ERYTHROPOIETIC ROLE OF RESIDENT MACROPHAGES IN HEMATOPOIETIC ORGANS

1 . A method of treating a blood disorder comprising erythropoietic stress in a subject, the method comprising administering to the subject an amount of an erythropoiesis-stimulating agent effective to treat a blood disorder comprising erythropoietic stress.

2 . The method of claim 1 , wherein the erythropoiesis-stimulating agent comprises an amount of CD169+ macrophages or is a CSF-1 agonist.

3 . The method of claim 2 , wherein the erythropoiesis-stimulating agent comprises an amount of CD169+ macrophages and wherein the CD169+ macrophages are allogeneic to, or syngeneic to, the subject.

4 . The method of claim 1 , wherein the erythropoietic stress is an anemia.

5 . The method of claim 1 , wherein the erythropoietic stress results from acute blood loss, acute or chronic hemolysis, a hemoglobinopathy, myeloablative injury, hematopoietic stem cell transplant, chemotherapy or irradiation-induced injury.

6 . A method of treating a blood disorder comprising an expanded erythron in a subject, the method comprising administering to the subject an amount of a CD169+ macrophage-ablating agent or CD169+ macrophage inhibiting agent effective to treat a blood disorder comprising an expanded erythron, or comprising administering to the subject an amount of an BMP4-abrogating agent effective to treat a blood disorder comprising an expanded erythron.

7 . The method of claim 6 , wherein the blood disorder comprises polycythemia vera.

8 . The method of claim 6 , wherein the CD169+ macrophage-ablating or CD 169+ macrophage-inhibiting agent is administered in a manner effective to deliver it to bone marrow and/or spleen of a subject.

9 . The method of claim 6 , wherein the CD169+ macrophage-ablating or CD169+ macrophage-inhibiting agent is a human CSF-1 receptor inhibitor.

10 . The method of claim 9 , wherein the human CSF-1 receptor inhibitor is an isolated anti-CSF-1 receptor antibody or a human CSF-1 receptor-binding fragment of such an antibody, or is a human CSF-1-binding nucleic acid aptamer.

11 . A method of determining the prognosis of an erythroid compartment in a subject having erythropoietic stress, comprising

obtaining a bone marrow sample and/or splenic sample from the subject and quantifying CD 169+ macrophages in the sample(s),

comparing the amount of CD169+ macrophages quantified to a predefined reference amount, and

determining the prognosis of the erythroid compartment as a negative or a positive prognosis, wherein an amount of CD 169+ macrophages quantified in excess of the reference amount indicates a positive prognosis, and an amount of CD169+ macrophages quantified below the reference amount indicates a negative prognosis.

12 . The method of claim 11 , further comprising administering a blood product and/or a erythropoiesis-stimulating agent to a subject identified to be in need thereof by being identified as having negative prognosis by the method.

13 . The method of claim 12 , wherein the blood product is administered as a blood transfusion.

14 . The method of claim 12 , wherein the erythropoiesis-stimulating agent comprises an amount of CD169+ macrophages or is a CSF-1 agonist.

15 . The method of claim 14 , wherein the erythropoiesis-stimulating agent comprises an amount of CD169+ macrophages and the CD169+ macrophages are allogeneic to the subject or syngeneic to the subject.

16 . The method of claim 11 , wherein the erythropoietic stress is an anemia.

17 . The method of claim 11 , wherein the erythropoietic stress results from acute blood loss, acute or chronic hemolysis, a hemoglobinopathy, myeloablative injury, hematopoietic stem cell transplant, chemotherapy or irradiation-induced injury.

18 - 21 . (canceled)

22 . A composition comprising isolated CD169+ macrophages and a pharmaceutically acceptable carrier.

23 . The composition of claim 22 , wherein the isolated CD169+ macrophages are enriched in the composition relative to the same volume in a human bone marrow or human splenic sample.

24 - 33 . (canceled)