AVROBIO Reports Third Quarter 2021 Financial Results and Provides Business Update Provided comprehensive safety update on AVROBIO s lentiviral gene therapy platform and programs at ESGCT 2021 Received FDA feedback on CMC

AVROBIO Reports Third Quarter 2021 Financial Results and

Provides Business Update

Provided comprehensive safety update on AVROBIO s lentiviral gene therapy platform and

programs at ESGCT 2021

Received FDA feedback on CMC requirements for anticipated Fabry disease registration trial;

registration study initiation anticipated for mid-2022

Cash runway extended into fourth quarter of 2023

Secured up to $65 million in availability of non-dilutive term loan financing

CAMBRIDGE, Mass., Nov. 4, 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 Sept. 30, 2021, and provided a business update.

believe the data update provided at the 2021 European Society of Gene & Cell Therapy (ESGCT) Virtual Congress in October continues to strengthen the risk/benefit profile of our

first-in-class lentiviral gene therapy platform, said Geoff MacKay, president and CEO of AVROBIO. The safety data to date, combined with the efficacy and

durability data previously announced, continue to support the potential of our one-time gene therapies to transform the lives of patients living with life-limiting lysosomal disorders.

Additionally, we recently received feedback from the U.S. Food and Drug Administration (FDA) on chemistry, manufacturing and controls (CMC) requirements

for the Fabry disease registrational trial and are planning to successfully meet regulatory requirements prior to the planned initiation of the registration trial in mid-2022, adds MacKay.

Activities across the pipeline remain robust. With approximately two years of cash runway, and multiple data and regulatory updates as well as several trial initiations expected over the next 12 months, we head into 2022 with strong business

momentum and in a solid financial position.

Program Updates and Milestones

Received feedback from FDA in September 2021 on CMC requirements for Fabry disease registration trial:

Provided comprehensive safety update on AVROBIO s Fabry disease and Gaucher disease programs at ESGCT:

Received Rare Pediatric Disease Designation from FDA for

AVR-RD-05, a gene therapy for Mucopolysaccharidosis Type II (MPSII) or Hunter syndrome

Multiple program milestones anticipated over the next 12 months:

Up to $65 million in availability of non-dilutive financing secured with Silicon Valley Bank

Appointed Essra Ridha, M.D., to chief medical officer, bringing wide-ranging expertise in early- and late-stage clinical development of ex

vivo lentiviral gene therapies, in October 2021

Third Quarter 2021 Financial Results

AVROBIO reported a net loss of $32.6 million for the third quarter of 2021 as compared to a net loss of $36.8 million for the comparable period in

2020. This decrease in net loss was driven by decreased research and development expenses, partially offset by increased general and administrative expenses.

Research and development expenses were $23.0 million for the third quarter of 2021 as compared to $28.5 million for the comparable period in 2020.

This decrease was driven by an $8.0 million upfront license fee we paid for our Hunter program during the third quarter of 2020, offset by increased program development activities related to the advancement of the company s pipeline.

General and administrative expenses were $9.6 million for the third quarter of 2021 as compared to $8.2 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

As of September 30, 2021, AVROBIO had $201.4 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 September 30, 2021, together with $15 million drawn at close from

the term loan announced today, will enable the company to fund its operating expenses and capital expenditure requirements into the fourth 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

Forward-Looking Statements

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 our product candidates, including timing and design of planned clinical trials for such 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, 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

Ten Bridge Communications

CONDENSED CONSOLIDATED BALANCE SHEETS

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS

(In thousands, except per share data)