SEC Form 3

FORM 3

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 INITIAL STATEMENT OF BENEFICIAL OWNERSHIP OF SECURITIES Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person* BAKER FELIX (Last) (First) (Middle) 667 MADISON AVENUE, 21ST FLOOR (Street) NEW YORK NY 10065 (City) (State) (Zip)	2. Date of Event Requiring Statement (Month/Day/Year) 06/22/2015	3. Issuer Name and Ticker or Trading Symbol ALEXION PHARMACEUTICALS INC [ ALXN ]
		4. Relationship of Reporting Person(s) to Issuer (Check all applicable) X Director 10% Owner Officer (give title below) Other (specify below)	5. If Amendment, Date of Original Filed (Month/Day/Year)
			6. Individual or Joint/Group Filing (Check Applicable Line) Form filed by One Reporting Person X Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Beneficially Owned
1. Title of Security (Instr. 4)	2. Amount of Securities Beneficially Owned (Instr. 4)	3. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	4. Nature of Indirect Beneficial Ownership (Instr. 5)

Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 4)	2. Date Exercisable and Expiration Date (Month/Day/Year)		3. Title and Amount of Securities Underlying Derivative Security (Instr. 4)		4. Conversion or Exercise Price of Derivative Security	5. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	6. Nature of Indirect Beneficial Ownership (Instr. 5)
	Date Exercisable	Expiration Date	Title	Amount or Number of Shares

1. Name and Address of Reporting Person* BAKER FELIX (Last) (First) (Middle) 667 MADISON AVENUE, 21ST FLOOR (Street) NEW YORK NY 10065 (City) (State) (Zip)

1. Name and Address of Reporting Person* BAKER JULIAN (Last) (First) (Middle) 667 MADISON AVENUE, 21ST FLOOR (Street) NEW YORK NY 10065 (City) (State) (Zip)

1. Name and Address of Reporting Person* BAKER BROS. ADVISORS LP (Last) (First) (Middle) 667 MADISON AVENUE, 21ST FLOOR (Street) NEW YORK NY 10065 (City) (State) (Zip)

1. Name and Address of Reporting Person* Baker Bros. Advisors (GP) LLC (Last) (First) (Middle) 667 MADISION AVENUE 21ST FLOOR (Street) NEW YORK NY 10065 (City) (State) (Zip)

1. Name and Address of Reporting Person* 667, L.P. (Last) (First) (Middle) 667 MADISON AVENUE 21ST FLOOR (Street) NEW YORK NY 10065 (City) (State) (Zip)

1. Name and Address of Reporting Person* Baker Brothers Life Sciences LP (Last) (First) (Middle) 667 MADISON AVENUE, 21ST FLOOR (Street) NEW YORK NY 10065 (City) (State) (Zip)

Explanation of Responses:

Remarks:

Felix J. Baker is a director of Alexion Pharmaceuticals, Inc. (the "Issuer"). For purposes of Section 16 of the Securities Exchange Act of 1934, as amended the Reporting Persons other than Felix J. Baker are deemed directors by deputization by virtue of their representation on the Board of the Issuer.

No securities are beneficially owned.

	/s/ Felix J. Baker	06/24/2015
	/s/ Julian C. Baker	06/24/2015
	Baker Bros. Advisors LP Name: Scott L. Lessing, Title: President /s/ Scott L. Lessing	06/24/2015
	Baker Bros. Advisors (GP) LLC, Name:Scott L. Lessing, Title: President /s/ Scott L. Lessing	06/24/2015
	Baker Bros. Advisors LP, Mgmt. Co. and Inv. Adviser to 667, L.P., pursuant to authority granted by Baker Biotech Capital, L.P., GP to 667, L.P. Name: Scott L. Lessing, Title: President /s/ Scott L. Lessing	06/24/2015
	Baker Bros. Advisors LP, Mgmt. Co. and Inv. Adviser to Baker Brothers Life Sciences, L.P., pursuant to authority granted by Baker Brothers Life Sciences Capital, L.P., GP to Baker Brothers Life Name: Scott L. Lessing, Title: President /s/ Scott L. Lessing	06/24/2015
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 5 (b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
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