AVROBIO Reports Second Quarter 2019 Financial Results and Provides Business Update Reported positive interim results from clinical trials of AVR-RD-01 investigational gene therapy in Fabry disease, including 87% substrat

AVROBIO Reports Second Quarter 2019 Financial Results

and Provides Business Update

Reported positive interim results from clinical trials of

AVR-RD-01 investigational gene therapy in Fabry disease, including 87% substrate reduction in first kidney biopsy at one year post-treatment

On track to dose first patients in Phase 1/2 clinical trials for Gaucher and cystinosis this year

Raised $129 million in net proceeds from follow-on equity offering in July, extending cash

runway into the second half of 2021

CAMBRIDGE, Mass., August 8, 2019 AVROBIO, Inc. (NASDAQ: AVRO) (the Company ), a Phase 2

clinical-stage gene therapy company, today reported financial results for the second quarter ended June 30, 2019 and provided a business update.

We have made substantial progress across our entire pipeline, especially in our clinical program for AVR-RD-01 in Fabry disease. We believe the compelling interim data from the Phase 2 and Phase 1 trials announced in July serves to both validate our approach to treating patients with Fabry disease, as well

as support our pipeline of investigational gene therapies for other lysosomal storage disorders, commented Geoff MacKay, President and Chief Executive Officer of AVROBIO. Clinical milestones anticipated later this year include the

transition to our plato platform and the dosing of the first patients in the Gaucher and cystinosis trials. With our balance sheet strengthened by our recent follow-on equity offering, we believe we are well positioned to continue executing on our development and commercialization strategies.

Program Updates and Milestones

Recruitment continues to progress in FAB-201 in the United States (U.S.), Canada and Australia. This trial will

continue to evaluate the safety and efficacy of AVR-RD-01 in up to 8 to 12 treatment-na ve patients. The remaining patients

in FAB-201 are planned to be dosed using plato, AVROBIO s commercially scalable platform, consisting of a

state-of-the-art four-plasmid vector system, automation of a closed cell manufacturing process and a conditioning regimen

utilizing therapeutic drug monitoring (TDM). A total of 8 patients have been dosed across FAB-201 and the investigator-sponsored Phase 1 clinical trial of AVR-RD-01, which completed enrollment in February 2019.

Second Quarter 2019 Financial Results

AVROBIO reported a net loss of $16.1 million for the second quarter of 2019 as compared to a net loss of $10.5 million for the comparable period in

2018. This increase was due to increased research and development expenses, as well as increased general and administrative expenses.

development expenses were $12.3 million for the second quarter of 2019 as compared to $7.4 million for the comparable period in 2018. This increase was driven by increased program development activities related to the advancement of the

Company s pipeline, as well as increased personnel-related costs resulting from an increase in employee headcount.

General and administrative

expenses were $4.3 million for the second quarter of 2019 as compared to $2.1 million for the comparable period in 2018. This increase was primarily due to an increase in employee headcount, expenses associated with being a publicly traded

company, including consulting and legal expenses, and the impact of non-cash stock-based compensation.

June 30, 2019, AVROBIO had $90.3 million in cash and cash equivalents, as compared to $126.3 million in cash and cash equivalents as of December 31, 2018. In July 2019, the Company raised net proceeds of approximately

$129.5 million from a follow-on equity offering. The Company expects that the net proceeds from the equity offering, along with AVROBIO s cash and cash equivalents as of June 30, 2019, will

enable the Company to fund its operating expenses and capital expenditure requirements into the second half of 2021.

AVROBIO, Inc. is a leading, Phase 2 gene therapy company focused on the development of its investigational gene therapy, AVR-RD-01, in Fabry disease, as well as additional gene therapy programs in other lysosomal storage disorders including Gaucher disease, cystinosis and Pompe disease. The

Company s plato platform includes a proprietary vector system, automated cell manufacturing solution and refined conditioning regimen deploying therapeutic drug

monitoring. AVROBIO is headquartered in Cambridge, MA and has offices in Toronto, ON. For additional information, visit www.avrobio.com.

Forward-Looking Statements

This press release contains

forward-looking statements, including statements made pursuant to the safe harbor provisions of the Private Securities Litigation Reform Act of 1995. These statements may be identified by words such as aims, anticipates,

believes, could, estimates, expects, forecasts, goal, intends, may, plans, possible, potential, seeks,

will, and variations of these words or similar expressions that are intended to identify forward-looking statements. These forward-looking statements include, without limitation, statements regarding our business strategy, prospective

products and goals, the therapeutic potential of our product candidates, the design, commencement, enrollment and timing of ongoing or planned clinical trials, clinical trial results, product approvals and regulatory pathways, potential regulatory

approvals and the timing thereof, anticipated benefits of our gene therapy platform including potential impact on our commercialization activities, the expected safety profile of our product candidates, timing and likelihood of success of our

current or future product candidates, plans and objectives of management for future operations, future results of anticipated products, and the market opportunity for our product candidates, and statements regarding the Company s financial and

cash position and expected cash runway. Any such statements in this press release that are not statements of historical fact may be deemed to be forward-looking statements. Results in preclinical or early stage clinical trials may not be indicative

of results from later stage or larger scale clinical trials and do not ensure regulatory approval. You should not place undue reliance on these statements, or the scientific data presented.

Any forward-looking statements in this press release are based on AVROBIO s current expectations,

estimates and projections about our industry as well as management s current beliefs and expectations of future events only as of today and are subject to a number of risks and uncertainties that could cause actual results to differ materially

and adversely from those set forth in or implied by such forward-looking statements. These risks and uncertainties include, but are not limited to, the risk that any one or more of AVROBIO s product candidates will not be successfully developed

or commercialized, the risk of cessation or delay of any ongoing or planned clinical trials of AVROBIO or our collaborators, the risk that AVROBIO may not realize the intended benefits of our gene therapy platform, including the features of our

plato platform, the risk that our product candidates or procedures in connection with the administration thereof will not have the safety or efficacy profile that we anticipate, the risk that prior results, such as signals of safety, activity or

durability of effect, observed from preclinical or clinical trials, will not be replicated or will not continue in ongoing or future studies or trials involving AVROBIO s product candidates, the risk that we will be unable to obtain and

maintain regulatory approval for our product candidates, the risk that the size and growth potential of the market for our product candidates will not materialize as expected, risks associated with our dependence on third-party suppliers and

manufacturers, risks regarding the accuracy of our estimates of expenses and future revenue, risks relating to our capital requirements and needs for additional financing, and risks relating to our ability to obtain and maintain intellectual

property protection for our product candidates. For a discussion of these and other risks and uncertainties, and other important factors, any of which could cause AVROBIO s actual results to differ materially and adversely from those contained

in the forward-looking statements, see the section entitled Risk Factors in AVROBIO s most recent Quarterly Report on Form 10-Q, as well as discussions of potential risks, uncertainties and

other important factors in AVROBIO s subsequent filings with the Securities and Exchange Commission. AVROBIO explicitly disclaims any obligation to update any forward-looking statements except to the extent required by law.

Christopher F. Brinzey

Westwicke, an ICR Company

CONDENSED CONSOLIDATED BALANCE SHEETS

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS

(In thousands, except share and per share data)