459. Long-Term Treatment of Canine Cyclic Neutropenia by G-CSF-Lentivirus

Cyclic neutropenia (CN) occurs both in man and grey collie dogs and is characterized by recurrent periods of neutropenia leading to bacterial infections and shortened life expectancy. Daily rG-CSF provides therapy for patients and dogs. To treat CN by gene therapy we constructed a VSV-G pseudotyped lentivirus encoding canine G-CSF cDNA regulated by CMV promoter, cPPT from HIV 1 and PRE from human hepatitis B virus. At 7 weeks of age when an affected grey collie dog was weaned, serial blood counts were monitored. These data showed the dog's absolute neutrophil counts (ANC) were cycling and observations over 4 cycles established a 12 day periodicity. The ANC mean|[plusmn]|SD during nadirs and peaks were 560|[plusmn]|787 cells/|[mu]|l and 10,760|[plusmn]|1,120 cells/|[mu]|l respectively and overall counts were 5,240|[plusmn]|4,790 cells/|[mu]|l. Having established that neutrophils were cycling, recombinant canine G-CSF was administered subcutaneously at a dose of 1.5 |[mu]|g/kg per weekday for two months. Although ANC continued to cycle, we observed significant increases in neutrophils both at the nadirs and the peaks of cycles (p<0.0001) with mean values of 4,860|[plusmn]|2,670 cells/|[mu]|l and 28,870|[plusmn]|9,830 cells/|[mu]|l respectively. Over this period the mean count was 17,820|[plusmn]|11,100 cells/|[mu]|l. After demonstrating that rG-CSF elevated neutrophil production cytokine administration was stopped and we administered IM 2|[times]|109 infectious units(IU) of G-CSF-lentivirus. The dog showed no ill effects to the virus injections. Serial monitoring of blood cells showed elevated ANC for over 17 months with mean value of 29,230|[plusmn]|12,930 cells/|[mu]|l (n=217) that was significantly increased over both no treatment and rG-CSF treatment (p<0.0001). The increases in ANC from recombinant G-CSF and lentivirus administration were associated with absence of clinical signs of infection and fever.