Natural history of mixed chimerism after bone marrow transplantation with CD6-depleted allogeneic marrow: a stable equilibrium

Mixed hematopoietic chimerism (MC) is a common finding after allogeneic bone marrow transplantation (BMT), but the natural history of this phenomenon remains unclear. To understand the evolution and the implications of this finding, we performed a prospective analysis of the development of mixed chimerism in 43 patients with hematologic malignancies who received bone marrow (BM) from human leukocyte antigen (HLA)-identical sibling donors. T-cell depletion in vitro with anti-T12 (CD6) monoclonal antibody and rabbit complement was used as the only method of graft-versus-host disease (GVHD) prophylaxis. Overall, MC was identified in peripheral blood (PB) and BM in 22 of 43 (51%) patients evaluated. MC was found by restriction fragment length polymorphism (RFLP) analysis in 21 of 40 (53%) patients, by cytogenetic analysis in 6 of 29 (21%) patients, and by red blood cell phenotyping in 4 of 9 (44%) patients. RFLP studies were performed at 0.5, 1, 3, 6, 9, and 12 months post-BMT and then every 6 months, and showed a high probability of developing MC in the first 6 months after BMT followed by stabilization after 12 months. Cytogenetic analysis was less sensitive in detecting MC. Once MC was detected after BMT, the percentage of recipient cells increased very slowly over more than 3 years of follow-up, and no patient reverted to complete donor hematopoiesis (CDH). Thus, recipient and donor cells remained in a relative state of equilibrium for prolonged periods that seemed to favor recipient cells over donor cells. Patient's disease, remission status, or intensity of the transplant preparative regimen did not influence the subsequent development of mixed chimerism. Early immunologic reconstitution was the only factor that correlated with the subsequent chimeric status of the patients. The percentage and absolute number of T3 (CD3) and T4 (CD4) positive cells at day 14 after BMT were significantly higher in the patients who maintained CDH but NK cell reconstitution was similar in both groups, suggesting that early reconstitution with T cells may play a role in preventing recovery of recipient cells after BMT. GVHD was also associated with maintenance of CDH, but the probability of relapse, survival, and disease-free survival was identical in patients with MC and CDH.     

Patterns of hematopoietic chimerism following bone marrow transplantation for childhood acute lymphoblastic leukemia from volunteer unrelated donors

Hematopoietic chimerism was analyzed in serial bone marrow samples taken from 28 children following T-cell depleted unrelated donor bone marrow transplants (UD BMT) for acute lymphoblastic leukemia (ALL). Chimeric status was determined by polymerase chain reaction (PCR) of simple tandem repeat (STR) sequences (maximal sensitivity, 0.1%). At least two serial samples were examined in 23 patients. Of these, two had evidence of complete donor engraftment at all times and eight showed stable low level mixed chimerism (MC) (<1% recipient hematopoiesis). All 10 of these patients remain in remission with a minimum follow-up of 24 months. By contrast, 13 patients demonstrated a progressive return of recipient hematopoiesis. Five of these relapsed (4 to 9 months post BMT), one died of cytomegalovirus pneumonitis and seven remain in remission with a minimum follow-up of 24 months. Five children were excluded from serial analysis as two serial samples were not collected before either relapse (3) or graft rejection (2). We conclude that as with sibling transplants, ex vivo T depleted UD BMT in children with ALL is associated with a high incidence of MC. Stable donor engraftment and low level MC always correlated with continued remission. However, detection of a progressive return of recipient cells did not universally correlate with relapse, but highlighted those patients at greatest risk. Serial chimerism analysis by PCR of STRs provides a rapid and simple screening technique for the detection of relapse and the identification of patients with progressive MC who might benefit from detailed molecular analysis for minimal residual disease following matched volunteer UD BMT for childhood ALL.     

Characterization of mixed chimerism in patients with chronic myeloid leukemia transplanted with T-cell-depleted bone marrow: involvement of different hematologic lineages before and after relapse

We have characterized mixed chimerism (MC) in five patients with chronic myeloid leukemia (CML) who received transplants with T-cell- depleted bone marrow (BM) and who relapsed within 4 years after transplantation. To study the possible relation of MC with relapse, we purified different populations of leukocytes and analyzed their donor/recipient origin by a method based on polymerase chain reaction amplification of minisatellite DNA regions. Our results show that before relapse, all hematopoietic recipient cells are T cells, whereas monocytes, B, and natural killer (NK) cells are of donor origin. This observation does not appear to be specific for CML as similar results were found in two control patients with acute myeloid leukemia (AML). At the time of (CML) relapse, recipient granulocytes, monocytes, and erythrocytes appeared and progressively replaced the respective lineages of donor origin. No other lineages seemed to be involved as B cells and NK cells remained of donor origin and no significant changes in the number of recipient T cells were detected. In this respect relapse of CML after BM transplantation (BMT) seems not to be very different from the primary disease in chronic phase before transplantation. Furthermore, we conclude that after BMT, an association between mixed chimerism before relapse and the (CML) relapse does exist because both phenomena are consequences of T-cell depletion of the BM graft. However, this correlation might well be indirect as the MC caused by the recipient T cells appears to be independent of the one caused by the recurrent disease.     

Graft-versus-host-reactive donor CD4 cells can induce T cell-mediated rejection of the donor marrow in mixed allogeneic chimeras prepared with nonmyeloablative conditioning

Murine mixed hematopoietic chimerism can be achieved following nonmyeloablative conditioning with cyclophosphamide, T cell-depleting monoclonal antibodies, and thymic irradiation. Donor lymphocyte infusions (DLIs) 35 days after bone marrow transplantation (BMT) convert mixed to full donor chimerism and mediate graft-versus-lymphoma effects without graft-versus-host disease. We evaluated the role of T-cell subsets in DLIs in converting mixed to full donor chimerism in a fully major histocompatibility complex-mismatched strain combination. Whereas DLIs administered on day 35 converted 100% of mixed chimeras to full donor chimerism, conversion was less frequent when either CD4 or CD8 cells were depleted, indicating that both subsets contribute to the conversion. Surprisingly, administration of CD8-depleted DLIs led to complete loss of donor chimerism in a high proportion (54%) of recipients compared with CD4-plus CD8-depleted DLIs (15%) or CD4-depleted DLIs (0%) (P <.05). DLIs administered at early time points after BMT (eg, day 21) also precipitated rejection of donor marrow by recipient alphabeta T cells, in association with donor CD4 cell expansion and high production of interleukin 2 (IL-2), IL-4, and interferon-gamma. Thus, DLIs can paradoxically induce marrow rejection by residual host alphabeta T cells. These results have implications for the timing of and use of subset depletion of DLIs in recipients of nonmyeloablative transplants.     

Comparison of outcomes after transplantation of peripheral blood stem cells versus bone marrow following an identical nonmyeloablative conditioning regimen

This is the first study to examine the outcomes in 54 patients with hematologic malignancies who received an HLA-matched related donor bone marrow (BM, n = 42) or GCSF-mobilized peripheral blood stem cells (PBSC, n = 12) following identical nonmyeloablative conditioning with the intention of induction of mixed chimerism (MC) followed by prophylactic donor leukocyte infusion (pDLI) to convert MC to full donor chimerism (FDC) and capture a graft-versus-tumor effect without clinical graft-versus-host disease (GVHD). Neutrophil and platelet recovery were faster and transfusion requirement was less in PBSC recipients (P < 0.05). A total of 48% of BMT recipients achieved FDC with a median conversion time of 84 days, including 13 following pDLI. In contrast, 83% (P = 0.04) in the PBSC group had spontaneous FDC at a median of 14 days, precluding the administration of pDLI. There was no significant difference in the incidences of acute or chronic GVHD, though the rates of chronic GVHD were considerably higher in PBSC group than in the BM group (6/7, 86% vs 10/24, 42%). CD4 and CD8 T-cell recovery was faster in PBSC recipients. In PBSC recipients, a higher number of CD34+ cells was associated with increased rates of severe, grade III-IV acute GVHD.     

Evaluation of mixed chimerism by in vitro amplification of dinucleotide repeat sequences using the polymerase chain reaction

The influence of mixed hematopoietic chimerism (MC) after allogeneic bone marrow transplantation remains unknown. Increasingly sensitive detection methods have shown that MC occurs frequently. We report a highly sensitive novel method to assess MC based on the polymerase chain reaction (PCR). Simple dinucleotide repeat sequences called microsatellites have been found to vary in their repeat number between individuals. We use this variation to type donor-recipient pairs following allogeneic BMT. A panel of seven microsatellites was used to distinguish between donor and recipient cells of 32 transplants. Informative microsatellites were subsequently used to assess MC after BMT in this group of patients. Seventeen of the 32 transplants involved a donor of opposite sex; hence, cytogenetics and Y chromosome-specific PCR were also used as an index of chimerism in these patients. MC was detected in bone marrow aspirates and peripheral blood in 18 of 32 patients (56%) by PCR. In several cases, only stored slide material was available for analysis but PCR of microsatellites or Y chromosomal material could be used successfully to assess the origin of cells in this archival material. Cytogenetic analysis was possible in 17 patients and MC was detected in three patients. Twelve patients received T-cell-depleted marrow and showed a high incidence of MC as revealed by PCR (greater than 80%). Twenty patients received unmanipulated marrow, and while the incidence of MC was lower (44%), this was a high percentage when compared with other studies. Once MC was detected, the percentages of recipient cells tended to increase. However, in patients exhibiting MC who subsequently relapsed, this increase was relatively sudden. The overall level of recipient cells in the group of MC patients who subsequently relapsed was higher than in those who exhibited stable MC. Thus, while the occurrence of MC was not indicative of a poor prognosis per se, sudden increases in the proportions of recipient cells may be a prelude to graft rejection or relapse.     

Hematopoietic donor chimerism and graft-versus-myeloma effect in relapse of multiple myeloma after allogeneic bone marrow transplantation

 A large group of patients relapsing after allogeneic bone marrow transplantation (BMT) have obtained remission after infusion of leukocytes from their original donor, suggesting a graft-versus-myeloma effect. However, side effects such as graft-versus-host disease and myelosuppression are severe, and sometimes fatal, complications of this therapeutic approach. Previously we demonstrated that patients with leukemia who lack donor hematopoiesis in relapse after BMT experience severe and lasting aplasia after infusion of donor leukocytes. In two patients – one with extramedullary and one with marrow relapse after a sex-mismatched transplantation – we analyzed hematopoietic chimerism by cell sorting and bone marrow cultures. CD34-positive cells, CD4-CD8-positive cells, committed progenitors, and LTC-IC were of donor origin, as demonstrated by two-color fluorescence in situ hybridization (FISH). Additionally, in relapse complete donor T-cell chimerism was seen. In contrast, plasma cells were of recipient origin in the patient who had a relapse in the bone marrow. Both patients were treated with infusions of donor leukocytes from their original donor. Neither patient suffered myelosuppression, and one achieved a stable complete remission. Received: February 26, 1999 / Accepted: April 14, 1999     

Minimal residual disease is more common in patients who have mixed T- cell chimerism after bone marrow transplantation for chronic myelogenous leukemia

Determining both lymphoid chimerism and the presence of minimal residual disease after allogeneic bone marrow transplantation (BMT) for chronic myelogenous leukemia (CML) could be helpful to the understanding of the biology of leukemic relapse in this disease. We prospectively investigated 32 patients with CML post-BMT by assessing T- cell chimerism and minimal residual disease using sensitive polymerase chain reaction (PCR) methodologies. Patients were studied between 1 and 24 months post-BMT. Thirty patients received a T-cell-depleted marrow grafts and 2 received unmanipulated marrow. All but 1 patient were conditioned with total body irradiation (TBI)+thiotepa+cyclophosphamide (Cy). The other patient received TBI+Cy as conditioning. The T cells were exclusively of donor origin in 12 of 16 patients who were tested at 1 month post-BMT, but were mixed chimeric in 11 of these patients by > or = 3 months. Once mixed T-cell chimerism was documented, no patient returned to having all donor T-cells. At a median follow-up of 12 months, minimal residual disease was present in 18 of 22 patients with mixed T-cell chimerism and in 3 of 10 patients with full donor chimerism. The actuarial molecular relapse rate at 24 months for the two groups is 91% and 33%, respectively (P < .02). The finding of BCR- ABL mRNA within the first 6 months of transplant or on two consecutive assays was highly predictive of subsequent cytogenetic or hematologic relapse (P = .032 and P < .02, respectively). Ten patients, 9 with mixed T-cell chimerism, have relapsed (4 clinical, 6 cytogenetic) at a median of 12 months post-BMT. These data suggest that mixed T-cell chimerism may be a marker for abrogation of graft-versus-leukemia activity that is thought to be pivotal in eradicating minimal residual disease after BMT for CML.     

Mixed chimerism in the B cell lineage is a rapid and sensitive indicator of minimal residual disease in bone marrow transplant recipients with pre-B cell acute lymphoblastic leukemia

One of the major problems after allogeneic bone marrow transplantation (BMT) is a high frequency of leukemia relapse. We have prospectively studied the presence of donor- and recipient-derived chimeric cells in bone marrow recipients with pre-B cell acute lymphoblastic leukemia (pre-B-ALL). The chimeric status of BMT recipients was compared to minimal residual disease (MRD) detection by analysis of immunoglobulin heavy chain (IgH) and T cell receptor (TcR) genes. Post-transplant blood and bone marrow samples from 12 patients with pre-B-ALL were studied. Five patients showed mixed chimerism (MC) in the CD19-positive cell fraction. Four of them have relapsed to date. The remaining patient with MC in the B cell lineage was also MRD positive in the same samples. All seven patients with donor chimerism in the B cell fraction remain in clinical remission (P = 0.01). In samples from all five patients having MC in the B cell lineage, the patient-specific IgH or TcR rearrangement was also detected. In three of four patients who relapsed, MC in the B cell lineage was seen more than 2.5 months prior to morphologically verified relapse. The results of this comparison suggest that routinely performed MC analysis of the affected cell lineage may facilitate post-BMT monitoring and rapid therapeutic decisions in transplanted patients with pre-B-ALL.     

Unrelated donor bone marrow transplantation to treat severe aplastic anaemia in children and young adults

Alternative donor bone marrow transplantation (BMT) to treat severe aplastic anaemia (SAA) in children and young adults has been complicated by high rates of graft rejection and severe graft-versus-host disease (GVHD). We hypothesized that increased immunosuppression combined with T-cell depletion of the marrow graft would enable successful use of unrelated donor BMT in this disease. Preconditioning consisted of cytosine arabinoside, cyclophosphamide, and total body irradiation (TBI). T-cell depletion was with the anti-CD3 antibody T10B9. GVHD prophylaxis consisted of cyclosporine A. 28 previously transfused patients were transplanted. Nine donor/recipient pairs were HLA matched. As of 1 January 1996, 15/28 (54%) patients are alive, transfusion independent and well with a range of follow-up of 13 months to 8 years (median 2.75 years). Fatalities include all three patients with non-engraftment and all three patients with grade III/IV GVHD. Other fatalities were due to infections or therapy-related toxicity. The incidence ≥ grade II acute GVHD was 28%. These data show that in children with SAA who have failed immunosuppression, unrelated donor BMT offers a reasonable hope of long-term survival.     

Prognostic value of hematopoietic chimerism in patients with acute leukemia after allogeneic bone marrow transplantation: a prospective study

Hematopoietic chimerism as a predictive marker for the relapse of acute leukemia after allogeneic BMT was evaluated in a prospective study. Monthly assays of hematopoietic chimerism were performed from peripheral blood samples by PCR amplification of short tandem repeats or amelogenin loci. Between December 1997 and June 1999, 33 patients enrolled and 30 were evaluable (two early deaths, one lack of informative bands for chimerism evaluation). There were 14 male and 16 female patients (15 AML and 15 ALL) with a median age of 31 years (range 16-46). Mixed chimerism (MC) was observed at least once in 14 of 30 patients (47%). There was no significant difference between 14 patients who showed MC (MC group) and 16 patients who did not show MC (complete chimerism (CC) group) in terms of age, sex, disease status at BMT, donor type, and the number of bone marrow cells infused. There was no significant difference in the neutrophil and platelet engraftment rates between the two groups. After a median follow up of 10.9 months (range 4.3-22.4), five patients in the CC group and two patients in the MC group relapsed (P = 0.27). All five patients who relapsed in the CC group maintained CC up to 1 month prior to clinical relapse. Our study demonstrated that the patients who showed MC post BMT did not have higher risk of relapse of acute leukemia when compared to patients who did not show MC. Sensitive PCR-based assays for hematopoietic chimerism applied on a monthly basis after allogeneic BMT could not predict relapse of acute leukemia.     

Immunologic effects of prophylactic donor lymphocyte infusion after allogeneic marrow transplantation for multiple myeloma

Reconstitution of T-cell immunity after bone marrow transplantation (BMT) is often delayed, resulting in a prolonged period of immunodeficiency. Donor lymphocyte infusion (DLI) has been used to enhance graft-versus-leukemia activity after BMT, but the effects of DLI on immune reconstitution have not been established. We studied 9 patients with multiple myeloma who received myeloablative therapy and T-cell-depleted allogeneic BMT followed 6 months later by infusion of lymphocytes from the same donor. DLI consisted of 3 x 10(7) CD4(+) donor T cells per kilogram obtained after in vitro depletion of CD8(+) cells. Cell surface phenotype of peripheral lymphocytes, T-cell receptor (TCR) V beta repertoire, TCR rearrangement excision circles (TRECs), and hematopoietic chimerism were studied in the first 6 months after BMT and for 1 year after DLI. These studies were also performed in 7 patients who received similar myeloablative therapy and BMT but without DLI. Phenotypic reconstitution of T and natural killer cells was similar in both groups, but patients who received CD4(+) DLI developed increased numbers of CD20(+) B cells. TCR V beta repertoire complexity was decreased at 3 and 6 months after BMT but improved more rapidly in patients who received DLI (P =.01). CD4(+) DLI was also associated with increased numbers of TRECs in CD3(+) T cells (P <.001) and with conversion to complete donor hematopoiesis (P =.05). These results provide evidence that prophylactic infusion of CD4(+) donor lymphocytes 6 months after BMT enhances reconstitution of donor T cells and conversion to donor hematopoiesis as well as promoting antitumor immunity.     

T-cell depletion of allogeneic bone marrow using anti-alphabetaTCR monoclonal antibody: prevention of graft-versus-host disease without affecting engraftment potential in rats.

Bone marrow chimerism may solve two major limitations in the transplantation of solid organs and cellular grafts: (1) the requirement for life-long immunosuppressive therapy, and (2) acute and chronic rejection. When untreated bone marrow is transplanted into major histocompatibility complex (MHC)-disparate rats, lethal graft-vs-host disease (GVHD) occurs in the majority of recipients. T-cell depletion using anti-CD3 and anti-CD5 monoclonal antibody (mAb) to avoid GVHD led to an increased occurrence of failure of engraftment. We previously identified a cellular population in mouse bone marrow that facilitates engraftment of highly purified hematopoietic stem cells (HSC) across complete MHC barriers. In light of the fact that facilitating cells have a CD8+/CD3+/TCR- phenotype and mostly coexpress CD5, we evaluated in this study whether T-cell depletion of rat bone marrow using anti-alphabetaTCR mAb would retain engraftment potential yet avoid GVHD. T-cell depletion of bone marrow was performed using anti-alphabetaTCR mAb and immunomagnetic beads. Recipients were conditioned with 1100 or 1000 cGy of total body irradiation and reconstituted with 100 x 10(6) T-cell depleted (TCD) MHC- and minor antigen-disparate bone marrow cells. Animals were monitored clinically and histologically for GVHD. Chimerism was assessed by flow cytometry. Immunomagnetic bead depletion resulted in a reduction of T cells from 1.92%+/-0.21% to 0.10%+/-0.04% of total bone marrow. T-cell depletion did not remove facilitating cells (CD8+/alphabetaTCR-/gammadeltaTCR-/NK3.2.3-) from bone marrow. Further, the engraftment potential of TCD bone marrow was not affected, as 100% of animals engrafted and high levels of donor chimerism were detectable. Animals reconstituted with TCD bone marrow showed no clinical evidence of GVHD and histology revealed none to minimal changes, whereas recipients transplanted with untreated bone marrow succumbed to severe lethal GVHD. T-cell depletion using antialphabetaTCR mAb and immunomagnetic beads selectively removes T cells from the bone marrow graft while sparing facilitating cells that are required for engraftment of allogeneic bone marrow across MHC barriers. Moreover, the cells required for engraftment of HSC do not produce GVHD.     

Long-term mixed chimerism after immunologic conditioning and MHC-mismatched stem-cell transplantation is dependent on NK-cell tolerance

T-cell tolerance is mandatory for major histocompatibility complex (MHC)-mismatched stem-cell transplantation without cytoreduction. Here, we used a cytotoxicity assay based on the infusion of differentially carboxyfluorescein succinimidyl ester (CFSE)-labeled syngeneic and donor splenocytes to determine the survival of donor cells in vivo. In vivo cytotoxicity data showed that treatment with anti-CD40 ligand monoclonal antibody in combination with a low dose of MHC-mismatched bone marrow cells was sufficient to induce T-cell tolerance. However, CFSE-labeled donor cells were still eliminated. A similar elimination pattern was observed in T-cell and natural killer T-cell (NKT-cell)-deficient mice, suggesting the involvement of natural killer (NK) cells. Indeed, in vivo NK-cell depletion resulted in a prolonged survival of CFSE-labeled donor cells, confirming the role of NK cells in this process. Transplantation of a megadose of MHC-mismatched bone marrow cells was required for a complete survival of CFSE-labeled donor cells. This NK-cell tolerance was donor specific and was associated with mixed chimerism. Additional NK-cell depletion significantly enhanced engraftment and allowed long-term chimerism after transplantation of a relatively low dose of donor bone marrow cells. These data demonstrate the importance of NK cells in the rejection of MHC-mismatched hematopoietic cells and may explain the high numbers of bone marrow cells required for transplantation over MHC barriers.     

Chronic myeloid leukemia presenting ALL-type BCR/ABL transcript

Summary We assessed the origin of peripheral blood cells and bone marrow cells of 92 samples obtained from 19 patients after allo BMT by two-step polymerase chain reaction (PCR) amplification of MCT118, one of the variable number of tandem repeat regions (VNTR) which has a different length in 19 of 32 sibling pairs examined, that can detect the DNA pattern of a minor cell population of only 1% without using radioisotopes. Mixed chimerism (MC) was detected in the hematopoietic cells of four patients. Two patients who showed progressive MC developed relapse of leukemia 3 months and 4 months after the detection of MC, and two patients died with bone marrow hypoplasia 61 days and 7 months after BMT. These data suggest the clinical importance of analyzing the correlation of MC and clinical complications after BMT by this method, which can be used to monitor MC in about two thirds of allo BMT patients with an adequate sensitivity.     

Removal of T cells from bone marrow for transplantation: a monoclonal antilymphocyte antibody that fixes human complement

Graft-versus-host disease is one of the major problems in clinical bone marrow transplantation. Many experiments in animals have shown that it could be greatly reduced if mature T lymphocytes were removed from the donor marrow. Here we describe a new rat monoclonal antibody, CAMPATH 1, which is suitable for depleting lymphocytes from human marrow grafts. CAMPATH 1 is an IgM that fixes human complement. It binds to both T and B lymphocytes and some monocytes but not to other hemopoietic cells. When peripheral blood mononuclear cells were treated with CAMPATH 1 and complement, more than 99% of lymphocytes were killed and viable T cells could no longer be detected. Under these conditions, in vitro multipotential erythroid and myeloid colony-forming cells were unaffected. As well as being used for in vitro treatment of bone marrow to remove T cells, CAMPATH 1 could potentially be applied to other experimental and clinical situations where depletion of lymphoid cells is required, including serotherapy to achieve immunosuppression for organ transplants or to treat lymphocytic leukemias.     

Early host CD8 T-cell recovery and sensitized anti-donor interleukin-2-producing and cytotoxic T-cell responses associated with marrow graft rejection following nonmyeloablative allogeneic bone marrow transplantation

OBJECTIVE: We developed a nonmyeloablative conditioning regimen for allogeneic bone marrow transplantation (BMT) followed by donor lymphocyte infusions (DLI) for treatment of chemotherapy refractory malignancies. Although the majority of patients who receive this regimen achieve lasting mixed or full allogeneic chimerism, approximately 30% show initial mixed chimerism followed by loss of the donor graft. These patients recover host hematopoiesis without significant cytopenias. To assess the role of immunologic rejection in graft loss, we compared T-cell recovery and in vitro alloresponses in six patients who lost their marrow graft to that in 16 concurrent patients with sustained donor chimerism. PATIENTS AND METHODS: Conditioning included pretransplant cyclophosphamide (150-200 mg/kg), thymic irradiation (700 cGy), and pre- and post-transplant equine antithymocyte globulin (ATG; ATGAM). HLA-identical related donor BMT was followed by DLI at approximately day 35 in patients without graft-vs-host disease. RESULTS: The group with transient chimerism showed significantly increased circulating host T-cell (median 416 cells/mm(3) vs 10 cells/mm(3), p<0.05) and CD8 T-cell numbers (354 cells/mm(3) vs 71 cells/mm(3), p<0.05) compared to the group with stable mixed or full donor chimerism within the first 100 days post-BMT. All DLI recipients who lost chimerism following DLI had greater than 80% recipient T cells at the time of DLI, whereas those with persistent chimerism had <60% host T cells. Graft rejection was associated with the development of a sensitized anti-donor bulk cytotoxic T-lymphocyte (CTL) response in 4 of 6 evaluated patients, compared to only 1 of 10 evaluated patients with sustained chimerism (p<0.05). Additionally, 3 of 5 evaluated transient chimeras showed high anti-donor CTL precursor frequencies in limiting dilution assays, and 3 of 4 evaluated transient chimeras showed high anti-donor interleukin-2 (IL-2)-producing T-helper (T(H)) cell frequencies. High anti-donor T(H) or cytotoxic T-lymphocyte precursors were not detected in sustained chimeras. CONCLUSION: These data indicate that loss of chimerism in patients receiving this nonmyeloablative regimen is due to immune-mediated rejection. This rejection appears to bemediated by recovering recipient cytolytic CD8(+) cells as well as IL-2-producing recipient T(H) cells. These data are the first to demonstrate sensitization of recipient anti-donor IL-2-producing cells in association with human marrow allograft rejection.     

Impact of pretransplant conditioning and donor T cells on chimerism, graft-versus-host disease, graft-versus-leukemia reactivity, and tolerance after bone marrow transplantation

Graft rejection, mixed chimerism, graft-versus-host disease (GVHD), leukemia relapse, and tolerance are interrelated manifestations of immunologic reactivity between donor and host cells that significantly affect survival after allogeneic bone marrow transplantation (BMT). In this report, a mouse model of BMT, in which the donor and host were compatible at the major histocompatibility complex (MHC), was used (1) to examine the interrelationship of pretransplant conditioning and T-cell content of donor BM with regard to lymphoid chimerism and GVHD and (2) to determine how these factors affected graft-versus-leukemia (GVL) reactivity and donor-host-tolerance. AKR (H-2k) host mice were administered optimal or suboptimal total body irradiation (TBI) as pretransplant conditioning followed by administration of BM cells from B10.BR (H-2k) donor mice with or without added spleen cells as a source of T lymphocytes. Transplanted mice were injected with a supralethal dose of AKR leukemia cells 20 and 45 days post-BMT to assess GVL reactivity in vivo. The pretransplant conditioning of the host and T-cell content of the donor marrow affected the extent of donor T-cell chimerism and the severity of GVH disease. GVL reactivity was dependent on transplantation of mature donor T cells and occurred only in complete chimeras. Transplantation of T-cell-deficient BM resulted in the persistence of host T cells, ie, incomplete donor T-cell chimerism, even when lethal TBI was used. Mixed chimerism was associated with a lack of GVL reactivity, despite the fact that similar numbers of donor T cells were present in the spleens of mixed and complete chimeras. In this model, moderate numbers of donor T cells facilitated complete donor T-cell engraftment, caused only mild GVHD, and provided a significant GVL effect without preventing the subsequent development of tolerance after conditioning with suboptimal TBI. In contrast, severe, often lethal, GVHD developed when the dose of TBI was increased, whereas tolerance and no GVH/GVL reactivity developed when the T-cell content of the marrow was decreased.     

Evidence for a graft-versus-mast-cell effect after allogeneic bone marrow transplantation

Mast cell leukemia (MCL) is a rare form of aggressive mastocytosis with a reported median survival below 6 months. Casuistic reports suggest the effectiveness of allogeneic bone marrow transplantation (BMT) for MCL. However, these reports lack clear evidence for a graft-versus-mast-cell (GvMC) effect. We prospectively investigated the GvMC at different time points after allogeneic BMT and donor-lymphocyte infusions (DLI). Samples were gathered from a patient with MCL treated with allogeneic BMT from an unrelated HLA identical donor. Parameters for detection of a GvMC effect included flow cytometrical analysis of mast cell (MC) populations in peripheral blood and BM, BM smear and histology, chimerism analysis of flow cytometrically sorted BM CD117+/CD34- MC and testing for anti-mast cell reactivity of donor lymphocytes by interferon (IFN)-gamma ELISPOT. DLIs reduced MC from 5 to 0.5%. MC chimerism analysis demonstrated a complete recipient genotype after BMT, suggesting that the persistent mastocytosis was part of residual neoplastic disease. At 3.7 years after BMT, there is some evidence for relapse. In summary, BMT and DLIs attenuated the mastocytosis from an aggressive to an indolent form and may have improved the patients' prognosis. The in vitro data of our study indicate for the first time the existence of a GvMC effect.     

The significance of host haemopoietic cells detected by cytogenetic analysis of bone marrow from recipients of bone marrow transplants

Bone marrow from 39 patients who received a bone marrow transplant (BMT) from a matched donor of different sex were studied by chromosome analysis for evidence of mixed haemopoietic chimaerism (MC). Recipient metaphases were detected in the bone marrow of 10 patients after BMT. Patients in whom MC was detected within 6 weeks of BMT did not all have a poor outcome. Two of seven are disease-free survivors at greater than 470 and greater than 632 d. All three patients in whom MC was diagnosed more than 6 weeks after BMT subsequently relapsed. Four factors appear to be important in determining the probability of relapse when MC is detected in a patient after BMT: the timing of detection of residual recipient cells; the proportion of these cells in the bone marrow; persistence of these cells in increasing proportions; and the karyotype of the recipient metaphases detected. Cytogenetic assessment may provide the earliest indication of relapse in these patients. In addition, this study provides further evidence that cyclophosphamide and total body irradiation, as used in these patients, may be inadequate conditioning therapy for BMT.