Predicting graft-versus-host disease in HLA-identical bone marrow transplant: a comparison of T-cell frequency analysis and a human skin explant model

Pharmacogenetics: An Important Part of Drug Development with A Focus on Its Application

Since the human genome project in 2003, the view of personalized medicine to improve diagnosis and cure diseases at the molecular level became more real. Sequencing the human genome brought some benefits in medicine such as early detection of diseases with a genetic predisposition, treating patients with rare diseases, the design of gene therapy and the understanding of pharmacogenetics in the metabolism of drugs. This review explains the concepts of pharmacogenetics, polymorphisms, mutations, variations, and alleles, and how this information has helped us better understand the metabolism of drugs. Multiple resources are presented to promote reducing the gap between scientists, physicians, and patients in understanding the use and benefits of pharmacogenetics. Some of the most common clinical examples of genetic variants and how pharmacogenetics was used to determine treatment options for patients having these variants were discussed. Finally, we evaluated some of the challenges of implementing pharmacogenetics in a clinical setting and proposed actions to be taken to make pharmacogenetics a standard diagnostic tool in personalized medicine.

Human regulatory T cells against minor histocompatibility antigens: ex vivo expansion for prevention of graft-versus-host disease

Alloreactive donor T cells against host minor histocompatibility antigens (mHAs) cause graft-versus-host disease (GVHD) after marrow transplantation from HLA-identical siblings. We sought to identify and expand regulatory CD4 T cells (Tregs) specific for human mHAs in numbers and potency adequate for clinical testing. Purified Tregs from normal donors were stimulated by dendritic cells (DCs) from their HLA-matched siblings in the presence of interleukin 2, interleukin 15, and rapamycin. Male-specific Treg clones against H-Y antigens DBY, UTY, or DFFRY-2 suppressed conventional CD4 T cell (Tconv) response to the specific antigen. In the blood of 16 donors, we found a 24-fold (range, 8-fold to 39-fold) excess Tconvs over Tregs reactive against sibling mHAs. We expanded mHA-specific Tregs from 4 blood samples and 4 leukaphereses by 155- to 405-fold. Cultured Tregs produced allospecific suppression, maintained demethylation of the Treg-specific Foxp3 gene promoter, Foxp3 expression, and transforming growth factor β production. The rare CD4 T conv and CD8 T cells in the end product were anergic. This is the first report of detection and expansion of potent mHA-specific Tregs from HLA-matched siblings in sufficient numbers for application in human transplant trials.

Serum proteomic profiling and haptoglobin polymorphisms in patients with GVHD after allogeneic hematopoietic cell transplantation

We studied serum proteomic profiling in patients with graft versus host disease (GVHD) after allogeneic hematopoietic cell transplantation (allo-HCT) by two-dimensional gel electrophoresis (2-DE) and mass spectrometry analysis. The expression of a group of proteins, haptoglobin (Hp), alpha-1-antitrypsin, apolipoprotein A-IV, serum paraoxonase and Zn-alpha-glycoprotein were increased and the proteins, clusterin precursor, alpha-2-macroglobulin, serum amyloid protein precursor, sex hormone-binding globulin, serotransferrin and complement C4 were decreased in patients with extensive chronic GVHD (cGVHD). Serum haptoglobin (Hp) levels in patients with cGVHD were demonstrated to be statistically higher than in patients without cGVHD and normal controls (p < 0.01). We used immunoblotting and PCR in combination with 2-DE gel image analysis to determine Hp polymorphisms in 25 allo-HCT patients and 16 normal donors. The results demonstrate that patients with cGVHD had a higher incidence of HP 2-2 phenotype (43.8%), in comparison to the patients without cGVHD (0%) and normal donors (18.7%), suggesting the possibility that specific Hp polymorphism may play a role in the development of cGVHD after allo-HCT. In this study, quantitative serum Hp levels were shown to be related to cGVHD development. Further, the data suggest the possibility that specific Hp polymorphisms may be associated with cGVHD development and warrant further investigation.

Skin explant model of human graft-versus-host disease: prediction of clinical outcome and correlation with biological risk factors

A human skin explant model has been used to predict the clinical outcome and to study the immunopathology of human graft-versus-host disease (GVHD). Whether the model gives the same predictive effect for GVHD in different hematopoietic stem cell transplantation (HSCT) settings has not been assessed. It is also unknown whether the skin explant result reflects the known biological risk factors for clinical GVHD. In this study, the skin explant model was used to detect graft-versus-host reactions (GVHR) in vitro for 225 eligible patient/donor pairs. The predicted skin GVHR grade was correlated with the outcome of clinical GVHD, as well as HLA matching status, sex mismatches, and patient age. In sibling HSCT under either myeloablative or reduced-intensity conditioning, a significant correlation was observed between the predicted skin GVHR and clinical GVHD (P < .001 and P = .033, respectively). In HSCT using unrelated donors, the involvement of T-cell depletion led to a sharp increase in false-positive GVHR results, and no correlation was observed between the predicted skin GVHR and clinical GVHD. The skin GVHR grade correlated significantly with the HLA matching status (HLA-matched sibling pairs, HLA-matched unrelated pairs, and HLA-unmatched unrelated pairs). Furthermore, HLA-matched sibling pairs with a female-to-male sex mismatch had a significantly higher overall skin GVHR grade and a higher ratio of high- versus low-grade skin GVHR than the sibling pairs with all other sex combinations. Patient age was not reflected in the skin explant result. In conclusion, the predictive value of the skin explant model for aGVHD varies depending on the clinical transplant protocols, such as the type of GVHD prophylaxis used. Nevertheless, the skin explant model remains a unique in vitro system that provides an in situ histopathologic readout for studying alloreactivity and human GVHD. The model has also the potential to aid the development of novel prophylaxis and treatment for GVHD.

The clinical spectrum of acute graft-versus-host disease

Acute graft-versus-host disease (GVHD), initiated by the reaction of donor T lymphocytes against nonshared recipient antigens, typically leads to a clinical syndrome characterized by cutaneous eruptions and intestinal and hepatic dysfunction. These three organ systems are considered in the clinical grading of acute GVHD. However, other targets may be involved. With conventional transplant conditioning regimens and in vivo prophylaxis, GVHD becomes clinically manifest within 2 to 4 weeks. With reduced-intensity conditioning, the onset of acute GVHD may be delayed until 2 to 3 months after transplantation. Hyperacute GVHD may occur within a week of transplantation after severely human leukocyte antigen (HLA)-mismatched transplants or transplants without GVHD prophylaxis. There is no reliable laboratory test for acute GVHD, and the diagnosis is based on clinical assessment.

Prediction of acute graft-versus-host disease and detection of distinct end-organ targets by enumeration of peripheral blood cytokine spot-forming cells

BACKGROUND

Acute graft-versus-host disease (aGVHD) remains a significant cause of morbidity and mortality after allogeneic hematopoietic stem cell transplantation. It was hypothesized that type 1 cytokines promoted aGVHD and type 2 cytokines inhibited it. However, recent publications demonstrated contradictory results in murine models. Type 1/2 paradigm in aGVHD remains to be determined in human.

METHODS

Using enzyme-linked immunospot assay that reflects ongoing immune status in vivo, we measured spot-forming cells (SFCs) for interferon (IFN)-gamma, interleukin (IL)-12, IL-4, and IL-10 in peripheral blood from 56 patients with hematological disorders who underwent allogeneic hematopoietic stem cell transplantation.

RESULTS

The numbers of IFN-gamma and IL-4 SFCs in patients with grade II approximately IV aGVHD were significantly higher than those in patients with grade 0 approximately I aGVHD. The enumeration of cytokine SFCs predicted aGVHD approximately 4 days before it became clinically evident, since IFN-gamma SFCs in asymptomatic phase that later progressed into grade II approximately IV aGVHD were elevated in 8 out of 8 evaluable patients. Similarly, IL-4 SFCs were elevated in 6 of 8 patients. In addition, Type 1 cytokine SFCs contributed to the intestinal, but not skin and hepatic aGVHD.

CONCLUSIONS

Enzyme-linked immunospot assay is clinically useful for predicting aGVHD and detecting distinct end-organ targets following allogeneic hematopoietic stem cell transplantation.

Limiting Dilution Analysis of Interleukin-2 Producing Helper T-cell Frequencies as a Tool in Allogeneic Hematopoietic Cell Transplantation

BACKGROUND

A reliable in vitro test that estimates the level of ongoing alloreactivity would be valuable in allogeneic hematopoietic cell transplantation (HCT) as a help to guide clinical interventions such as donor lymphocyte infusions and changes in the immunosuppression. In the present study, the use of limiting dilution analysis of interleukin-2 (IL-2) producing helper T lymphocyte frequencies (HTL assay) as a way to quantify alloreactivity following HCT was investigated.

METHODS

Serial HTL assays were performed following allogeneic HCT with myeloablative or nonmyeloablative conditioning in 26 patients with hematologic malignancies.

RESULTS

Deviations from single-hit kinetics were frequently observed in the HTL assays and a nonlinear model was therefore used for analysis. The results of this analysis suggested the presence of an inhibitory cell population. Inhibition was observed in the majority of patients and was not restricted to a specific transplant regimen. Inhibition occurred more often with high frequencies of IL-2 producing cells, indicating a physiological role of the putative inhibitory cell population in the regulation of an immune response. Higher frequencies of IL-2 producing cells were observed in patients with acute graft-versus-host disease grades II-IV than in patients with grades 0-I (P = 0.046), indicating that the degree of ongoing alloreactivity is indeed quantified by the HTL assay.

CONCLUSIONS

We find that the HTL assay may yield interesting insight into regulation of immune responses following allogeneic HCT, but because of the complexity of the results obtained, its use as a routine procedure to guide immunosuppression cannot be recommended.

Skin biopsies for early diagnosis and prognosis of graft-versus-host disease in recipients of allogeneic stem cells from blood or bone marrow

A total of 61 patients with haematological malignancies were randomised either to allogeneic transplantation with blood stem cells (BSC) or bone marrow (BM), of whom 37 patients gave their consent to participate in a skin biopsy trial. Skin biopsies were performed before and after transplantation. The main objective was to assess whether biopsies of normal and affected skin from patients allografted with BSC showed a different histopathological and immunohistochemical pattern as compared to biopsies taken from patients allografted with BM. In addition, we wished to clarify whether sequential skin biopsies could be of prognostic value with regard to graft-versus-host disease (GVHD). Biopsies from normal or affected skin in BSC allografted did not disclose a different pattern as compared to BM transplants. Biopsies taken before the outbreak of acute and chronic GVHD showed no substantial differences between the groups. Irrespective of the type of allograft, the immunohistochemical picture of affected skin consistent with acute GVHD was dominated by a significantly higher number of T-lymphocytes (CD8+). Biopsies from normal skin before the outbreak of GVHD had no predictive value with regard to the development of acute or chronic GVHD. Immunohistochemistry is of supplementary help in distinguishing changes caused by cytotoxic agents from those caused by acute GVHD.

Improved detection of clinically significant host-reactive antigens prior to HLA-identical sibling peripheral blood stem cell transplantation using a dendritic cell-based helper T-lymphocyte precursor assay

SUMMARY

Graft-versus-host disease (GVHD) due to host-reactive antigenic differences between HLA-identical pairs remains an important cause of morbidity and mortality after allogeneic transplantation. The helper T-lymphocyte precursor (HTLp) assay, using peripheral blood mononuclear cells (PBMCs), has been variably shown to detect such host-reactive differences. We assessed whether using dendritic cells (DCs) as the stimulator cells would improve the ability of the HTLp assay to detect these differences. We used PBMCs (standard HTLp assay) or monocyte-derived DCs (DC-HTLp assay) as the stimulator cells for 12 HLA-identical sibling pairs undergoing allogeneic peripheral blood stem cell transplantation. HTLp frequencies were greater by the DC-HTLp assay (median 1:77 712 vs 1:727 514; P=0.008). The standard HTLp assay did not predict for acute GVHD (P=0.42), whereas a trend was noted for the DC-HTLp assay (P=0.095). Of note, of seven patients developing moderately severe to severe acute GVHD, four had a significantly greater DC-HTLp frequency compared to the standard HTLp frequency, whereas all four patients who developed no to moderate acute GVHD had similar HTLp frequencies whether PBMCs or DCs were used as the stimulator cells. Although the small number of donor/recipient pairs assessed limits the strength of any conclusions, our study suggests that the DC-HTLp assay is better able to detect clinically significant host-reactive antigenic differences between HLA-identical siblings.

Interleukin-10 modulation of alloreactivity and graft-versus-host reactions

BACKGROUND

The biological properties of interleukin (IL)-10 in tolerance induction and inhibition of alloreactivity have suggested a therapeutic use of this cytokine as an additional or alternative prophylaxis for graft-versus-host disease (GvHD). However, the effects of exogenous IL-10 on GvHD are mainly studied in animal models, and the results remain conflicting. This study aims to demonstrate, for the first time, whether the addition of exogenous IL-10 can reduce the severity of graft-versus-host reactions (GvHR) in humans.

METHODS

The regulatory role of exogenous IL-10 in GvHR was investigated using an in vitro human skin explant model. The effects of IL-10 on skin GvHR were tested in parallel with allo-antigen induced T-cell proliferation, cytolytic reactivity, and cytokine production.

RESULTS

In the presence of IL-10, the mixed lymphocyte reaction (MLR) primed responder cells showed significantly lower proliferative and cytolytic responses compared with the responder cells from the control MLR carried out in the absence of IL-10. The responder cells from IL-10 containing MLR induced significantly less severe skin GvHR and displayed a significantly reduced T-cell activation and cytokine production. A significant correlation was observed between the levels of TNF-alpha production and the sensitivity to IL-10 modulation of GvHR.

CONCLUSIONS

The addition of exogenous IL-10 strongly inhibited the broad alloreactivity initiated by primary MLR and significantly reduced the overall severity of skin GvHR induced by MLR primed responder cells. Responder cells producing high TNF-alpha following allogeneic stimulation appeared to be less sensitive to IL-10 modulation of GvHR.

The helper T lymphocyte precursor (HTLp) frequency does not predict outcome after HLA-identical sibling donor G-CSF-mobilised peripheral blood stem cell transplantation

Here, we report the first study assessing the helper T lymphocyte precursor (HTLp) frequency as a predictor of outcome in patients undergoing allogeneic PBSC transplantation. The HTLp assay uses limiting dilution analysis to measure the frequency, in PBMCs from the donor, of T lymphocytes capable of producing IL-2 in response to histocompatibility antigenic differences on PBMCs from the recipient. This assay has shown promise as a functional histocompatibility assessment used to predict the risk of recipients of HLA-matched donor bone marrow developing severe acute GVHD: the higher the HTLp frequency, the greater the significance of any histoincompatibility, and the greater the risk of severe acute GVHD. In the current report, the HTLp frequency was measured in 28 HLA-identical sibling pairs who subsequently underwent allogeneic PBSC transplantation for haematological malignancies. The HTLp frequency did not predict for acute GVHD (P = 0.38), chronic GVHD (P = 0.95), transplant-related mortality (P = 0.79), relapse (P = 0.39) or overall survival (P = 0.84). Converting the HTLp frequency to HTLp infused per kilogram of recipient body weight also did not predict for any of the outcome measures. We conclude that, although the HTLp assay may be useful for patients undergoing BMT, it does not predict for outcome after HLA-identical sibling donor G-CSF-mobilised PBSC transplantation.

In situ dissection of the graft-versus-host activities of cytotoxic T cells specific for minor histocompatibility antigens

Minor histocompatibility antigens (mHags) are immunogenic peptides from polymorphic cellular proteins that induce strong T-cell responses after human leukocyte antigen (HLA)-matched, mHag-mismatched stem-cell transplantation. mHags with broad or limited tissue expression are target antigens for graft-versus-host (GvH) and graft-versus-leukemia (GvL) reactivities. Separation of these activities is crucial for adoptive immunotherapy of leukemia without GvH disease. Therefore, using a skin-explant assay we investigated the in situ activities of cytotoxic T lymphocytes (CTLs) specific for the ubiquitously expressed mHag H-Y and for the hematopoietic-restricted mHags HA-1 and HA-2. H-Y-specific CTLs, visualized by tetrameric HLA-mHag peptide complexes, infiltrated male skin sections within 24 hours, induced severe GvH reactions of grade III-IV and produced high levels of IFN-gamma. In contrast, CTLs specific for the hematopoietic system-specific mHags HA-1 and HA-2 induced no or low GvH reactions above background and produced little or no interferon-gamma, unless the skin sections were preincubated with HA-1/HA-2 synthetic peptides. These results provide the first in situ dissection of GvH effects by mHag-specific CTLs and show that ubiquitously expressed mHags are the prime targets of GvH disease.

Histological correlation between different centers using the skin explant model to predict graft-versus-host disease following bone marrow transplantation

Acute graft-versus-host disease (GVHD) remains the major complication of allogeneic stem cell transplantation (SCT) with an incidence of 40-60% and a mortality of up to 50%. Several assays have been developed to try to predict the development of GVHD including the mixed lymphocyte culture reaction, cytotoxic and helper T lymphocyte precursor frequency assays. In the Northern region of England we have used an in vitro skin explant model for predicting GVHD in MHC compatible bone marrow transplant recipients since 1988. The aims of the present study was to test the reproducibility of the model in two other bone marrow transplant centers in Europe. The assay consists of incubating patient skin explants with effector cells from mixed donor versus recipient lymphocyte cultures and the subsequent detection of graft-versus-host reactions by histopathological grading (0-IV) of the skin explants. 503 slides from 134 patients were evaluated. All were graded for negative GVHR grade 0-I or positive grade II-IV. Results from control and test slides significantly correlated between centers to the p value of 0.0001 by Fisher's exact probability test. These results show that the skin explant assay is reproducible between centers and supports the continued use of the assay to predict GVHD in allogeneic stem cell transplant recipients.

Induction of cytomegalovirus (CMV)-specific T-cell responses using dendritic cells pulsed with CMV antigen: a novel culture system free of live CMV virions

Recipients of allogeneic transplants are at risk of cytomegalovirus (CMV) infection and disease during the period of immune compromise after transplantation. The limitations of current antiviral pharmacotherapy have led to attempts to develop alternative strategies for preventing or treating CMV infection, such as adoptive transfer of donor-derived virus-specific T cells. Methods for generating CMV-specific T cells either use live CMV to infect autologous antigen-presenting cells (APCs) or require some knowledge of the immunodominant peptides involved in the immune response. A novel culture system was developed that does not use live virions and in which the APCs are monocyte-derived dendritic cells (DCs). APCs were pulsed with CMV antigen and cocultured with autologous peripheral blood lymphocytes from donors seropositive for CMV. The culture-output cells consisted of both CD4- and CD8-expressing T cells. Proliferation, as determined by a tritium-thymidine-incorporation assay, showed significant CMV-antigen specificity in cultures from 15 of 15 donors seropositive for CMV. In cytotoxicity assays, cytotoxic T lymphocytes from 10 of 12 cocultures specifically lysed autologous CMV-infected fibroblasts or DCs but not HLA-mismatched or uninfected target cells, and this activity was shown to be blocked by HLA class 1 blocking antibodies. T-cell-receptor spectratyping of cells from the cultures typically showed complex size-distribution patterns, with all size classes of a normal preculture distribution present. However, a few size-class peaks were expanded compared with the preculture patterns and these may have represented expansions of CMV-specific T-cell clones. Advantages of this culture system are that it requires no live virions and no detailed knowledge of the antigenic peptides involved and it is applicable to CMV-seropositive donors of any HLA type.

Prevention of acute graft-versus-host-disease by selective depletion of T cells reactive with minor histocompatibility antigens on epithelial cells

Graft-versus-host disease (GVHD) is a major obstacle in allogeneic hematopoietic stem cell transplantation (HSCT). Mature donor T-cells present in the graft play a pivotal role in the development of acute GVHD. On the other hand, mature donor T-cells in the graft are also crucial for the elimination of residual tumor cells still present in the patient after HSCT. Whether donor T cells act non-specifically against the patient, including an overlapping GVHD/GVL reactivity, or some donor T cells have GVHD reactivity while other donor T cells have GVL reactivity is still unclear. Some in-vitro data are suggestive that selective T cell depletion techniques are possible by which GVHD-reactive T cells can be eliminated while GVL-reactive T cells are preserved. Here we update some approaches of selective T cell depletion that have been developed in our laboratory.

Cytotoxic T lymphocyte precursor frequency as a predictor of acute graft-versus-host disease in bone marrow transplantation from HLA-identical siblings

The measurement of precursor frequencies of donor anti-recipient cytotoxic T lymphocytes (CTL-p) has been shown to predict the incidence and the severity of acute graft-versus-host disease (aGVHD) in unrelated donor bone marrow transplantation (BMT). In HLA-identical sibling BMT, where aGVHD is most likely caused by minor histocompatibility antigen mismatches, this assay did not appear to be sensitive enough to provide similar predictive information. In this study, the CTL-p frequencies and the incidence and severity of aGVHD in 51 onco-hematological patients transplanted from HLA-identical siblings were compared. Sibling donors were selected on the basis of HLA identity using serological typing for HLA-A, B, C antigens, whereas HLA-DRB was tested by molecular analysis. Sibling identity was also confirmed by DNA heteroduplex analyses. Fifteen out of 21 (71%) patients with high precursor frequency (>1:100 x 10(3)) and 12 out of 30 (40%) with low precursor frequency (<1:100 x 10(3)) experienced clinically significant (II-IV) aGVHD. A significant correlation (P = 0.04) between CTL-p frequency and severe aGVHD was demonstrated. Moreover there was a positive trend for a high frequency response according to an increasing grade of aGVHD, which was statistically significant (P = 0.04). In our experience the CTL-p assay is a helpful predictive test for aGVHD in HLA-identical sibling BMT, indicating high risk patients possibly requiring additional prophylaxis.

T-cell frequency analysis does not predict the incidence of graft-versus-host disease in HLA-matched sibling bone marrow transplantation

BACKGROUND

Graft-versus-host disease (GVHD) is a major and sometimes fatal complication of allogeneic bone marrow transplantation (BMT). The prediction of GVHD remains an important issue in preventing morbidity and mortality after allogeneic BMT. In the past 10 years, there has been great interest in using the frequency analysis of alloreactive helper and cytotoxic T lymphocyte precursors (HTLp and CTLp) to detect recipient-specific alloreactivity and thus predict GVHD in HLA-matched related and unrelated BMT. However, the results remain controversial. The intention of the present study was to investigate whether alloreactive HTLp and CTLp frequencies measured in donor peripheral blood before BMT would be a useful predictor for the occurrence of acute GVHD after HLA-matched sibling BMT.

METHOD

A combined limiting dilution assay was used to determine alloreactive HTLp and CTLp frequencies for 42 HLA-matched sibling patient/donor pairs. The pretransplantation host-reactive HTLp and CTLp frequencies were then correlated with post-transplantation clinical outcomes of acute GVHD. The association between HTLp/CTLp frequencies and the incidence of acute GVHD was determined using the Fisher's exact test.

RESULTS

The mean values of HTLp and CTLp frequencies for this cohort of HLA-matched sibling patient/donor pairs were 1:321,322 (range 1:71,000 to 1:1000,000) and 1:195,260 (range 1:3,717 to 1:1000,000), respectively. Acute GVHD (> or =II) was observed in one of four patients with high (>1:100,000) HTLp frequencies and 20 of 36 patients with low (<1:100,000) HTLp frequencies. Similarly, 6 of 10 patients with high (>1: 100,000) CTLp frequencies and 14 of 29 patients with low (<1:100,000) CTLp frequencies developed acute GVHD (> or =II). The overall correlation between hostreactive HTLp/CTLp frequencies and the incidence of acute GVHD in this cohort of patients was 42.5% and 53.9%, respectively. There was no significant difference in the incidence of acute GVHD between the patients with either high or low host-reactive HTLp/ CTLp frequencies (P=0.331 and 0.716, respectively). The data were also analyzed separately for the adult patient group based on GVHD prophylaxis with either cyclosporine alone or the combination of cyclosporine and methotrexate. Within these two prophylaxis groups, neither HTLp nor CTLp frequencies correlated with acute GVHD.

CONCLUSION

Host-reactive HTLp and CTLp frequency analysis did not provide informative prediction for the occurrence of acute GVHD after HLA-matched sibling BMT.

Determination of helper T-cell precursor frequencies against non-haemopoietic cells: comparison of co-stimulation provided by anti-CD28 antibody versus the cellular ligand B7-1

Helper T-cell precursor frequency assays (HTLp-assays) are commonly used in transplantation to examine the frequency of T cells reactive against donor or host alloantigens. In these assays, peripheral blood mononuclear cells (PBMCs) are most often used as stimulator cells. However, cells targeted after transplantation do not always belong to the haematopoietic lineage and may express different alloantigens, especially minor histocompatibility antigens (mHags). Non-haematopoietic cells lack expression of the B7 co-stimulatory molecules needed to activate primary T cells that can be supplied by anti-CD28 (alphaCD28) antibodies or transfection with B7-1 coding sequences. At present, it is not known how these two ways of supplied co-stimulation compare in HTLp assays. B7-1-transfected A431 keratinocytes (A431B7-1) induced higher proliferative responses in allogeneic primary T cells and more interleukin (IL) 2 production than that induced by A431 cells plus alphaCD28, whereas the kinetics of proliferation and IL-2 production were similar. Neither cross-linking of alphaCD28 bound to T cells nor prevention of IL-2 resorption by the anti-IL-2 receptor resulted in improved proliferation or IL-2 production. Results of HTLp assays indicated that A431B7-1 activated on average 7.5 times more alloreactive IL-2-producing T cells than A431 cells plus alphaCD28. We conclude that primary T-cell alloresponses against major histocompatibility complexes (MHCs) and mHags expressed on non-haematopoietic cells can be measured in HTLp assays using supplied co-stimulation, although alphaCD28 yields an intrinsic underestimation of actual frequencies.

An in vivo model of human skin acute graft-versus-host disease: transplantation of cultured human epidermal cells and dermal fibroblasts with human lymphocytes into SCID mice

The ability of mixed epidermal cell-lymphocyte reactions to detect allogeneic reactivities in an in vivo model was investigated by developing an in vivo model of acute graft-versus-host disease (GVHD), using SCID mice with a C.B-17 background in which human skin structures were generated by transplantation of cultured human epidermal cells (HEC) with dermal fibroblasts (HDFC). Suspensions containing cultured HEC and HDFC from a single donor were mixed with autologous peripheral blood mononuclear cells (PBMNC) or with PBMNC from unrelated individuals, and were injected into the flanks of C.B-17-SCID mice. Ten and 21 days after injection, subcutaneous nodules generated in the mice were examined histologically and immunohistochemically. Cystic structures developing after injection of HEC and HDFC without human PBMNC showed normal epidermislike tissue. Human skin generated in SCID mice injected with HEC and HDFC with auto-PBMNC showed no graft-versus-host reaction (GVHR) histologically, whereas those mice injected with PBMNC from siblings that shared an HLA haplotype showed mild GVHR. Human skin in SCID mice injected with HEC and HDFC with histoincompatible unrelated PBMNC showed moderate to severe GVHR. The severity of GVHR paralleled the dose of unrelated PBMNC, and GVHR was prevented by peroral treatment with cyclosporine A. Immunohistochemically, inflammatory cells infiltrating human cutaneous tissue formed in the SCID mice were stained by an anti-human CD45RO antibody that reacts with human T cells but not with murine lymphocytes, and most T cells were stained by an anti-human CD8 antibody recognizing HLA class I antigens. These findings are similar to those in clinical skin graft-versus host disease (GVHD) observed in patients undergoing allogeneic bone marrow transplantation. This experimental system should be useful as an in vivo model of human skin GVHD.

A human skin explant model for predicting graft-versus-host disease following bone marrow transplantation

Graft-versus-host disease (GVHD) is the most serious complication following bone marrow transplantation, with an incidence of 40-60%. The disease can be fatal in 50% of cases, even in patients receiving marrow from an HLA identical sibling. Several assays have been developed to try to predict the development of GVHD, including mixed lymphocyte culture reaction, cytotoxic T lymphocyte precursor, and helper T lymphocyte precursor frequency assays. This review describes an in vitro skin explant model which has been used since 1988 for both predicting acute GVHD in HLA identical sibling bone marrow transplantation and studying the pathophysiology of the disease. The model involves sensitising donor lymphocytes in vitro in a primary mixed lymphocyte reaction and then evaluating the secondary response on patient skin biopsies by grading the graft-versus-host reactivity (grades I-IV) histopathologically. From analysis of collective data the model is a clear predictor of GVHD and superior to the other assays widely used, with a correlation of 82% with clinical outcome. The skin explant model allows the investigator to study the pathogenesis of GVHD. The cytokines TNF alpha and IFN gamma are shown to be important mediators of cellular damage in graft-versus-host reactions. Recent work has also involved using the model to study the alloreactivity of cord blood. The model is currently being assessed in several bone marrow transplantation centres in Europe on different patient groups including those who receive marrow from haploidentical and matched unrelated donors.