Prolonged multilineage clonal hematopoiesis in a rhesus recipient of CD34 positive cells marked with a RD114 pseudotyped oncoretroviral vector

The ability to efficiently transfer a gene into repopulating hematopoietic stem cells would create many therapeutic opportunities. We have evaluated the ability of particles bearing an alternative envelope protein, that of the feline endogenous virus (RD114), to transduce stem cells in a nonhuman primate autologous transplantation model using rhesus macaques. We have previously shown this pseudotyped vector to be superior to the amphotropic vector at transducing cells in umbilical cord blood capable of establishing hematopoiesis in immunodeficient mice. Gene transfer efficiency as reflected by the number of genetically modified cells in hematopoietic tissues varied among the five monkeys studied from low levels (<1%) in three animals to much higher levels in two (20-60%). An animal that exhibited extremely high levels for several weeks was found by vector genome insertion site analysis to have reconstitution predominantly with a single clone of cells. This variability among animals is in keeping with computer simulations of reconstitution with limiting numbers of stem cells genetically modified at about 10% efficiency. Our studies provide insights into the biology of hematopoietic reconstitution and suggest approaches for increasing stem cell targeted gene transfer efficiency.

PANTHER: a browsable database of gene products organized by biological function, using curated protein family and subfamily classification

The PANTHER database was designed for high-throughput analysis of protein sequences. One of the key features is a simplified ontology of protein function, which allows browsing of the database by biological functions. Biologist curators have associated the ontology terms with groups of protein sequences rather than individual sequences. Statistical models (Hidden Markov Models, or HMMs) are built from each of these groups. The advantage of this approach is that new sequences can be automatically classified as they become available. To ensure accurate functional classification, HMMs are constructed not only for families, but also for functionally distinct subfamilies. Multiple sequence alignments and phylogenetic trees, including curator-assigned information, are available for each family. The current version of the PANTHER database includes training sequences from all organisms in the GenBank non-redundant protein database, and the HMMs have been used to classify gene products across the entire genomes of human, and Drosophila melanogaster. The ontology terms and protein families and subfamilies, as well as Drosophila gene c;assifications, can be browsed and searched for free. Due to outstanding contractual obligations, access to human gene classifications and to protein family trees and multiple sequence alignments will temporarily require a nominal registration fee. PANTHER is publicly available on the web at http://panther.celera.com.

Comparison of various envelope proteins for their ability to pseudotype lentiviral vectors and transduce primitive hematopoietic cells from human blood

Substantial effort has been invested in developing methodologies for efficient gene transfer into human, repopulating, hematopoietic stem cells. Oncoretroviral vectors are limited by the lack of nuclear mitosis in quiescent stem cells during ex vivo transduction, whereas the preintegration complex of lentiviral vectors contains nuclear-localizing signals that permit genome integration without mitosis. We have developed a flexible and versatile system for generating lentiviral vector particles and have pseudotyped such particles with amphotropic, ecotropic, feline endogenous virus (RD114) or vesicular stomatitis virus (VSV-G) envelope proteins. Particles of all four types could be concentrated approximately 100-fold by ultracentrifugation or ultrafiltration. RD114 or amphotropic particles were more efficient than VSV-G-pseudotyped particles at transducing human cord blood CD34(+) cells and clonogenic progenitors within that population. Amphotropic particles transduced cytokine-mobilized, human peripheral blood CD34(+) cells capable of establishing hematopoiesis in immunodeficient mice more efficiently than the other two types of particles. We conclude that the use of amphotropic pseudotyped lentiviral vector particles rather than the commonly used VSV-G-pseudotyped particles should be considered in potential applications of lentiviral vectors for gene transfer into this therapeutically relevant target cell population.