Expanded Access and Open Label Extension Study of SER-109 to Prevent Recurrent Clostridium Difficile Infection

This is an open-label study of SER-109 in patients who received a dose of SER-109 or placebo
in Study SERES-004 and experienced a CDI recurrence within 8 weeks of receipt of study drug.
In addition, SERES-005 has been amended to expand access to treatment with SER-109 to an
intermediate-size patient population of adults 18 years of age or older with recurrent
Clostridium difficile infection (CDI) (a serious disease), who would have qualified for the
SERES-004 study.

Inclusion Criteria:

1. Signed informed consent, indicating that the patient understands the purpose of and
procedures required for the study. Patients who are unable to provide informed
consent will not be included in the study.

2. Male or female patients ≥ 18 years of age.

3. Previously enrolled in Study SERES-004 and had CDI recurrence within 8 weeks after
receipt of study drug, OR If not previously enrolled in Study SERES-004, a documented
history of ≥ 3 episodes of CDI within the previous 9 months, inclusive of the current
episode with ≥ 1 of the historical episodes having the date, test results, and
antibiotic treatment received documented. Efforts should be made to acquire history
of additional CDI episodes.

4. If not previously enrolled in Study SERES-004, a qualifying episode of CDI as defined
by:

1. ≥ 3 unformed stools per day for 2 consecutive days

2. A positive C. difficile stool test

3. The requirement of CDI standard-of-care antibiotic therapy (defined as 10 to 21
days of treatment with vancomycin or fidaxomicin but excluding pulse-tapered
antibiotic regimens).

4. An adequate clinical response defined as no evidence of diarrhea (< 3 unformed
stools in 24 hours) for 2 or more consecutive days before randomization.

5. If female, patient is non-lactating, and is either:

1. Not of childbearing potential, defined as postmenopausal for at least 1 year or
surgically sterile due to bilateral tubal ligation, bilateral oophorectomy, or
hysterectomy.

2. Of childbearing potential and is practicing at least 1 highly effective method
of birth control including the barrier method; oral or parenteral
contraceptives; a vasectomized partner; or abstinence from sexual intercourse.
The investigator will discuss with the patient the option of practicing more
than 1 of the above methods for the duration of the study.

6. If male and partner is of childbearing potential, patient agrees to practice at least
1 highly effective method of birth control for the duration of the study.

7. Is not taking probiotics, or discontinues probiotics prior to study start and will
not take probiotics for the duration of the study.

Exclusion Criteria:

1. Female patients who are pregnant, breastfeeding, lactating, or planning to become
pregnant during the study.

2. Known or suspected toxic megacolon and/or known small bowel ileus.

3. Active irritable bowel syndrome with diarrhea within the previous 12 months.

4. Admitted to or expected to be admitted to an acute care facility or intensive care
unit for medical reasons (not just boarding). Patients discharged from an acute care
facility before Day 1 or residing in nursing homes or rehabilitation facilities may
be enrolled.

5. Taking antibacterial therapy other than vancomycin (non-tapered) or fidaxomicin for
most recent episode of CDI within 14 days before enrollment. A single-day antibiotic
prophylactic regimen is permitted.

6. Use of any probiotics.

7. Major gastrointestinal surgery (e.g., significant bowel resection or diversion)
within 3 months before enrollment (this does not include appendectomy or
cholecystectomy) or any history of total colectomy or bariatric surgery.

8. History of inflammatory bowel disease (ulcerative colitis, Crohn's disease,
microscopic colitis) with diarrhea believed to be caused by active inflammatory bowel
disease in the past 24 months.

9. Unable to stop loperamide, diphenoxylate/atropine, or cholestyramine before the
study.

10. Unable to stop opiate treatment unless on a stable dose, including PRN dosing, as of
onset of diarrhea and no increase in dose planned for the duration of the study.

11. Known positive stool cultures for other enteropathogens including, but not limited
to, Salmonella, Shigella, and Campylobacter within the 30 days before enrollment.

12. Known stool studies positive for ova and/or parasites within the 30 days before
enrollment.

13. Poor concurrent medical risks with clinically significant co-morbid disease such
that, in the opinion of the investigator, the patient should not be enrolled.

14. Received an investigational vaccine against C. difficile.

15. Known active intravenous drug or alcohol abuse or other drugs of abuse.