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Published on: August 25, 2017
Use of an oversized AAV8 vector for CPS1 deficiency results in long-term survival and ammonia control
Taryn Diep1, Wesley Zhou1, Rachel E Reyes1,2,3
1Department of Surgery, David Geffen School of Medicine at UCLA, Los Angeles, CA, USA.
Insights
Gene therapy using an oversized adeno-associated virus (AAV) vector successfully treated Carbamoyl phosphate synthetase 1 (CPS1) deficiency in mice. This approach controlled hyperammonemia, demonstrating potential for treating this severe urea-cycle disorder.
Area of Science:
- Biochemistry
- Genetics
- Molecular Biology
Background:
- Carbamoyl phosphate synthetase 1 (CPS1) deficiency is a severe urea-cycle disorder causing hyperammonemia and high neonatal mortality.
- Current treatments are limited, creating a significant unmet medical need, particularly for neonates.
- Adeno-associated virus (AAV)-based gene therapy development is challenged by the large CPS1 cDNA size and high protein expression requirements.
Purpose of the Study:
- To develop and evaluate an oversized AAV vector gene therapy for Carbamoyl phosphate synthetase 1 (CPS1) deficiency.
- To assess the efficacy of this gene therapy in a mouse model of CPS1 deficiency, focusing on ammonia control and long-term survival.
Main Methods:
- An oversized AAV vector (AAV8.CPS1) was engineered using small liver-specific promoters/enhancers and a minimal polyadenylation signal to constrain genome size.
- The AAV8.CPS1 vector was administered to Cps1flox/flox mice, a model for CPS1 deficiency.
- Outcomes including survival, ammonia levels, glutamine levels, and physical condition were monitored over nine months.
Main Results:
- AAV8.CPS1 administration resulted in long-term survival (9 months) and effective ammonia control in treated mice.
- All control mice injected with a null vector died from marked hyperammonemia.
- Female mice showed improved survival compared to treated males; glutamine remained elevated, but ammonia was controlled.
Conclusions:
- The study demonstrates proof of concept for an oversized AAV gene therapy approach for CPS1 deficiency.
- This strategy addresses the challenges of large cDNA size and high protein requirements for treating urea-cycle disorders.
- The findings highlight the potential of gene therapy for severe genetic metabolic diseases requiring substantial hepatic protein expression.
Abstract:
Carbamoyl phosphate synthetase 1 (CPS1) deficiency, a urea-cycle disorder, results in hyperammonemia initiating a sequence of adverse events that can lead to coma and death if not treated rapidly. There is a high unmet need for an effective therapeutic for this disorder, especially in early neonatal patients where mortality is excessive. However, development of an adeno-associated virus (AAV)-based approach is hampered by large cDNA size and high protein requirement. We developed an oversized AAV vector as a gene therapy to treat CPS1 deficiency. In order to constrain genome size, we utilized small liver-specific promoter/enhancers and a minimal polyadenylation signal. Long-term survival (9 months, end of study) with ammonia control was achieved in AAV8.CPS1-administered Cps1flox/flox mice, while all null vector-injected controls died with marked hyperammonemia; female mice demonstrated improved survival over treated males. While glutamine remained elevated compared to controls, ammonia was controlled in surviving animals. Mice maintained their weights and were not sarcopenic. While drinking water did contain carglumic acid, no nitrogen scavengers were administered. Although there were concerns with vector genomic integrity, these findings demonstrate proof of concept for an oversized gene-therapy approach for a challenging urea-cycle disorder where high-level hepatic protein is essential for survival.
