Inducible depletion of hematopoietic stem cells in vivo challenges niche availability as the critical determinant for bone marrow engraftment

Gerbaulet, Alexander; Schoedel, Kristina B.; Goethert, Joachim R.; Voehringer, David; Waskow, Claudia; Roers, Axel

doi:10.1016/j.exphem.2013.05.167

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“…Furthermore, it will be important to determine in future experiments whether host myelosuppression alone (through antibody treatments or other specific approaches) at any level is sufficient to ensure high and durable engraftment. In fact, the requirement of ''niche'' availability has been challenged when selective ablation of stem cells failed to achieve engraftment (Gerbaulet et al, 2013). Although homing and BM lodgment of infused HSCs can be achieved irrespective of host HSC ablation, the microenvironmental conditions necessary for their initial expansion in BM may not be present (Andrade et al, 2011).…”

Section: Discussionmentioning

confidence: 99%

Modeling Promising Nonmyeloablative Conditioning Regimens in Nonhuman Primates

et al. 2014

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Minimal conditioning or even no conditioning would be the preferred preparation for most gene therapy applications for nonmalignant diseases. However, reduced intensity conditioning (RIC) regimens in patients with nonhematologic malignancies have not led to long-term engraftment unless a selective advantage was present for the transplanted donor cells. Similar findings have also been observed in a number of large animal studies. Inadequate myelosuppression levels were thought to be responsible for the outcomes. To address this issue several innovative protocols in small animals have been presented with selective hematopoietic myelosuppression and less systemic toxicity. Such protocols promised to curb the transplant-related morbidity and mortality in myeloablative conditioning and provide effective long-term engraftment, especially in patients with gene-corrected autografts. In the present study we have tested some of these promising RIC regimens in nonhuman primates, a clinically relevant large animal model. Our data suggest that transient myelosuppression induced by anti-c-Kit antibody in conjunction with low-dose irradiation may lead to long-term engraftment, albeit at low levels. The animals with busulfan conditioning with or without anti-c-Kit that received gene-modified autologous transplants with green fluorescent protein expression had similar myelosuppression, but failed long-term engraftment and despite immunosuppressive treatment had all the hallmarks seen previously in similar models without immunosuppression. Our preliminary data expand current knowledge of RIC and emphasize the need to explore whether specific and directed myelosuppression alone is adequate in the absence of microenvironmental modulation, or whether innovative combinations are necessary for safe and effective engraftment.

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Section: Discussionmentioning

confidence: 99%