Fludarabine-based Reduced Intensity Conditioning for Allogeneic Hematopoietic Stem Cell Transplantation in a Pediatric Patient With Bone Marrow Failure Syndrome Type 3

Abstract Abstract 4557 BACKGROUND: Natural killer (NK) cells are innate immune effectors that directly lyse virally infected or malignant cells. There are 2 different subsets of NK cells with distinct phenotypic and functional characteristics: the CD56dim subset, which composes 90% of peripheral blood NK cells and has a cytotoxic function, and the CD56bright subset, which cooperates with dendritic cells and T cells in lymph nodes to secrete interferon and promote adaptive immune responses. NK cells are the first donor-derived lymphocyte subset to reconstitute after hematopoietic stem cell transplantation, reaching normal levels after 1 month. Nearly all phenotyping studies of NK subsets after haploidentical hematopoietic stem cell transplantation (HHSCT) reveal a rapid reconstitution of NK cells towards the CD56bright subset. In addition, Y.-J. Chang et al found the highest 2-year survival in patients with a high number of CD56bright NK cells after unmanipulated HHSCT. We analyzed reconstitution of the NK compartment between days 90 and 180 after unmanipulated bone marrow HHSCT with reduced intensity conditioning (RIC). METHODS: Six adults received unmanipulated bone marrow HHSCT after RIC (fludarabine 30 mg/m2 [day –6 to –2], cyclophosphamide 14.5 mg/kg [day –6 and –5], and busulfan i.v. 3.2mg/kg [day –3]) at our institution between July 2007 and July 2010. Prophylaxis for acute graft-versus-host disease (GvHD) consisted of cyclophosphamide 50mg/kg (days +3 and +4) and cyclosporine A and mycophenolate mofetil from day +5 onwards. We monitored the reconstitution kinetics of circulating NK cells (CD56+, CD3–), and the CD56bright and CD56dim subsets by multiparametric flow cytometry (FC 500 Beckman® Coulter) at day +90 and day +180 after transplantation. Patient characteristics and clinical outcomes are shown in Table 1. 6 patients who underwent allogeneic HLA-identical sibling HSCT with RIC during the same period were used as controls. RESULTS: After HHSCT, NK cells reached normal levels in all patients but one at day +90, with a median number of NK cells of 111/mm3 (range, 25–195/mm3). At day +180 the median number of NK cells was 92/mm3 (range, 4–272/mm3). When we analyzed the absolute number of CD56bright and CD56dim subsets at day +90, we observed 2 patterns: Two patients showed skewed NK cell reconstitution towards CD56bright (Patient no. 3: 54 CD56bright/mm3; 11 CD56dim/mm3. Patient no. 4: 70 CD56bright/mm3; 17 CD56dim/mm3). Three patients reconstituted with a CD56dim/CD56bright ratio towards the CD56dim cell subset, similar to that of healthy adults (Patient no. 1: 17 CD56bright/mm3; 178 CD56dim/mm3. Patient no. 5: 9 CD56brigh/mm3; 135 CD56dim/mm3. Patient no. 6: 20 CD56bright/mm3; 116 CD56dim/mm3). One patient did not achieve adequate NK cell reconstitution (Patient no. 2: 15 CD56bright/mm3; 10 CD56dim/mm3). In contrast, in the control group, an increase in the CD56bright NK cell subset was not observed in any of the patients at any point. It is worth noting that 2 of the 3 patients with better clinical outcome (no GvHD, no relapse), namely patients no. 3 and no. 4 were the ones with skewed NK cell reconstitution towards the CD56bright NK cell subset. The other patient with a better clinical outcome (patient no. 6) had a normal CD56dim/CD56bright ratio at day +90. However, he showed an early CD56bright reconstitution (363 CD56bright/mm3; 34 CD56dim/mm3) in an additional determination on day +30. NK cell subsets reconstitution kinetics is shown in Figure 1. CONCLUSIONS: In our experience, NK cell reconstitution is adequate after RIC unmanipulated bone marrow HHSCT. Some patients recovered with a high proportion of CD56bright NK cells, as previously reported in other studies on HHSCT. Although limited by the sample size, our results are consistent with the previously observed survival advantage of patients with high early levels of CD56bright NK cells after unmanipulated haploidentical transplantation. Disclosures: No relevant conflicts of interest to declare.

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A Human Bone Marrow Failure Syndrome Caused By a Homozygous Mutation in MYSM1

Blood ◽

10.1182/blood.v126.23.1204.1204 ◽

2015 ◽

Vol 126 (23) ◽

pp. 1204-1204 ◽

Cited By ~ 1

Author(s):

Ehsan Bahrami ◽

Tomas Racek ◽

Maximilian Witzel ◽

Jacek Puchalka ◽

Naschla Greif-Kohistani ◽

...

Keyword(s):

Bone Marrow ◽

Stem Cell ◽

B Cells ◽

Hematopoietic Stem Cell Transplantation ◽

Stem Cell Transplantation ◽

Cell Transplantation ◽

Cell Lines ◽

Bone Marrow Failure ◽

Bone Marrow Failure Syndrome ◽

Hematopoietic Stem

Abstract Inherited bone marrow failure syndromes comprise a heterogeneous group of genetic disorders characterized by dysfunction of hematopoietic stem or progenitor cells. We present a consanguineous pedigree with two siblings with early-onset, progressive bone marrow failure (neutropenia, anemia, thrombocytopenia) associated with trigonocephaply, hyperplastic gingiva, cataract, accessory mammilla, dental changes and mild neurocognitive developmental delay. Pancytopenia at birth as well as non-compaction cardiomyopathy was observed in one of the patients. Bone marrow histology showed marked hypocellularity with decrease of all hematopoietic cell lines but without cellular atypia, monocytosis, blast excess or fibrosis. Fanconi anemia was excluded by mitomycin C induced chromosomal breakage studies. Immunophenotyping of peripheral blood cells showed a reduction of mature B cells, reduced switched memory B cells, whereas the level of activated B-cells and plasma blasts were increased. T cell proliferation upon PHA and specific antigens was normal. Using whole exome sequencing in patients and both parents we could identify a single potentially disease causing homozygous stop codon mutation (NM_001085487: c.1168G>T: p.E390*) in MYSM1 (Myb-Like, SWIRM And MPN Domain-Containing Protein 1). A family with two affected patients carrying the same mutation has been reported previously (Alsultan A et al, Blood 122:3844, 2013). MYSM1 is a Histone H2A deubiquitinase that has previously been implicated in controlling hematopoietic stem cells, progenitor B cells, and NK cells in mice (Nijnik A et al, Blood 119:1370, 2012). MYSM1 protein was absent in patients' EBV-transformed B cell lines (EBV-LCLs). MYSM1-deficient EBV-LCLs had elevated γ-H2AX levels, indicative of increased genomic instability. Upon exposure to UV light, we observed a sustained expression of p53 and phospho-p53 as well as p38 MAPK and phospho-p38 MAPK in patients' fibroblasts in comparison to fibroblasts from healthy individuals. In view of the progressive pancytopenia, both siblings underwent allogeneic hematopoietic stem cell transplantation from 10/10 HLA-matched family donors after reduced intensity conditioning with alemtuzumab, fludarabine and treosulfan at 2 and 4 years of age, respectively. The procedure was well tolerated, and both siblings exhibit full donor hematopoietic reconstitution at 21 and 26 months after transplant. In summary, we here identify a novel human bone marrow failure syndrome caused by MYSM1-deficiency that can be cured by allogeneic hematopoietic stem cell transplantation. Disclosures No relevant conflicts of interest to declare.

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