A Study to Evaluate Long-term Safety in Participants Who Have Participated in Other Luspatercept (ACE-536) Clinical Trials

Inclusion Criteria:

Participants must meet all the following criteria to be enrolled in this study:

   1. Participant is ≥ 18 years at the time of signing the informed consent form (ICF).

   2. Participant is willing and able to adhere to the study visit schedule and other
   protocol requirements.

   3. Participant has been participating in a luspatercept trial and continues to fulfill
   all the requirements of the parent protocol and the participant has been either:

      1. Assigned to luspatercept treatment, continues to receive clinical benefit in the
      opinion of the investigator and should continue to receive luspatercept
      treatment, OR

      2. Assigned to placebo arm in the parent protocol (at the time of unblinding or in
      follow-up) and should cross over to luspatercept treatment, OR

      3. Assigned to the Follow-up Phase of the parent protocol, previously treated with
      luspatercept or placebo in the parent protocol who shall continue into Long-term
      Post-treatment Follow-up Phase in the rollover study until the follow-up
      commitments are met (unless requirements are met as per parent protocol to
      crossover to luspatercept treatment).

   4. Participant understands and voluntarily signs an informed consent document prior to
   any study-related assessments or procedures being conducted.

   5. Participant demonstrates compliance, as assessed by the investigator, with the parent
   study protocol requirements.

   6. Applies to on treatment Participants only- females of childbearing potential (FCBP)
   defined as a sexually mature woman who:

1) has achieved menarche at some point, 2) has not undergone a hysterectomy or bilateral
oophorectomy, or 3) has not been naturally postmenopausal (amenorrhea following cancer
therapy or amenorrhea due to other medical reasons does not rule out childbearing
potential) for at least 24 consecutive months (ie, has had menses at any time in the
preceding 24 consecutive months) and must:

   1. Have two negative pregnancy tests as verified by the investigator prior to starting
   study therapy. She must agree to ongoing pregnancy testing during the course of the
   study, and after end of study therapy. This applies even if the participant practices
   true abstinence* from heterosexual contact.

   2. Either commit to true abstinence* from heterosexual contact (which must be reviewed on
   a monthly basis and source documented) or agree to use, and be able to comply with
   highly effective, contraception without interruption, 35 days prior to starting
   investigational product (IP), during the study therapy (including dose interruptions),
   and for 84 days after discontinuation of study therapy.

   7. Applies to on treatment participants only- Male participants must:

a. Practice true abstinence (which must be reviewed on a monthly basis) or agree to use a
condom during sexual contact with a pregnant female or a female of childbearing potential
while participating in the study, during dose interruptions and for at least 84 days
following investigational product discontinuation even if he has undergone a successful
vasectomy.

Exclusion Criteria:

The presence of any of the following will exclude a participant from enrollment:

   1. Applies to on treatment participants only- Concomitant use of any
   medications/procedures that are prohibited in the parent luspatercept protocol.

   2. Participant has met one or more criteria for study discontinuation as stipulated in
   the parent luspatercept protocol.

   3. Applies to on treatment participants only- More than 26 days between last luspatercept
   dose in the parent protocol and first dose into ACE-536-LTFU-001 protocol unless dose
   delay or dose discontinuation criteria met.

   4. Applies to on treatment participants only- Pregnant or breastfeeding females.

   5. Participant has any significant medical condition, laboratory abnormality, psychiatric
   illness, or is considered vulnerable by local regulations (eg, imprisoned or
   institutionalized) that would prevent the subject from participating in the study.

   6. Participant has any condition including the presence of laboratory abnormalities,
   which places the subject at unacceptable risk if he/she were to participate in the
   study.

   7. Participant has any condition that confounds the ability to interpret data from the
   study.