PRTX-100-202 Open-Label, Dose Escalation Study in Adult Patients With ITP

Inclusion Criteria:

1. Willing and able to provide written informed consent prior to initiation of any
study-related procedures

2. Male or female ≥ 18 years of age

3. ITP that has persisted for ≥ 3 months. ITP must be diagnosed in accordance The
American Society of Hematology 2011 Evidence-based Practice Guideline for Immune
Thrombocytopenia (Neunert et al. 2011) or the International Consensus Report on The
Investigation and Management of Primary Immune Thrombocytopenia (Provan et al. 2010),
as locally applicable.

4. Received ≥ 1 typical regime for the treatment of ITP. Splenectomy is considered one
standard ITP treatment

5. A mean platelet count of < 30,000/μL, with no individual platelet count > 35,000/μL;
or for those subjects receiving a constant dose of permitted treatments for ITP: a
mean platelet count < 50,000/μL, with no count greater than 55,000/μL. (Note: The mean
platelet count must be determined based on 2 platelet counts including one obtained
within ≤ 7 days of first PRTX-100 dose and the other within ≤ 30 days of the first
dose of PRTX-100.)

6. If on corticosteroids, a dose of < 1 mg/kg prednisone per day or equivalent that has
been stable for ≥ 21 days prior to the first dose of PRTX-100. High-dose pulse steroid
therapy is NOT allowed within 14 days prior to the first dose of PRTX-100.

7. If receiving eltrombopag or romiplostim, the dose must have been stable for ≥ 21 days
prior to the first dose of PRTX-100

8. If on steroid-sparing adjunctive immunosuppression with cyclosporine, azathioprine,
mycophenolate, or 6-mercaptopurine, the dose must have been stable for ≥ 30 days prior
to the first dose of PRTX-100 and must be expected to remain stable through study Day
29, unless dose reduction is required due to toxicities. Treatment with other
cytotoxic agents (e.g. cyclophosphamide, vincristine) are not allowed within three
months prior to the first dose of PRTX- 100.

9. Any prior treatment with rituximab or any other anti-CD20 agent must have been > 6
months prior to the first dose of PRTX-100

10. If female, must not be pregnant (pregnancy testing will be performed locally in all
female patients of childbearing potential), must not be nursing and must be one of the
following:

- Surgically sterile (bilateral tubal ligation, hysterectomy)

- Postmenopausal with last natural menses > 24 months prior

- Premenopausal and using an acceptable form of birth control. Acceptable forms of
birth control include: hormonal contraceptives (implantable, oral, patch) used
for ≥ 2 months prior to screening or double barrier methods (any combination of
two of the following: intrauterine device [IUD], male or female condom with
spermicidal gel, diaphragm, sponge, cervical cap). All premenopausal females must
have a negative urine or serum pregnancy test at screening and on Day 1 prior to
first PRTX-100 treatment.

Exclusion Criteria:

1. Splenectomy ≤ 90 days prior to the first dose of PRTX-100

2. Unstable coronary artery disease or other medical condition (such as type 1 diabetes)
that, in the Investigator's opinion, might increase the risk to the patient

3. Evidence of active infection requiring antibiotic therapy ≤ 14 days prior to the first
dose of PRTX- 100

4. Myelodysplastic syndrome. If clinically significant anemia or pancytopenia exists,
documentation of a bone marrow aspirate within 24 months prior to the first dose of
PRTX-100 showing no evidence of myelodysplasia is required.

5. Medical history of vasculitis or lupus erythematosus

6. Propensity to allergic reactions defined as a history of allergic reaction to more
than one medication

7. History of any treatment for cancer within the past two years other than basal cell or
squamous cell carcinoma of the skin that has been treated with curative intent

8. Seropositive for human immunodeficiency virus (HIV)

9. History of acute/chronic hepatitis B or C and/or carriers of hepatitis B or C
(positive for hepatitis B surface antigen or positive anti-hepatitis C antibody test)
and evidence of current or active infection (e.g. HCV RNA test)

10. History suggestive of substance abuse

11. History or evidence on physical examination or screening laboratory tests of any
systemic disease or any acute or chronic illness that, in the opinion of the
investigator, may interfere with the evaluation of the safety or immunogenicity of the
study drug

12. Treatment with IVIG ≤ 14 days prior to the first dose of PRTX-100

13. Treatment with an anti-Rh D antigen agent (e.g. WinPho) ≤ 14 days prior to the first
dose of PRTX-100

14. Use of any investigational drug, other than eltrombopag or romiplostim, ≤ 30 days or 5
half-lives of the investigational drug (whichever is longer) prior to the first dose
of RTX-100

15. Not willing to stay at the study site for 4 hours after each PRTX-100 infusion