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Research Update
RESEARCH UPDATE
Gene Therapy for Hemophilia A
A
nimal models of hemophilia A have been successfully treated with gene therapy. A gene encoding clotting factor VIII was delivered into the animals’ cells using a retroviral vector. The study was reported in the 26 April 2005 issue of the Proceedings of the National Academy of Sciences. “We are really pleased with the results, because the animals produced about 20 times more factor than has been achieved in prior attempts using gene therapy for hemophilia A in dogs,” says senior author Katherine Parker Ponder in a related press release. The blood of the mice and dogs in this study has maintained a normal level of clotting factor activity for over a year, and the animals have had no incidents of bleeding. The viral vector carrying factor VIII genes was injected into the blood of 11 newborn hemophilic mice and two newborn hemophilic dogs. The viral vector also contained a short liver-specific promoter. The mice achieved an average of 139 percent of normal factor VIII activity and the dogs an average of 115 percent of normal factor VIII activity in a blood-clotting assay. In comparison, untreated animals with hemophilia A have less than one percent normal factor VIII activity. Working with newborn animals has certain advantages. Their livers are still growing, so that genes integrated into a liver cell will be reproduced with each new generation of cells. The treated mice had an average of two factor VIII genes per liver cell. In the dogs, an average of one in eight liver cells had the new gene. Second, newborn mice and dogs have less mature immune systems than do adults, making it less likely they will raise an immune response to the introduced factor VIII. The immune reaction, known as inhibitor formation, dimin-
822
ishes the activity of the clotting factor and has caused failure in previous attempts to correct hemophilia in mice using gene therapy. The Proceedings of the National Academy of Science, doi: 10.1073/pnas.0409249102
Yeast Screen Identifies Potential HIV Targets
H
ost genes required to support the replication of HIV are a potential source of new drug targets, but relatively few target genes have been identified thus far. A study by Dr. Suzanne Sandmeyer and colleagues describes over 100 host genes that affect the replication of a model retrovirus. The results are reported in the May 2005 issue of Genome Research. Many organisms harbor mobile nonpathogenic molecular relatives of retroviruses. In budding yeast, these mobile elements—called Ty or transposable yeast elements—encode proteins that are homologs of retroviral proteins. The proteins encoded by Ty elements and the steps of the life cycle in yeast are similar to the animal retrovirus counterparts, suggesting that these simple elements in a singlecelled organism could be a useful model for studying how retroviruses such as HIV interact with their hosts. The workers screened a collection of over 4457 mutant yeast strains representing most of the known genes in yeast. They then solicited the help of computer scientist Pierre Baldi to focus on gene functions likely to be particularly significant in the Ty3 lifecycle. Together, they developed an interactive program called Gonet that allowed them to identify clusters that are likely to affect key points in the Ty3 lifecycle. In total, they identified 130 genes that affect the replication of the retrovirus-like element Ty3. Over half of the genes identified in this study have at least one clear rela-
tive or homolog in the human genome, thus providing a rich source of candidate retrovirus host genes. Genome Research, online edition, doi: 10.1101/gr.3739005
Microarrays Identify New HSC Control Genes
A
study published in the May 2005 issue of Developmental Cell identifies new key players in the regulation of hematopoietic stem cells. The hematopoietic stem cell (HSC) can renew itself or differentiate into progenitors that then form red blood cells, various types of white blood cells, or platelets. Blood cells must be renewed throughout the lifetime of an animal, so control and regulation of HSCs is critical for survival. The workers used microarray analysis to examine purified subsets of defined blood-cell populations containing progenitors or HSCs from multiple stages of human development. The researchers identified two genes that act independently to enhance cell-cycle progression and inhibit cell death specifically in HSCs. The role of one gene, HES-1, ties in with the cellcycle-associated Notch signaling pathway. The second gene, HLF, is a DNAbinding transcription factor involved in preventing premature HSC death. Increasing the amount of either gene in human HSCs increased their capacity to form blood cells when they were transferred into mice. The researchers conclude that HES1 and HLF are regulators of HSC behavior. Because HES-1 and HLF impact HSC function via two different mechanisms involving integral pathways common to all human cells, the authors suggest that HSC behavior may be controlled by general rather than HSC-specific genes. Developmental Cell, online edition, doi: 10.1016/j.devcell.2005.03.004
MOLECULAR THERAPY Vol. 11, No. 6, June 2005 Copyright © The American Society of Gene Therapy
Gene Therapy for Hemophilia A
A
nimal models of hemophilia A have been successfully treated with gene therapy. A gene encoding clotting factor VIII was delivered into the animals’ cells using a retroviral vector. The study was reported in the 26 April 2005 issue of the Proceedings of the National Academy of Sciences. “We are really pleased with the results, because the animals produced about 20 times more factor than has been achieved in prior attempts using gene therapy for hemophilia A in dogs,” says senior author Katherine Parker Ponder in a related press release. The blood of the mice and dogs in this study has maintained a normal level of clotting factor activity for over a year, and the animals have had no incidents of bleeding. The viral vector carrying factor VIII genes was injected into the blood of 11 newborn hemophilic mice and two newborn hemophilic dogs. The viral vector also contained a short liver-specific promoter. The mice achieved an average of 139 percent of normal factor VIII activity and the dogs an average of 115 percent of normal factor VIII activity in a blood-clotting assay. In comparison, untreated animals with hemophilia A have less than one percent normal factor VIII activity. Working with newborn animals has certain advantages. Their livers are still growing, so that genes integrated into a liver cell will be reproduced with each new generation of cells. The treated mice had an average of two factor VIII genes per liver cell. In the dogs, an average of one in eight liver cells had the new gene. Second, newborn mice and dogs have less mature immune systems than do adults, making it less likely they will raise an immune response to the introduced factor VIII. The immune reaction, known as inhibitor formation, dimin-
822
ishes the activity of the clotting factor and has caused failure in previous attempts to correct hemophilia in mice using gene therapy. The Proceedings of the National Academy of Science, doi: 10.1073/pnas.0409249102
Yeast Screen Identifies Potential HIV Targets
H
ost genes required to support the replication of HIV are a potential source of new drug targets, but relatively few target genes have been identified thus far. A study by Dr. Suzanne Sandmeyer and colleagues describes over 100 host genes that affect the replication of a model retrovirus. The results are reported in the May 2005 issue of Genome Research. Many organisms harbor mobile nonpathogenic molecular relatives of retroviruses. In budding yeast, these mobile elements—called Ty or transposable yeast elements—encode proteins that are homologs of retroviral proteins. The proteins encoded by Ty elements and the steps of the life cycle in yeast are similar to the animal retrovirus counterparts, suggesting that these simple elements in a singlecelled organism could be a useful model for studying how retroviruses such as HIV interact with their hosts. The workers screened a collection of over 4457 mutant yeast strains representing most of the known genes in yeast. They then solicited the help of computer scientist Pierre Baldi to focus on gene functions likely to be particularly significant in the Ty3 lifecycle. Together, they developed an interactive program called Gonet that allowed them to identify clusters that are likely to affect key points in the Ty3 lifecycle. In total, they identified 130 genes that affect the replication of the retrovirus-like element Ty3. Over half of the genes identified in this study have at least one clear rela-
tive or homolog in the human genome, thus providing a rich source of candidate retrovirus host genes. Genome Research, online edition, doi: 10.1101/gr.3739005
Microarrays Identify New HSC Control Genes
A
study published in the May 2005 issue of Developmental Cell identifies new key players in the regulation of hematopoietic stem cells. The hematopoietic stem cell (HSC) can renew itself or differentiate into progenitors that then form red blood cells, various types of white blood cells, or platelets. Blood cells must be renewed throughout the lifetime of an animal, so control and regulation of HSCs is critical for survival. The workers used microarray analysis to examine purified subsets of defined blood-cell populations containing progenitors or HSCs from multiple stages of human development. The researchers identified two genes that act independently to enhance cell-cycle progression and inhibit cell death specifically in HSCs. The role of one gene, HES-1, ties in with the cellcycle-associated Notch signaling pathway. The second gene, HLF, is a DNAbinding transcription factor involved in preventing premature HSC death. Increasing the amount of either gene in human HSCs increased their capacity to form blood cells when they were transferred into mice. The researchers conclude that HES1 and HLF are regulators of HSC behavior. Because HES-1 and HLF impact HSC function via two different mechanisms involving integral pathways common to all human cells, the authors suggest that HSC behavior may be controlled by general rather than HSC-specific genes. Developmental Cell, online edition, doi: 10.1016/j.devcell.2005.03.004
MOLECULAR THERAPY Vol. 11, No. 6, June 2005 Copyright © The American Society of Gene Therapy