Alector : Virtual Key Opinion Leader Event on Frontotemporal Dementia

Virtual KOL Event: Frontotemporal Dementia

June 11, 2021

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, including statements regarding our future financial condition, results of operations, business strategy and plans, plans, timelines and expectations related to AL001 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, 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," "target," "will" or the negative of these terms or other similar expressions.

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: the ability of our clinical trials to demonstrate safety and efficacy of our product candidates, and other positive results; the timing and focus of our future clinical trials, and the reporting of data from those trials; our plans relating to commercializing our product candidates, if approved; the expected potential benefits of strategic collaborations with third parties and our ability to attract collaborators with development, regulatory and commercialization expertise; our estimates of the number of patients who suffer from the diseases we are targeting; our ability to expand our product candidates into additional indications and patient populations; the beneficial characteristics, safety, efficacy, and therapeutic effects of our product candidates; our plans relating to the further development and manufacturing of our product candidates, including additional indications we may pursue; our continued reliance on third parties to conduct additional clinical trials of our product candidates, and for the manufacture of our product candidates for preclinical studies and trials; our plans and ability to obtain or protect intellectual property rights; the accuracy of our estimates regarding expenses, future revenue, capital requirements, and needs for additional financing; our financial performance; and the sufficiency of our existing cash and cash equivalents to fund our future operating expenses and capital expenditure requirements. 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, as discussed in greater detail in our filings with the Securities and Exchange Commission (SEC), including without limitation in our Quarterly Report on Form 10-Q, as filed on May 5, 2021 with the Securities and Exchange Commission ("SEC"). 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. Except as required by law, we undertake no obligation to update publicly any forward-looking statements for any reason after the date of this presentation.

In addition, statements that "we believe" and similar statements reflect our beliefs and opinions on the relevant subject. These statements are based upon information available to us as of the date of this presentation, and while we believe such information forms a reasonable basis for such statements, such information may be limited or incomplete, and our statements should not be read to indicate that we have conducted an exhaustive inquiry into, or review of, all potentially available relevant information. These statements are inherently uncertain and investors are cautioned not to unduly rely upon these statements.

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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Agenda and speakers

Topic	Speaker	Timing
Introductory remarks	Shehnaaz Suliman, MD	7:30 AM - 7:35 AM PST
	President and Chief Operating Officer	10:30 AM - 10:35 AM EST
Immunoneurology and PGRN franchise overview	Arnon Rosenthal, Ph.D.	7:35 AM - 7:40 AM PST
	Chief Executive Officer and Co-Founder	10:35 AM - 10:40 AM EST
Alector's AL001 program in frontotemporal	Robert Paul, MD, Ph.D.	7:40 AM - 7:45 AM PST
dementia	Chief Medical Officer	10:40 AM - 10:45 AM EST
GRN-related FTD and trials	Jonathan Rohrer, Ph.D., FRCP	7:45 AM - 8:30 AM PST
		10:45 AM - 11:30 AM EST
The FTD disease cascade and biomarkers	Henrik Zetterberg, MD, Ph.D.	8:30 AM - 9:15 AM PST
		11:30 AM - 12:15 PM EST
Looking ahead to AAIC	Robert Paul, MD, Ph.D.	9:15 AM - 9:25 AM PST
		12:15 PM - 12:25 PM EST
Closing remarks and Q&A	Shehnaaz Suliman, MD	9:25 AM - 10:00 AM PST
	President and Chief Operating Officer	12:25 PM - 1:00 PM EST

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AL001 in frontotemporal dementia with progranulin gene mutation (FTD-GRN)

Results from Alector's Phase 2 study of AL001 in FTD-GRN patients to be

presented at AAIC on July 29, 2021 at 8 AM MT

• 12-monthdata for FTD-GRN patients
• Cognitive outcome assessment data [CDR-NACC-FTLD]
• Disease-relevantbiomarkers [plasma, CSF and vMRI]

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Immunoneurology and PGRN franchise overview

Arnon Rosenthal, Ph.D.

Chief Executive Officer & Co-Founder

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