Alector : August 2022 Corporate Presentation

Alector Company Overview

August 2022

Forward-Looking Statement

This presentation contains forward-looking statements that involve substantial risks and uncertainties. All statements other than statements of historical facts contained in this presentation are forward-looking statements. In some cases, you can identify forward-looking statements by terminology such as "anticipate," "believe," "continue," "could," "estimate," "expect," "intend," "may," "plan," "potentially," "predict," "should," "will" or the negative of these terms or other similar expressions. Forward-looking statements contained in this presentation also include, but are not limited to, statements regarding: our future financial condition, results of operations, business strategy and plans, plans, timelines and expectations related to our product candidates and our other clinical and pre-clinical programs, including with respect to the availability of data, the initiation of future clinical trials and plans and expectations regarding planned regulatory filings with respect to such programs; and objectives of management for future operations, as well as statements regarding industry trends.

We have based these forward-looking statements largely on our current expectations and projections about future events and trends that we believe may affect our financial condition, results of operations, business strategy and financial needs. These forward-looking statements are subject to a number of risks, uncertainties and assumptions, including, among other things: Alector's plans relating to the development and manufacturing of its product candidates and research programs; the ability of Alector, Inc.'s ("Alector") clinical trials to demonstrate safety and efficacy of its product candidates, and other positive results; the timing and focus of Alector's future clinical trials, and the reporting of data from those trials; Alector's plans relating to commercializing its product candidates, if approved, including the geographic areas of focus and sales strategy; the expected potential benefits of strategic collaborations with third parties and Alector's ability to attract collaborators with development, regulatory and commercialization expertise; Alector's estimates of the number of patients in the United States who suffer from the diseases it is targeting and the number of patients that will enroll in its clinical trials; the size of the market opportunity for Alector's product candidates in each of the diseases it is targeting; Alector's ability to expand its product candidates into additional indications and patient populations; the success of competing therapies that are or may become available; the beneficial characteristics, safety, efficacy, and therapeutic effects of Alector's product candidates; the timing or likelihood of regulatory filings and approvals, including Alector's expectation to seek special designations, such as orphan drug designation, for its product candidates for various diseases; Alector's ability to obtain and maintain regulatory approval of its product candidates; Alector's plans relating to the further development and manufacturing of its product candidates, including additional indications that it may pursue; existing regulations and regulatory developments in the United States and other jurisdictions; Alector's continued reliance on third parties to conduct additional clinical trials of its product candidates, and for the manufacture of its product candidates for preclinical studies and clinical trials; and the other risks, uncertainties and assumptions discussed in the public filings we have made and will make with the Securities and Exchange Commission ("SEC"). These risks are not exhaustive. New risk factors emerge from time to time and it is not possible for our management to predict all risk factors, nor can we assess the impact of all factors on our business or the extent to which any factor, or combination of factors, may cause actual results to differ materially from those contained in, or implied by, any forward-looking statements. You should not rely upon forward-looking statements as predictions of future events. Although we believe that the expectations reflected in the forward-looking statements are reasonable, we cannot guarantee future results, levels of activity, performance or achievements.

This presentation also contains results based on data from our clinical trials. These clinical trials are ongoing and this presentation does not speak to, and you should make no assumptions about, any additional data. In addition, the information we have chosen to publicly disclose regarding our product candidates has been selected from a more extensive amount of available information. You or others may not agree with what we determine is the material or otherwise appropriate information to include in our disclosure, and any information we determine not to disclose may ultimately be deemed significant with respect to future decisions, conclusions, views, activities or otherwise. If the initial data that we report differ from updated, late, final or actual results, or if others, including regulatory authorities, disagree with the conclusions reached, our ability to obtain approval for, and commercialize our other product candidates may be harmed, which could harm our business, financial condition, results of operations and prospects.

Except as required by law, we undertake no obligation to update any statements in this presentation for any reason after the date of this presentation.

We have filed Current Reports on Form 8-K, Quarterly Reports on Form 10-Q, Annual Reports on Form 10-K, and other documents with the SEC. You should read these documents for more complete information about us. You may obtain these documents for free by visiting EDGAR on the SEC website at www.sec.gov.

This presentation discusses certain investigational therapeutic agents, which have not yet been approved for marketing by the U.S. Food and Drug Administration. No representation is made as to the safety or effectiveness of our product candidate for the therapeutic use for which it is being studied.

This presentation contains statistical data based on independent industry publications or other publicly available information, as well as other information based on our internal sources. We have not independently verified the accuracy or completeness of the data contained in these industry publications and other publicly available information. Accordingly, we make no representations as to the accuracy or completeness of that data.

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Experienced Leadership and Advisors Guide Clinical and Corporate Execution

M A N A G E M E N T

Arnon Rosenthal, PhD

CEO, Co-founder

Sara Kenkare-Mitra, PhD

President, Head of R&D

Gary Romano, MD, PhD

CMO

Peter Heutink, PhD

Incoming CSO

Marc Grasso, MD

CFO

Robert King, PhD

CDO

Kristina Vlaovic

SVP, Regulatory and

Pharmacovigilance

BOARD OF DIRECTORS

Arnon Rosenthal, PhD

David Wehner

Kristine Yaffe, MD

Louis Lavigne

Paula Hammond, PhD

Richard Scheller, PhD

Terry McGuire

Tillman Gerngross, PhD

Elizabeth Garofalo, MD

SCIENTIFIC ADVISORY BOARD

Thomas C. Südhof, PhD

Richard Scheller, PhD

Liqun Luo, PhD

Steve Hauser, MD

Adam Boxer, MD, PhD

Lewis Lanier, PhD

Berislav Zlokovic, MD, PhD

Michael Heneka, MD

Robert Vassar, PhD

Aaron Gitler, PhD

Martin Kampmann, PhD

Proprietary and Confidential Property of Alector

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Translating Scientific Insights into a Broad Portfolio of First-in-Class Programs

NOVEL

APPROACH

MULTIPLE CLINICAL TRIALS

Founded to pioneer a new field of research:

Immuno-neurology

Phase III Clinical Program

for FTD-PGRN

Informed by neuroscience,	Substantial IP portfolio
human genetics and	established: 20 issued patents,
immunology	450+ patent applications

Clinical Programs for	Pre-Clinical Programs
AD, FTD-GRN, FTD-	for AD, PD, Solid tumors
C9ORF72, ALS

WORLD CLASS PARTNERS

$700M upfront	$205M upfront payment
$1.5B+ milestone	$20M equity investment
50-50 U.S. profit share	$986M milestone payments
Tiered double-digit royalties ex-U.S.	Global 50-50 profit share

STRONG		$809 MILLION IN CASH
FINANCIALS

FTD = Frontotemporal dementia, PD = Parkinson's Disease, AD = Alzheimer's Disease, ALS = Amyotrophic lateral sclerosis

Proprietary and Confidential Property of Alector

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Immuno-Neurology: Alector's Therapeutic Strategy for Degenerative Brain Disorders

Recruiting microglia, the brain's immune system,

to potentially cure neurodegeneration

Immuno-neurology

Therapeutics

Ineffective and	Effective and
beneficial microglia
damaging microglia

Using the immuno-oncology concept of harnessing

the immune system as a broad, effective

and long-lasting therapy

Multiple programs are in or entering the clinic for

multiple neurodegenerative diseases

Human Genetics

Develop drugs targeting risk

genes for neurodegeneration to functionally enhance protective functions of these risk genes

Immunology

Target checkpoint
regulators on
microglia and
harness microglia as	Neuroscience
broad therapy for	Rejuvenate microglia and
neurodegeneration
harness their physiological
	role as guardians of brain
	health

Immuno-neurology: targeting the brain immune system as a
novel therapeutic strategy for dementia and neurodegeneration	5