Selective immunodepletion of endogenous stem cell niche for engraftment
The present invention provides a clinically applicable method of stem cell transplantation that facilitates engraftment and reconstitutes immunocompetence of the recipient without requiring radiotherapy or chemotherapy, and without development of GVHD or graft rejection. Aspects of the present invention are based on the discovery that the depletion of the endogenous stem cell niche facilitates efficient engraftment of stem cells into that niche. In particular, the present invention combines the use of selective ablation of endogenous stem cells, in combination with the administration to the recipient of exogenous stem cells, resulting in efficient, long-term engraftment and tolerance.
1. A method of hematopoietic stem cell engraftment in a human subject, the method comprising sequential steps of:
(i) an ablative treatment to ablate endogenous hematopoietic stem cells; comprising systemically administering to said subject a monoclonal antibody that specifically binds to human c-kit in a dose effective to selectively ablate at least 20% of endogenous hematopoietic stem cells in bone marrow of the subject, in the absence of radiation or chemotherapy
(ii) a wash-out period of from 7 to 9 days following administration of the monoclonal antibody that specifically binds to human c-kit; and
(iii) transplantation of allogeneic or autologous exogenous hematopoietic stem cells in a dose effective to achieve long term multilineage peripheral blood chimerism, wherein transplantation is performed within 3 days following completion of the wash-out period.
2. The method according to claim 1 , wherein said exogenous stem cells are genetically modified stem cells.
3. The method according to claim 2 , wherein said human suffers from a genetic blood disorder.
4. The method according to claim 3 , wherein said genetic blood disorder is a hemoglobinopathy.
5. The method according to claim 1 , wherein the method is repeated at least twice.
6. The method according to claim 1 , wherein a conditioning agent is administered prior to infusion of exogenous stem cells.
7. The method of claim 6 , wherein the conditioning agent is an antibody specific for one or more of CD4; an NK cell specificity, a macrophage specificity, and CD8.
8. The method of claim 1 , wherein the effective dose of exogenous hematopoietic stem cells is 10 4 to 10 6 cells/kg.
9. The method of claim 1 , wherein completion of the ablative treatment is when the antibody that specifically binds to c-kit is present in the subject circulation at a concentration of less than 10 ng/ml in the bloodstream.
10. The method of claim 1 , wherein completion of the ablative treatment is such that the concentration in patient circulation of the antibody that specifically binds to c-kit is decreased at least 1000-fold from peak levels.
11. The method of claim 1 , wherein the method provides for up to 90% donor cell chimerism.
12. The method of claim 1 , wherein the antibody that specifically binds to c-kit is active in interfering with c-kit growth factor signaling.
13. The method of claim 1 , wherein the antibody that specifically binds to c-kit is active in inducing antibody-dependent cellular cytotoxicity.
14. The method of claim 1 , wherein the antibody that specifically binds to c-kit is conjugated to a toxin.
15. The method of claim 8 , wherein the exogenous hematopoietic stem cells are purified, CD34 + Thy-1 + peripheral blood hematopoietic stem cells.