Team reprograms blood cells into HSCs in mice

Lab mouse

Researchers have found a way to reprogram mature blood cells from mice into hematopoietic stem cells (HSCs), according to a paper published in Cell.

The team used 8 transcription factors to reprogram blood progenitor cells and mature mouse myeloid cells into HSCs.

These cells, called induced HSCs (iHSCs), have the functional hallmarks of natural HSCs, are able to self-renew like natural HSCs, and can give rise to all of the cellular components of the blood.

“Blood cell production invariably goes in one direction—from stem cells, to progenitors, to mature effector cells,” said study author Derrick J. Rossi, PhD, of Boston Children’s Hospital in Massachusetts.

“We wanted to reverse the process and derive HSCs from differentiated blood cells using transcription factors that we found were specific to HSCs.”

To that end, Dr Rossi and his colleagues screened gene expression in 40 different types of blood and blood progenitor cells from mice. From this screen, the team identified 36 transcription factors that are expressed in HSCs but not in the cells that arise from them.

In a series of mouse transplantation experiments, the researchers found that 6 of the 36 transcription factors—Hlf, Runx1t1, Pbx1, Lmo2, Zfp37, and Prdm5—plus 2 additional factors not originally identified in their screen—Mycn and Meis1—were sufficient to reprogram 2 kinds of blood progenitor cells—pro/pre-B cells and common myeloid progenitor cells—into iHSCs.

The team reprogrammed their source cells by exposing them to viruses containing the genes for all 8 transcription factors and a molecular switch that turned the factor genes on in the presence of doxycycline. They then transplanted the exposed cells into recipient mice and activated the genes by giving the mice doxycycline.

The resulting iHSCs were capable of generating the entire blood cell repertoire in the transplanted mice, showing they had gained the ability to differentiate into all blood lineages. Stem cells collected from those recipients were capable of reconstituting the blood of secondary transplant recipients, proving that the 8-factor cocktail could instill the capacity for self-renewal.

Taking the work a step further, the researchers treated mature mouse myeloid cells with the same 8-factor cocktail. The resulting iHSCs produced all of the blood lineages and could regenerate the blood of secondary transplant recipients.

Study author Stuart Orkin, MD, of the Dana-Farber Cancer Institute in Boston, noted that the use of mice as a kind of reactor for reprogramming marks a novel direction in HSC research.

“In the blood research field, no one has the conditions to expand HSCs in the tissue culture dish,” he said. “Instead, by letting the reprogramming occur in mice, Rossi takes advantage of the signaling and environmental cues HSCs would normally experience.”

Dr Orkin added that iHSCs are nearly indistinguishable from normal HSCs at the transcriptional level. Unfortunately, though, these findings are far from translation to the clinic.

Researchers must still ascertain the precise contribution each of the 8 transcription factors makes in the reprogramming process and determine whether approaches that do not rely on viruses and transcription factors can have similar success.

In addition, studies are needed to test whether these results can be achieved using human cells and if other, non-blood cells can be reprogrammed to iHSCs.

Lab mouse

Researchers have found a way to reprogram mature blood cells from mice into hematopoietic stem cells (HSCs), according to a paper published in Cell.

The team used 8 transcription factors to reprogram blood progenitor cells and mature mouse myeloid cells into HSCs.

These cells, called induced HSCs (iHSCs), have the functional hallmarks of natural HSCs, are able to self-renew like natural HSCs, and can give rise to all of the cellular components of the blood.

“Blood cell production invariably goes in one direction—from stem cells, to progenitors, to mature effector cells,” said study author Derrick J. Rossi, PhD, of Boston Children’s Hospital in Massachusetts.

“We wanted to reverse the process and derive HSCs from differentiated blood cells using transcription factors that we found were specific to HSCs.”

To that end, Dr Rossi and his colleagues screened gene expression in 40 different types of blood and blood progenitor cells from mice. From this screen, the team identified 36 transcription factors that are expressed in HSCs but not in the cells that arise from them.

In a series of mouse transplantation experiments, the researchers found that 6 of the 36 transcription factors—Hlf, Runx1t1, Pbx1, Lmo2, Zfp37, and Prdm5—plus 2 additional factors not originally identified in their screen—Mycn and Meis1—were sufficient to reprogram 2 kinds of blood progenitor cells—pro/pre-B cells and common myeloid progenitor cells—into iHSCs.

The team reprogrammed their source cells by exposing them to viruses containing the genes for all 8 transcription factors and a molecular switch that turned the factor genes on in the presence of doxycycline. They then transplanted the exposed cells into recipient mice and activated the genes by giving the mice doxycycline.

The resulting iHSCs were capable of generating the entire blood cell repertoire in the transplanted mice, showing they had gained the ability to differentiate into all blood lineages. Stem cells collected from those recipients were capable of reconstituting the blood of secondary transplant recipients, proving that the 8-factor cocktail could instill the capacity for self-renewal.

Taking the work a step further, the researchers treated mature mouse myeloid cells with the same 8-factor cocktail. The resulting iHSCs produced all of the blood lineages and could regenerate the blood of secondary transplant recipients.

Study author Stuart Orkin, MD, of the Dana-Farber Cancer Institute in Boston, noted that the use of mice as a kind of reactor for reprogramming marks a novel direction in HSC research.

“In the blood research field, no one has the conditions to expand HSCs in the tissue culture dish,” he said. “Instead, by letting the reprogramming occur in mice, Rossi takes advantage of the signaling and environmental cues HSCs would normally experience.”

Dr Orkin added that iHSCs are nearly indistinguishable from normal HSCs at the transcriptional level. Unfortunately, though, these findings are far from translation to the clinic.

Researchers must still ascertain the precise contribution each of the 8 transcription factors makes in the reprogramming process and determine whether approaches that do not rely on viruses and transcription factors can have similar success.

In addition, studies are needed to test whether these results can be achieved using human cells and if other, non-blood cells can be reprogrammed to iHSCs.

Lab mouse

Researchers have found a way to reprogram mature blood cells from mice into hematopoietic stem cells (HSCs), according to a paper published in Cell.

The team used 8 transcription factors to reprogram blood progenitor cells and mature mouse myeloid cells into HSCs.

These cells, called induced HSCs (iHSCs), have the functional hallmarks of natural HSCs, are able to self-renew like natural HSCs, and can give rise to all of the cellular components of the blood.

“Blood cell production invariably goes in one direction—from stem cells, to progenitors, to mature effector cells,” said study author Derrick J. Rossi, PhD, of Boston Children’s Hospital in Massachusetts.

“We wanted to reverse the process and derive HSCs from differentiated blood cells using transcription factors that we found were specific to HSCs.”

To that end, Dr Rossi and his colleagues screened gene expression in 40 different types of blood and blood progenitor cells from mice. From this screen, the team identified 36 transcription factors that are expressed in HSCs but not in the cells that arise from them.

In a series of mouse transplantation experiments, the researchers found that 6 of the 36 transcription factors—Hlf, Runx1t1, Pbx1, Lmo2, Zfp37, and Prdm5—plus 2 additional factors not originally identified in their screen—Mycn and Meis1—were sufficient to reprogram 2 kinds of blood progenitor cells—pro/pre-B cells and common myeloid progenitor cells—into iHSCs.

The team reprogrammed their source cells by exposing them to viruses containing the genes for all 8 transcription factors and a molecular switch that turned the factor genes on in the presence of doxycycline. They then transplanted the exposed cells into recipient mice and activated the genes by giving the mice doxycycline.

The resulting iHSCs were capable of generating the entire blood cell repertoire in the transplanted mice, showing they had gained the ability to differentiate into all blood lineages. Stem cells collected from those recipients were capable of reconstituting the blood of secondary transplant recipients, proving that the 8-factor cocktail could instill the capacity for self-renewal.

Taking the work a step further, the researchers treated mature mouse myeloid cells with the same 8-factor cocktail. The resulting iHSCs produced all of the blood lineages and could regenerate the blood of secondary transplant recipients.

Study author Stuart Orkin, MD, of the Dana-Farber Cancer Institute in Boston, noted that the use of mice as a kind of reactor for reprogramming marks a novel direction in HSC research.

“In the blood research field, no one has the conditions to expand HSCs in the tissue culture dish,” he said. “Instead, by letting the reprogramming occur in mice, Rossi takes advantage of the signaling and environmental cues HSCs would normally experience.”

Dr Orkin added that iHSCs are nearly indistinguishable from normal HSCs at the transcriptional level. Unfortunately, though, these findings are far from translation to the clinic.

Researchers must still ascertain the precise contribution each of the 8 transcription factors makes in the reprogramming process and determine whether approaches that do not rely on viruses and transcription factors can have similar success.

In addition, studies are needed to test whether these results can be achieved using human cells and if other, non-blood cells can be reprogrammed to iHSCs.