Preclinical modeling of myelodysplastic syndromes.

Myelodysplastic syndromes (MDS) represent a heterogeneous group of hematological clonal disorders. Here, we have tested the bone marrow (BM) cells from 38 MDS patients covering all risk groups in two immunodeficient mouse models: NSG and NSG-S. Our data show comparable level of engraftment in both models. The level of engraftment was patient specific with no correlation to any specific MDS risk group. Furthermore, the co-injection of mesenchymal stromal cells (MSCs) did not improve the level of engraftment. Finally, we have developed an in vitro two-dimensional co-culture system as an alternative tool to in vivo. Using our in vitro system, we have been able to co-culture CD34+ cells from MDS patient BM on auto- and/or allogeneic MSCs over 4 weeks with a fold expansion of up to 600 times. More importantly, these expanded cells conserved their MDS clonal architecture as well as genomic integrity.

High concordance of genomic and cytogenetic aberrations between peripheral blood and bone marrow in myelodysplastic syndrome (MDS).

Bone marrow (BM) genetic abnormalities in myelodysplastic syndrome (MDS) have provided important biological and prognostic information; however, frequent BM sampling in older patients has been associated with significant morbidity. Utilizing single-nucleotide polymorphism array (SNP-A) and targeted gene sequencing (TGS) of 24 frequently mutated genes in MDS, we assessed the concordance of genetic abnormalities in BM and peripheral blood (PB) samples concurrently from 201 MDS patients. SNP-A karyotype in BM was abnormal in 108 (54%) and normal in 93 (46%) patients, with 95% (190/201) having an identical PB karyotype. The median copy number (CN) for deletions was significantly lower in BM (CN:1.4 (1-1.9)) than in PB (CN:1.5 (1-1.95), P<0.001). Using TGS, 71% (130/183) patients had BM somatic mutations with 95% (124/130) having identical mutations in PB. The mutant allele burden was lower in PB (median 27% (1-96%)) compared with BM (median 29% (1-100%); P=0.14) with no significant difference in the number, types of mutations or World Health Organization subtype. In all patients with discordant SNP (n=11) and mutation (n=6) profiles between BM and PB, shared abnormalities were always present irrespective of treatment status. Overall, 86% of patients had a clonal aberration with 95% having identical SNP-A karyotype and mutations in PB, thus enabling frequent assessment of response to treatment and disease evolution especially in patients with fibrotic or hypocellular marrows.

Allogeneic stem cell transplantation using alemtuzumab-containing regimens in severe aplastic anemia.

Alemtuzumab, a humanized anti-CD52, IgG1 monoclonal antibody, is used to reduce graft-versus- host disease (GVHD) and aid engraftment after allogeneic haemopoietic stem cell transplant (HSCT). Its associated low incidence of GVHD makes it an attractive alternative to anti-thymocyte globulin (ATG) in transplant conditioning regimen for severe aplastic anaemia (SAA). We have reviewed the use of alemtuzumab-based conditioning regimen for HSCT in SAA and show that it results in sustained haematological engraftment, a very low incidence of chronic GVHD without an increase in viral infections. Intriguingly, alemtuzumab appears to induce tolerance post-HSCT with the findings of stable mixed T cell chimerism with full donor myeloid chimerism and the absence of chronic GVHD, and which persist on withdrawal of post-graft immunosuppression. Finally, its low toxicity profile may permit future application of HSCT to older patients with SAA who fail to respond to immunosuppressive therapy.