A preclinical model of double- versus single-unit unrelated cord blood transplantation

CD4+ T-cell alloreactivity toward mismatched HLA class II alleles early after double umbilical cord blood transplantation

Although double umbilical cord blood transplantation (dUCBT) in adult patients may be associated with less graft failure compared with single UCBT, hematopoietic recovery generally originates from a single cord blood unit (CBU). CBU predominance is still incompletely understood. We recently showed that blood CD4⁺ T-cell numbers rapidly increase after dUCBT, and early CD4⁺ T-cell chimerism predicts for graft predominance. Given the frequent HLA class II allele mismatches between CBUs in dUCBT, we hypothesized that alloreactive HLA class II-specific CD4⁺ T cells from the "winning" CBU may contribute to rejection of the "loser" CBU. We evaluated whether CD4⁺ T cells originating from the predominant (PD)-CBU would recognize HLA class II allele mismatches, expressed by the nonengrafting (NE)-CBU. Alloreactive effector CD4⁺ T cells toward 1 or more mismatched HLA class II alleles of the NE-CBU were detected in 11 of 11 patients, with reactivity toward 29 of 33 (88%) tested mismatches, and the strongest reactivity toward DR and DQ alleles early after dUCBT. Mismatched HLA class II allele-specific CD4⁺ T cells recognized primary leukemic cells when the mismatched HLA class II allele was shared between NE-CBU and patient. Our results suggest that cytotoxicity exerted by CD4⁺ T cells from the PD-CBU drives the rapid rejection of the NE-CBU, whose alloreactive effect might also contribute to graft-versus-leukemia.

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.

Sustained donor engraftment in recipients of double-unit cord blood transplantation is possible despite donor-specific human leukoctye antigen antibodies

The impact of human leukocyte antigen (HLA) donor-specific antibodies (DSA) on cord blood (CB) engraftment is controversial. We evaluated the influence of pre-existing HLA-antibodies (HLA-Abs) on engraftment in 82 double-unit CB recipients (median age, 48 years) who underwent transplantation for hematologic malignancies. Of 28 patients (34%) with HLA-Abs, 12 had DSA (median mean fluorescence intensity 5255; range, 1057 to 9453). DSA patients had acute leukemia (n = 11) or myelodysplasia (n = 1) and all received either high-dose or reduced-intensity (but myeloablative) conditioning. After myeloablative CB transplantation (CBT) (n = 67), sustained donor engraftment was observed in 95% without HLA-Abs (median, 23 days), 100% with nonspecific HLA-Abs (median, 23 days), and 92% with DSA (median, 31 days, P = .48). Of 6 patients with HLA-Abs to 1 unit, 3 engrafted with that unit and 3 with the other. Of 6 patients with HLA-Abs against both units, 1 had graft failure despite being 100% donor, and 5 engrafted with 1 unit. Successful donor engraftment is possible in patients with DSA after myeloablative double-unit CBT. Our data suggest potential deleterious effects of DSA can be abrogated in patients with hematologic malignancies.

G9a/GLP-dependent histone H3K9me2 patterning during human hematopoietic stem cell lineage commitment

G9a and GLP are conserved protein methyltransferases that play key roles during mammalian development through mono- and dimethylation of histone H3 Lys 9 (H3K9me1/2), modifications associated with transcriptional repression. During embryogenesis, large H3K9me2 chromatin territories arise that have been proposed to reinforce lineage choice by affecting high-order chromatin structure. Here we report that in adult human hematopoietic stem and progenitor cells (HSPCs), H3K9me2 chromatin territories are absent in primitive cells and are formed de novo during lineage commitment. In committed HSPCs, G9a/GLP activity nucleates H3K9me2 marks at CpG islands and other genomic sites within genic regions, which then spread across most genic regions during differentiation. Immunofluorescence assays revealed the emergence of H3K9me2 nuclear speckles in committed HSPCs, consistent with progressive marking. Moreover, gene expression analysis indicated that G9a/GLP activity suppresses promiscuous transcription of lineage-affiliated genes and certain gene clusters, suggestive of regulation of HSPC chromatin structure. Remarkably, HSPCs continuously treated with UNC0638, a G9a/GLP small molecular inhibitor, better retain stem cell-like phenotypes and function during in vitro expansion. These results suggest that G9a/GLP activity promotes progressive H3K9me2 patterning during HSPC lineage specification and that its inhibition delays HSPC lineage commitment. They also inform clinical manipulation of donor-derived HSPCs.

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.

Cord blood transplants: one, two or more units?

PURPOSE OF REVIEW

This review summarizes the current status of double-unit cord blood transplantation (CBT) to improve engraftment, reduce transplant-related mortality, and improve disease-free survival.

RECENT FINDINGS

Transplantation of cord blood provides a potentially curative therapy for many patients without a suitably human leukocyte antigen-matched related or unrelated donor. Single-unit CBT outcomes have been compromised, however, in adults and larger children by limited cell dose. The introduction of double-unit CBT has improved engraftment and transplant-related mortality in adult patients transplanted for hematologic malignancies, with recent data also suggesting a protection against relapse. These improved outcomes are seen despite only a single unit being responsible for sustained donor hematopoiesis in nearly all patients. The study of double-unit CBT provides unique insights into transplant biology, with emerging data suggesting unit dominance is related to unit viability and unit-versus-unit immune interactions. Multiple unit CBT further serves as a platform to test novel graft manipulations.

SUMMARY

The development of double-unit CBT now allows the majority of patients, regardless of size or racial/ethnic background, access to transplant therapy. Ongoing investigation will serve to further improve outcomes and expand the role of CBT in the future.