Statistical Analysis Plan CITN12 -03 NCT 01881867 Version 2.0 13Nov2018 Protocol : A Phase 2 Study of recombinant glycosylated human interleukin- 7 (CYT107) after completion of standard FDA approved therapy with sipuleucel -T (Provenge®) for patients with asymptomatic or minimally symptomatic metastatic castration -resistant prostate cancer (mCRPC) Statistical Analysis Plan CITN12 -03 NCT 01881867 Version 2.0 13Nov2018 STATISTICAL CONSIDERATIONS Study Design/Endpoints The proposed clinical trial is a phase II, open- label, multicenter, randomized study of the administration of CYT107 after the completion of standard FDA -approved therapy with sipuleucel -T for patients with asymptomatic or minimally symptomatic mCRPC. Patients who have completed a standard course of sipuleucel -T will be randomly assigned to either observation or 10 μg/kg of subcutaneous CYT107 every week for 4 doses beginning 3 to 7 days after completing sipuleucel -T therapy. Day 0 is the day of the first injection of CYT107. The first six patients randomly assigned to receive CYT107 will be followed for an additional 4 weeks prior to the study expanding past six patients, as a lead- in phase to ensure safety and tolerability of the selected CYT107 dose. Treatment Schema Cohort CYT107 Dose Frequency 1 - Observation No CYT107 dose -------- 2 - CYT107 10 μg/kg Days 0, 7, 14 and 21 IL-7 is expected to increase the peak and the persistence of the immune response. The persistence might be the most important for effective immunotherapy, i.e. increasing the “area under the curve”. Thus, the primary endpoint for sizing the trial will be quantification of T-cell responses to PA2024 measured at day 70 (week 11), 7 weeks after the last CYT107 injection. T cell responses will be measured by interferon -gamma ELISPOT as the most quantifiabl y and reproducible assay. In the IMPACT study, 2 weeks after last sipuleucel -T administration, the background -subtracted mean PA2024 ELISPOT was 40 SFC/ 3x105 PBMC with a standard deviation of 69 based on n = 63. At 10 weeks after the last administration the background- subtr acted mean PA2024 ELISPOT was 23 SFC/ 3x105 PBMC with a standard deviation of 36 based on n = 42. Participant leukapheresis samples from pre -and post -Provenge® vaccine will be used when possible to allow planned a more comprehensive evaluation of longitudinal vaccine responses. Primary Endpoint: With 38 patients per group with evaluable data (40 patients per group, assuming 5% missing immunogenicity data), there is 80% power to detect a difference between a mean of 47 in the sipuleucel -T plus CYT107 group and a mean of 23 in the sipuleucel -T alone group, assuming the same standard deviation of 36 in both groups. This calculation is based on a two- sided t - test with a significance level of 0.05. The presumption is that the effect of CYT107 will be positive on all of the immune parameters and that the effect on each assay will track with positive effects on the other immune assays such that there should be similar power to detect differences in the other endpoints. These, however, are not considered primary e ndpoints, Statistical Analysis Plan CITN12 -03 NCT 01881867 Version 2.0 13Nov2018 and hence no multiplicity adjustment will be made. The Mann- Whitney -Wilcoxon (MWW) Test will be used as part of the statistical analysis; the power is roughly equivalent to that based on the t -test. The effect of CYT107 will also be positive on c linical activity, but the results are likely to be more variable. Sample Size/Accrual Rate 80 patients total will be enrolled in this study, 6 -8 patients per month accrual total at approximately 12 CITN sites . Patients without adequate sampling for immune responses will be replaced. Accrual Targets Ethnic Category Sex/Gender Males Total Hispanic or Latino + 15 = 15 Not Hispanic or Latino + 65 = 65 Ethnic Category: Total of all subjects + 80 (B1) = 80 (C1) Racial Category American Indian or Alaskan Native + 12 = 12 Asian + 8 = 8 Black or African American + 31 = 31 Native Hawaiian or other Pacific Islander + 8 = 8 White + 21 = 21 Racial Category: Total of all subjects + 80 (B2) = 80 (C2) Stratification Factors Patients will be stratified for prior abiraterone or neo -adjuvant chemotherapy with or without abiraterone in order to balance arms. Analysis of Secondary Endpoints 1.