Pre-existing AAV Capsid-specific CD8+ T Cells are Unable to Eliminate AAV-transduced Hepatocytes

Abstract

The goal of these studies was to test whether adeno-associated virus (AAV) capsid-specific CD8(+) T cells cause loss of hepatic AAV-mediated gene expression in experimental animals. Mice immunized with adenoviral vectors expressing AAV capsid or with AAV vectors developed CD8(+) T cells in blood, lymphatic tissues, and liver to epitopes shared between AAV2 and AAV8, and serotype-specific neutralizing antibodies. At the height of the T cells' effector phase, mice were infused with a heterologous AAV vector expressing human factor IX under a hepatocyte-specific promoter. Despite the presence of lytic CD8(+) T cells in the liver, hepatic Factor IX expression was sustained and comparable in AAV-preimmune and naïve animals. These results suggest that, in mice, pre-existing CD8(+) T cells to AAV capsid do not affect the longevity of AAV-mediated hepatic gene transfer. These results are in contrast to the outcome of a recent gene therapy trial of hemophilia B patients who were treated by hepatic gene transfer of AAV2 vectors expressing Factor IX. The loss of Factor IX expression, accompanied by a rise in liver enzymes and detectable frequencies of circulating AAV capsid-specific T cells, suggested T-cell-mediated destruction of transduced hepatocytes following reactivation of AAV-specific T cells upon AAV transfer.

Immunity to adeno-associated virus vectors in animals and humans: a continued challenge

“…50 Several studies demonstrated that AAV capsid-specific CTLs also do not appear to play a role in elimination of AAVtransduced cells in mouse models. 85,86 The fact that capsid-specific T cells in animal models were unable to lyse AAV-transduced hepatocytes sparked a scientific debate about alternative explanations other than capsid cross-presentation. One interesting consideration was that latent AAV genomes, which occur endogenously with high abundance in humans, might have become activated by homologous recombination with vector genomes-leading to the expression of capsid proteins.…”

Augmentation of Primary Influenza A Virus-Specific CD8+ T Cell Responses in Aged Mice through Blockade of an Immunoinhibitory Pathway

“…RBCs were lysed with ACK lysis buffer (Life Technologies, Grand Island, NY) treatment for 1-5 min. Lymphocytes were isolated from spleen and liver as described previously (39). Lymphocytes were isolated from lungs as follows.…”

“…Splenocytes were in addition stained with a live cell dye, Abs to CD8 and CD44 and the NP-tet to determine percentages of NP-responsive CD8 + T cells. Percent-specific lysis was calculated as described (39).…”

AAV for pain: steps towards clinical translation

“…The investigators therefore suggested that the loss of transgene production was caused by cellular immunity. 38,[41][42][43] The notion that cellular immunity is directed against the capsid protein may seem counterintuitive, because the vector does not express the capsid gene; instead, the capsid protein present in the recombinant vector at the time of administration seems to persist for several weeks in vivo, marking targeted cells for immunemediated cytotoxic destruction. The scientific quandary ironically derives from the fact that no such reaction seems to occur in any animal model.…”