Subretinal gene replacement rescues retinal phenotype in BBS10 mouse

Abstract

Purpose : To assess toxicity and efficacy of subretinal gene replacement in BBS10 mice. Overexpression toxicity in BBS1 mice occurred with gene therapy;BBS1 is part of the BBSome, while BBS10 is part of the BBS/CCT chaperonin complex.

Methods : A knock out mouse model of Bardet Biedl Syndrome type 10 (BBS10) was developed. AAV2/5-Bbs10FLAG and AAV2/Anc80-Bbs10FLAG vectors were created. Subretinal 2 ul injections of 1E12, 2E12 or 4E12VG/ml were performed in 62 Bbs10-/-and 12 WT mice. Immunoblotting and immunohistochemistry were utilized to assess protein production and restoration of Bbs10 gene function. ERG, OCT, and visually guided swim assay (VGSA) were used to assess efficacy. Due to COVID-19, long term data was collected only for 12 mice treated with 2E9 or 4E9 AAV2/Anc80-Bbs10FLAG and 3 controls.

Results : Neither AAV2/5-Bbs10FLAG nor AAV2/Anc80-Bbs10FLAG were toxic in WT or Bbs10-/-. One month after injection, FLAG was detected in treated, but not untreated Bbs10-/-eyes, documenting presence of BBS10 protein.BBS7,undetectable or barely detectable within photoreceptor cilia in untreated Bbs10^-/-eyes,was present in photoreceptor cilia in treated Bbs10^-/-eyes.VGSA was partially rescued via either AAV2/5 or AAV2/Anc80 treated at P30-P60 when tested in the dark at age 3.5 months(p= 1.36E-005)and in both light and dark at age 7 months (p=. <0.0001 light; p= 0.0094 dark). VGSA improvement endured in AAV2/Anc80 treated mice at 9-12 months old(p=0.0113). Treated eyes had higher amplitude ERG than untreated fellow eyes at 10-11.5 months old (highest p=0.0425). OCT at 11-14 months demonstrated presence of outer nuclear layer in 5/11 treated eyes compared to 0/11 untreated fellow eyes and 0/6 untreated control eyes. 5Hz flicker response was not present at any age in untreated Bbs10^-/-(n=18 eyes), but developed in 9 of 12 eyes treated before 4 months old. 4 of 12 treated eyes still had recordable 5 Hz at 11-14 mos, all treated with 4E9. Histology at 11 months demonstrated robust ONL, inner and outer segments with numerous cones, and normal localization of STX3 adjacent to the injection site in 2 treated eyes.

Conclusions : In the Bbs10^-/-mouse subretinal gene therapy with AAV2/Anc80-Bbs10FLAG rescues retinal phenotype . Lack of 5 Hz flicker ERG response in untreated eyes was rescued with early high titer gene therapy suggesting that BBS10 plays an early role in cone development and/or function. Human BBS10 clinical trials are needed.

This is a 2021 ARVO Annual Meeting abstract.