Donor Hemopoietic Cells Research Articles

Stable engraftment, as well as graft versus host disease-free and relapse-free survival brought by the combination of CD7 targeted universal chimeric antigen receptor-T, and donor hemopoietic stem cells: Indication of a case report.

CD7 targeted CAR-T has demonstrated potential in the treatment of T cell malignancies but no study has been reported about its potential in the prophylaxis of GVHD in allo-HSCT. Here we reported a special case that a boy diagnosed with refractory acute T lymphoblastic leukemia (T-ALL) was treated with universal CD7 targeted CAR-T (CD7 UCAR-T) and parent-derived peripheral blood stem cells (PBSCs). Complete remission and full engraftment of donor was observed. In the later four months of follow-up, in the absence of any immunodepression treatment, no signs of GVHD were observed. This case initially demonstrates the potential of CD7 UCAR-T in the prophylaxis of GVHD.

Good Engraftment but Quality and Donor Concerns for Cryopreserved Hemopoietic Progenitor Cell Products Collected During the COVID-19 Pandemic

Changes to donor availability, collection center capacity, and travel restrictions during the early phase of the COVID-19 pandemic led to routine cryopreservation of most unrelated donor products for hematopoietic transplantation prior to the recipient commencing the conditioning regimen. We investigated the effect of this change on unrelated donor product quality and clinical outcomes. Product information was requested from transplantation centers in Australia and New Zealand and clinical outcome data from the Australasian Bone Marrow Transplant Recipient Registry (ABMTRR). In total, 191 products were collected between April 1, 2021, and September 30, 2021, and most (74%) were from international collection centers. Median post-thaw CD34 recovery was 78% (range 25% to 176%) and median post-thaw CD34 viability was 87% (range 34% to 112%). Median time to neutrophil recovery was 17 days (interquartile range 10 to 24 days), and graft failure occurred in 6 patients (4%). These clinical outcomes were similar to those of “fresh” unrelated donor transplants reported to the ABMTRR in 2019. However, recipient transplantation centers reported problems with 29% of products in the form of damage during transit, low cell dose, inadequate labeling, missing representative samples, or missing documentation. These problems were critical in 7 cases (4%). At last follow-up, 22 products (12%) had not been infused. Routine cryopreservation of unrelated donor hemopoietic progenitor cell products has enabled safe continuation of allogeneic transplant services during the COVID-19 pandemic. However, practices for product tracing, documentation, and transportation can be optimized, and measures to reduce the incidence of unused unrelated donor product are required.

Variable CD34+ recovery of cryopreserved allogeneic HPC products: transplant implications during the COVID-19 pandemic

AbstractDonor registries and transplantation societies recommend cryopreservation of unrelated donor hemopoietic progenitor cell (HPC) products before the recipient commences conditioning therapy to mitigate the donor and travel risks associated with the COVID-19 pandemic. However, little is known regarding the postthaw quality of such allogeneic products or the effect of precryopreservation storage and processing on these characteristics. We investigated the postthaw CD34+ cell recovery and viability of 305 allogeneic HPC products cryopreserved at 9 laboratories across Australia. Median postthaw CD34+ cell recovery was 76% and ranged from 6% to 122%. Longer transit time before cryopreservation, white cell count (WCC) during storage, and complex product manipulation before cryopreservation were independently associated with inferior postthaw CD34+ cell recovery. Longer precryopreservation transit time and WCC were also associated with inferior postthaw CD34+ cell viability. We conclude that although postthaw CD34+ cell recovery and viability of cryopreserved allogeneic HPC is generally acceptable, there is a significant risk of poor postthaw product quality, associated with prolonged storage time, higher WCC, and complex product manipulation precryopreservation. Awareness of expected postthaw recovery and practices that influence it will assist collection, processing, and transplant centers in optimizing outcomes for transplant recipients.

Hemopoiesis Regulated Negatively In Aged Monkeys

Biological aging is associated with a progressive loss of regulation of cellular, tissue and organ interaction, ultimately resulting in senescence. In humans, accelerated marrow adipogenesis has been associated with aging and several chronic conditions, including diabetes mellitus and osteoporosis. Studies of the hemopoietic system using nonhuman primates have provided important information for understanding the mechanism of human hemopoiesis. Excellent reconstitution of donor hemopoietic cells in a collagen gel group has been observed in the long term in mice. We therefore investigated whether the method would be helpful for reconstituting hemopoiesis in the fatty tibias of monkeys. Nine- to 11-year-old monkeys were used for this study to examine if hemopoiesis could be restored in the fatty marrow of old monkeys. Bone marrow cells were collected from the humerus using the perfusion method, mixed with cultured bone marrow stroma cells in collagen gel, and then injected into the tibia of the same monkey. Clot sections were made from the tibias 1, 2 and 6 weeks after the bone marrow transplantation. However, no bone marrow cells were observed at any of the time points. These results suggested that adipocytes negatively regulate bone marrow reconstitution. Disclosures: No relevant conflicts of interest to declare.

Combination of Intra-Bone Marrow–Bone Marrow Transplantation and Subcutaneous Donor Splenocyte Injection Diminishes Risk of Graft-Versus-Host Disease and Enhances Survival Rate

The combination of allogeneic bone marrow transplantation (allo-BMT) and donor lymphocyte infusion (DLI) is a useful method for establishing donor chimerism and preventing a relapse of leukemia/lymphoma. However, there is a risk of inducing uncontrollable fatal graft-versus-host disease (GVHD). In fact, allo-BMT plus intravenous (IV)-DLI using donor splenocytes induces fatal GVHD in recipient mice. In this study, we examined the effects of the combination of intra-bone marrow (IBM)-BMT and the subcutaneous injection of donor splenocytes (SC-DLI) on the allo-BMT system. Recipient BALB/c mice were conditioned by sublethal irradiation (5 Gy), followed by IBM-BMT plus IV-DLI or SC-DLI in C57BL/6 mice. The IV-DLI group showed better engraftment of donor hemopoietic cells than the control group (without DLI) but showed fatal GVHD. The SC-DLI group, however, showed good reconstitution and mild GVHD. These results suggest that the combination of SC-DLI and IBM-BMT promotes the reconstitution of hemopoiesis and helps reduce the risk of GVHD.

A New Bone Marrow Transplantation Method for Stem Cell Disorders

Using animal models for autoimmune diseases, we have previously shown that allogeneic bone marrow transplantation (BMT) can be used to treat autoimmune diseases and that autoimmune diseases are hemopoietic stem cell (HSC) disorders. We have recently developed a new BMT method. The method consists of a perfusion method (PM) plus intrabone marrow (IBM)-BMT. The PM, in comparison with conventional aspiration, can minimize the contamination of BMCs with T cells from peripheral blood, and consequently no graft-versus-host disease develops. Because bone marrow cells collected by the PM contain not only HSCs but also mesenchymal stem cells (MSCs), the injection of both cells directly into the bone marrow cavity facilitates the engraftment of donor hemopoietic cells. Using this new method, we show that most age-associated diseases, such as osteoporosis and emphysema, are MSC disorders and, on the basis of this evidence, propose a new concept of stem cell disorders, including HSC and MSC disorders. We believe that the advent of IBM-BMT and our proposed concept herald a revolution in the field of transplantation (BMT and organ transplantation) and regeneration medicine.

Intra-Bone Marrow Injection of Donor Bone Marrow Cells Suspended in Collagen Gel Retains Injected Cells in Bone Marrow, Resulting in Rapid Hemopoietic Recovery in Mice

We have recently developed an innovative bone marrow transplantation (BMT) method, intra-bone marrow (IBM)-BMT, in which donor bone marrow cells (BMCs) are injected directly into the recipient bone marrow (BM), resulting in the rapid recovery of donor hemopoiesis and permitting a reduction in radiation doses as a pretreatment for BMT. However, even with this IBM injection, some of the injected BMCs were found to enter into circulation. Therefore, we attempted to modify the method to allow the efficient retention of injected BMCs in the donor BM. The BMCs of enhanced green fluorescent protein transgenic mice (C57BL/6 background) were suspended in collagen gel (CG) or phosphate-buffered saline (PBS), and these cells were then injected into the BM of irradiated C57BL/6 mice. The numbers of retained donor cells in the injected BM, the day 12 colony-forming units of spleen (CFU-S) counts, and the reconstitution of donor cells after IBM-BMT were compared between the CG and PBS groups. The number of transplanted cells detected in the injected BM in the CG group was significantly higher than that in the PBS group. We next carried out CFU-S assays. The spleens of mice in the CG group showed heavier spleen weight and considerably higher CFU-S counts than in the PBS group. Excellent reconstitution of donor hemopoietic cells in the CG group was observed in the long term (>100 days). These results suggest that the IBM injection of BMCs suspended in CG is superior to the injection of BMCs suspended in PBS.

Stem cell transplantation for autoimmune diseases: What can we learn from experimental models?

Using animal models for autoimmune diseases, we have previously shown that allogeneic bone marrow transplantation (allo BMT) can be used to treat autoimmune diseases. Using cynomolgus monkeys, we have recently developed new BMT methods for the treatment of autoimmune diseases. The methods include the perfusion method (PM) for the collection of bone marrow cells (BMCs), and intra-bone marrow (IBM)-BMT for the direct injection of collected whole BMCs into the bone marrow cavity. The PM, in comparison with the conventional aspiration method, can minimize the contamination of BMCs with T cells from the peripheral blood. Therefore, without removing T cells, no graft-versus-host disease (GvHD) develops in the case of the PM. Since BMCs collected by the PM contain not only hemopoietic stem cells (HSCs) but also mesenchymal stem cells (MSCs), the injection of both cells directly into the bone marrow cavity (IBM–BMT) facilitates the engraftment of donor hemopoietic cells. In organ allografts with IBM–BMT, no graft failure occurs even if the radiation dose is reduced. In addition, IBM–BMT is applicable to regeneration therapy and various age-associated diseases such as osteoporosis, since it can efficiently recruit donor-derived normal MSCs.We have also found that IBM–BMT in conjunction with donor lymphocyte infusion can prevent GvHD, but suppress tumor growth. We believe that this strategy heralds a revolution in the field of transplantation (BMT and organ allografts) and regeneration therapy.

CD4+ T Cells Generated De Novo from Donor Hemopoietic Stem Cells Mediate the Evolution from Acute to Chronic Graft-versus-Host Disease

Acute and chronic graft-versus-host disease (GVHD) remain the major complications limiting the efficacy of allogeneic hemopoietic stem cell transplantation. Chronic GVHD can evolve from acute GVHD, or in some cases may overlap with acute GVHD, but how acute GVHD evolves to chronic GVHD is unknown. In this study, in a classical CD8+ T cell-dependent mouse model, we found that pathogenic donor CD4+ T cells developed from engrafted hemopoietic stem cells (HSCs) in C57BL/6SJL(B6/SJL, H-2(b)) mice suffering from acute GVHD after receiving donor CD8+ T cells and HSCs from C3H.SW mice (H-2(b)). These CD4+ T cells were activated, infiltrated into GVHD target tissues, and produced high levels of IFN-gamma. These in vivo-generated CD4+ T cells caused lesions characteristic of chronic GVHD when adoptively transferred into secondary allogeneic recipients and also caused GVHD when administered into autologous C3H.SW recipients. The in vivo generation of pathogenic CD4+ T cells from engrafted donor HSCs was thymopoiesis dependent. Keratinocyte growth factor treatment improved the reconstitution of recipient thymic dendritic cells in CD8+ T cell-repleted allogeneic hemopoietic stem cell transplantation and prevented the development of pathogenic donor CD4+ T cells. These results suggest that de novo-generated donor CD4+ T cells, arising during acute graft-versus-host reactions, are key contributors to the evolution from acute to chronic GVHD. Preventing or limiting thymic damage may directly ameliorate chronic GVHD.

Innovative BMT methods for intractable diseases

We have recently established new bone marrow transplantation (BMT) methods for the treatment of intractable diseases. The methods include the perfusion method (PM) for the collection of bone marrow cells, and intra-bone marrow (IBM)-BMT for the direct injection of collected whole bone marrow cells into the bone marrow cavity. The PM, in comparison with the conventional aspiration method, can minimize the contamination of bone marrow cells (BMCs) with T cells from the peripheral blood. Therefore, without removing T cells, no graft-versus-host disease (GvHD) develops in the case of the PM. Since BMCs collected by the PM contain not only hemopoietic stem cells (HSCs) but also mesenchymal stem cells (MSCs), the injection of both cells directly into the bone marrow cavity (IBM-BMT) facilitates the engraftment of donor hemopoietic cells. In organ allografts with IBM-BMT, no graft failure occurs even if the radiation dose is reduced. In addition, IBM-BMT is applicable to regeneration therapy and various age-associated diseases such as osteoporosis, since it can efficiently recruit donor-derived normal MSCs. Finally, we show that IBM-BMT in conjunction with donor lymphocyte infusion (DLI) can prevent GvHD but suppress tumor growth. We believe that this strategy heralds a revolution in the field of transplantation (BMT and organ allografts) and regeneration therapy.

Intra-bone Marrow-Bone Marrow Transplantation: A New Strategy for Treatment of Stem Cell Disorders

We have established new bone marrow transplantation (BMT) methods for the treatment of stem cell disorders such as autoimmune diseases. The methods include the perfusion method (PM) and intra-bone marrow (IBM)-BMT. PM, in comparison with the conventional aspiration method, can minimize the contamination of bone marrow cells (BMCs) with T cells from the peripheral blood. Therefore, without removing T cells, no graft-versus-host disease develops in the case of PM. Because BMCs collected using the PM contain not only hemopoietic stem cells (HSCs) but also mesenchymal stem cells (MSCs), the injection of both cells directly into the bone marrow cavity (IBM-BMT) facilitates the engraftment of donor hemopoietic cells. With IBM-BMT, no graft failure therefore occurs even if the radiation dose is reduced. IBM-BMT is applicable to regeneration therapy and various age-associated diseases such as osteoporosis, because it can efficiently recruit donor-derived normal MSCs into the bone marrow. We believe that this strategy heralds a revolution in the field of transplantation and regenerative therapy.

A two-step model of acute CD4 T-cell mediated cardiac allograft rejection.

CD4 T cells are both necessary and sufficient to mediate acute cardiac allograft rejection in mice. This process requires "direct" engagement of donor MHC class II molecules. That is, acute rejection by CD4+ T cells requires target MHC class II expression by the donor and not by the host. However, it is unclear whether CD4+ T cell rejection requires MHC class II expression on donor hemopoietic cells, nonhemopoietic cells, or both. To address this issue, bone marrow transplantation in mice was used to generate chimeric heart donors in which MHC class II was expressed either on somatic or on hemopoietic cells. We report that direct recognition of hemopoietic and nonhemopoietic cells are individually rate limiting for CD4+ T cell-mediated rejection in vivo. Importantly, active immunization with MHC class II(+) APCs triggered acute rejection of hearts expressing MHC class II only on the somatic compartment. Thus, donor somatic cells, including endothelial cells, are not sufficient to initiate acute rejection; but they are necessary as targets of direct alloreactive CD4 T cells. Taken together, results support a two-stage model in which donor passenger leukocytes are required to activate the CD4 response while direct interaction with the somatic compartment is necessary for the efferent phase of acute graft rejection.

Production of donor T cells is critical for induction of donor-specific tolerance and maintenance of chimerism.

Nonmyeloablative conditioning has significantly reduced the morbidity associated with bone marrow transplantation. The donor hemopoietic cell lineage(s) responsible for the induction and maintenance of tolerance in nonmyeloablatively conditioned recipients is not defined. In the present studies we evaluated which hemopoietic stem cell-derived components are critical to the induction of tolerance in a total body irradiation-based model. Recipient B10 mice were pretreated with mAbs and transplanted with allogeneic B10.BR bone marrow after conditioning with 100-300 cGy total body irradiation. The proportion of recipients engrafting increased in a dose-dependent fashion. All chimeric recipients exhibited multilineage donor cell production. However, induction of tolerance correlated strictly with early production of donor T cells. The chimeras without donor T cells rejected donor skin grafts and demonstrated strong antidonor reactivity in vitro, while possessing high levels of donor chimerism. These animals lost chimerism within 8 mo. Differentiation into T cells was aborted at a prethymic stage in recipients that did not produce donor T cells. Moreover, donor Ag-driven clonal deletion of recipient T cells occurred only in chimeras with donor T cells. These results demonstrate that donor T cell production is critical in the induction of transplantation tolerance and the maintenance of durable chimerism. In addition, donor T cell production directly correlates with the deletion of potentially alloreactive cells.

Quantification of donor and recipient hemopoietic cells by real-time PCR of single nucleotide polymorphisms.

Analysis of changes in recipient and donor hemopoietic cell origin is extremely useful to monitor the effect of stem cell transplantation (SCT) and sequential adoptive immunotherapy by donor lymphocyte infusions (DLI). We developed a sensitive and accurate method to quantify the percentage of recipient and donor cells by real-time PCR using single nucleotide polymorphisms (SNPs) as markers. Allele-specific PCR of seven SNPs resulted in specific markers for donor or recipient in 97% of HLA-identical sibling pairs. Both, recipient- and donor-derived hemopoietic cells can be simultaneously analyzed in 67% sibling pairs. We expect this can be increased to approximately 99% by developing three additional SNP-PCR. Serial dilution of SNP-positive DNA into either SNP-negative DNA or water revealed a detection limit of 0.1-0.01% depending on the amount of input DNA and start C(t) of the used SNP-PCR. Application of our real-time SNP-PCR method for a CML patient treated by allogeneic SCT and DLI demonstrated its feasibility to follow donor T-cell chimerism and early detection of residual and recurrent autologous hemopoiesis in response to treatment. This detailed monitoring of the genetic origin of hemopoietic cells, in particular immune effector cells and target cells after SCT and DLI, may substantially contribute to understanding of the mechanisms that play a role in the success of treatment.

Promotion of skin graft tolerance across MHC barriers by mobilization of dendritic cells in donor hemopoietic cell infusions.

Flt3 ligand (FL) dramatically increases the number of immunostimulatory dendritic cells (DC) and their precursors in bone marrow (BM) and secondary lymphoid tissues. Herein we tested the ability of FL-mobilized donor hemopoietic cells to promote induction of skin graft tolerance across full MHC barriers. C57BL/10 (B10; H2(b), IE(-)) mice were given 10(8) spleen cells (SC) from normal or FL-treated, H-2-mismatched B10.D2 (H2(d), IE(+)) donors i.v. on day 0, 200 mg/kg i.p. cyclophosphamide on day 2, and 10(7) T cell-depleted BM cells from B10.D2 mice on day 3. B10.D2 skin grafting was performed on day 14. Indefinite allograft survival (100 days) was induced in recipients of FL-SC, but not in mice given normal SC. Tolerance was associated with blood macrochimerism and was confirmed by second-set skin grafting with donor skin 100 days after the first graft. In tolerant mice, peripheral donor-reactive T cells expressing TCR Vbeta11 were deleted selectively. Immunocompetence of tolerant FL-SC-treated mice was proven by rapid rejection of third-party skin grafts. To our knowledge this is the first report that mobilization of DC in donor cell infusions can be used to induce skin graft tolerance across MHC barriers, accompanied by specific deletion of donor-reactive T cells.

Successful allogeneic bone marrow transplantation (BMT) by injection of bone marrow cells via portal vein: stromal cells as BMT-facilitating cells.

We examined the importance of the coadministration of bone marrow (BM) stromal cells with BM cells via the portal vein. A significant increase in the number of day-14 colony-forming unit-spleen (CFU-S) was observed in the recipient mice injected with hemopoietic stem cells (HSCs) along with donor BM stromal cells obtained after three to four weeks of culture. Histological examination revealed that hematopoietic colonies composed of both donor hemopoietic cells and stromal cells coexist in the liver of these mice. However, when donor HSCs plus BM stromal cells were administered i.v., neither the stimulatory effects on CFU-S formation nor the hemopoietic colonies in the recipient liver were observed. These findings suggest that the interaction of HSCs with stromal cells in the liver is the first crucial step for successful engraftment of allogeneic HSCs. It is likely that donor stromal cells and HSCs trapped in the liver migrate into the recipient BM and spleen, where they form CFU-BM and CFU-S, respectively.

Extending the role of allogeneic stem-cell transplantion

Allogeneic bone-marrow transplantation (allo-BMT) permits the administration of high-dose chemotherapy and radiotherapy for tumour eradication. When followed by infusion of normal donor haemopoietic cells and posttransplant immunosuppression to prevent graft rejection, allo-BMT is curative for a wide variety of haematological cancers, including acute and chronic myeloid leukaemia (CML). The success of allo-BMT is not entirely dependent on the administration of myeloablative pretransplant conditioning therapy to eliminate residual tumour cells and allow engraftment.

Alternative donor transplants for patients with advanced hematologic malignancies, conditioned with thiotepa, cyclophosphamide and antithymocyte globulin.

Preparative regimens without total body irradiation (TBI) have been reported for alternative donor hemopoietic stem cell transplants (HSCT). Between 7 September 1994 and 7 June 1999 48 patients with advanced hematologic malignancies were conditioned with thiotepa (THIO) 15 mg/kg, cyclophosphamide (CY) 150 mg/kg and antithymocyte globulin (ATG). Donors were HLA mismatched family members (1-2 antigens) (FAM) (n = 24, median age 31 years) or HLA matched unrelated donors (UD) (n = 24, median age 34 years). GVHD prophylaxis was cyclosporine and methotrexate. Stem cell source was peripheral blood (n = 8) or bone marrow (n = 40). Hematologic recovery was seen in 42/46 (91%) evaluable patients and complete chimerism in 31/37 patients (85%). Acute GVHD grades III-IV were seen in 10/46 patients surviving 10 days (21%) and extensive chronic GVHD in 2/36 patients surviving 100 days (5%). Twenty-six patients died (54%), eight of recurrent disease (17%) and 18 of transplant-related complications (37%): main causes of TRM were GVHD (15%), infections (15%) and graft failure (4%). Twenty-two patients (46%) survive with a median follow-up of 877 days (287-1840). The actuarial 3-year survival is 49% for FAM and 42% for UD transplants. Results obtained with this regimen in unrelated grafts for advanced CML (n = 15) were not significantly different when compared to 21 concurrent UD grafts for advanced CML prepared with CY-TBI. In conclusion, the combination of THIO-CY-ATG allows engraftment of alternative donor hemopoietic stem cells. Results are similar when using unrelated matched donors or partially mismatched family donors, and not significantly different when compared to patients conditioned with CY-TBI.

Successful allogeneic bmt by injection of bmcs from portal vein

Abstract Our serial studies of BMT through the intravenous (IV) route have demonstrated that successful allogeneic BMT (allo-BMT) can be achieved if donor bones (to recruit bone marrow stromal cells: BMSCs) are cografted with bone marrow cells even in chimerism-resistant combinations, such as [DBA/2→B6] (Exp. Hematol. 23:347, 1995) and [Normal MRL/lpr mice (J. Immunol. 152:3119,1994). Donor-type BMSCs were found in the host bone marrow and thymus. We have also found that MHC restriction exists between hemopoietic stem cells (HSCs) and BMSCs (Blood 89:49,1997). Here, we report on the importance of cografting BMSCs in allo-BMT via the portal vein (PV) route. A significant increase in the number of day 14-CFU-S was observed in the recipient mice portal venously injected with both HSCs and donor BMSCs cultured for 3–4 wks. Histological examination revealed that hematopoietic colonies composed of both donor hemopoietic cells and BMSCs co-exist in the recipient liver. Both survival and hemopoietic reconstitution in [DBA/2→B6] mice were also enhanced when injected via the PV but not IV. We have previously reported that HSCs trapped in the liver after injecting BMCs via the PV can induce clonal anergy of CD8 + T cells. In the present study, we have found that donor BMSCs trapped in the recipient liver support the hemopoietic colony formation of donor HSCs. The BMSCs also seem to protect the HSCs from the attack of radioresistant host M∅, T cells and NK cells. As a result, CFU-S formation markedly increases, and a higher survival rate can ultimately be achieved. Thus, MHC-compatible BMSCs can contribute greatly to successful allo-BMT.

T Cells Specific for a Polymorphic Segment of CD45 Induce Graft-Versus-Host Disease with Predominant Pulmonary Vasculitis

To study the character of graft-vs-host disease (GVHD) induced by T cells specific for hemopoietic cells, T cells specific for a polymorphic segment of CD45 were transferred into CD45 congenic mice. C57BL/6 mice that express the CD45b allele were immunized with a 13 mer peptide representing the polymorphic segment (p257-268) of CD45a protein. Conversely, C57BL/6 mice congenic for CD45a were immunized with the CD45b peptide. CD4+ T cells specific for allelic CD45 peptides were elicited. Importantly, T cells specific for CD45 peptides proliferated specifically and vigorously in response to spleen cells expressing the appropriate polymorphic CD45 protein. T cells specific for CD45 induced a substantial graft-vs-host response (GVHR) with predominant early pulmonary vasculitis and later more widespread interstitial mononuclear cell infiltration and alveolitis. No GVHR was induced in bone marrow chimeras expressing only donor hemopoietic cells. Thus, donor T cell recognition of host hemopoietic cells is sufficient to elicit GVHR, but the classical skin, liver, and gut manifestations of GVHD were not observed. The CD45-specific T cells used secreted Th1 cytokines, but without detectable soluble IL-2. Studies using CD45-specific T cells with different effector functions might allow further dissection of donor cell requirements for GVHD syndromes.