Lethal GVHD across minor histocompatibility barriers: nature of the effector cells and role of the H-2 complex

Regulatory T cell niche in the bone marrow, a new player in Haematopoietic stem cell transplantation

Challenges in haematopoietic stem cell transplantation such as low bone marrow (BM) engraftment, graft versus host disease (GvHD) and the need for long-term immunosuppression could be addressed using T regulatory cells (Tregs) resident in the tissue of interest, in this case, BM Tregs. Controlling the adverse immune response in haematopoietic stem cell transplantation (HSCT) and minimising the associated risks such as infection and secondary cancers due to long-term immunosuppression is a crucial aspect of clinical practice in this field. While systemic immunosuppressive therapy could achieve reasonable GvHD control in most patients, related side effects remain the main limiting factor. Developing more targeted immunosuppressive strategies is an unmet clinical need and is the focus of several ongoing research projects. Tregs are a non-redundant sub-population of CD4⁺ T cells essential for controlling the immune homeostasis. Tregs are known to be reduced in number and function in autoimmune conditions. There is considerable interest in these cells as cell therapy products since they can be expanded in vitro and infused into patients. These trials have found Treg therapy to be safe, well-tolerated, and with some early signs of efficacy. However, Tregs are a heterogeneous subpopulation of T cells, and several novel subpopulations have been identified in recent years beyond the conventional thymic (tTregs) and peripheral (pTregs). There is increasing evidence for the presence of resident and tissue-specific Tregs. Bone marrow (BM) Tregs are one example of tissue-resident Tregs. BM Tregs are enriched within the marrow, serving a dual function of immunosuppression and maintenance of haematopoietic stem cells (HSCs). HSCs maintenance is achieved through direct suppression of HSCs differentiation, maintaining a proliferating pool of HSCs, and promoting the development of functional stromal cells that support HSCs. In this review, we will touch upon the biology of Tregs, focusing on their development and heterogeneity. We will focus on the BM Tregs from their biology to their therapeutic potential, focusing on their use in HSCT.

Minor Histocompatibility Antigen-Specific T Cells

Minor Histocompatibility (H) antigens are major histocompatibility complex (MHC)/Human Leukocyte Antigen (HLA)-bound peptides that differ between allogeneic hematopoietic stem cell transplantation (HCT) recipients and their donors as a result of genetic polymorphisms. Some minor H antigens can be used as therapeutic T cell targets to augment the graft-vs.-leukemia (GVL) effect in order to prevent or manage leukemia relapse after HCT. Graft engineering and post-HCT immunotherapies are being developed to optimize delivery of T cells specific for selected minor H antigens. These strategies have the potential to reduce relapse risk and thereby permit implementation of HCT approaches that are associated with less toxicity and fewer late effects, which is particularly important in the growing and developing pediatric patient. Most minor H antigens are expressed ubiquitously, including on epithelial tissues, and can be recognized by donor T cells following HCT, leading to graft-vs.-host disease (GVHD) as well as GVL. However, those minor H antigens that are expressed predominantly on hematopoietic cells can be targeted for selective GVL. Once full donor hematopoietic chimerism is achieved after HCT, hematopoietic-restricted minor H antigens are present only on residual recipient malignant hematopoietic cells, and these minor H antigens serve as tumor-specific antigens for donor T cells. Minor H antigen-specific T cells that are delivered as part of the donor hematopoietic stem cell graft at the time of HCT contribute to relapse prevention. However, in some cases the minor H antigen-specific T cells delivered with the graft may be quantitatively insufficient or become functionally impaired over time, leading to leukemia relapse. Following HCT, adoptive T cell immunotherapy can be used to treat or prevent relapse by delivering large numbers of donor T cells targeting hematopoietic-restricted minor H antigens. In this review, we discuss minor H antigens as T cell targets for augmenting the GVL effect in engineered HCT grafts and for post-HCT immunotherapy. We will highlight the importance of these developments for pediatric HCT.

Identification of a major susceptibility locus for lethal graft-versus-host disease in MHC-matched mice

Graft-vs-host disease (GVHD) is the major cause of morbidity and mortality after allogeneic hemopoietic cell transplantation. From a genetic perspective, GVHD is a complex phenotypic trait. Although it is understood that susceptibility results from interacting polymorphisms of genes encoding histocompatibility Ags and immune regulatory molecules, a detailed and integrative understanding of the genetic background underlying GVHD remains lacking. To gain insight regarding these issues, we performed a forward genetic study. A MHC-matched mouse model was used in which irradiated recipient BALB.K and B10.BR mice demonstrate differential susceptibility to lethal GHVD when transplanted using AKR/J donors. Assessment of GVHD in (B10.BR x BALB.K)F(1) mice revealed that susceptibility is a dominant trait and conferred by deleterious alleles from the BALB.K strain. To identify the alleles responsible for GVHD susceptibility, a genome-scanning approach was taken using (B10.BR x BALB.K)F(1) x B10.BR backcross mice as recipients. A major susceptibility locus, termed the Gvh1 locus, was identified on chromosome 16 using linkage analysis (logarithm of the odds, 9.1). A second locus was found on chromosome 13, named Gvh2, which had additive but protective effects. Further identification of Gvh genes by positional cloning may yield new insight into genetic control mechanisms regulating GVHD and potentially reveal novel approaches for effective GVHD therapy.

Prediction of graft-versus-host disease in humans by donor gene-expression profiling

BACKGROUND

Graft-versus-host disease (GVHD) results from recognition of host antigens by donor T cells following allogeneic hematopoietic cell transplantation (AHCT). Notably, histoincompatibility between donor and recipient is necessary but not sufficient to elicit GVHD. Therefore, we tested the hypothesis that some donors may be "stronger alloresponders" than others, and consequently more likely to elicit GVHD.

METHODS AND FINDINGS

To this end, we measured the gene-expression profiles of CD4(+) and CD8(+) T cells from 50 AHCT donors with microarrays. We report that pre-AHCT gene-expression profiling segregates donors whose recipient suffered from GVHD or not. Using quantitative PCR, established statistical tests, and analysis of multiple independent training-test datasets, we found that for chronic GVHD the "dangerous donor" trait (occurrence of GVHD in the recipient) is under polygenic control and is shaped by the activity of genes that regulate transforming growth factor-beta signaling and cell proliferation.

CONCLUSIONS

These findings strongly suggest that the donor gene-expression profile has a dominant influence on the occurrence of GVHD in the recipient. The ability to discriminate strong and weak alloresponders using gene-expression profiling could pave the way to personalized transplantation medicine.

Distinct roles for donor- and host-derived antigen-presenting cells and costimulatory molecules in murine chronic graft-versus-host disease: requirements depend on target organ

The application of allogeneic stem cell transplantation (alloSCT) is limited by graft-versus-host disease (GVHD). GVHD can be divided into acute and chronic forms that likely have different requirements for initiation and pathogenesis mechanisms. In prior studies we demonstrated that residual host antigen-presenting cells (APCs) were required to initiate acute GVHD (aGVHD) mediated by CD8 T cells. In contrast, here we demonstrate that either donor or host APCs can initiate CD4-mediated GVHD in a model that has features of chronic GVHD (cGVHD). Both donor and host APCs must provide CD80/86-dependent costimulation to elicit maximal cGVHD, and there is no GVHD when both donor and host lack CD80/86. Finally, we were surprised to find that, although either donor or host APCs are sufficient to stimulate skin cGVHD, donor APCs play a dominant role in intestinal cGVHD. Both CD40 and CD80/86 are critical for donor APC function in intestinal cGVHD, but only CD80/86 is required for skin cGVHD. Thus, there are target-tissue–specific differences in APC requirements. These results identify differences in APC requirements between CD8-mediated aGVHD and CD4-mediated cGVHD. They further highlight donor APCs as additional targets for GVHD therapy.

Target Antigens Determine Graft-versus-Host Disease Phenotype

Chronic graft-vs-host disease (cGVHD) is an increasingly frequent complication of allogeneic stem cell transplantation. Phenotypically, cGVHD differs from patient to patient; in particular, a subset of patients develops extensive cutaneous fibrosis. Similarly, graft-vs-host disease (GVHD) is distinct in inbred murine donor:recipient pairings, indicating a genetic component to disease phenotype. The B10.D2 -->BALB/c (H-2d) strain pairing uniquely recapitulates key pathologic features of fibrotic human cutaneous cGVHD. To distinguish whether this genetic component is due to differences in genes that modulate immune responses or to the specific Ags targeted, we asked whether skin-dominant cGVHD also develops in the B10 -->BALB.B (H-2b) and B10.BR -->BALB.K (H-2k) MHC-congenic pairings. Because each MHC haplotype presents different peptides and selects different T cell repertoires, GVHD in each donor:recipient pair undoubtedly targets different Ags. We found that, in contrast to BALB/c recipients, BALB.B mice never manifested skin disease while BALB.K mice developed a modified form of skin disease. Instead, BALB.B and BALB.K recipients developed systemic GVHD which was absent in BALB/c mice. Moreover, in (B10 x B10.D2)F1 -->(BALB.B x BALB/c)F1 H-2b/d transplants, recipients developed both cutaneous and systemic disease. Thus, the selection of immunodominant Ags determines the target and character of GVHD, providing insight into the genetic basis for different forms of GVHD.

Kinetics of gene expression in murine cutaneous graft-versus-host disease

The kinetics of gene expression associated with the development of cutaneous graft-versus-host disease (GVHD) were examined in a mouse model of MHC-matched allogeneic hematopoietic stem cell transplantation. Ear skin was obtained from recipient mice with or without GVHD between 7 and 40 days after transplantation for histopathological analysis and gene expression profiling. Gene expression patterns were consistent with early infiltration and activation of CD8(+) T and mast cells, followed by CD4(+) T, natural killer, and myeloid cells. The sequential infiltration and activation of effector cells correlated with the histopathological development of cutaneous GVHD and was accompanied by up-regulated expression of many chemokines and their receptors (CXCL-1, -2, -9, and -10; CCL-2, -5, -6, -7, -8, -9, -11, and -19; CCR-1 and CCR-5), adhesion molecules (ICAM-1, CD18, Ly69, PSGL-1, VCAM-1), molecules involved in antigen processing and presentation (TAP1 and TAP2, MHC class I and II, CD80), regulators of apoptosis (granzyme B, caspase 7, Bak1, Bax, and BclII), interferon-inducible genes (STAT1, IRF-1, IIGP, GTPI, IGTP, Ifi202A), stimulators of fibroblast proliferation and matrix synthesis (interleukin-1beta, transforming growth factor-beta1), and markers of keratinocyte proliferation (keratins 5 and 6), and differentiation (small proline-rich proteins 2E and 1B). Many acute-phase proteins were up-regulated early in murine cutaneous GVHD including serum amyloid A2 (SAA2), SAA3, serpins a3g and a3n, secretory leukocyte protease inhibitor, and metallothioneins 1 and 2. The kinetics of gene expression were consistent with the evolution of cutaneous pathology as well as with current models of disease progression during cutaneous GVHD.

Variable hematopoietic graft rejection and graft-versus-host disease in MHC-matched strains of mice

MHC typing for human hematopoietic cell transplantation (HCT) from unrelated donors is currently performed by using a combination of serologic and molecular techniques. It has been determined that allelic differences in human MHC molecules, revealed by nucleotide sequencing but not by serologic typing, substantially influence graft rejection and graft-versus-host disease, two serious complications of clinical HCT. We studied transplantation of purified hematopoietic stem cells in a series of mouse strains that were matched at the MHC but had different background genes, and we observed striking differences in engraftment resistance and graft-versus-host disease severity, both factors depending on the donor-recipient strain combination. The individual mouse lines studied here were established nearly a century ago, and their MHC types were determined exclusively by serologic techniques. We considered the possibility that serologically silent MHC polymorphisms could account for our observations and, therefore, we performed DNA sequencing of the class I and II MHC alleles of our mouse strains. At each locus, exact homology was found between serologically MHC-matched strains. Our results likely extend to all serologically MHC-matched mouse strains used in modern research and highlight the profound and variable influence that non-MHC genetic determinants can have in dictating outcome after HCT.

Refractory chronic GVHD emerging after splenectomy in a marrow transplant recipient with accelerated phase CML

We report a 39-year-old female patient who underwent HLA-identical sibling allogeneic BMT for CML in accelerated phase. Severe pancytopenia refractory to G-CSF associated with progressive splenomegaly and RBC/platelet transfusion dependency were present from day +60 after BMT. MRD assessed by FISH and RT-PCR multiplex for BCR-ABL rearrangement was negative, and complete chimerism was documented by VNTR on days +100, +180, +360 and 2 years after BMT. Splenectomy was performed on day +225 and pancytopenia resolved but chronic extensive graft-versus-host disease developed, with hepatic cholestasis, diffuse scleroderma and sicca-like syndrome. She was sequentially and progressively treated with different immunosuppressive therapy combinations with no clear benefit. On day +940, she presented with infection over the previously present ulcers on both limbs, which culminated in septic shock and death on day +1041. We conclude that, although splenectomy may reverse poor graft function after allogeneic BMT, hyposplenism may trigger or worsen chronic extensive GVHD leading to increased morbidity and mortality.

Differences in MHC-class I presented minor histocompatibility antigens extracted from normal and graft-versus-host disease (GVHD) mice

Graft-versus-host disease (GVHD) may develop after allogeneic bone marrow transplantation (BMT) between donors and recipients incompatible for minor histocompatibility antigens (mHAg). Here, we examined the possible relationship between tissue-specific distribution of dominant mHAg peptides and specific organ destruction caused by GVHD. In the B6 anti-Balb/b (H-2b) strain combination, a GVHD developed against Balb/b mHAgs. Despite the high number of incompatible mHAgs between these two strains, both cytotoxic T lymphocyte (CTL) response and GVHD could be attributed to a limited number of dominant mHAgs. We studied CTL-defined expression of dominant mHAgs in normal tissues and their GVHD-related modifications. mHAg peptides were prepared by acid elution and reversed-phase high pressure liquid chromatography fractionation from the spleen, liver, gut and skin as GVHD target tissues and from the heart and kidney as control tissues. Peptidic fractions extracted from normal and GVHD tissues were incubated with RMA-S targets and analysed using bulk B6 anti-Balb/b CTL. In each tissue several fractions were recognized with a given pattern of mHAg expression. GVHD induced qualitative and quantitative changes in antigenic peptide expression. Modifications in mHAg presentation during GVHD concerned preferentially GVHD target organs as opposed to non-GVHD target organs. In addition, when immunizing tissues were derived from GVHD mice instead of normal mice, the profile of CTL recognition was different. In conclusion, these data indicate that broad differences could exist in peptide presentation between various normal and GVHD-target organs.

Monitoring of donor/recipient T-cell engraftment kinetics in myeloablative allogeneic stem cell transplantation using short tandem repeat amplification from cell lysates

Molecular monitoring of donor/recipient T-cell kinetics early post-transplant can provide clues to the immunological events that govern host-versus-graft reaction (HVGR) and graft versus-host-disease (GVHD). We have previously used fluorescence in situ hybridization (FISH) with X and Y probes to monitor recipient T (R-T) cell clearance early after myeloablative allogeneic stem cell transplantation (ASCT). We demonstrated that impaired clearance of residual host-T-cells in the early days post-transplant was associated with graft rejection, while enhanced clearance could be an indicator of increased donor anti-host alloreactivity and predictive of acute GVHD. Although FISH is the most accurate quantitative molecular tool for the determination of the exact donor/recipient-T-cell numbers at any time points post-transplant, it has the disadvantage of being limited to sex mismatched donor/recipient pairs. Our goal was to develop a molecular approach that, irrespective of gender, would be comparable to FISH in accurately determining host residual T-cell clearance after myeloablative conditioning for ASCT. We have genotyped DNA from cell lysates using polymerase chain reaction (PCR) amplification of short tandem repeats (STR) with fluorescently labeled oligonucleotide primers, and used the Genescan 672 software for accurate quantitative analysis of the amplified alleles. Here, we show that this approach allowed us to achieve in T-cells accurate quantitative analyses of amplified donor/recipient alleles in sex matched patients on days +5, +8 and +12 post-transplant, despite severe leukopenia.

Adoptive transfer of minor histocompatibility antigen-specific T lymphocytes eradicates leukemia cells without causing graft-versus-host disease

Adoptive transfer of T cells reactive to minor histocompatibility antigens has the unmatched ability to eradicate malignant hematopoietic cells. Unfortunately, its use is hampered by the associated graft-versus-host disease. The critical issue of a possible dissociation of the antileukemic effect and graft-versus-host disease by targeting specific minor histocompatibility antigens remains unresolved because of the unknown nature and number of minor histocompatibility antigens necessary or sufficient to elicit anti-leukemic activity and graft-versus-host disease. We found that injection of T lymphocytes primed against a single major histocompatibility complex class I-restricted immunodominant minor histocompatibility antigen (B6dom1) caused no graft-versus-host disease but produced a curative anti-leukemic response. Avoidance of graft-versus-host disease required that no other host-reactive T cells be co-injected with T cells primed with B6dom1. Here we show that effective and non-toxic immunotherapy of hematologic malignancies can be achieved by targeting a single immunodominant minor histocompatibility antigen.

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.

The effect of graft-versus-host disease on T cell production and homeostasis

The aim of this work was to decipher how graft-versus-host disease (GVHD) affects T cell production and homeostasis. In GVHD+ mice, thymic output was decreased fourfold relative to normal mice, but was sufficient to maintain a T cell repertoire with normal diversity in terms of Vbeta usage. Lymphoid hypoplasia in GVHD+ mice was caused mainly by a lessened expansion of the peripheral postthymic T cell compartment. In 5-bromo-2'-deoxyuridine pulse-chase experiments, resident T cells in the spleen of GVHD+ mice showed a normal turnover rate (proliferation and half-life). When transferred into thymectomized GVHD- secondary hosts, T cells from GVHD+ mice expanded normally. In contrast, normal T cells failed to expand when injected into GVHD+ mice. Thus, the reduced size of the postthymic compartment in GVHD+ mice was not due to an intrinsic lymphocyte defect, but to an extrinsic microenvironment abnormality. We suggest that this extrinsic anomaly is consistent with a reduced number of functional peripheral T cell niches. Therefore, our results show that GVHD-associated T cell hypoplasia is largely caused by a perturbed homeostasis of the peripheral compartment. Furthermore, they suggest that damage to the microenvironment of secondary lymphoid organs may represent an heretofore unrecognized cause of acquired T cell hypoplasia.

Biochemical and Immunogenetic Analysis of an Immunodominant Peptide (B6dom1) Encoded by the Classical H7 Minor Histocompatibility Locus

Of the many minor histocompatibility (H) Ags that have been detected in mice, the ability to induce graft vs host disease (GVHD) after bone marrow transplantation is restricted to a limited number of immunodominant Ags. One such murine Ag, B6dom1, is presented by the H2-Db MHC class I molecule. We present biochemical evidence that the natural B6dom1 peptide is indistinguishable from AAPDNRETF, and we show that this peptide can be isolated from a wide array of tissues, with highest levels from the lymphoid organs and lung. Moreover, we employ a novel, somatic cell selection technique involving CTL-mediated immunoselection coupled with classical genetics, to show that B6dom1 is encoded by the H7 minor H locus originally discovered ∼40 years ago. These studies provide a molecular genetic framework for understanding B6dom1, and exemplify the fact that mouse minor H loci that encode immunodominant CTL epitopes can correspond to classical H loci originally identified by their ability to confer strong resistance to tumor transplantation. Additionally, these studies demonstrate the utility of somatic cell selection approaches toward resolving H Ag immunogenetics.

Combined immunophenotyping and FISH with sex chromosome-specific DNA probes for the detection of chimerism in epidermal Langerhans cells after sex-mismatched bone marrow transplantation

Langerhans cells (LC) of the skin represent bone marrow-derived dendritic antigen-presenting cells and are therefore important in pathophysiological processes such as rejection, graft-versus-host disease, and graft-versus-leukemia-reaction after bone marrow transplantation (BMT). For understanding of these diseases, the evaluation of the chimeric status of LC following BMT is of great interest. To analyze the sex chromosome constitution of LC in the skin, we established a modified and refined technique of combined immunophenotyping and fluorescence in situ hybridization (FISH) and investigated frozen sections of skin biopsies from nine patients after allogeneic sex-mismatched BMT and of two healthy donors for control. LC were specifically labeled using a fluorescent CD1 a antibody and hybridized simultaneously with X and Y chromosome-specific DNA probes. The results of this practical application on nine leukemia patients show the appearance of donor-type LC and the persistence of host-type LC at various times (36 up to 1395 days) after sex-mismatched BMT. Complete chimerism of LC could not be detected in any case. The frequency of recipient-specific LC ranged from 7% to 92% and showed no correlation with time postgrafting. We conclude from our results of 1461 analyzed LC that combined immunophenotyping and interphase cytogenetic analysis by FISH is the method of choice for the assessment of chimerism in a particular cell type after sex-mismatched BMT. Its practical application on other tissues affected by BMT-related pathophysiological processes reveals further knowledge of the time-dependent course of chimeric patterns after BMT.

Serum levels of cytokines and secondary messages after T-cell-depleted and non-T-cell-depleted bone marrow transplantation: influence of conditioning and hematopoietic reconstitution

Cytokines are increasingly recognized as important mediators of graft-versus-host disease (GVHD). Measurements of cytokine serum levels in patients with GVHD, and successful prevention and treatment of the disease with the use of cytokine antagonists to either the cytokine or its receptor, are only two of several factors demonstrating the involvement of cytokines in GVHD. To further investigate the role of cytokines in the pathomechanism of acute GVHD, we investigated endogenous serum levels of various cytokines and dependent molecules in sera of 14 patients after T-cell-depleted (TCD) bone marrow transplantation (BMT) and compared the results with those of 12 patients undergoing non-TCD BMT. The effect of various conditioning regimens and of hematopoietic reconstitution on cytokine serum levels was analyzed in detail in these cohorts of patients by measuring interferon (IFN)-gamma, IFN-alpha, tumor necrosis factor-alpha, interleukin-6, neopterin, and beta2-microglobulin. The analyses showed that an increase in IFN-gamma and neopterin serum levels was a specific feature of cyclophosphamide administration and was not observed after other cytostatic drugs or total body irradiation, and that an increase in IFN-gamma, neopterin, beta2-microglobulin, and IFN-alpha release depends on the presence of T cells in the graft. We conclude that significant cytokine serum alterations were noted after TCD BMT as compared with after non-TCD BMT. These alterations, besides depletion of cytotoxic effector cells, might be involved in preventing GVHD after TCD BMT. In addition, more attention should be devoted to the cytokine release-inducing capacity of the conditioning regimen, because such a release might influence the occurrence of transplant-related complications after BMT.

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.

The role of alloreactive cytotoxic and lymphokine-secreting T lymphocytes in the development of acute graft-versus-host disease

The development of acute graft-versus-host disease (GVHD) after allogeneic bone marrow transplantation is mediated by alloreactive donor T cells infused with the bone marrow inoculum. This review discusses the role and significance of host-specific cytotoxic and lymphokine-secreting donor T cells for the prediction and generation of acute GVHD.

Characterization of skin-infiltrating cells during acute graft-versus-host disease following bone marrow transplantation using unrelated marrow donors

To characterize skin-infiltrating T lymphocytes during acute GVHD, skin biopsies were obtained from two patients who received unrelated marrow matched for HLA-A, -B, -DR, and -DQ but mismatched for -DP. A total of 120 T-cell clones were generated. Phenotype analysis of the clones showed that the majority of cells were CD4+ and expressed alpha/beta TCR. HLA-DP oligonucleotide genotyping of the clones revealed the presence of lymphoid chimerism. PLT assay showed the lack of HLA specificity, including mismatched HLA-DP. However, mAb to HLA antigens blocked proliferation of the majority of the clones, indicating that the clones recognized HLA-associated molecules. Interestingly, proliferation of two CD4+ T-cell clones was inhibited by class I mAb. A few of the clones revealed augmented proliferation in the presence of CMV antigens and a few revealed cytolytic activity. The above study suggests that (a) CD4+ helper T cells may be primarily responsible for immunopathogenesis of skin manifestations during acute GVHD, (b) there is a mixed lymphoid chimerism in skin during acute GVHD, (c) HLA-DP may not be a factor contributing to the development of acute GVHD, (d) the peptide of the HLA groove or superantigen associated with HLA molecules may be the stimulatory antigen, and (e) CMV antigens appear to stimulate some of the skin-infiltrating T lymphocytes.

Locoregional immunotherapy of head and neck cancers utilizing allogeneic spleen cells--a report of 2 cases

Frozen-stored human spleen cells (SC) cultured with streptococcus preparation OK-432 acquired direct cytotoxicity to autologous as well as allogeneic tumor cells. The activated cells started to produce cytocidal cytokine TGIF, which is distinct from previously known cytokines. We examined the possibility of allogeneic adoptive immunotherapy (AIT) using these OK-432-stimulated spleen cells (OK-SC) in two cancer patients. Rapid necrosis of cancer tissue and remarkable decreases of tumor markers in tumor effusion were observed. There were no severe side effects.

[Immunologic aspects of bone marrow transplantation]

Allogeneic bone marrow transplantation is concerned by immunology by at least two aspects: the first one is the acceptance of the graft by the host and reciprocally and the second one is that it constitutes an unique human model of immune reconstitution. In this review of the immunological aspects, we deal with the selection of the bone marrow donor (related or not) especially on the base of HLA compatibility and the graft-versus-host disease (GVH) with the clinical manifestations, the usual treatments, the supposed cellular mechanisms and the risk factors of developing such complications. The graft versus leukemia effect (GVL) which may be linked to the GVH disease and the mechanisms of rejection and take of the graft are also reviewed as well as the immune reconstitution following the immune deficiency due to the conditioning treatment and the occurrence of a GVH disease.

Characterization of the T cells in aged rat bone marrow

In this study, we determined the characteristics of CD3-positive (CD3+) T cells existing in rat bone marrow (BM). In contrast to splenic T cells, BM CD3+ T cells are composed of a higher proportion of CD8+ T cells, and the number of both cell types increased with age. Such CD3+ T cells in aged rats showed a similar usage of TCR V beta as splenic T cells, suggesting that BM CD3+ T cells are thymus-dependent and composed of an ordinary population in view of the expression of the TCR beta-chain. Purified T cells obtained from aged rat BM showed a markedly proliferative response by stimulation with immobilized anti-CD3 mAb, as did splenic T cells. However, the addition of BM non-T cells completely inhibited the response of both BM and splenic T cells in vitro. These results suggest that T cells in rat BM are negatively regulated by BM non-T cells in their response to the TCR-mediated signal not to disrupt the microenvironment of the BM.

Immunohistological study of distribution of gamma/delta lymphocytes after allogeneic bone marrow transplantation

The distribution of T lymphocytes expressing the gamma/delta form of the T cell receptor was studied in the liver, intestine, and major lymphoid organs, after bone marrow transplantation (BMT), including cases of graft versus host disease (GvHD). The number of gamma/delta as a proportion of the total number of CD3 positive cells did not differ from that found in normal tissues; the higher percentage normally found in the intestinal epithelium and splenic red pulp was maintained. This, and the results of a previous study undertaken on the skin, provide no evidence that gamma/delta T cells have a particularly important role in T cell regeneration after marrow transplantation or in the pathogenesis of the epithelial lesions associated with GvHD.

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.

Transfer of long-lasting tumor immunity by immune T cells from MHC congenic mice: migration, survival and tumor-protectivity of cytotoxic donor cells

Immunocompetent B10.D2 (H-2d) mice are able to reject the highly malignant lymphoma ESb of DBA/2 (H-2d) origin very effectively. Seven days after intravenous injection of the ESb tumor cells, B10.D2 mice developed a strong tumor-rejection response which was associated with the generation of anti-tumor T cells in their spleens with direct cytotoxic activity. Most of the cytotoxic potential was directed against the minor histocompatibility differences as demonstrated by the lysis of unrelated DBA/2 derived Eb tumor cells and normal DBA/2 but no B10.D2 derived ConA lymphoblasts. A previously performed clonal analysis, however, revealed a minority population of CTL clones which specifically recognized the ESb specific transplantation antigen (ESb-TATA). When transferred systemically into DBA/2 mice, the B10.D2 anti-ESb immune spleen cells could delay the outgrowth of s.c. transplanted ESb tumor cells. When the ESb tumor cells were experimentally distributed in a s.c. implanted sponge-matrix, the i.v. injected B10.D2 immune cells could confer complete protective immunity against the metastatic tumor, provided the recipients were pre-treated with 5 Gy to allow a better take of the allogeneic cells. The distribution of intravenously injected B10.D2 donor spleen cells was assessed in the recipients up to 50 days by cytotoxicity testing and assaying for the expression of the beta 2 microglobulin allelic form b (beta 2mb). These tests revealed a high propensity of donor cells to populate the spleen and lymph nodes of the DBA/2 recipients. Again this was particularly marked in sublethally irradiated mice where a long-lasting lymphoid chimerism was established.

Evaluation of in vitro cytotoxic T lymphocyte assays as a predictive test for the occurrence of graft vs host disease

The potential value of in vitro cytotoxic T lymphocyte (CTL) assays for predicting the occurrence of graft vs host disease (GVHD) following allogeneic bone marrow transplantation was evaluated in 12 mouse donor-host combinations associated with various degrees of GVHD. These donor-host combinations were selected after evaluation of GVHD triggered by minor histocompatibility antigens (MiHA) in 24 allogeneic strain combinations derived from six strains of H-2b mice. Recipients (n = 475), previously submitted to total body irradiation (9.5 Gy), were transplanted with 10(7) bone marrow cells along with 5 x 10(7) spleen cells. While lethal GVHD was observed in half of the strain combinations, it was possible to select 12 donor-host combinations characterized by severe, mild, or absent GVHD. When levels of anti-host CTL activity were assessed following in vivo priming and in vitro boosting, strong CTL-mediated cytotoxicity was observed in all combinations whether they developed GVHD or not. CTL frequency measured by limiting dilution analysis (LDA) ranged from 1/16880-1/306. The Spearman rank test revealed no positive correlation between GVHD intensity and donor anti-host CTL activity assayed either in bulk culture experiments or in LDA conditions. These results indicate that MiHA capable of triggering potent CTL responses in vitro do not necessarily initiate GVHD, and that in vitro measurement of donor CTL activity against host-type Con A blasts is not a predictive assay for anti-MiHA GVHD. However, the possibility to recruit CTL populations targeting host MiHA expressed specifically on hematopoietic cells suggests a novel therapeutic strategy for the cure of hematopoietic malignancies. Indeed, transplantation of donor hematopoietic stem cells supplemented with T cells aimed at MiHA specifically expressed by host hematopoietic cells, could possibly potentiate the desirable graft vs leukemia effect without increasing the risk of GVHD.

Cytotoxic folliculitis in GvHD. Evidence of follicular stem cell injury and recovery

Recent observations indicate that stem cells of the murine hair follicle exist exclusively as a subpopulation of relatively undifferentiated outer root sheath cells located in the bulge region at the mid-portion of the follicle. Because it has been hypothesized that stem cells of interfollicular epidermis may represent targets of cytotoxic responses in acute graft-versus-host disease (AGVHD), we studied murine AGVHD and observed sequential skin biopsies for the presence and evolutionary pattern of follicular injury. Highly purified subsets of donor T cells were used to produce AGVHD to multiple minor histocompatibility (H) antigens in two strain combinations of mice matched for the major histocompatibility complex (MHC). In the C3H.SW- greater than B6 strain combination, only CD8+ effector cells produced histologic evidence in skin of AGVHD, which peaked three weeks post-transplant. In the B10.D2- greater than DBA/2 strain combination, CD4+ effector cells, and to a lesser extent, CD8+ cells, mediated disease, which peaked during the fourth week post-transplant. Analysis of skin from both strain/effector cell combinations revealed follicular infiltrates preferentially involving follicular stem cell (FSC) regions (bulge) of anagen follicles between the second and third weeks post-transplant. These infiltrates often preceded infiltration of adjacent interfollicular epidermis and were associated with follicular involution to telogen (resting) phase. By the fourth week post-transplant, greater than 50% of follicles were in telogen phase and residual inflammation was minimal. This provided a unique opportunity to observe follicular recovery from telogen.(ABSTRACT TRUNCATED AT 250 WORDS)

An unusual presentation of chronic graft-versus-host disease in an unrelated bone marrow transplantation

The case described is that of an unrelated bone marrow transplantation in a 43-year-old man. Although the major histocompatibility complex met the criteria for a perfect genotypic match, de novo graft-versus-host disease developed with unusual manifestations involving structures of the oral cavity and associated areas. The loss of taste and smell, as well as profound xerostomia, was treated by stimulating salivary flow. Synergistic sialagogues were used with the hope that an increase in salivary production would mediate an improvement in taste and smell.

Intestinal graft-versus-host disease is initiated by donor T cells distinct from classic cytotoxic T lymphocytes

In these studies, the role of T helper and T cytotoxic cells in generating intestinal graft-vs.-host disease (GVHD) was examined. Treatment of C57BL/6J (B6) splenocytes with L-leucyl-L-leucine methyl ester (Leu-Leu-OMe) selectively removes natural killer cells, cytotoxic T lymphocyte (CTL) precursors, and the capacity to cause lethal GVHD in irradiated B6xDBA/2 F1 (B6D2F1) mice while preserving T helper cell function. Neither control nor Leu-Leu-OMe-treated DBA/2 donor spleen and bone marrow cells were found to induce lethal GVHD in B6D2F1 recipients. However, extensive colonic GVHD developed in B6D2F1 recipients of DBA/2 bone marrow and spleen cells. Enteropathic GVHD in DBA/2----B6D2F1 mice was reduced in severity after anti-L3T4 + C treatment of donor cells, and was eliminated by anti-Thy1.2 + C or the combination of anti-L3T4 and anti-Lyt2 + C treatment of the donor cell inoculum. However, neither anti-Lyt2 + C, Leu-Leu-OMe, nor anti-Lyt2 + C and Leu-Leu-OMe treatment of donor cells significantly decreased severity of gut GVHD. Leu-Leu-OMe treatment of DBA/2 or B6 SpC was comparably effective in preventing in vitro or in vivo generation of B6D2F1-specific CTL. These findings, therefore, demonstrate that histologically severe enteropathic GVHD does not require participation of CTL and is not always associated with high mortality rates.

The mixed epidermal cell lymphocyte-reaction is the most predictive factor of acute graft-versus-host disease in bone marrow graft recipients

Risk factors for acute graft-versus-host disease (GvHD) remain controversial. We performed uni- and multivariate statistical analyses on a series of 37 patients receiving a non-depleted allogeneic bone marrow transplant from an HLA-identical sibling donor for a haematological malignancy, in order to identify risk factors for GvHD. Three factors were associated with development of moderate to severe GvHD: a positive mixed epidermal cell-lymphocyte reaction (MECLR) between donor and recipient, previous pregnancies in female donors and chronic myeloid leukaemia diagnosis. The MECLR was the most important predictive factor, selected in first rank by the stepwise linear discriminant analysis. Combining these three prognostic factors in the jackknifed procedure, we could correctly classify 33/37 patients in two groups: grade O-I versus grade II-IV acute GvHD. These results should apply to donor selection and to predict donor/recipient pairs at high risk of GvHD who might benefit of bone marrow T-cell depletion and those at low risk for whom depletion could be avoided.

Hepatic lesions induced by graft-versus-host reaction across MHC class II antigens: an implication for animal model of primary biliary cirrhosis

To induce graft-versus-host reaction (GVHR), C57B1/6 (B6) spleen cells were injected into (B6 x bm1)F1, (B6 x bm12)F1, and (bm1 x bm12)F1 mice. Since the strains bm1 and bm12 are mutant at the H-2Kb and I-Ab regions of major histocompatibility complex (MHC), respectively, we can assess MHC class I- or class II-different GVHR. As reported earlier, immunological perturbations assessed by the number of immunoglobulin-producing cells and immune complex deposition in renal glomeruli were demonstrated in MHC class II-different GVHR. A conspicuous finding in this report is that epithelioid granuloma formation was observed in the portal area and around the central vein of liver of (B6 x bm12)F1 mice injected with B6 spleen cells. The epithelioid granuloma formation was not observed in (B6 x bm1)F1 nor (bm1 x bm12)F1 recipient mice. Degenerative changes resembling chronic nonsuppurative destructive cholangitis in primary biliary cirrhosis were also observed in the bile duct epithelium in (B6 x bm12)F1 and (bm1 x bm12)F1 mice. These lesions were already obvious at the 2 week postinjection of donor cells and were continuously observed up to 10 weeks when immunological perturbations subsided. Thus, class II-disparate GVHR in this experimental system might provide a novel animal model of protracted disease, primary biliary cirrhosis.

A human complement-fixing monoclonal anti-human lymphocyte antibody of rat origin

MARCH 1E11 is an IgM monoclonal anti-human lymphocyte antibody of rat origin with the capacity to utilise both human and rabbit complement. The antibody reacts with all thymocytes and with all peripheral blood T and B lymphocytes. The treatment of human bone marrow or human peripheral blood mononuclear cells (PBMC) with MARCH 1E11 and either pooled human serum or autologous serum as a complement source resulted in cytolysis of greater than 99% of OKT3-positive lymphocytes. Under these conditions, progenitor cell recovery (colony-forming unit (CFU-c), burst forming unit--erythroid (BFU-e) and colony-forming unit--mixed (CFU-mix)) was greater than 90% of that of untreated cells. The response of treated marrow or PBMC to phytohaemagglutinin stimulation and in mixed leucocyte reactions demonstrated a reduction in thymidine incorporation to values similar to those obtained for unstimulated cells. The antibody does not cause modulation of the cell surface antigen and does not react significantly with non-lymphoid tissues. This monoclonal antibody may be useful for in vitro elimination of T lymphocytes from allogeneic bone marrow used for transplantation. The antibody may also be useful for treatment protocols requiring lymphoid depletion or immunosuppression as in organ transplantation.

Hematopoietic factors in graft-versus-host reaction

Graft-versus-host (GVH) reaction has a curious unsolved area in the immunopathogenesis and pathophysiology of the immunohematopoietic system, and GVH disease remains one of the major obstacles in clinical allogeneic bone marrow transplantation. T lymphocytes and T lymphocyte subpopulations are now recognized to be initiators of this GVH reaction and disease. Also, T lymphocytes are known to be accessory cells in the regulation of hematopoiesis, and produce a variety of lymphokines relevant to hematopoiesis. Admittedly, remarkable hematopoietic changes can be found in GVH reaction, but the cellular mechanisms underlying these changes are so complex they have yet to be fully elucidated. In fact, elevated serum levels of myeloid and erythroid colony-stimulating activities were found in mice suffering from GVH disease in which marked granulopoiesis and suppression of erythropoietic differentiation were seen. In addition, each granulocyte/macrophage colony-stimulating factor (GM-CSF) or burst-promoting activity (BPA) could be detected in sera from patients with GVH disease following allogeneic bone marrow transplantation. There seems to be at least two mechanisms involved in the control of hematopoiesis with either humoral or local environmental factor, probably via the T lymphocytes or T lymphocyte subpopulations activated by alloantigens or autologous non-T cells.

HLA-DP and bone marrow transplantation: DP-incompatibility and severe acute graft versus host disease

Thirteen recipients of HLA-haploidentical, DR compatible bone marrow (BM) and the corresponding BM donors were HLA-DP typed using primed lymphocyte typing (PLT). Severe acute GVHD (greater than or equal to grade 2) developed within 3 months after BM-transplantation in all of eight recipients of DP incompatible BM, but in none of five recipients of DP-compatible BM. This difference was highly significant (p less than 0.001, Fisher's exact test). Moreover, severe acute GVHD was significantly increased in recipients of haploidentical, DR compatible, but DP incompatible BM as compared to severe acute GVHD in 88 recipients of HLA-identical BM (p less than 0.0001). In contrast, there was no difference in acute GVHD between recipients of haploidentical, DR and DP compatible BM and recipients of HLA-identical BM. The data presented here provide strong evidence for the first time that HLA-DP antigens play a role as transplantation antigens.

Monoclonal antibody analysis of skin in chronic murine graft vs host disease produced across minor histocompatibility barriers

Chronic graft vs host disease (GVHD) across minor histocompatibility barriers was produced in BALB/c mice by the injection of spleen cells from B10.D2 mice. Changes in the skin were analyzed in frozen sections using a panel of monoclonal antibodies detected by immunoperoxidase methods. Compared to control animals, a number of changes occurred in the skin of animals with chronic GVHD. In the epidermis, there were increased numbers of Thy-1-positive dendritic cells; keratinocytes expressed Thy-1 and Ia antigens. T lymphocytes appeared in both dermis and epidermis. In the early stages, cells with "helper" and "suppressor" phenotypes were present, while at later times "helper" cells remained in the epidermis and "suppressor" cells remained in the dermis. Cells bearing markers of macrophages were prominent in both dermis and epidermis after the second week. Of great interest was the appearance of spindle-shaped cells in the dermis which expressed Thy-1 and Ia. These cells resembled fibroblasts which may be activated to produce the excess collagen seen in the skin of chronic GVHD.

Depletion of T lymphocytes from human bone marrow by the use of counterflow elutriation centrifugation

Normal donor bone marrow buffy coat (BMBC) cells were fractionated into three subsets by counterflow elutriation centrifugation. Fraction 1 (Fr-1) was lymphocyte-enriched, fraction 2 (Fr-2) was a mixture of lymphocytes and myelomonocytic cells, and fraction 3 (Fr-3) was enriched for myelomonocytic cells. The extent of T cell depletion was determined by limiting dilution analysis of the growth of T cells. The cells in each group were stimulated with phytohemagglutinin and cultured in the presence of interleukin-2. These conditions allowed clonogenic growth of one of three T cells purified from peripheral blood. After a 3-week culture period, replicate wells were scored for growth and precursor frequency was determined. The frequency of T cells in BMBC was 1/22 (n = 4), 1/16 in FR-1 (n = 4), and 1/246 in Fr-2 (n = 2), and in Fr-3 it ranged from 1/3,000 to 1/10,000 (n = 4). For comparison, depletion of T cells from bone marrow by cytofluorographic sorting with OKT-11 and twice E-rosetting yielded 98.1% and 97.4% removal of T cells, respectively. Thus, the clonogenic assay assured that more than 99.3% of the original T cells were depleted by elutriation; however, hematopoietic progenitor assay (CFU-GM, CFU-GEMM, and BFU-E) showed no enrichment in any particular fraction, implying that the progenitors measured in this assay are of diverse sizes. Elutriation represents a useful method for depletion of T cells from human bone marrow. Limiting dilution assay of T cell growth is a sensitive measure to monitor T cell depletion.

Functions of purified L3T4+ and Lyt-2+ cells in vitro and in vivo

The expression of L3T4 and Lyt-2 cell surface molecules separates T cells into two broad, non-overlapping subsets: typical T helper cells are L3T4+ Lyt-2- whereas most T killer cells and their precursors are L3T4- Lyt-2+. This review compares highly purified populations of unprimed L3T4+ and Lyt-2+ cells for their capacity to respond to class I vs. class II H-2 alloantigens. Various parameters are considered, including generation of mixed lymphocyte reactions (MLR) and cell mediated lympholysis (CML) in vitro, proliferative responses in irradiated mice, graft-versus-host reactions and skin allograft rejection. In all of these assays the two T cell subsets exhibit marked specificity in their response to H-2 alloantigens, L3T4+ cells responding only to class II and not class I differences and Lyt-2+ cells showing reciprocal specificity. Contrary to current dogma, the bulk of the evidence suggests that primary responses of Lyt-2+ cells do not depend on exogenous help provided by other T cells.

Correlation between donor cytomegalovirus immunity and chronic graft-versus-host disease after allogeneic bone marrow transplantation

Chronic graft-versus-host disease (GvHD) in bone marrow allograft recipients is frequently preceded by a cytomegalovirus (CMV) infection. To elucidate whether an immune reaction of transplanted donor cells against CMV was involved in the pathogenesis of chronic GvHD, the effect of donor pretransplant CMV immune status on chronic GvHD incidence was analyzed. In 43 bone marrow recipients at risk, the 2-yr cumulative chronic GvHD probability was 55% when the donor was immune, in contrast to 16.5% when the donor was non-immune (p less than 0.002). No correlation between recipient pretransplant CMV immunity and chronic GvHD was observed. Donor CMV immunity did not correlate with acute GvHD or posttranplant CMV infection and seemed to predispose for chronic GvHD regardless of donor and recipient age. However, the proportion of CMV immune donors increased with increasing donor and recipient age. This may account for the higher incidence of chronic GvHD in older patients. The present study suggests that chronic GvHD may be mediated by a reaction of immune donor cells against CMV infected recipient cells.

Cutaneous acute graft-versus-host disease to minor histocompatibility antigens in a murine model: histologic analysis and correlation to clinical disease

Graft-versus-host disease (GVHD) can occur in bone marrow-transplant recipients even when donor and host are identically matched at the major histocompatibility complex. GVHD in this context presumably arises because of differences in minor histocompatibility antigens. Murine GVHD to minor histocompatibility antigens has been studied in an effort to determine whether skin is a target of the immune response in this model system. T cell-depleted marrow cells (10(7)) from B10.BR (H-2k) mice were supplemented with varying numbers of nylon wool-enriched splenic B10.BR T cells and transplanted intravenously into irradiated (1100 R) CBA (H-2k) mice. Sequential biopsies of ear skin were obtained at weekly intervals over a 7-week period. Histopathologic evaluation revealed basal cell layer vacuolization, exocytosis, and satellitosis of mononuclear cells in the epidermis. Dyskeratosis was observed only in animals receiving T cells, and proved to be the most reliable histologic parameter of disease with the number of dyskeratotic cells per linear millimeter of epidermis correlating both with severity of clinical disease and with the number of transplanted T cells. Ultrastructural examination revealed exocytosis of mononuclear cells into the epidermis where they were frequently apposed to degenerating and necrotic keratinocytes. These data indicate that the skin is an informative target organ for study of experimental GVHD to minor histocompatibility antigens.

Isolation of two early B lymphocyte progenitors from mouse marrow: a committed pre-pre-B cell and a clonogenic Thy-1-lo hematopoietic stem cell

Two novel early B lymphocyte precursor populations have been identified by their capacity to differentiate in Whitlock-Witte bone marrow cultures. Cells expressing neither the B lineage antigen B220 nor Thy-1 contain committed B cell precursors which differentiate in short-term culture into pre-B and B cells. The other population expresses low levels of Thy-1, and lacks B220 as well as the T cell markers L3T4 and Lyt-2. The Thy-1+ cells which initiate long-term B cell cultures contain clonogenic B cell precursors at a frequency of 1 in 11, a 100-fold enrichment over unseparated bone marrow. Thy-1+ cells are also highly enriched for myeloid-erythroid precursors (CFU-S). Thy-1+ cells allow long-term survival of lethally irradiated mice and fully reconstitute the hematopoietic system, including T and B lymphocyte compartments. These results indicate that this population (approximately 0.1% of bone marrow) may contain the pluripotent hematopoietic stem cell.