA-DR2 and -DR3 were significantly increased in the SLE population compared to normal subjects (DR2: 21.4% vs 10.7% chi 2 = 4.5. DR3: 29.6% vs 13.3%; chi 2 = 8.3). A high frequency of C4A and CYP21A gene deletions was also found in SLE patients (SLE 52%, normals 24%). All of 22 SLE patients, and 12 of 15 normal subjects who had C4A and CYP21A gene deletions had a 10.0kb Taq 1 DRB RFLP attributable to the presence of HLA-DR3. Family studies showed linkage of C4A/CYP21A deletions with HLA-B8 and -DR3, and confirmed the previously demonstrated association of the HLA-B8, DR3, C4A*Q0, C4*B1, Bf*S, C2*C haplotype with SLE. Deletions affecting the C4A and CYP21A genes were the commonest cause of C4A null alleles in SLE. No strong association between C4 null phenotype or C4 gene deletion, as determined by RFLP, was observed in patients who possessed DR2.