Background: In acquired severe aplastic anemia (aSAA), oligoclonal expansion of dysregulated CD8+ cytotoxic T cells, abnormal function of CD4+ T helper cells, along with elevated production of IFN-γ and TNF-α have been associated with the apoptosis of hematopoietic stem and progenitor cells (HSPC) (Young, N Engl J Med, 2018). Liao and Cairo et al (Cell Transplantation, 2014) have demonstrated that cord blood-derived unrestricted somatic stem cells (USSCs) could significantly reverse the abnormal/inverted ratio of CD4:CD8 T cells, increases the number of FOXP3A positive Treg cells and decrease the level of IFN-γ in an animal model of recessive dystrophic epidermolysis bullosa (RDEB). Alternative therapies are in great need for patients with aSAA as immunosuppressive therapy (IST) overall responses are sub-optimal.


  1. To determine the effect of USSCs on HSPC survival, differentiation and phosphorylation pathways in an ex-vivo culture of aSAA with human CD34+ cells.

  2. To determine the effect of USSCs administration on blood cell count recovery, bone marrow (BM) cellularity and survival in an in-vivo inflammatory cytokine mediated mice model of aSAA.

Design/Methods: Human HSPC were cultured with SCF, FLT3 and human TPO. HSPCs alone, with and without IFN-γ and TNF-α served as controls. USSCs (transwell and direct) were added to the culture. HSPC were harvested and assayed for their survival at day 7 and 14. Annexin-V+/PI+ were referred to as late apoptotic cells. Each experimental condition was set up in triplicate. The cells were cultured at 37°C with 5% CO2. Multi-lineage differentiation capacity was assessed with a selective colony forming units (CFU) assay and compared between experimental groups. Signaling pathways were determined using phosphor-flow cytometric analysis of pSTAT1. For the immune mediated mouse model of aSAA, 8-week-old C57BL/6 mice were irradiated with 6.5Gy TBI. Spleen lymphocytes were collected from FVB donors, and injected 4 hours post-radiation into B6 recipient mice via the retro-orbital vein, at 1-1.5 × 106 cells/recipient in 100μL PBS. Each experimental group (PBS control and USSCs) included 20 mice per group. Mice were continuously monitored for their survival. Peripheral blood (PB) was analyzed using a VETSCAN® HM5 Analyzer. Mean ± SEM of the blood counts was compared between experimental groups. Mice femur bones were extracted and cleaned of soft tissue, fixed and sectioned. Paraffin sections were stained with Hematoxylin and Eosin (H&E) to assess morphology.

Results: The myelosuppressive effect of IFN-γ and TNF-α was significantly rescued (4-fold increase) by the addition of USSCs (transwell) at day 7. After 28 days direct co-culture with USSCs increased CD34+ survival as well (p<0.001) from 5 to 35 cells/µl. A significantly higher percent of viable cells (73% versus 63%) was observed among the USSCs treated cells (P<0.05). Phosphor-flow cytometric analysis demonstrated an almost 50% decrease in pSTAT1 in the presence of USSCs (p<0.05). Based on CFU analysis, CD34+ cells cultured in the presence of USSCs were able to produce more CFU (52, SD±3.7) at day 7 (p<0.01) compared to IFN-γ and TNF-α treated cells (16, SD±2.8). Also, USSCs were associated with more BFU (p<0.05) at day 14. In our immune mediated aplastic anemia mice model, treatment with USSCs was associated with substantial prolonged mice survival (p=0.02) (Figure 1a). Evaluation of PB counts demonstrated increased hemoglobin levels at day 14 in the USSCs treated mice (p<0.05) 5.6g/dL (SD±0.6), compared to PBS treated mice 2.1g/dL (SD±0.1). BM evaluation of USSCs treated mice versus PBS control displayed higher cellularity in the USSCs treated sections (Figure 1b).

Conclusions: Cellular therapy, such as USSCs, may be instrumental in the treatment of aSAA, specifically by increasing BFU-E and eventually hemoglobin levels. Future studies will need to be done to investigate the exact mechanisms of action and the clinical efficacy of this novel cellular therapy.

Cairo:Omeros: Consultancy, Speakers Bureau; Servier: Consultancy, Speakers Bureau; AbbVie: Consultancy; Nektar: Consultancy; Jazz: Consultancy, Speakers Bureau; AstraZeneca: Consultancy; Amgen: Speakers Bureau; Sanofi: Speakers Bureau; Sobi: Speakers Bureau.

Author notes


Asterisk with author names denotes non-ASH members.

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