13D Filing: Baker Bros. Advisors and Idera Pharmaceuticals Inc. (IDRA)

CUSIP No.   45168K306

Page   6   of   10   Pages

Amendment No. 1 to Schedule 13D

This Amendment No. 1 to Schedule 13D amends and supplements
the previously filed Schedules 13D filed by Baker Bros. Advisors LP (the “Adviser”), Baker Bros. Advisors (GP), LLC
(the “Adviser GP”), Julian C. Baker and Felix J. Baker. Except as supplemented herein, such statements, as heretofore
amended and supplemented, remain in full force and effect.

The Adviser GP is the sole general partner of the Adviser. Pursuant
to the management agreements, as amended, among the Adviser, Baker Brothers Life Sciences, L.P. (“Life Sciences”),
14159, L.P. (“14159”), and 667, L.P. (“667”, and together with Life Sciences and 14159, the “Funds”)
and their respective general partners, the Funds respective general partners relinquished to the Adviser all discretion and authority
with respect to the investment and voting power of the securities held by the Funds, and thus the Adviser has complete and unlimited
discretion and authority with respect to the Funds’ investments and voting power over investments.

 

ITEM 2.

Identity and Background.

 

(a)

The Reporting Persons are:

1.

The Adviser

2.

The Adviser GP

3.

Felix J. Baker

4.

Julian C. Baker

(b)

The business address of each of the Reporting Persons is:

c/o
Baker Bros. Advisors LP

860
Washington Street, 3^rd Floor

New
York, NY 10014

(c) The Adviser is an entity engaged in investment activities,
and the Adviser GP is in the business of acting as its general partner and, through the Adviser, investment activities. The principal
business of each of Julian C. Baker and Felix J. Baker is to serve as a managing member of the Adviser GP.

(d) and (e) During the past five years, none of the Reporting
Persons nor any of the Funds (as defined below) has been (i) convicted in a criminal proceeding (excluding traffic violations or
similar misdemeanors) or (ii) a party to a civil proceeding of a judicial or administrative body of competent jurisdiction and
as a result of such proceeding was or is subject to a judgment, decree or final order enjoining future violations of, or prohibiting
or mandating activities subject to, federal or state securities laws or finding any violation with respect to such laws.

(f) The Adviser is a limited partnership organized under the
laws of the State of Delaware. The Adviser GP is a limited liability company organized under the laws of the State of Delaware.
The citizenship of each of Julian C. Baker and Felix J. Baker is the United States of America.

 

Item 3.

Source and Amount of Funds or Other Consideration.

Item 3 of Amendment No. 1 is supplemented and amended, as the
case may be, as follows:

The disclosure regarding the purchases in Item 4 below is incorporated
herein by reference.