UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

o

Rule 13d-1(b)

x

Rule 13d-1(c)

o

Rule 13d-1(d)

CUSIP No. 014442107

1

Names of Reporting Persons
Merck & Co., Inc.

2

Check the Appropriate Box if a Member of a Group (See Instructions)

(a)

o

(b)

o

3

SEC Use Only

4

Citizenship or Place of Organization
New Jersey

Number of
Shares
Beneficially
Owned by
Each
Reporting
Person With:

5

Sole Voting Power
3,545,719

6

Shared Voting Power
0

7

Sole Dispositive Power
3,545,719

8

Shared Dispositive Power
0

9

Aggregate Amount Beneficially Owned by Each Reporting Person
3,545,719

10

Check Box if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  o

11

Percent of Class Represented by Amount in Row (9)
5.1%*

12

Type of Reporting Person (See Instructions)
HC

CUSIP No. 014442107

1

Names of Reporting Persons
Merck Sharp & Dohme Corp.

2

Check the Appropriate Box if a Member of a Group (See Instructions)

(a)

o

(b)

o

3

SEC Use Only

4

Citizenship or Place of Organization
New Jersey

Number of
Shares
Beneficially
Owned by
Each
Reporting
Person With:

5

Sole Voting Power
3,545,719

6

Shared Voting Power
0

7

Sole Dispositive Power
3,545,719

8

Shared Dispositive Power
0

9

Aggregate Amount Beneficially Owned by Each Reporting Person
3,545,719

10

Check Box if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  o

11

Percent of Class Represented by Amount in Row (9)
5.1%*

12

Type of Reporting Person (See Instructions)
CO

CUSIP No. 014442107

1

Names of Reporting Persons
MRL Ventures Fund LLC

2

Check the Appropriate Box if a Member of a Group (See Instructions)

(a)

o

(b)

o

3

SEC Use Only

4

Citizenship or Place of Organization
Delaware

Number of
Shares
Beneficially
Owned by
Each
Reporting
Person With:

5

Sole Voting Power
3,545,719

6

Shared Voting Power
0

7

Sole Dispositive Power
3,545,719

8

Shared Dispositive Power
0

9

Aggregate Amount Beneficially Owned by Each Reporting Person
3,545,719

10

Check Box if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  o

11

Percent of Class Represented by Amount in Row (9)
5.1%*

12

Type of Reporting Person (See Instructions)
OO

Item 1.

(a)

Name of Issuer:
Alector, Inc.

(b)

Address of Issuer’s Principal Executive Offices:
151 Oyster Point Blvd, Suite 300, South San Francisco, California 94080

Item 2.

(a)

Name of Person Filing:
(1) Merck & Co., Inc.

(2) Merck Sharp & Dohme Corp.

(3) MRL Ventures Fund LLC

(b)

Address of Principal Business Office or, if none, Residence:
(1) Merck & Co., Inc.: 2000 Galloping Hill Road, Kenilworth, NJ 07033

(2) Merck Sharp & Dohme Corp.: One Merck Drive, Whitehouse Station, NJ 08889

(3) MRL Ventures Fund LLC: 320 Bent Street, 4th Fl, Cambridge, MA 02141

(c)

Citizenship:
(1) Merck & Co., Inc.: New Jersey

(2) Merck Sharp & Dohme Corp.: New Jersey

(3) MRL Ventures Fund LLC: Delaware

(d)

Title and Class of Securities:
Common Stock

(e)

CUSIP No.:
014442107

Item 3.

If this statement is filed pursuant to §§ 240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:

(a)

o

Broker or dealer registered under section 15 of the Act;

(b)

o

Bank as defined in section 3(a)(6) of the Act;

(c)

o

Insurance company as defined in section 3(a)(19) of the Act;

(d)

o

Investment company registered under section 8 of the Investment Company Act of 1940;

(e)

o

An investment adviser in accordance with Rule 13d-1(b)(1)(ii)(E);

(f)

o

An employee benefit plan or endowment fund in accordance with Rule 13d-1(b)(1)(ii)(F);

(g)

o

A parent holding company or control person in accordance with Rule 13d-1(b)(1)(ii)(G);

(h)

o

A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);

(i)

o

A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940;

(j)

o

A non-U.S. institution in accordance with Rule 240.13d-1(b)(1)(ii)(J);

(k)

o

Group, in accordance with Rule 240.13d-1(b)(1)(ii)(K). If filing as a non-U.S. institution in accordance with

Rule 240.13d-1(b)(1)(ii)(J), please specify the type of institution:____________________________

Item 4.

Ownership

Provide the following information regarding the aggregate number and percentage of the class of securities of the issuer identified in Item 1.

(a)

Amount beneficially owned:   

3,545,719

The reported securities are owned directly by MRL Ventures Fund LLC (“MRLV”), which is a wholly owned subsidiary of Merck Sharp & Dohme Corp. (“MSD”), which is a wholly owned subsidiary of Merck & Co., Inc. (“Merck”). MSD and Merck are indirect beneficial owners of the reported securities.

(b)

Percent of class:   

5.1%

(c)

Number of shares as to which such person has:

(i)

Sole power to vote or to direct the vote:   

See Cover Pages Items 5-9.

(ii)

Shared power to vote or to direct the vote:    

See Cover Pages Items 5-9.

(iii)

Sole power to dispose or to direct the disposition of:   

See Cover Pages Items 5-9.

(iv)

Shared power to dispose or to direct the disposition of:   

See Cover Pages Items 5-9.

Item 5.

Ownership of Five Percent or Less of a Class.

Not Applicable.

Item 6.

Ownership of More than Five Percent on Behalf of Another Person.

Not Applicable.

Item 7.

Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on By the Parent Holding Company or Control Person.

The reported securities are owned directly by MRLV, which is a wholly owned subsidiary of MSD, which is a wholly owned subsidiary of Merck. MSD and Merck are indirect beneficial owners of the reported securities.

Item 8.

Identification and Classification of Members of the Group.

Not Applicable.

Item 9.

Notice of Dissolution of Group.

Not Applicable.

Item 10.

Certifications.

By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under § 240.14a-11.

MRL VENTURES FUND LLC

By:

/s/ Jon Filderman

Name:

Jon Filderman

Title:

Secretary

MERCK SHARP & DOHME CORP.

By:

/s/ Faye C. Brown

Name:

Faye C. Brown

Title:

Assistant Secretary

MERCK & CO., INC.

By:

/s/ Faye C. Brown

Name:

Faye C. Brown

Title:

Senior Assistant Secretary