Separation of graft-vs.-tumor effects from graft-vs.-host disease in allogeneic hematopoietic cell transplantation

Allogeneic hematopoietic cell transplantation (HCT) is an increasingly widely used treatment modality in hematological malignancies. Alloreactivity mediated by donor T cells (and, in some settings, by donor natural killer cells) can produce durable immunologic control or eradication of residual malignancy after allogeneic HCT. However, graft-vs.-tumor (GVT) effects are variably effective and are often accompanied by deleterious alloreactivity against normal host tissue, manifesting as graft-vs.-host disease (GVHD). A major focus of current research in HCT is the separation of beneficial GVT effects from GVHD. Here we review a number of approaches currently under investigation to specifically augment GVT effects, including the identification of minor histocompatibility antigens (mHA), adoptive immunotherapy with tumor-specific or mHA-specific cytotoxic T lymphocytes, vaccination of the donor or recipient to stimulate tumor-specific immunity, and adoptive transfer of natural killer cells. In addition, we review strategies being investigated to specifically suppress GVHD while sparing GVT, including the manipulation and infusion of regulatory T cells, the use of novel pharmacologic and biologic agents, and the use of mesenchymal stem cells. Ultimately, advances in separation of GVT from GVHD will further enhance the potential of allogeneic HCT as a curative treatment for hematological malignancies.     

Pathophysiologic mechanisms of acute graft-vs.-host disease.

Graft-vs.-host disease (GVHD) remains the major toxicity of allogeneic bone marrow transplantation. Mechanistic studies in experimental animal models provide a better understanding of the complex relationships and cascade of events mediated by cellular and inflammatory factors. Also, advances in basic immunology have cleared the way for a more precise view of allogeneic reactions between donor and host. In addition, the use of mutant mice lacking critical cytolytic proteins has helped map out the molecular pathways by which GVHD targets organ damage. In this article, these mechanisms are reviewed and synthesized into a coherent conceptual framework, providing a state-of-the-art summary of the pathophysiology of acute GVHD.     

Improved survival from potentially lethal graft-vs.-host disease by donor pretreatment with a recipient-specific blood transfusion. I. Requirements for induction and specificity of the effect.

Pretreatment of prospective donors of hemopoietic cells with a single recipient-specific blood transfusion can significantly decrease the morbidity and mortality of graft-vs.-host disease (GVHD) in lethally irradiated, allogeneically reconstituted mice. This beneficial effect of donor pretreatment could be demonstrated in donor-recipient strain combinations that were H-2 + non-H-2, H-2, or only class II-disparate, but not in the class I-disparate C57BL-B6.C-H-2bm1 strain combination. The effect was proportional to the amount of recipient-strain blood used for transfusion. Donor transfusion with a single dose of 1 ml recipient-specific whole blood resulted in minimum GVHD, lower doses being less or not effective. The interval between donor pretreatment and the use of their hemopoietic cells for reconstitution appeared to be important. The best survival was found at an interval of 4 days. Multiple transfusion was not more effective than a single one. We compared the effectiveness of whole blood and irradiated spleen cells for donor pretreatment. Both protocols have been shown previously to suppress anti-recipient delayed-type hypersensitivity. It appeared that the blood transfusion protocol was superior to the spleen cell protocol. The beneficial effect appeared to be recipient specific, since a third-party blood transfusion did not improve GVHD. We found that the beneficial effect of donor blood transfusion was due to suppression of the anti-host immune response. The donor blood transfusion was able to induce bystander suppression to alloantigens that were not used for the induction of suppression, provided they were co-expressed with the specific alloantigens by the recipients. This also indicates that, although the induction of suppression is specific, the ultimate suppressive effect is non-specific.     

Improved survival from potentially lethal graft-vs.-host disease by donor pretreatment with a recipient-specific blood transfusion. II. Evidence for a principal role of the CD4+ T cell subset

Pretreatment of prospective donors of hemopoietic cells with a single recipient-specific blood transfusion can significantly decrease the morbidity and mortality of potentially lethal graft-vs.-host disease (GVHD) in lethally irradiated, allogeneically reconstituted mice. In a previous report we described the requirements for induction of this blood transfusion effect. In the present study we addressed in particular the mechanism underlying this effect. The beneficial effect of blood transfusion appeared to be due to the white blood cell population in the transfused blood. X-irradiation (20 Gy) of the blood prior to transfusion did not abrogate the effect, which makes a veto cell mechanism unlikely. The blood transfusion effect in this model appeared to be mediated by the CD4⁺ T cell subset, since purified CD4⁺ spleen cells from transfused donors caused considerably less morbidity and mortality than naive CD4⁺ spleen cells. Apparently CD8⁺ cells were not involved, because their absence did not affect the beneficial effect. This observation was further confirmed by the finding that treatment of recipient mice that were reconstituted with spleen cells from transfused donors with anti-CD8 monoclonal antibody (mAb) did not abrogate the blood transfusion effect. Interestingly, the blood transfusion effect was enhanced by administration of anti-CD4 mAb to the recipients. The anti-CD4 mAb might impair the interaction between T cells and antigen-presenting cells, resulting in functional inactivation.     

Prevention of lethal graft-vs.-host disease by a single low dose injection of anti-T cell monoclonal antibody to the allograft recipients.

We investigated the capacity of monoclonal antibody (mAb) treatment to prevent graft-vs.-host disease (GVHD) in lethally irradiated, allogeneically reconstituted mice, employing anti-T cell (subset) mAb and a fully allogeneic strain combination. In this strain combination, purified CD4+ cells were able to induce a lethal GVH reaction, whereas purified CD8+ cells were not. In the same strain combination, a single intraperitoneal injection of IgG2b anti-Thy-1 mAb, one day after reconstitution, caused a dose-dependent improvement of the survival. A single injection of a dose as low as 12.5 micrograms per mouse was already effective. Intravenous and intraperitoneal administration of the mAb appeared equally effective. For effective prevention of GVHD the treatment could be postponed until the 4th day after transplantation, but treatment delayed until day 6 was no longer effective. Treatment with IgG2b mAb specific for either helper or cytotoxic T cells also led to improvement of GVHD and survival, but was less effective than treatment with anti-Thy-1 mAb. Clinically, there was a difference in the effectiveness of anti-CD4 and anti-CD8 treatment, since symptoms of GVHD started earlier in the anti-CD8 treated group and the survival was better in the anti-CD4 treated group. These results press for prospective clinical studies employing anti-T cell mAb treatment early after allogeneic bone marrow transplantation, especially in HLA mismatched cases.     

Graft-facilitating doses of ex vivo activated gammadelta T cells do not cause lethal murine graft-vs.-host disease.

The purpose of this study was to examine the ability of gamma(delta) T cells to cause graft-vs.-host disease (GVHD) after allogeneic bone marrow transplantation (BMT) and to determine whether these cells offered any therapeutic advantages relative to alphabeta T cells. Due to the paucity of naive gamma(delta) T cells in mice and humans, gamma(delta), T cells (obtained from alpha(beta) T cell-deficient murine donors) were ex vivo activated and expanded in interleukin (IL)-2 so as to achieve sufficient cell numbers and to serve as a more clinically feasible strategy. After transplantation into lethally irradiated hosts, donor gamma(delta) T cells were detected in target organs of GVHD such as the spleen and intestines 2 weeks after BMT and constituted the primary T cell subpopulation. Large doses (150 x 10(6)) of activated gamma(delta) T cells, which we have previously shown capable of facilitating engraftment in MHC-disparate recipients, failed to cause fatal GVHD in lethally irradiated recipients of MHC-incompatible donor marrow grafts (C57BL/6 [H-2b]-->B10.BR [H-2k] and C57BL/6 [H-2b]-B6D2F1[H-2b/d]). The absence of GVHD was confirmed by histologic analysis of target organs, splenic B cell reconstitution, and appropriate negative selection in the thymus, that were all comparable to those observed in mice transplanted with T cell-depleted BM only. While early splenic reconstitution was attributable to donor gamma(delta) T cells, analysis of durably engrafted chimeras 2 months posttransplant revealed that the vast majority of donor splenic T cells expressed the alpha(beta) T cell receptor. The results of secondary adoptive transfer assays showed that these cells were tolerant of recipient alloantigens in vivo, demonstrating that gamma(delta) T cells did not prevent the subsequent development of donor anti-host tolerance in BM-derived alpha(beta) T cells. When comparatively evaluated, the minimal number of naive alpha(beta) T cells necessary for donor engraftment caused significantly more fatal GVHD than the corresponding minimal dose of activated gamma(delta) T cells and thus had a superior therapeutic index. These studies indicate that doses of activated gamma(delta) T cells that are able to promote alloengraftment do not cause lethal GVHD in mice transplanted with MHC-incompatible marrow grafts.     

Nitric oxide mediates intestinal pathology in graft-vs.-host disease.

We have investigated the involvement of nitric oxide (NO) in intestinal graft-vs.-host reaction (GvHR) in mice. Treatment of mice with L-NG-monomethyl arginine (L-NMMA), a specific inhibitor of NO synthesis, abolished the mucosal pathology of intestinal GvHR and reduced the associated lymphocytic infiltration of the epithelium. L-NMMA had no effect on splenomegaly in GvHR, nor did it interfere with the growth of an undifferentiated crypt stem cell line, or the production of tumor necrosis factor-alpha by activated macrophages in vitro. In contrast, L-NMMA inhibited the enhanced activity of natural killer (NK) cells which occurs in GvHR. We conclude that a NO-dependent mechanism is essential for intestinal immunopathology in GvHR and that this may reflect a role for NO in NK cell function.     

Graft-vs.-host and graft-vs.-leukemia reactions after delayed infusions of donor T-subsets.

Infusions of donor leukocytes have been given to allogeneic bone marrow recipients after transplant to treat leukemia relapse. Treatment with these delayed infusions of donor cells has been called delayed or donor leukocyte infusion (DLI). While graft-vs.-host disease (GVHD) has typically been less severe than expected after DLI, it still remains a significant risk factor. Recently, we used a full major histocompatibility complex (MHC)-mismatched model (C57BL/6 into AKR) to determine how increased immunogenetic disparity affects GVH and graft-vs.-leukemia (GVL) reactions after DLI. In contrast to an MHC-matched model (B10.BR into AKR), GVHD was still observed when MHC-mismatched donor T cells were infused 3 weeks posttransplant. Limiting dilution analysis was used to determine the frequency of alloreactive cytotoxic T lymphocytes (CTL) and interleukin (IL)-2-secreting T helper cells in the spleens of MHC-mismatched recipients 7 days after DLI treatment. GVHD correlated with elevated frequencies of alloreactive T-helper cells. One strategy for reducing the severity of GVHD after DLI is the selective administration of CD4 or CD8 T-subsets. Delayed infusion of purified T-subsets 3 weeks posttransplant resulted in significantly less GVHD than infusion of a mixture of the two subsets. No GVH-associated mortality was observed after DLI with purified donor CD4+ T cells. In GVL studies, MHC-mismatched CD8+ T cells were the most potent antitumor effectors against an acute T cell leukemia. The GVL effect of MHC-mismatched T-subsets was compared with that of MHC-matched subsets. When naive MHC-matched cells were given as DLI, depletion of either T-subset eliminated the GVL effect. CD8+ T cells from MHC-matched donors primed against host alloantigens, however, mediated a CD4 (T-helper)-independent GVL reaction. Together, these results suggest that administration of T-subsets can significantly reduce GVHD after DLI without loss of the beneficial GVL effect.     

Lymphohematopoietic graft-vs.-host reactions can be induced without graft-vs.-host disease in murine mixed chimeras established with a cyclophosphamide-based nonmyeloablative conditioning regimen.

Mixed hematopoietic chimerism can be induced in mice receiving allogeneic bone marrow transplantation (BMT) after nonmyeloablative host conditioning with depletion T cells with of anti-T cell monoclonal antibodies (mAbs), low-dose (3 Gy) total-body irradiation (TBI), and local thymic irradiation (7 Gy). These mice are specifically tolerant to donor and host antigens. When nontolerant donor T cells are given to chimeras several months after BMT, full donor-type chimerism develops, but graft-vs.-host disease (GVHD) does not occur. The induction of such lymphohematopoietic GVH reactions without GVHD could provide an approach to separating graft-vs.-leukemia (GVL) from GVHD in patients with hematologic malignancies. To make the nonmyeloablative conditioning regimen described above more cytoreductive for such malignancies, we have now modified it by replacing TBI with cyclophosphamide (CP). Treatment with anti-CD4 and anti-CD8 mAbs on day -5, 200 mg/kg CP on day -1, and 7 Gy thymic irradiation on day 0 was only slightly myelosuppressive and allowed fully major histocompatibility complex (MHC)-mismatched (with or without multiple minor antigen disparities) allogeneic bone marrow to engraft and establish long-term mixed chimerism in 40 to 82% of recipients in three different strain combinations. The administration of nontolerant donor spleen cells at 5 weeks or at 5, 8, and 11 weeks posttransplant was capable of eliminating host hematopoietic cells, leading to full or nearly full donor chimerism in six of six and two of four chimeric animals in two different strain combinations. No clinical evidence of GVHD was observed in any recipients of these donor leukocyte infusions (DLI). These studies demonstrate that induction of mixed chimerism with nonmyeloablative conditioning followed at appropriate times by DLI might allow lymphohematopoietic GVH reactions, and hence GVL effects, to eliminate chronic hematologic malignancies without causing clinically significant GVHD.     

Adoptive transfer of murine syngeneic graft-vs.-host disease by CD4+ T cells

Syngeneic graft-vs.-host disease (SGVHD) develops in rodents following the treatment of lethally irradiated, bone marrow (BM) reconstituted animals with a short course of the immunosuppressive agent cyclosporine A (CsA). Using an in vivo depletion approach, we recently demonstrated that CD4(+), but not CD8(+), T cells participated in inducing SGVHD. Studies were therefore undertaken to adoptively transfer SGVHD into lethally irradiated, syngeneic BM reconstituted secondary recipients. Whole T cell populations as well as purified CD4(+)T cells isolated from SGVHD, but not normal or transplant control, animals mediated the transfer of SGVHD into secondary recipients. These cells have an apparent specificity for enteric bacterial antigens. The pathologic process that developed was identical to that observed in the animals with de novo SGVHD after syngeneic BMT and CsA therapy. It was shown that a radiation-sensitive mechanism prevented the transfer of SGVHD into normal, nonirradiated secondary recipients. The ability to reproducibly transfer SGVHD into secondary recipients will enhance our ability to study regulatory mechanisms that are altered during CsA therapy and permit the development of murine CsA-induced SGVHD.     

Cyclosporine, methotrexate, and prednisone compared with cyclosporine and prednisone for prevention of acute graft-vs.-host disease: effect on chronic graft-vs.-host disease and long-term survival.

Graft-vs.-host disease (GVHD) is a major predictor of outcome following allogeneic bone marrow transplantation (BMT). For patients alive at day 100 after BMT, the presence or absence of chronic GVHD is one of the most important determinants of survival and quality of life. We wished to determine the effects on chronic GVHD of two regimens used for the prophylaxis of acute GVHD: cyclosporine, methotrexate, and prednisone (CSA/MTX/PSE) and cyclosporine and prednisone (CSA/PSE). One hundred forty-nine evaluable patients were entered into the acute GVHD study. As of 31 March 1997, 63 months after the last patient underwent BMT, the median survival time was 4.5 years (range 0.09-9.9). The incidence of chronic GVHD was independent of the prophylactic regimen (55 vs. 54%), and extensive chronic GVHD occurred in 25 and 24% of patients receiving CSA/MTX/PSE and CSA/PSE, respectively. Of note, the median Karnofsky performance status of both groups was 100% (range 70-100%), reflecting the low incidence of extensive chronic GVHD. Survival rates free of chronic GVHD were 52 vs. 42% (p = 0.29) for patients receiving CSA/MTX/PSE vs. CSA/PSE. The incidence of relapse was also similar in both groups of patients. These data suggest that the combinations of CSA/MTX/PSE and CSA/PSE result in comparable chronic GVHD-free survival without an increase in leukemic relapse.     

Complete sequential regeneration of graft-vs.-host-induced severely dysplastic thymuses. Implications for the pathogenesis of chronic graft-vs.-host disease.

This study presents the sequential morphologic regeneration of graft-vs.-host (GVH)-induced dysplastic thymuses in long-term survivors of GVH reactions. GVH reactions were induced in adult C57BL/6xAF1 (B6AF1) hybrids by injecting 20 x 10(6) A strain parental lymphoid cells (PLC). Starting on day 30 after GVH induction, five to ten animals were randomly selected from a pool of GVH-reactive mice and killed at various times. Each animal was tested for thymic histology and T cell functions. Thymuses taken on day 30 after GVH induction displayed severe dysplasia as characterized by lymphocytic depletion, complete effacement of cortico-medullary demarcation, and reduction and total loss of medullary epithelial cells or both. Starting by days 60-70 after GVH induction, at least four stages of thymic regeneration were identified. Day 60-70 thymuses displayed cortical regeneration and the reappearance of cortico-medullary demarcation. The medulla of these thymuses, although containing dark individual epithelial cells and numerous lymphocytes, was devoid of pale epithelial cells (stage 1). The medulla of thymuses on day 100 after GVH induction displayed a few sparcely distributed pale epithelial cells and numerous lymphocytes as well as dark epithelial cells (stage 2). The medulla of thymuses examined 130 days after GVH induction displayed numerous pale individual epithelial cells and a few pale epithelial cell clusters. Such thymuses also showed a reduction in the number of medullary lymphocytes (stage 3). Finally, the medulla of thymuses 150-160 days after GVH induction displayed numerous pale epithelial cell clusters and Hassall's bodies. These thymuses were indistinguishable from normal adult thymuses (stage 4). All of the animals tested up to day 130 after GVH induction showed no significant T cell function. Animals displaying stage 4 of thymic regeneration showed significant proliferative responses to T cell mitogen, concanavalin A (conA), and six of ten animals also displayed a few plaque forming cells (PFC) to sheep red blood cells (SRBC) in their spleens. Furthermore, all animals (10 of 10) killed on day 180 after GVH induction displayed significant T cell functions.(ABSTRACT TRUNCATED AT 400 WORDS)     

In situ analyses of in ovo graft-vs.-host reaction induced by thymic nurse cell lymphocytes

In both mammalian and avian systems, thymic nurse cells (TNC) have been shown to harbor a heterogeneous population of T lymphocytes (TNC-L) some of which exhibit a postselectional phenotype. By tranplanting micromanipulated single chicken TNC onto the chorionallantoic membrane (CAM) of major histocompatibility complex (MHC)-disparate embryos, an experimental system which allows for the detection of lymphocytes with graft-vs.-host (GVH) reactivity, we demonstrate here that TNC enclose lymphocytes that can develop into both CD4⁺ single-positive (sp) and CD8⁺ sp, T cell receptor (TcR)αβ⁺, or TcRγδ⁺ cells. This finding was additionally confirmed by serial transfer of primary expanded alloreactive T cells onto the CAM of secondary hosts. All donor TNC-L expressed MHC class II molecules and the interleukin-2 receptor a chain in primary and secondary GVH reactions. Furthermore, we observed selective accumulation of CD8⁺ and TcRγδ⁺ host lymphocytes in the CAM upon the induction of a local GVH reaction, most probably as a consequence of the pathological alteration of the epithelium.     

Translational opportunities for targeting the Th17 axis in acute graft-vs.-host disease

Allogeneic stem cell transplantation (allo-SCT) is a curative therapy for different life-threatening malignant and non-malignant hematologic disorders. Acute graft-vs.-host disease (aGVHD) and particularly gastrointestinal aGVHD remains a major source of morbidity and mortality following allo-SCT, which limits the use of this treatment in a broader spectrum of patients. Better understanding of aGVHD pathophysiology is indispensable to identify new therapeutic targets for aGVHD prevention and therapy. Growing amount of data suggest a role for T helper (Th)17 cells in aGVHD pathophysiology. In this review, we will discuss the current knowledge in this area in animal models and in humans. We will then describe new potential treatments for aGVHD along the Th17 axis.     

The induction of organ-specific antibodies during the graft-vs.-host reaction

During the parent (P) into F1 hybrid graft-vs.-host reaction (GVHR), nuclear, leukocyte and erythrocyte autoantibodies are commonly seen. The specificity of these autoantibodies is reminiscent of those found in systemic lupus erythematosus (SLE) patients and SLE-prone mice. Organ-specific antibodies, however, including thyro-globulin (Tg) antibodies do not arise spontaneously. There have been conflicting reports about the ability of exogenous Tg to induce an anti-Tg response during the GVHR. We have re-examined this question in greater detail. Using the murine P----F1 GVHR system, the results of this work demonstrate that mouse thyroglobulin (MTg)-specific antibodies can be induced during a GVHR. However, mice must both be undergoing a GVHR, and have received exogenous MTg. The highest autoantibody response occurs if mice are injected with mouse thyroid extract or purified MTg at the time of P----F1 cell transfer. The anti-MTg response is MTg dose dependent. The ability to induce anti-MTg antibody was not major histocompatibility complex restricted, for both the DBA/2----B6D2F1 (low responder H-2 haplotypes to MTg), and AKR or DBA/2----AKD2F1 (high/low responder----high responder haplotype) GVHR gave similar responses. The anti-MTg titers peaked between days 7-10 and declined thereafter. In contrast, antibodies to dsDNA were not present at this early time, but developed after several weeks. We conclude that organ-specific autoantibodies can be induced during a GVHR if the appropriate antigen(s) are presented near the time of GVHR induction.     

Abrogation of the lethal graft-vs.-host reaction developed to non-H-2 antigens: involvement of T suppressor cells distinct from veto cells

The mortality induced by graft-vs.-host reaction (GVHR) in (DBA/2 x B10.D2)F1 recipients transplanted with cells from H-2d-identical B10.D2 donors can be abrogated by preimmunizing the donors with parent-strain spleen cells from normal DBA/2 mice. The experiments described here were designed to explore the possibility that the observed protection might be mediated by veto cells contained in the immunizing cell inoculum; the reasoning was based on an analogy with the cytotoxic T lymphocyte response to non-H-2 antigens where suppression can be mediated by veto cells, present in the spleens of normal mice, which are radiosensitive and largely Lyt-2+. We show that the intensity of the protection against GVHR mortality is a function of the immunizing cell dose, and that protection remains effective when optimal doses of immunizing cells are (a) irradiated or (b) pretreated with anti-Thy-1 serum. GVHR suppression is abrogated when, before transfer to F1 recipients, suppressor cells from spleens of immunized donors are pretreated with antiserum directed against Lyt-1.2 (expressed by B10.D2 but not by DBA/2, which expresses Lyt-1.1); in contrast, it is not significantly affected when these same cells are pretreated with anti-Lyt-2.2 alloantiserum. We conclude that when the antigen load is great enough the immunizing cells play a largely passive role in the observed suppression. The protection against GVHR mortality seen in this H-2-compatible combination is transferable by Lyt-1+2- suppressor T cells originating in mice given high doses of alloantigen. These suppressor cells are therefore distinct from the splenic veto T cells effective against cytotoxic T lymphocyte responses to non-H-2 antigens. The mechanism of the observed suppression and its relationship to Mls product(s) are discussed.     

Ly and Ia phenotype of suppressor T cells induced by graft-vs.-host reaction.

Suppressor T cells were generated in (CBA X C57BL)F1 mice undergoing graft-vs.-host (GvH) reaction and treated with anti-Ly and anti-Ia antisera to determine their membrane antigen phenotype. Pretreatment of CBA-induced GvH suppressor T cells with anti-Ly-1.1, anti-Ly-2.1 or anti-Iak antisera plus complement abrogated their suppressive properties when tested against primed F1 spleen cells in vitro. In contrast, concanavalin A (Con A)-induced suppressor T cells were insensitive to anti-Ly-1.1 serum. It is concluded that GvH-induced suppressor T cells are Ly-1+,2+,3+,Ia+, and thus distinct from Con A or antigen-induced suppressor T cells.     

A retrospective comparison of allogeneic peripheral blood stem cell and bone marrow transplantation results from a single center: a focus on the incidence of graft-vs.-host disease and relapse.

To detect the effect of the stem cell source, allogeneic peripheral blood stem cell transplantations (alloPBSCTs) performed between 1995 and 1997 from human leukocyte antigen (HLA)-identical siblings in 40 patients with acute and chronic hematological disorders were compared with a historical group of 40 patients with similar variables who had received allogeneic bone marrow transplants (alloBMTs) between 1993 and 1995. Patients in both groups were identical except that both the recipient and the donor ages were, on average, higher in the alloPBSCT group (26 vs. 36 [p = 0.005] and 27 vs. 32 [p = 0.024], respectively). Patients received similar therapy excluding posttransplant granulocyte colony-stimulating factor administration (97% in alloBMT vs. 12.5% in alloPBSCT). The median time to reach neutrophil counts >0.5 x 10(9)/L and platelet counts >20 x 10(9)/L was 13 and 14 days, respectively, in patients receiving alloPBSCTs compared with 19 and 27 days in patients receiving alloBMTs (p = 0.0014 and p = 0.0002). The alloPBSCT group required similar transfusions of red blood cells or platelets. The incidence of grade II-IV acute graft-vs.-host disease (aGVHD) was similar in both groups. However, chronic GVHD (cGVHD) of all grades developed in 78.1% of patients in the alloPBSCT group after a median follow-up period of 12.5 (range 0.5-34) months. In alloBMT recipients, cGVHD of all grades developed in 21.4% after a median follow-up period of 38 (range 0.5-62) months (p = 0.00001). Day 100 transplant-related mortality was also similar: 20% (8 of 40) in the alloBMT patients and 17.5% (7 of 40) in the alloPBSCT group. Although not statistically significant, a relatively higher relapse rate occurred in the alloBMT group (21.4 vs. 10.7%). The estimated disease-free survival in month 24 was 51.3% for alloBMT and 54.6% for alloPBSCT, and the estimated overall survival in month 24 was 56.1% for alloBMT and 64.6% for alloPBSCT. In conclusion, this retrospective comparison suggests that alloPBSCT from HLA-identical donors is associated with faster engraftment, fewer transfusions, and no greater incidence of aGVHD, but a high incidence of cGVHD.     

Human-mouse lymphoid chimeras: host-vs.-graft and graft-vs.-host reactions.

Human peripheral blood lymphocytes (huPBL) were injected into mice with severe combined immune deficiency (SCID). It was ascertained that murine natural killer (NK) cells were capable of affecting engraftment of human lymphocytes in SCID mice. The presence of host NK cells resulted in the clearance of the human lymphocytes. Human T lymphocytes were the primary cell to engraft in the SCID recipients, with human T cells being detected in the spleen, lymph nodes, bone marrow and peritoneal cavity of the mice up to several months after transfer. No human T cells were detected in the murine thymus and the level of engraftment in the periphery could be highly variable. Additionally, there appeared to be significant reactions between the human lymphocytes and the murine host resulting in a xenogeneic graft-vs.-host reaction (XGVHR). The predominant manifestation involved splenomegaly resulting from an expansion of murine hematopoietic cells in the spleens of these xenogeneic chimeras. The severity of the XGVHR could be correlated with the extent of human T cell engraftment and the recovered human T cells were found to be in a proliferative state. Thus, there appear to be significant host-vs.-graft and graft-vs.-host interactions occurring in human/mouse lymphocyte chimeras.