Sustained elevation of neutrophils in rats induced by lentivirus-mediated G-CSF delivery.
BACKGROUND
Patients with severe chronic and cyclic neutropenia, characterized by neutrophil numbers <500 cells/microl, are treated daily with recombinant granulocyte colony-stimulating factor (G-CSF). As an alternative delivery approach we investigated the ability of lentivirus vectors to provide sustained G-CSF expression.


METHODS
Fischer rats were injected intramuscularly (IM) with vesicular stomatitis virus G (VSV-G)-pseudotyped lentivirus pRRL-CMV-G-CSF-SIN that encoded rat G-CSF cDNA regulated by the human cytomegalovirus (CMV) promoter and incorporated a self-inactivating (SIN) construct in the 3' long terminal repeat (LTR). Control rats received normal saline or lentivirus encoding the enhanced green fluorescent protein (eGFP). Rats were serially monitored for blood cell production and tissues assayed for provirus distribution.


RESULTS
Rats receiving a single IM injection of lentivirus exhibited elevated neutrophil counts for 14 months. Virus administration of 6 x 10(7) infectious units induced sustained levels of neutrophil production having a mean +/- standard deviation (SD) of 5650 +/- 900 cells/microl and rats that received a 10-fold lower dose of virus showed mean neutrophil counts of 3340 +/- 740 cells/microl. These were significantly higher than the mean of control animals receiving saline or control lentivirus (1,760 +/- 540 cells/microl, P < 0.0001). White blood cell (WBC) counts were significantly elevated in treated over control animals (P < 0.0001). Hematocrits (P > 0.3), lymphocytes (P > 0.2) and platelets (P > 0.1) were not significantly different between control and treated animals. Genomic DNA from muscle at the injection sites was positive for provirus, whereas lung, spleen, liver, kidney and non-injected muscle samples were all negative, suggesting lack of virus spread.


CONCLUSIONS
These studies indicate that lentivirus vectors administered IM provide sustained, therapeutic levels of neutrophils and suggest this approach to treat patients with severe and cyclic neutropenia.
Barry
Simon
S
Department of Pediatrics, University of Washington School of Medicine, Seattle, WA 98195, USA.
Brzezinski
Margaret
M
Yanay
Ofer
O
Seppen
Jurgen E
JE
Osborne
William R A
WR
D000818:Animals; D015316:Genetic Therapy / Q000379:methods*; D005822:Genetic Vectors / Q000008:administration & dosage / Q000235:genetics / Q000627:therapeutic use*; D016179:Granulocyte Colony-Stimulating Factor / Q000235:genetics / Q000627:therapeutic use*; D049452:Green Fluorescent Proteins / Q000235:genetics; D006400:Hematocrit; D016086:Lentivirus / Q000235:genetics*; D007958:Leukocyte Count; D009503:Neutropenia / Q000628:therapy*; D009504:Neutrophils / Q000502:physiology; D016133:Polymerase Chain Reaction; D011533:Proviruses / Q000302:isolation & purification*; D051381:Rats; D011916:Rats, Inbred F344; D014721:Vesicular stomatitis Indiana virus / Q000235:genetics
C485184:enhanced green fluorescent protein; D016179:Granulocyte Colony-Stimulating Factor; D049452:Green Fluorescent Proteins