Inclusion Criteria:

- Asymptomatic or minimally symptomatic metastatic castration-resistant prostate cancer
(mCRPC)

- Patients must have successfully completed therapy with sipuleucel-T within 3-7 days
of planned CYT107 study drug treatment

- Assessable disease with a positive bone scan and/or measurable disease on computed
tomography (CT) scan and/or magnetic resonance imaging (MRI) of the abdomen and
pelvis

- Prior orchiectomy or must be on ongoing luteinizing hormone-releasing hormone (LHRH)
agonist or antagonist (e.g., degarelix) therapy

- No ongoing anti-androgen therapy; patients must be off anti-androgen therapy for at
least 30 days

- Patients receiving any other hormonal therapy, including any dose of megestrol
acetate (Megace), Proscar (finasteride), any herbal product known to decrease
prostate specific antigen (PSA) levels (e.g. Saw Palmetto, PC-SPES), or any systemic
corticosteroid, must discontinue the agent for at least 30 days prior to study
treatment

- Absolute neutrophil count (ANC) >= 1500/µL

- Bilirubin < 1.5 x upper limit of normal (ULN)

- Hemoglobin >= 10 g/dL

- PSA >= 2 ng/mL

- Platelets >= 100,000/mcL

- Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) =< 2.5 x ULN

- Creatinine clearance >= 60 mL/min by the Cockcroft-Gault equation

- Testosterone =< 50 ng/dL (documented at any time while on LHRH agonist or antagonists
odds ratios [ors]/orchiopexy [p] orchiectomy)

- Eastern Cooperative Oncology Group (ECOG) performance status of 0-1 or a Karnofsky
performance status of >= 80%

- Life expectancy of at least 6 months

- Prior local radiation therapy must be completed at least 30 days prior to enrollment
and the patient must have recovered from all toxicity

- Prior "systemic" radiopharmaceuticals (strontium, samarium) must be completed >= 8
weeks prior to enrollment

- Patients must agree to use adequate contraception (barrier method for males) for the
duration of study participation, and for four months after discontinuing therapy,
because of the unknown potential risk to a gamete and/or developing embryo from this
investigational therapy

- Ability to understand and the willingness to sign a written informed consent document

Exclusion Criteria:

- Prior chemotherapy for prostate cancer, with the exception of neoadjuvant
chemotherapy, because of the potential effect of chemotherapy on the immune system

- Prior investigational immunotherapy

- Prostate cancer pain requiring regularly scheduled narcotics

- Pathologic long-bone fractures, imminent pathologic long-bone fracture (cortical
erosion on radiography > 50%) or spinal cord compression

- Current treatment with systemic steroid therapy (inhaled/topical steroids are
acceptable); systemic corticosteroids must be discontinued for at least 30 days prior
to first CYT107 injection

- Known central nervous system metastases

- No documented cirrhosis or documented acute hepatitis; Note: a positive hepatitis B
serology indicative of previous immunization (i.e., hepatitis B surface antibody
[HBsAb] positive and hepatitis B core antibody [HBcAb] negative), or a fully resolved
acute hepatitis B (HBV) infection is not an exclusion criterion

- No history of severe asthma, as defined by prior or current use of systemic
corticosteroids for disease control, with the exception of physiological replacement
doses of cortisone acetate or equivalent, as defined by a dose of 10 mg or less

- Medical or psychiatric illness that would, in the opinion of the investigator,
preclude participation in the study or the ability of patients to provide informed
consent for themselves

- Cardiovascular disease that meets one of the following: congestive heart failure (New
York Heart Association class III or IV), active angina pectoris, or recent myocardial
infarction (within the last 6 months)

- Concurrent or prior malignancy except for the following:

- Adequately treated basal or squamous cell skin cancer

- Adequately treated stage I or II cancer from which the patient is currently in
complete remission

- Any other cancer from which the patient has been disease-free for 5 years

- Known human immunodeficiency virus (HIV) or other history of immunodeficiency
disorder; HIV-positive patients on combination antiretroviral therapy are ineligible
because of the potential for pharmacokinetic interaction with CYT107; other trials
are examining the effect of CYT107 in patients with HIV infection

- Prisoners or subjects who are compulsorily detained (involuntarily incarcerated) for
treatment of either a psychiatric or medical (e.g. infectious) illness

- Any underlying medical or psychiatric condition, which in the opinion of the
investigator will make the administration of CYT107 hazardous or obscure the
interpretation of adverse events (AEs), such as a condition associated with frequent
diarrhea

- Prior treatment with anti-cytotoxic T-lymphocyte antigen 4 (CTLA-4) or experimental
check point inhibitor such as anti-programmed-death (PD)1

- History of allergic reactions attributed to compounds of similar chemical or biologic
composition to CYT107

- Patients who have received prior immunosuppressive therapy within 30 days prior to
enrollment

- Active (as defined by requiring immunosuppressive therapy) or history of clinically
significant autoimmune disease (as defined by previously requiring immunosuppressive
therapy)

- Patients who have received hepatotoxic drugs less than 7 days prior to enrollment

- Patients who have received prior biologic agents less than 30 days prior to
enrollment

- Uncontrolled intercurrent illness including, but not limited to, ongoing or active
infection, congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or
psychiatric illness/social situations that would limit compliance with study
requirements

- Patients who have a history of any hematopoietic malignancy

- History of pulmonary disease such as emphysema or chronic obstructive pulmonary
disease (COPD), (forced expiratory volume [FEV] > 60% of predicted for height and age
required in patients with prolonged smoking history or symptoms or respiratory
dysfunction)