AVROBIO Reports Second Quarter 2021 Financial Results and Provides Business Update U.S. Food and Drug Administration granted Fast Track Designation to AVR-RD-04 for cystinosis Company is planning to initiate multiple reg

AVROBIO Reports Second Quarter 2021 Financial Results and

Provides Business Update

U.S. Food and Drug Administration granted Fast Track Designation to

AVR-RD-04 for cystinosis

Company is planning to

initiate multiple registration trials in 2022

Multiple data and regulatory updates anticipated over next 12 months

CAMBRIDGE, Mass., Aug. 5, 2021 AVROBIO, Inc. (Nasdaq: AVRO), a leading clinical-stage gene therapy company with a mission to free people

from a lifetime of genetic disease, today reported financial results for the quarter ended June 30, 2021, and provided a business update.

from the patients dosed to date across three indications continue to support our first-in-class, one-time investigational gene

therapies as potentially transformative treatments for the more than 50,000 people worldwide living with the life-limiting lysosomal disorders we are researching, said Geoff MacKay, president and CEO of AVROBIO. In the second half of

this year, we plan to share updated safety data from our ongoing clinical trials and plan to meet with regulatory agencies to discuss initiating potential registration trials in 2022 for Fabry disease, cystinosis and Gaucher disease type 3. With our

Pompe disease and Hunter syndrome programs anticipated to enter the clinic in 2022, we remain fiercely committed to our purpose: to free people living with genetic disease from a lifetime of symptoms, chronic treatment and inevitable disease

Multiple program milestones anticipated over the next 12 months

AVR-RD-01 in Fabry disease:

AVR-RD-04 in cystinosis:

Gaucher disease programs:

Second Quarter 2021 Financial Results

net loss of $31.4 million for the second quarter of 2021 as compared to a net loss of $28.8 million for the comparable period in 2020. This increase was driven by increased research and development expenses as well as increased general and

administrative expenses.

Research and development expenses were $22.5 million for the second quarter of 2021 as compared to

$20.9 million for the comparable period in 2020. 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, which includes the impact of non-cash stock-based compensation.

administrative expenses were $8.9 million for the second quarter of 2021 as compared to $8.0 million for the comparable period in 2020. This increase was primarily due to an increase in employee headcount, which includes the impact of non-cash stock-based compensation, which was offset by a decrease in facilities costs, professional fees and legal fees.

As of June 30, 2021, AVROBIO had $226.4 million in cash and cash equivalents, as compared to $259.7 million in cash and cash equivalents as of

Dec. 31, 2020. Based on the company s current operating plan, AVROBIO expects its cash and cash equivalents as of June 30, 2021 will enable the company to fund its operating expenses and capital expenditure

requirements into the first quarter of 2023.

Our vision is to bring personalized gene therapy to the world. We aim to prevent, halt or reverse disease throughout the body with a single dose of gene

therapy designed to drive durable expression of therapeutic protein, even in hard-to-reach tissues and organs including brain, muscle and bone. Our ex vivo lentiviral

gene therapy pipeline includes clinical programs in Fabry disease, Gaucher disease type 1 and cystinosis, as well as preclinical programs in Hunter syndrome, Gaucher disease type 3 and Pompe disease. AVROBIO is powered by our

industry-leading plato gene therapy platform, our foundation designed to deliver gene therapy worldwide. We are headquartered in Cambridge, Mass., with an office in Toronto,

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 and phrases such as aims,

anticipates, believes, could, designed to, estimates, expects, forecasts, goal, intends, may, plans,

possible, potential, seeks, will, and variations of these words and phrases or similar expressions that are intended to identify forward-looking statements. These forward-looking statements include,

without limitation, statements regarding our business strategy for and the

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

regulatory pathways, our plans and expectations with respect to the development of AVR-RD-01,

AVR-RD-04 and AVR-RD-06, including timing and design of potential registration trials for

such product candidates, the intended use of such trials as our registration trials for these product candidates, and anticipated interactions with regulatory agencies, the timing of new clinical and regulatory updates, anticipated benefits of our

gene therapy platform including potential impact on our commercialization activities, timing and likelihood of success, the expected benefits and results of our implementation of the plato

platform in our clinical trials and gene therapy programs, the expected safety profile of our investigational gene therapies, and statements regarding our 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 regulatory agencies may disagree with

our anticipated development approach for our product candidates such as AVR-RD-01,

AVR-RD-04 and AVR-RD-06, including that regulatory agencies may require additional

clinical testing prior to initiating registration trials for such product candidates, that we may not be able to utilize our planned registration trial of AVR-RD-01 for

full approval but instead be required to conduct additional testing, that we may be required to conduct our planned testing in a more time-consuming, expensive, challenging or otherwise different manner than we envision or have conducted for our

existing trials, particularly in light of the FDA s preference for clinical trials to be double-blinded and potentially include sham controls, the risk that we may not be able to utilize our envisioned surrogate endpoint to support full

approval of AVR-RD-01 but instead be required to measure a different endpoint such as a clinical outcome, the risk that AVROBIO may not successfully recruit or enroll a

sufficient number of patients for our clinical trials, 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, risks relating to clinical trial and business interruptions resulting from the COVID-19 outbreak or similar public

health crises, including that such interruptions may materially delay our enrollment and development timelines and/or increase our development costs or that data collection efforts may be impaired or otherwise impacted by such crises, 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, 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

Ten Bridge Communications

CONDENSED CONSOLIDATED BALANCE SHEETS

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS

(In thousands, except per share data)