In utero depletion of fetal hematopoietic stem cells improves engraftment after neonatal transplantation in mice

Abstract

• In utero injection of an antibody against the c-Kit receptor can effectively deplete host HSCs in mice.• In utero depletion of host HSCs leads to significantly increased engraftment after neonatal congenic hematopoietic cell transplantation.Although in utero hematopoietic cell transplantation is a promising strategy to treat congenital hematopoietic disorders, levels of engraftment have not been therapeutic for diseases in which donor cells have no survival advantage. We used an antibody against the murine c-Kit receptor (ACK2) to deplete fetal host hematopoietic stem cells (HSCs) and increase space within the hematopoietic niche for donor cell engraftment. Fetal mice were injected with ACK2 on embryonic days 13.5 to 14.5 and surviving pups were transplanted with congenic hematopoietic cells on day of life 1. Low-dose ACK2 treatment effectively depleted HSCs within the bone marrow with minimal toxicity and the antibody was cleared from the serum before the neonatal transplantation. Chimerism levels were significantly higher in treated pups than in controls; both myeloid and lymphoid cell chimerism increased because of higher engraftment of HSCs in the bone marrow. To test the strategy of repeated HSC depletion and transplantation, some mice were treated with ACK2 postnatally, but the increase in engraftment was lower than that seen with prenatal treatment. We demonstrate a successful fetal conditioning strategy associated with minimal toxicity. Such strategies could be used to achieve clinically relevant levels of engraftment to treat congenital stem cell disorders. (Blood. 2014;124(6):973-980) IntroductionHematopoietic stem cell (HSC) transplantation is a promising strategy to treat many nonmalignant genetic disorders such as hemoglobinopathies, immunodeficiencies, and inborn errors of metabolism, 1 and may even provide tolerance for solid organ transplants.2 However, this approach often requires host myeloablation and immunosuppression, which carries significant morbidity. 3,4 Transplantation into the immunologically naive fetal environment to circumvent the host immune response is an attractive alternative strategy to achieve sustained engraftment and donor-specific tolerance. This approach of in utero hematopoietic cell transplantation (IUHCTx) has been successful in many animal models, but clinical applications remain hampered by low levels of engraftment that are not sufficient to ameliorate symptoms or cure most diseases (reviewed in Nijagal et al 5 ). Because the only clinical successes have been achieved in fetuses with severe combined immunodeficiency, [6][7][8] it has been suggested that success is limited by barriers such as rejection of the stem cell graft and lack of space within the hematopoietic niche (reviewed in Flake and Zanjani 9 ). We and others have previously explored the role of an immune response to donor cells and reported that the maternal immune system is a significant barrier to engraftment. 10,11 The fetal host can become tolerant to transplanted cells through clonal de...

Systemic multilineage engraftment in mice after in utero transplantation with human hematopoietic stem cells

“…CD34 1 cells were isolated and transplanted into fetal mice at embryonic day 13.5 (E13.5) or E14.5 as previously described 23 with or without preconditioning with ACK2. 17 Chimerism levels were checked at 4-week intervals and at harvest using flow cytometry and immunohistochemistry.…”

“…11,12 Clinically, IUHCT has been successful for fetuses with severe combined immunodeficiency (SCID), 13,14 but therapeutic uses for other diseases, including hemoglobinopathies, have seen limited success. 15 Further investigations identified multiple barriers to successful engraftment, including lack of space within the hematopoietic niche 16,17 and the maternal immune system. 2,18 Among available animal models of IUHCT, the fetal mouse remains an efficient and reproducible model to study the differentiation of stem cells in a nonirradiated host.…”

Musical chairs: in utero HCT via mobilization

“…Future development of isoformspecific inhibitors of HMGB1 may mitigate excessive inflammation and thrombosis without affecting the beneficial effects of HMGB1 in the resolution of inflammation and tissue repair. 10 Conflict-of-interest disclosure: The author declares no competing financial interests. n REFERENCES Musical chairs: in utero HCT via mobilization…”

“…9 It has also been shown that ACK2 can be safely injected directly into fetal mice; when followed by a transplant of congenic HSCs, it results in approximately 15% multilineage donor engraftment. 10 Such a combined approach would consist of the music starting (mobilization of host HSCs from the endogenous niche via blockade of a4b1-integrin), followed by removal of some of the participants from the game (partial depletion of host HSCs via antic-kit), and then followed by addition of the new contestants (infusion of the donor HSCs). Once the music stops (fading of the a4b1-integrin blockade), the overabundance of donor HSCs would hopefully have a competitive advantage for successfully sitting down into the chairs (the HSC niche).…”

Cytoreductive conditioning for severe combined immunodeficiency – help or hindrance?

“…However, the benefit for the individual patient has to be balanced against the risks of adverse effects [7]. Antibody-based conditioning alone [16,17] appears to be less effective than as part of a minimal intensity regimen [18].…”