GenSight Biologics : Notice of General Meeting on June 11, 2019

CONVENING OF THE COMBINED GENERAL MEETING

ON JUNE 11, 2019

GENSIGHT BIOLOGICS

A French Société Anonyme (corporation)

with share capital of 718,113.53 Euros

74 rue du Faubourg Saint Antoine 75012 Paris

751 164 757 Paris Trade and Companies Registry

Summary

BRIEF STATEMENT OF THE COMPANY'S SITUATION ..............................................................	1
AGENDA..............................................................................................................................	8
TEXT OF THE DRAFT RESOLUTIONS.....................................................................................	10
REPORT OF THE BOARD OF DIRECTORS TO THE COMBINED GENERAL MEETING OF JUNE 11,
2019..................................................................................................................................	22
PARTICIPATE IN THE GENERAL MEETING ............................................................................	39
REQUEST FOR ADDITIONAL DOCUMENTS AND INFORMATION............................................	41

BRIEF STATEMENT OF THE COMPANY'S SITUATION

GenSight Biologics S.A. is a clinical-stage biopharma company focused on discovering and developing innovative gene therapies for retinal neurodegenerative diseases and central nervous system disorders. GenSight Biologics' pipeline leverages two core technology platforms, the Mitochondrial Targeting Sequence (MTS) and optogenetics to help preserve or restore vision in patients suffering from blinding retinal diseases. GenSight Biologics' lead product candidate, GS010, is in Phase III trials in Leber Hereditary Optic Neuropathy (LHON), a rare mitochondrial disease that leads to irreversible blindness in teens and young adults. Using its gene therapy-based approach, GenSight Biologics' product candidates are designed to be administered in a single treatment to each eye by intravitreal injection to offer patients a sustainable functional visual recovery.

Financial Situation

The Company's operating income increased by 17.4% from €3.7 million in 2017 to €4.3 million in 2018. This income was primarily in the form of research tax credit (Crédit Impôt Recherche), amounting to €3.7 million and €4.3 million in 2017 and 2018, respectively.

Research and Development expenses increased by 55.5% from €18.7 million in 2017 to €29.0 million in 2018. This significant increase reflects a continuous ramp up of research and development activities, both in CMC and manufacturing activities in anticipation for regulatory submission of GS010 expected in Europe at the end of 2019, and in clinical development with three Phase III trials ongoing with GS010 and one Phase I/II trial with GS030, as well as a license milestone payment related to GS030 entering Phase I/II in October 2018.

General and administrative expenses decreased by 14.2% over the period, amounting to €8.2 million and €7.0 million in 2017 and 2018, respectively. This decrease was primarily related to personnel expenses, and more specifically to decreasing social contributions and non-cashshare-based compensation expenses in relation with performance shares granted to management and employees in 2016 and 2017.

• GENSIGHT BIOLOGICS CONVENING / Combined General Meeting on June 11, 2019

Sales and marketing expenses increased by 60.0% over the period, amounting to €0.8 million and €1.4 million in 2017 and 2018, respectively.

The Company's net loss in 2017 amounted to €24.1 million compared to €33.5 million in 2018. The loss per share (based on the weighted average number of shares outstanding over the period) amounted to €(1.10) and €(1.37) for 2017 and 2018, respectively.

Net cash flows from operating activities in 2017 and 2018 were €(18.8) million and €(28.4) million, respectively, primarily as a result of the significant increase in operating expenses, partly compensated by a decrease in non-cashshare-based compensation expenses over the period.

Net cash flows from financing activities amounted to €20.9 million and €(0.1) million in 2017 and 2018, respectively, primarily as a result of the net proceeds of the private placement in June 2017.

Research and Development

On January 10, 2018, Gensight Biologics announced UK Medicines and Healthcare Regulatory Agency (MHRA) acceptance of the Company's Clinical Trial Application (CTA) to initiate the PIONEER Phase I/II study of GS030 in patients with Retinitis Pigmentosa (RP). PIONEER is a first-in-man,multi-center, open label dose-escalation study to evaluate the safety and tolerability of GS030 in subjects with Retinitis Pigmentosa. GS030 is the combination of a gene therapy (GS030-DP) administered via a single intravitreal injection and a wearable optronic visual stimulation device (GS030-MD).

On April 3, 2018, GenSight Biologics announced topline results from the REVERSE Phase III clinical trial evaluating the safety and efficacy of a single intravitreal injection of GS010 (rAAV2/2-ND4) in 37 subjects whose visual loss due to 11778-ND4 Leber Hereditary Optic Neuropathy (LHON) commenced between 6 and 12 months prior to study treatment. Topline results further highlight the favorable safety and tolerability profile of GS010, and demonstrate a clinically meaningful improvement of +11 ETDRS letters (-0.218 LogMAR) in treated eyes at 48 weeks as compared to baseline in all 37 patients. Unexpectedly, untreated contralateral eyes (treated with a sham injection) show a similar improvement of +11 ETDRS letters (-0.211 LogMAR). Due to this improvement in untreated eyes, the trial did not meet its primary endpoint, defined as a difference of improvement in visual acuity in GS010-treated eyes compared to sham-treated eyes at 48 weeks.

The critical secondary endpoint of the change in retinal ganglion cell macular volume measured from baseline to week 48 demonstrated a statistically significant difference (p = 0.0189) between all GS010-treated eyes and all sham-treated eyes, with untreated eyes losing 0.038 cubic mm of macular ganglion cell volume while treated eyes preserved their ganglion cell volume (-0.003 cubic mm).

The secondary endpoint of change in thickness of the temporal quadrant and papillomacular bundle of the retinal nerve fiber layer from baseline to week 48 demonstrated a large statistically significant difference (p = 0.0359) between all GS010-treated eyes and all sham- treated eyes, with untreated eyes showing a loss of 3.4 μm while treated eyes showed a limited loss of 0.6 μm.

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On June 12, 2018, GenSight Biologics reported additional results from the REVERSE Phase III clinical trial.

Further analyses now demonstrate that, although some secondary endpoints did not show significant or meaningful changes, contrast sensitivity as determined by Pelli-Robson low- vision testing almost doubled in the GS010-treated eyes compared to sham-treated eyes. GS010-treated eyes started with lower contrast sensitivity (0.25 LogCS on average) than sham- treated eyes (0.35 LogCs on average). At week 48, GS010-treated eyes gained on average +0.20 LogCS, and the contrast sensitivity in shamtreated eyes remained stable (+0.08 LogCS on average).

In addition, post hoc analyses revealed trends that suggest GS010 may have a larger positive impact on the visual acuity of patients at relatively less advanced or severe stages of the disease:

• Subjects who entered study with better vision (on-chart eyes) tended to have better clinical outcomes. At week 48, in on-chartbest-seeing eyes, GS010-treated eyes gained on average +12 ETDRS letters (-0.236 LogMAR) compared to +4 ETDRS letters (-0.075 LogMAR) in sham-treated eyes.
• Subjects whose vision loss was less than 9 months tended to have better clinical outcomes. 75% of GS010-treated eyes that showed a trend in visual acuity improvement at week 48 had vision loss for less than 9 months at time of treatment administration.
• Subjects who were younger (< 21 years) at enrollment tended to have better clinical outcomes

On September 13, 2018, GenSight Biologics provided an update on the clinical and regulatory pathways for GS010. The revised regulatory pathway incorporates the findings of the REVERSE (CLIN03B) clinical trial, key results of which were announced in June 2018.

The unexpected results on BCVA highlighted the importance of gaining more insights into the results observed at Week 48 by obtaining an earlier readout prior to the planned Week 96 analysis. GenSight has therefore added a Week 72 (18-month) readout to planned post-hoc analyses.

On October 18, 2018, GenSight Biologics reported additional results at Week 72 from the REVERSE Phase III clinical trial.

At 72 weeks, a clinically meaningful improvement from baseline in mean visual acuity of +15 letters (-0.294 LogMAR) was observed in GS010-treated eyes, with concomitant contralateral improvement of +12 letters (-0.246 LogMAR)1 in sham-treated eyes. This improvement, which extends the positive trend that had been reported at Week 48, points to a sustained functional outcome for the trial subjects.

Continued improvement was also observed in contrast sensitivity as determined by Pelli- Robson low-contrast testing. At 72 weeks, GS010-treated eyes and sham-treated eyes gained on average +0.21 LogCS and +0.15 LogCS versus baseline, respectively. The proportion of treated eyes that achieved a clinically meaningful improvement of at least 0.3 LogCS (45.9%) was statistically significantly higher than that of sham-treated eyes (24.3%; p=0.0047).

The visual function outcomes were accompanied by evidence that GS010 was engaging its anatomic targets, the ganglion cells. At 72 weeks, high-resolutionSpectral-Domain Optical

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Coherence Tomography (SD-OCT) objectively demonstrated sustained preservation of the retina anatomy relevant to LHON in GS010-treated eyes. The ganglion cell layer macular volume was preserved (+0.000 mm3) in treated eyes, while sham-treated eyes deteriorated from baseline (-0.044 mm3). The difference was statistically significant (p=0.0060). Drug- treated eyes also showed a limited loss in thickness of the temporal quadrant of the retinal fiber layer of -1.6 µm, compared to a loss of -3.6 µm in sham-treated eyes (p=0.0521).

On October 26, 2018, GenSight Biologics announced that the first subject was treated in the first-in-man PIONEER Phase I/II clinical trial of GS030 at the Moorfields Eye Hospital in London, United Kingdom. PIONEER is a first-in-man,multi-center, open label dose-escalation study to evaluate the safety and tolerability of GS030 in 18 subjects with Retinitis Pigmentosa. GS030 combines a gene therapy (GS030- DP) administered via a single intravitreal injection with a wearable optronic visual stimulation device (GS030-MD).

On December 12, 2018, GenSight Biologics reported that Week 72 analyses of the data from its Phase III REVERSE clinical trial revealed a sustained improvement in composite scores and selected sub-scores of a questionnaire used to measure patient perceptions of vision-related quality of life and ability to carry out daily activities impacted by loss of visual acuity.

All 37 patients in REVERSE were asked to complete the National Eye Institute Visual Function Questionnaire-25 (NEI VFQ-25), a reliable and valid vision-specificquality-of-life instrument that measures patients' perception of their ability to perform daily activities requiring high- acuity vision and their general sense of well-being. The test defines sub-scales for functions such as near-distance vision and vision-related dependency as well as measures of well-being such as ocular pain and vision-related mental health. These sub-scale scores are aggregated into a composite score, excluding the general health rating question.

At Week 72, REVERSE patients reported mean improvement from baseline for NEI VFQ-25 scores in domains important to patients with loss of central vision: near activities, distance activities, vision-specific dependency and composite score. An improvement had already been observed at Week 48, confirming sustained enhancement of ability to perform activities of daily living. In addition, large improvements were also noted in other domains relevant to LHON patients: role difficulties, general vision, and overall mental health. Again, the improvements observed at Week 48 were sustained at Week 72. The relevant comparison in REVERSE is against patients' own baseline, because the NEI VFQ-25 is assessed by patient; by design, all REVERSE patients received an injection in one eye.

On February 4, 2019, GenSight Biologics reported results from the first scheduled readout, at Week 48, of the RESCUE Phase III clinical trial evaluating the safety and efficacy of a single intravitreal injection of GS010 (rAAV2/2-ND4) in 39 subjects whose visual loss due to 11778- ND4 Leber Hereditary Optic Neuropathy (LHON) occurred up to 6 months prior to study treatment. These subjects received GS010 in one eye and a sham injection in the other eye, with drug treatment randomized between best- and worst-affected eyes.

Visual loss in LHON usually progresses such that vision reaches a nadir in 3 to 5 months, before stabilizing; the duration of this progression to nadir varies from patient to patient. In RESCUE, mean best-corrected visual acuity (BCVA) of GS010-treated eyes and sham-treated eyes evolved with similar trajectories, worsening to a low point before showing an improvement at Week 48. At Week 48, change from baseline for GS010-treated eyes was -19 ETDRS letters equivalent, while that for sham-treated eyes -20 ETDRS letters equivalent. These figures incorporate a recovery from the nadir of vision loss for drug- and sham-treated eyes: mean

GENSIGHT BIOLOGICS CONVENING / Combined General Meeting on June 11, 2019

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