Interleukin-15 enhances immune reconstitution after allogeneic bone marrow transplantation

Interleukin-15 (IL-15) is a gamma-common cytokine that plays an important role in the development, survival, and proliferation of natural killer (NK), NK T, and CD8+ T-cells. We administered IL-15 to recipients of an allogeneic bone marrow transplantation (allo BMT) to determine its effects on immune reconstitution. Posttransplantation IL-15 administration significantly increased donor-derived CD8+ T (mostly CD122(+)CD44(+)CD8+ T-cells), NK, and NK T-cells at day +28 in young and old recipients of allo BMT. This was associated with enhanced T-cell and NK-cell function. IL-15 stimulated homeostatic proliferation of donor CD8+ T-cells in recipients of carboxyfluorescein diacetate succinimidyl ester-labeled donor T-cell infusions. Posttransplantation IL-15 administration also resulted in a decrease in apoptotic CD8+ T-cells, an increase in Bcl-2-expressing CD8+ T-cells, and an increase in the fraction of Ki67+ proliferative NK and CD8+ T-cells in recipients of allo BMT. IL-15 did not exacerbate graft-versus-host disease (GVHD) in recipients of T-cell-depleted BMT but could aggravate GVHD in some cases in recipients of a T-cell-repleted BMT. Finally, we found that IL-15 administration could enhance graft-versus-leukemia activity. In conclusion, IL-15 can be administered safely to recipients of a T-cell-depleted allo BMT to enhance CD8+ T, NK, and NK T-cell reconstitution.     

Mesenchymal stem cells obtained after bone marrow transplantation or peripheral blood stem cell transplantation originate from host tissue

Mesenchymal stem cells (MSC) obtained from human bone marrow have been described as adult stem cells with the ability of extensive self-renewal and clonal expansion, as well as the capacity to differentiate into various tissue types and to modulate the immune system. Some data indicate that leukapheresis products may also contain non-hematopoietic stem cells, as they occur in whole bone marrow transplantation (BMT). However, there is still controversy whether MSC expand in the host after transplantation like blood progenitor cells do. Therefore, we were interested in finding out if graft MSC can be detected in leukapheresis products and in bone marrow after BMT and peripheral blood stem cell transplantation (PBSCT). Every sample from total bone marrow transplants exhibited growth of MSC after in vitro culture, but not one of nine leukapheresis products did. In addition, bone marrow aspirates of 9 patients receiving BMT and of 18 patients after PBSCT were examined for origin of MSC. Almost all MSC samples exhibited a complete host profile, whereas peripheral blood cells were of donor origin. We conclude that even if trace amounts of MSC are co-transplanted during PBSCT or BMT, they do not expand significantly in the host bone marrow.     

Cellular and humoral immune reconstitution after autologous peripheral blood stem cell transplantation (PBSCT)

Immune reconstitution after autologous peripheral blood stem cell transplantation (PBSCT) is of particular interest because of its importance for clinical outcome. Despite prolonged immunosuppression, especially of CD4(+) cells, few infections after neutrophil recovery occur. Only reactivation of varicella zoster virus (VZV) is more frequent in the first year after transplantation. From August 1997 to May 2001, we prospectively evaluated 38 patients prior to conditioning and during follow-up of 12 months post-transplant for virus antibodies [measles, mumps, rubella, polio, herpes simplex, varicella zoster, mononucleosis, cytomegalovirus (CMV)] and lymphocyte subpopulations by flow cytometry. CD3(+) T lymphocytes, CD8(+) T cells, and B-lymphocyte reconstitution in our study confirms previous reports. Complete CD4(+) lymphocyte reconstitution was not achieved in the 12 months post-transplant leading to a suppressed CD4/CD8 ratio. IgG antibody titers against measles, mumps, rubella, and polio were present in almost all patients pretransplant and during 12 months post-transplant, indicating persistent humoral immunity. CD3(+) and CD8(+) counts of patients with clinical VZV reactivation ( n=5) post-transplant were significantly higher (median: 1201/microl and 938/microl, respectively) than in patients without VZV reactivation (median: 594/microl and 482/microl, respectively) 6-12 months post-transplant. Positive CMV titers pretransplant ( n=19) were also correlated with higher CD3(+) and CD8(+) counts 3-6 months post-transplant (median: 1050/microl and 1056/microl, respectively) compared to CMV-negative patients (738/microl and 584/microl, respectively), although none of the patients suffered from CMV disease. Therefore, we conclude that persistent viral infections can contribute to the CD8(+) T-cell reconstitution after PBSCT by oligoclonal expansion of antigen-specific memory CD8(+) T cells.     

Influence of human cytomegalovirus on immune reconstitution after bone marrow transplantation

HCMV infection diagnosed by the highly sensitive polymerase chain reaction (PCR) technology in blood, urine and skin biopsies of patients after bone marrow transplantation (BMT) correlated with the reconstitution of peripheral blood lymphocytes and dermal immunohistological alterations to evaluate the interaction of viral infection with the recovery of the immune system, as well as with the induction or aggravation of graftversus-host disease (GVHD). In a prospective study 73% of 63 patients showed viremia at a median time of 25 days after BMT. Only 44% of these cases that also presented with a higher frequency of acute GVHD symptoms developed HCMB disease later on. In the skin, similar immunohistological alternations, as well as frequent primary local HCMV infection before the development of cutaneous signs of GVHD, was found, suggesting the direct involvement of anti-HCMV immune responses in the induction of GVHD-associated organ lesions.     

Analysis of immune reconstitution after autologous bone marrow transplantation in systemic sclerosis

OBJECTIVE: To analyze hematopoietic and immune reconstitution after autologous hematopoietic stem cell transplantation (HSCT) in 7 patients with systemic sclerosis (SSc). METHODS: Two groups of patients were retrospectively constituted according to whether they had a favorable clinical response (group A; n = 4) or no response or a relapse of disease (group B; n = 3) after HSCT. Immune reconstitution was analyzed every 3 months using lymphocyte immunophenotyping, alpha/beta T cell receptor (TCR) diversity analysis, and ex vivo thymic function analysis by quantification of TCR rearrangement excision circles (TRECs). RESULTS: Patients had similar characteristics at study entry, except for a lower modified Rodnan skin thickness score (P = 0.03) and a lower Health Assessment Questionnaire score (P = 0.05) in group A than in group B. The number of reinjected cells and the time to hematopoietic reconstitution were similar in both groups. The absolute numbers of CD19+ and CD20+ B cells were lower in group A than in normal controls (P < 0.05) and within the normal range in group B. Absolute numbers of T and natural killer lymphocytes were normal before HSCT. Numbers of CD3+ cells remained low thereafter. Numbers of CD8+ cells were back to normal 3 months after HSCT in both groups. B cell counts were low until 6 months after HSCT in group A and stayed in the normal range in group B. The CD3+ defect was sustained in group A, with an opposite trend and a faster CD4+ reconstitution profile in group B. The T cell repertoire was skewed before and until 1 year after HSCT, with shared expansions before and after transplant in a given individual. TREC values correlated negatively with C-reactive protein levels (r(s) = -0.41, P = 0.001) and positively with CD19+ (r(s) = 0.35, P = 0.001) and CD20+ (r(s) = 0.34, P = 0.002) lymphocyte counts. CONCLUSION: B and T lymphocyte populations remained disturbed for at least 1 year after HSCT in SSc patients, which may reflect the persistence of an underlying disease mechanism.     

Acceleration of hemopoietic recovery after autologous bone marrow transplantation by low doses of peripheral blood stem cells.

Twenty patients with advanced malignant disease submitted to autologous bone marrow transplantation with marrow either unpurged (10 patients) or purged in vitro with mafosfamide (10 patients) after ablative chemotherapy, received simultaneously autologous peripheral blood stem cells (PBSC) collected during one to three 3 h cytapheresis procedures. The kinetics of the hematological recovery of these patients were compared to those of a group of patients suffering from similar diseases and grafted in the same institution with either unpurged marrow only (14 patients) or purged in vitro with mafosfamide (six patients). The median times to reach 10(9)/l leukocytes, 0.5 x 10(9)/l polymorphs, and 50 x 10(9)/l platelets were reduced by 10, 10, and 13 days, respectively, in patients transfused with both autologous bone marrow and peripheral blood stem cells as compared to those receiving bone marrow only. A reduction in the numbers of days spent in hospital post-transplantation (p less than 0.01), of days of fever greater than 38 degrees C (p = NS), and of platelet (p = 0.07) and of red blood cell transfusions (p less than 0.01) were also observed in the group of patients grafted with bone marrow and PBSC.     

Allogeneic peripheral blood stem cell versus bone marrow transplantations: CD34+ cell mobilisation,graft composition,immune reconstitution and clinical outcome

The use of peripheral blood, after G-CSF mobilization, as a source of allogeneic hematopoietic stem cells is being increasingly considered. Some significant data were given by 3 large randomized trials comparing bone marrow (BM) and peripheral blood stem cells (PBSC). Numbers of CD34+ and CD3+ harvested cells were significantly higher in PBSCT group and the hematopoietic recovery was significantly faster after PBSCT. While the American trial showed significant increased rates of acute GVHD and an higher survival and disease-free survival in favour of PBSC, the 2 other studies showed a significant increase of chronic GVHD after PBSCT. The French group investigated whether there was a correlation between cellular composition of PBSC and outcome after transplant. Neither hematological recovery, acute or chronic GVHD nor disease relapse, were significantly associated with CD3+ cell doses. However, high CD34+ cell doses (>8.3×10⁶/Kg) were associated with faster hematopoietic recovery and higher probability of extensive cGVHD at 5 years and DFS was significantly higher in patients receiving low CD34+ cell dose. In parallel, in this study, we evaluated and compared different immune parameters in the graft and after transplantation. Absolute values of mononuclear cells/kg were significantly higher in PBSC grafts than in BM grafts. Analysis of CD25, CD95, HLA-DR and CD45RA expression showed that PBSC grafts T cells exhibited a lower activation level. We found no preferential G-CSF-induced mobilisation of so-called “suppressive” CD3+ cells. In contrast, G-CSF reduced 2- to 3-fold the frequency of IFN-gamma-, IL-2- and TNF-alpha-secreting cells within the NK, NK-T and T-cell subsets and severely reduced the potential for IFN-gamma production at the single-cell level. Thirty days after transplantation, T-cell blood counts were 3-fold higher after PBSC. After PBSCT, T cells were less activated, and at day 30 CD4+, CD8+, CD45RA+ counts were correlated with the number of mononuclear cells infused with the graft, this was not observed after BMT. We showed that Anti-A and/or anti-B Ab titers were significantly increased in PBSCT vs BMT recipients at day 30 and mostly after minor ABO mismatch transplant. PBSCT were significantly associated with increased detection of anti-HLA antibodies early after transplantation. This difference was further increased when analysis was restricted to anti-HLA IgG Ab-negative donor/recipient pairs. The higher number of B cells in the PBSC could be associated with enhanced Ab production early after transplantation. Regarding mini-allotransplants, in France, in a retrospective analysis, we did not show any difference between PBSC and BM in term of disease response, chimerism and overall survival but a significant impact of number of CD34+ cells on early chimerism after transplant. This kind of tranplant might include donor lymphocyte infusion (DLI) strategy and we showed in our center that previous PBSC donation selectively impaired the yields of total MNC and total CD3+ cells recovery after donation but did not affect neither CD19+ nor CD3? CD56+ recoveries when compared to the cohort of BM donations. The use of G-CSF mobilised peripheral blood, as a source of allogeneic stem cells is increasingly considered, especially for mini-allotransplants which justify further studies to identify the different biological characteristics of this source and its clinical impact. *** DIRECT SUPPORT *** A00RC002 00004     

Hemopoietic reconstitution after bone marrow transplantation

Forty-one patients underwent bone marrow transplantation (BMT) for treatment of severe aplastic anemia or hematologic malignancies. Hemopoietic reconstitution after BMT was monitored by peripheral blood counts, counts of bone marrow cellularity, and clonal assays for hemopoietic progenitors (CFUc, CFUe, and BFUe), along with bone marrow morphology. The number of transplanted nucleated cells and the number of transplanted progenitors (CFUc, CFUe, and BFUe) correlated significantly with the time of reticulocyte recovery. The number of transplanted CFUc correlated significantly with the time of granulocyte recovery. Platelet recovery occurred late and showed large variations. No correlation between the transplanted cells and the recovery of nucleated cells or hemopoietic progenitors (CFUc, CFUe, and BFUe) in the bone marrow was found. Bone marrow cellularity and hemopoietic progenitors showed a rapid, but incomplete, recovery during the first 56 days after BMT. Hematologic studies on seven long-term survivors with an uncomplicated posttransplantation course revealed subnormal bone marrow cellularity and hemopoietic progenitor incidence up to three years after BMT, despite normal peripheral blood counts. The low progenitor incidence could be explained by a proliferative defect of the stem cells, compensated for by an amplification in the more differentiated compartment of hemopoiesis.     

Mesenchymal stem cells remain of host origin even a long time after allogeneic peripheral blood stem cell or bone marrow transplantation

OBJECTIVE: Plasticity of hematopoietic stem cells (HSC) has gained major interest in stem cell research. In order to investigate whether HSC may differentiate into mesenchymal stem cells (MSC), we assessed chimerism in peripheral blood (PB), mononuclear cell fractions (MNC) of bone marrow, and MSC derived from bone marrow (BM) from 27 up to 4225 days after allogeneic transplantation. PATIENTS AND METHODS: We applied fluorescence in situ hybridization using X/Y gene probes in sex-mismatched and STR-PCR in sex-matched patients. MSC could have been generated in 27 of 55 bone marrow samples derived from 20 patients. Fifteen patients received peripheral blood stem cell transplants (PBSCT), including CD34-selected PBSCT in two. Five patients received bone marrow. RESULTS: While all patients had chimerism in PB and MNC of the BM, in all but one patient BM-derived MSC were of recipient origin. This single patient showed reproducibly MSC of donor origin in a frequency of 1% after having received a CD34-selected PBSCT. Looking at graft collections, MSCs were easily generated from BM specimens, while no MSC could be derived from PBSC samples. CONCLUSION: Even though HSC have been found to differentiate into a variety of nonhematological cell types, they usually do not differentiate into MSC after allogeneic transplantation.     

Recombinant human G-CSF-mobilized peripheral blood stem cells for second allogeneic transplant after bone marrow graft rejection in children

Two children affected by severe aplastic anaemia and sickle cell anaemia rejected the allogeneic bone marrow transplantation from an HLA-matched unrelated volunteer and an HLA-identical sibling, respectively. In both cases a second transplant using granulocyte-colony stimulating factor (G-CSF) mobilized peripheral blood stem cells (PBSC) was performed. Donors were the HLA-haploidentical mother and the same HLA-identical sibling who was employed for the first marrow allograft, respectively. Treatment with G-CSF and PBSC collection were well tolerated. Both patients had engraftment of donor haemopoiesis and did not experience severe graft-versus-host disease. These cases confirm that PBSC transplant should be considered as a feasible treatment to reverse graft failure in paediatric patients.     

Glutamine-enriched parenteral nutrition after autologous peripheral blood stem cell transplantation: effects on immune reconstitution and mucositis

BACKGROUND AND OBJECTIVES: Glutamine (gln), a non-essential amino acid, has recently received increasing attention because it becomes essential during stress and catabolic states: glutamine seems to modulate immune function and to promote faster intestinal healing after chemotherapy. We designed two consecutive randomized clinical trials to evaluate the role of glutamine-enriched parenteral nutrition (GEPN) in patients with hematologic malignancies submitted to high dose chemotherapy and autologous peripheral blood stem cell transplantation (aPBSCT) or immunoselected CD34+ aPBSCT. DESIGN AND METHODS: In study1, the Gln group (12 patients) received total parenteral nutrition (TPN) enriched with glutamine 20 g from day +1 after aPBSCT, while the placebo group (15 patients) received TPN lacking in glutamine (placebo). In study2, the Gln group (10 patients) received TPN enriched with glutamine 13.46 g from day +1, while the placebo group (11 patients) received a placebo. RESULTS: In the first study, a lymphocyte count >0.5 109/L was achieved on day 16.5 in the Gln group and on day 29 in the placebo group (p=0.005); in the second study, the lymphocyte count >0.5 109/L was achieved on day 18 in the Gln group and on day 29 in the placebo group (p=0.009). Lymphocyte subset analysis showed an increase of CD3+ and CD4+ and normalization of the CD16+CD56+ subset. Furthermore patients receiving GEPN showed a decrease in the mucositis severity peak calculated by the DMS (daily mucositis score: sum of the daily score of signs and symptoms) (p=0.047). INTERPRETATION AND CONCLUSIONS: GEPN is safe and effective and improves lymphocyte recovery after aPBSCT; further studies are needed to assess the clinical benefits of such an approach in order to justify its economic impact.     

Prompt engraftment using autologous peripheral blood stem cells for double autologous bone marrow rescue

A patient with Hodgkin's Disease, stage IIIA, was treated for recurrent disease with autologous peripheral blood stem cells after ablative chemotherapy. Bone marrow rescue occurred promptly and his disease was significantly reduced. Ablative chemotherapy was administered again and a second bone marrow rescue with peripheral blood stem cells was successful. Sequential peripheral blood stem cell bone marrow rescue, following high dose chemotherapy, may provide an alternative approach in selected patients.     

Reduced-intensity stem cell transplantation using allogeneic peripheral blood stem cells from the same donor for relapsed leukemia after bone marrow transplantation

We report the clinical courses of two cases with relapsed acute lymphoblastic leukemia (ALL) after allogeneic bone marrow transplantation (BMT). After reinduction chemotherapy, the patients received reduced-intensity stem cell transplantation using allogeneic peripheral blood stem cells harvested from their previous BMT donors. The conditioning regimen used consisted of fludarabine and melphalan. Graft-versus-host disease (GVHD) prophylaxis was performed with low dose cyclosporin A (CsA, 1 mg/kg/day d.i.v.) on its own. The regimen related toxicity was minimal, and stable engraftment was achieved. Since acute GVHD had not developed by day 30, CsA was stopped abruptly in both cases. After CsA withdrawal, acute GVHD developed, and subsequent chronic GVHD. One of two cases is alive without any relapse of the leukemia 40 months after the peripheral blood stem cell transplantation (PBSCT). In the other case, ALL relapsed 15 months after the PBSCT, however, complete remission was again induced concomitantly with reactivated GVHD. In both these cases, the results suggest that using PBSC as a stem cell source and abrupt cessation of GVHD prophylaxis provided a potent graft-versus-leukemia effect.     

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.     

Monitoring of human herpesviruses after allogeneic peripheral blood stem cell transplantation and bone marrow transplantation

Herpesviruses frequently cause serious complications after allogeneic bone marrow transplantation (allo-BMT). Recent studies have shown more rapid immune reconstitution after allogeneic peripheral blood stem cell transplantation (allo-PBSCT) compared with allo-BMT. However, it has not been clarified whether the improved immune reconstitution after allo-PBSCT is associated with a lower incidence of herpesvirus infections. We monitored the emergence of Epstein-Barr virus (EBV), cytomegalovirus (CMV), human herpesvirus 6 (HHV-6) and HHV-7 DNA by a nested-double polymerase chain reaction in peripheral blood leucocytes from 22 allo-BMT and 16 allo-PBSCT patients. Each virus had an unique temporal profile of detection. HHV-6 DNA was detected most frequently at 3 weeks after transplantation, whereas CMV and EBV DNA were detected later (2-3 months). Detection rates of HHV-6 DNA at 3 and 4 weeks after allo-BMT were significantly higher than those after allo-PBSCT (9/16 v 2/13 at 3 weeks, P < 0.01; 10/21 v 1/15 at 4 weeks, P < 0.01). Detection rates of the other three herpesviruses after the two types of allogeneic transplantation were not significantly different throughout observation period. Furthermore, detection of HHV-6 DNA within the first 4 weeks was associated with delayed platelet engraftment after both allo-BMT and allo-PBSCT (P < 0.01). These results suggest an advantage for allo-PBSCT over allo-BMT in terms of suppression of HHV-6 reactivation and prevention of subsequent complications.     

Immune reconstitution after allogeneic marrow transplantation compared with blood stem cell transplantation

Allogeneic peripheral blood stem cell grafts contain about 10 times more T and B cells than marrow grafts. Because these cells may survive in transplant recipients for a long time, recipients of blood stem cells may be less immunocompromised than recipients of marrow. Immune reconstitution was studied in 115 patients randomly assigned to receive either allogeneic marrow or filgrastim-mobilized blood stem cell transplantation. Between day 30 and 365 after transplantation, counts of most lymphocyte subsets were higher in the blood stem cell recipients. The difference was most striking for CD4 T cells (about 4-fold higher counts for CD45RA(high) CD4 T cells and about 2-fold higher counts for CD45RA(low/-)CD4 T cells; P <.05). On assessment using phytohemagglutinin and herpesvirus antigen-stimulated proliferation, T cells in the 2 groups of patients appeared equally functional. Median serum IgG levels were similar in the 2 groups. The rate of definite infections after engraftment was 1.7-fold higher in marrow recipients (P =.001). The rate of severe (inpatient treatment required) definite infections after engraftment was 2.4-fold higher in marrow recipients (P =.002). The difference in the rates of definite infections was greatest for fungal infections, intermediate for bacterial infections, and lowest for viral infections. Death associated with a fungal or bacterial infection occurred between day 30 and day 365 after transplantation in 9 marrow recipients and no blood stem cell recipients (P =.008). In conclusion, blood stem cell recipients have higher lymphocyte-subset counts and this appears to result in fewer infections. (Blood. 2001;97:3380-3389)     

Distinct reconstitution of neutrophil functions after allogeneic peripheral blood stem cell transplantation

Purpose The study investigated in detail neutrophil functions shortly after allogeneic peripheral blood stem cell transplantation (PBSCT). Methods Different functions of neutrophils in 14 patients who received allogeneic PBSCT were investigated. The migratory capacity as well as the ability to induce oxidative burst following stimulation with either Phorbol-12-myristate-13-acetate (PMA), the chemotactic peptide N-formyl-Met-Leu-Phe (f-MLP) or opsonized Escherichia coli was analysed after engraftment (between day +30 and +40) and compared with the results obtained from healthy volunteers. Results There are no differences in terms of the migratory capacity (P = 0.17), as well as regarding the oxidative burst after incubation with PMA (P = 0.08) or f-MLP (P = 0.06), compared with healthy men. In contrast, the capacity of neutrophils to induce oxidative burst following stimulation with E. coli is highly impaired (P = 0.0001) in patients shortly after engraftment. Conclusion The recovery of neutrophils after allogeneic PBSCT is not only influenced by the varying time of engraftment, but also represents a process that differs in distinct biological functions compared to normal granulopoieses.     

Transplantation of ABO-incompatible bone marrow and peripheral blood stem cell components

Hemolysis may occur during infusion of an ABO-incompatible HSC component if the recipient has isoagglutinins directed against donor red blood cells, or later as a result of the production by donor lymphocytes of isoagglutinins directed against recipient ABO-antigens. Peripheral blood stem cell (PBSC) components collected by apheresis contain few red cells but considerably greater numbers of lymphocytes than marrow. We reviewed the transplant courses of 158 recipients of marrow (n = 90) or PBSC (n = 68) from HLA-identical, ABO-incompatible sibling donors. No patient experienced immediate or delayed hemolysis attributable to the ABO incompatibility. Recipients of minor ABO-incompatible red cell-replete marrow required fewer red cell transfusions during the first week after transplantation than recipients of PBSC or marrows depleted of red cells; the red cell transfusion requirements for the following 3 weeks did not differ. The maximum level of bilirubin did not differ for patients classified by ABO incompatibility or source of HSC. The development of positive antiglobulin tests occurred for eight marrow recipients from a separate group of 22 patients (17 marrow, five PBSC) for whom this testing was performed. None of these patients developed overt hemolysis. These data indicate that hemolysis complicating ABO-incompatible transplantation is not common after either marrow or PBSC transplantation. Bone Marrow Transplantation (2000) 26, 749-757.