Pre-existing AAV capsid-specific CD8+ T cells are unable to eliminate AAV-transduced hepatocytes

Area of Science:

• Immunology
• Gene Therapy
• Hepatology

Background:

• Adeno-associated virus (AAV) vectors are crucial for in vivo gene therapy.
• Immune responses, particularly CD8(+) T cells, can limit the efficacy of AAV-mediated gene transfer.
• The role of pre-existing T cell immunity to AAV capsids in long-term gene expression remains unclear.

Purpose of the Study:

• To investigate whether pre-existing adeno-associated virus (AAV) capsid-specific CD8(+) T cells impact the duration of hepatic gene expression mediated by AAV vectors.
• To compare the immune response and gene expression outcomes in mice with pre-existing AAV immunity versus naive controls.

Main Methods:

• Mice were immunized with adenoviral or AAV vectors to induce AAV capsid-specific CD8(+) T cells and neutralizing antibodies.
• At the peak of the T cell response, mice received a heterologous AAV vector encoding human Factor IX under a hepatocyte-specific promoter.
• Hepatic Factor IX expression levels were monitored and compared between pre-immunized and naive mice.

Main Results:

• Mice with pre-existing CD8(+) T cells targeting shared AAV2 and AAV8 epitopes developed robust T cell and antibody responses.
• Despite the presence of cytotoxic CD8(+) T cells in the liver, sustained hepatic Factor IX expression was observed.
• Factor IX expression levels were comparable between AAV-pre-exposed and naive mice, indicating no significant impact of pre-existing T cells on gene transfer longevity.

Conclusions:

• Pre-existing CD8(+) T cell immunity to AAV capsid does not appear to compromise the long-term efficacy of hepatic AAV-mediated gene transfer in this mouse model.
• These findings contrast with observations in human hemophilia B trials, where T cell responses were associated with loss of gene expression, highlighting potential species-specific differences in immune surveillance of AAV gene therapy.