Stable mixed donor-donor chimerism after double cord blood transplantation

Stable mixed double donor chimerism: Absence of war doesn't necessarily mean peace

Double cord blood transplantation has successfully been introduced to remedy the obstacle of a limited stem cell dose in a single cord blood graft. After a short initial period, the sustained hematopoiesis is derived almost exclusively from one of the donated units. In a recent publication in Clinical and Experimental Immunology we investigated two rare individuals in which both cord blood units co-existed for more than two years after transplantation.

Long-Term Stable Mixed Chimerism after Hematopoietic Stem Cell Transplantation in Patients with Non-Malignant Disease, Shall We Be Tolerant?

Long-term stable mixed chimerism is a rare and poorly understood phenomenon post hematopoietic stem cell transplantation. This study aims to shed light on whether the two hematopoietic systems in patients with mixed chimerism remain functional. Additionally, we investigate possible immunologic differences in these individuals compared to patients with only donor derived immune cells. Patients with donor and mixed chimerism, at median 10 (5–16) years post-HSCT for non-malignant diseases, were assessed regarding clinical situation and immune system (phenotypical and functional). No difference in long-term outcome was seen in terms of general wellbeing, central phenotypic immune system features (e.g., differentiation status, CD4/CD8 ratio, B and NK-cell frequency) and antibody responses to immunizations. At a median of 10 years post transplantation, patients with mixed chimerism had significantly higher IgG3 and platelet levels. Additionally, these patients had higher NKT-cell levels (CD94+CD8+ and CD56+CD8+) than patients with donor chimerism. In depth phenotypic analysis of patients with mixed chimerism demonstrated recipient-derived fractions in most immune cell lineages (e.g., T-cell, B-cell and NK-cell subsets). Recipient cells were also capable of responding to mitogenic stimulation with production of several cytokines. In conclusion, long-term mixed chimerism did not negatively affect patient wellbeing and long-term outcome. Moreover, recipient-derived immunity may still be functional in these patients, suggesting an active state of tolerance and immunologic dependence on both hematopoietic systems.

Double umbilical cord blood transplantation: relevance of persistent mixed-unit chimerism

Double umbilical cord blood transplantation (UCBT) was developed as a strategy to circumvent the cell dose limitation of single UCBT with a concomitant potential benefit of lowering the rate of leukemia relapse. Sustained hematopoiesis after double UCBT usually is derived from a single donor unit, as only a few patients have been reported to display stable mixed-unit chimerism for varying periods of time. Explanations for the 1 unit dominance, predictors for identifying unit superiority, and persistence of long-term mixed-unit chimerism remain elusive. Review of published literature revealed only 11 of 280 patients (4%) with mixed-unit chimerism for at least 1 year after transplantation, with 3 patients receiving reduced-intensity conditioning regimens. Mixed-unit chimerism was more likely if both units were closely HLA matched to each other. Outcome data for patients with stable mixed-unit chimerism, for the most part, were scarcely reported. Analysis of the small sample size revealed a potential advantage of stable mixed-unit chimerism on enhancing the graft-versus-leukemia effect; however, definitive conclusions cannot be made on the effect of mixed-unit chimerism on the rates of graft-versus-host disease. Therefore, gathering outcome data prospectively in larger clinical series will help answer the question of whether stable mixed-unit chimerism is either beneficial and, therefore, should be strived for, detrimental and, thus, needs to be eliminated, or if it is of no clinical consequence.

Rapid induction of single donor chimerism after double umbilical cord blood transplantation preceded by reduced intensity conditioning: results of the HOVON 106 phase II study

Double umbilical cord blood transplantation is increasingly applied in the treatment of adult patients with high-risk hematological malignancies and has been associated with improved engraftment as compared to that provided by single unit cord blood transplantation. The mechanism of improved engraftment is, however, still incompletely understood as only one unit survives. In this multicenter phase II study we evaluated engraftment, early chimerism, recovery of different cell lineages and transplant outcome in 53 patients who underwent double cord blood transplantation preceded by a reduced intensity conditioning regimen. Primary graft failure occurred in one patient. Engraftment was observed in 92% of patients with a median time to neutrophil recovery of 36 days (range, 15-102). Ultimate single donor chimerism was established in 94% of patients. Unit predominance occurred by day 11 after transplantation and early CD4(+) T-cell chimerism predicted for unit survival. Total nucleated cell viability was also associated with unit survival. With a median follow up of 35 months (range, 10-51), the cumulative incidence of relapse and non-relapse mortality rate at 2 years were 39% and 19%, respectively. Progressionfree survival and overall survival rates at 2 years were 42% (95% confidence interval, 28-56) and 57% (95% confidence interval, 43-70), respectively. Double umbilical cord blood transplantation preceded by a reduced intensity conditioning regimen using cyclophosphamide/fludarabine/4 Gy total body irradiation results in a high engraftment rate with low non-relapse mortality. Moreover, prediction of unit survival by early CD4(+) lymphocyte chimerism might suggest a role for CD4(+) lymphocyte mediated unit-versus-unit alloreactivity. www.trialregister.nl NTR1573.

Double umbilical cord blood transplantation for hematological malignancies: a long-term analysis from the SFGM-TC registry

Allogeneic hematopoietic stem cell (HSC) transplantation is a curative treatment for many hematologic malignancies for which umbilical cord blood (UCB) represents an alternative source of HSCs. To overcome the low cellularity of one UCB unit, double UCB transplantation (dUCBT) has been developed in adults. We have analyzed the outcome of 136 patients who underwent dUCBT reported to the SFGM-TC registry between 2005 and 2007. Forty-six patients received myeloablative regimens, and 90 patients received reduced-intensity conditioning regimens. There were 84 cases of leukemia, 17 cases of non-Hodgkin lymphoma, 11 cases of myeloma, and 24 other hematologic malignancies. At transplantation, 40 (29%) patients were in complete remission. At day 60 after transplantation, the cumulative incidence of neutrophil recovery was 91%. We observed one UCB unit domination in 88% of cases. The cumulative incidence of day 100 acute graft-versus-host disease, chronic graft-versus-host disease, transplant-related mortality, and relapse at 2 years were 36%, 23%, 27%, and 28% respectively. After a median follow-up of 49.5 months, the 3-year probabilities of overall and progression-free survival were 41% and 35%, respectively, with a significant overall survival advantage when male cord engrafted male recipients. We obtained a long-term plateau among patients in complete remission, which makes dUCBT a promising treatment strategy for these patients.

Factors with an impact on chimerism development and long-term survival after umbilical cord blood transplantation

BACKGROUND

Umbilical cord blood transplantation (UCBT) is increasingly used and produces similar results to matched unrelated donor transplantation.

METHODS

We performed a retrospective single-center analysis of 50 umbilical cord blood transplantations UCBTs performed from 2001 to 2010, including 37 single and 13 double umbilical cord blood transplantations UCBTs.

RESULTS

The rate of engraftment of neutrophils was 88% at a median time of 29 days (range, 3-79). Complete donor chimerism (DC) within the CD19, CD3, and CD33 cell lineages was seen in 74%, 72%, and 76% of the patients, respectively. DC was associated with acute graft-versus-host disease (GVHD) grades II to IV for the CD3 cell lineage (P=0.01) and, in multivariate analysis, with total body irradiation for all lineages (P<0.01). Overall survival (OS) at 1 and 5 years was 55% and 43%. Nonmalignant diseases were associated with better 5-year OS (72%) than malignancies (28%; P=0.026). In multivariate analysis, a negative correlation was seen between OS and age (hazard ratio [HR], 1.04; 95% confidence interval [95% CI], 1.02-1.06; P<0.001), acute GVHD grades III and IV (HR, 3.43; 95% CI, 1.95-6.02; P<0.001), and mesenchymal stem cell treatment (HR, 2.66; 95% CI, 1.11-6.35; P=0.027). Transplant-related mortality at 100 days and 1 year was 16% and 30%. The incidence of acute GVHD grades II to IV was 34%. Acute GVHD grades III and IV was associated with ABO incompatibility (HR, 2.61; P=0.05) and myeloablative conditioning (HR, 4.17; P=0.047).

CONCLUSIONS

The outcome in patients with nonmalignant diseases was acceptable, but transplant-related mortality in the whole group remains high. A significantly higher rate of DC was associated with total body irradiation-based conditioning and with acute GVHD grades II and IV.

Chimerism and use of mesenchymal stem cells in umbilical cord blood transplantation

We performed a retrospective single-center analysis of 50 umbilical cord blood transplantations (UCBTs), focusing on chimerism development. Complete donor chimerism (DC) was associated with acute graft-vs.-host disease (aGVHD) grades II-IV for the CD3 (+) cell lineage (p = 0.01) and, in multivariate analysis, with total body irradiation (TBI) for all lineages (p < 0.01). Overall survival (OS) was negatively associated with patient age, (p < 0.001); aGVHD grades III-IV, (p < 0.001); and treatment with mesenchymal stem cells (MSCs) (p = 0.027). In conclusion, though multiple factors may have contributed, the association of TBI and DC might be worthy of consideration in the treatment of patients with malignant disease in the UCBT setting. The negative influence of MSCs on OS may be a reason for more careful usage of this treatment modality in combination with UCBT.

Double umbilical cord blood transplantation: a study of early engraftment kinetics in leukocyte subsets using HLA-specific monoclonal antibodies

Single cord blood unit (CBU) predominance is usually established within the first month after double umbilical cord blood transplantation (UCBT). However, the kinetics of engraftment of the different leukocyte subsets and the mechanism of graft predominance is largely unknown. To investigate whether a differential engraftment might reveal a specific subset that could play a key role in the mechanism of graft predominance, we studied early engraftment kinetics of different leukocyte subpopulations by flow cytometry using human monoclonal antigen-specific human leukocyte antigen antibodies, directed against mismatched human leukocyte antigen-A or -B antigens between recipient and CBUs. Twenty-two patients, who had received a double UCBT preceded by a reduced-intensity conditioning regimen, were evaluated at days +11, +18, +25, and +32 posttransplantation. Single CBU predominance in the various leukocyte subsets was established within 18 days posttransplantation. CD4+ T cells of the dominant CBU showed early peripheral blood expansion. Moreover, chimerism in CD4+ and CD8+ T cell and natural killer cell subsets at day +11 was predictive of ultimate graft predominance. These findings show that engraftment kinetics of the various leukocyte subsets vary considerably after double UCBT and may suggest an important role for CD4+ T cells in a presumed alloreactive graft-versus-graft rejection.

Validation of human monoclonal HLA Class I antibodies to evaluate the kinetics of donor chimerism in different cell subsets after double-cord-blood transplantation in the NOD/SCID model

BACKGROUND

Double-cord-blood transplantation (DCBT) in patients is typically accompanied by predominance of a single unit. The causative mechanism, however, is unknown. Identifying the dynamics of mixed donor chimerism in general and in specific subpopulations may help to resolve this question. We conducted studies in a mouse model to develop a new analytic method using anti-human HLA Class I allele-specific monoclonal antibodies (HLA-MoAbs) in flow cytometry.

STUDY DESIGN AND METHODS

Single-cord-blood transplantation or DCBT from HLA-mismatched donors was performed in NOD/SCID mice. Bone marrow (BM) and peripheral blood were collected from 3 to 20 weeks after transplantation. Donor chimerism was determined quantitatively within human platelets (hPLTs), human CD45+ (hCD45+) cells, and human myeloid and lymphocyte subsets by flow cytometry.

RESULTS

Both cord donors stably engrafted in NOD/SCID. The sensitivity to detect chimerism measured with all HLA-MoAbs was 1% (>10 cells/µL). In mouse BM, the percentage of human cells measured with hCD45+ versus HLA-MoAbs correlated excellently (r = 0.999). Donor origin could be defined with HLA-MoAbs for nearly all (>93.6%) human cells in mouse peripheral blood and BM in all lineages. Chimerism of hPLTs in peripheral blood correlated well with hCD45+ cells in BM enabling frequent measurement of chimerism from early after transplantation onward.

CONCLUSION

This approach using HLA-MoAbs enables longitudinal analysis of double-mixed human chimeric populations despite low absolute concentrations of human hematopoietic cell subsets in peripheral blood and BM in mice. Lacking reactivity with mouse cells, the HLA-MoAbs are suitable for use in other mouse models and in humans to identify the mechanisms involved in DCBT.

An overview of the progress on double umbilical cord blood transplantation

Umbilical cord blood transplantation has been increasingly used over the past years for both malignant and non-malignant hematologic and other diseases as an alternative to mismatched-related or matched-unrelated bone marrow or peripheral blood hematopoietic stem cell transplantation. A disadvantage of cord blood is its low cell content which limits cord blood transplantation to generally low weight recipients, such as children. Various alternatives have been used to overcome this limitation, including co-infusion of two partially HLA-matched cord blood units. According to Eurocord Registry data, this strategy has been applied in approximately 993 adult patients with hematologic diseases since the first double umbilical cord blood transplantation in 1999. In fact, since 2005, the number of adult patients receiving double umbilical cord blood transplantation has surpassed the number of adults transplanted with single cord blood units. The engraftment rate is comparable for both single and double umbilical cord blood transplantation, although the latter is accompanied by a higher incidence of grade II acute graft-versus-host disease and lower leukemia relapse for patients in first complete remission. In the majority of patients undergoing double umbilical cord blood transplantation, transient chimerism, due to the presence of cells from both donor units early post transplant, is replaced by sustained dominance of one unit from which long-term hematopoiesis is derived. Although the biology and the factors that determine unit dominance have not been clarified, the implication of immune-mediated mechanisms has been reported. Preliminary data have demonstrated the safety of double umbilical cord blood transplantation. Ongoing clinical trials and prolonged follow up of the patients will clarify the immunology and determine the efficacy of this approach. We present here a brief overview of the clinical experience on double umbilical cord blood transplantation and its underlying biology.

Characterization of long-term mixed donor-donor chimerism after double cord blood transplantation

Double cord blood transplantation (DCBT) with two matched or partially matched cord blood units has been implemented successfully to circumvent the limitations of graft cell dose associated with single CBT. After DCBT, sustained haematopoiesis is derived almost exclusively from only one of the donated units. None the less, we previously observed two of six evaluable DCBT patients still having mixed donor-donor chimerism at 28 and 45 months post-transplantation, respectively. In the present study we utilize flow cytometry techniques to perform the first thorough analysis of phenotype and functionality of cord blood units in patients with mixed donor-donor chimerism. Our results suggest that the two stable cord blood units are different phenotypically and functionally: one unit shows more naive T cells, lower T cell cytokine production and higher frequencies of natural killer cells, the other shows higher frequencies of well-differentiated and functional lymphocytes. Additionally, in comparison with control patients having a single prevailing cord blood unit, the patients with donor-donor chimerism exhibit less overall T cell cytokine production and a smaller fraction of memory T cells. Furthermore, our results indicate that human leucocyte antigen-C match of donor units may partly explain the development of a donor-donor mixed chimerism.