14. STATISTICAL CONSIDERATIONS DF/HCC Protocol #: 18-280 Protocol Version Date: 10.17.2020 37 14.1 Study Design The study is designed as a Phase II open label study of vaccination with DC/myeloma fusions/GM-CSF plus nivolumab therapy as part of treatment for patients with relapsed multiple myeloma. Patients meeting initial eligibility will undergo harvesting tumor cells and undergo vaccine production. During this period patients will receive an initial cycle of nivolumab and will then undergo a series of vaccinations on day 1 of cycles 1-3. 25 evaluable patients will be enrolled. Therapy with nivolumab will continue for three additional cycles. Based on a prior phase II study of vaccination of myeloma patients with the DC/MM fusion vaccine approximately 50% patients demonstrated a >10-fold increase in IFNγ expression to the baseline. Therefore, the combination of vaccination and nivolumab will be considered promising if the study shows evidence of at least 75% patients with >10-fold increase in IFNγ expression, and would not be considered promising if >10-fold increase is observed in 50% or less patients. With total n=25 patients, the combination will be considered promising for further study if 17 or more patients demonstrate significant immune response. This decision rule has a 0.1 (significance level) probability of accepting the combination for further study if the true underlying significant immune response is 50% and a 0.85 (power) probability of accepting the combination if the true underlying immune response is 75%. For the absolute increase in IFNγ expression, with n=25 patients, we will have at least 90% power to detect an effect size of 0.66 (one-sided Wilcoxson rank sum test, significant level of 0.05), which corresponds to a 0.36 difference in log10 IFNγ fold increase assuming a standard deviation of 0.54 or a 2.3 difference in IFNγ expression fold increase assuming a standard deviation of 3.5. We estimate the median fold increase in IFNγ expression of vaccination alone be 14 (DFCI trial 04098). Therefore, the fold-change that can be detected in the combination is at least 16.1. As a secondary clinical endpoint, response will be assessed according to IMWG response criteria. In a prior phase I trial of DC/MM vaccination in patients with relapsed MM, 69% (11/16) patients had disease stabilization. No patients demonstrated disease response (PR, VGPR, or CR). In the present phase II trial, overall response rate per IMWG criteria will be assessed. An exact binomial test with a 10% one-sided significance level will have 82% power to detect the difference between the ORR proportion of 0.15 (null hypothesis) and the alternative ORR proportion of 0.35 when the sample size is 25. An ORR of 35% is considered worthy of further study in a larger trial. If 3 or more patients experience a TLT, accrual will be suspended. True but Unknown Rate of DLT 0.10 0.20 0.25 0.30 0.40 Probability of continuation of enrollment (≤ 2 TLT in 10 pts) 0.930 0.678 0.526 0.383 0.167 If the true rate of TLT is 25%, the probability of observing 2 or fewer TLTs within a cohort of 10 patients is 0.526. 14.1.1 Primary Immunologic Endpoint Myeloma reactive T-cells : Log transformations will be used to induce normality in quantitative measurements, and if still non-normal, then nonparametric tests will be used. The primary endpoint of log 10 peak change in tumor reactive T cells from baseline will be quantified. A secondary analysis of peak change in tumor reactive T cells will be done by comparing the proportions of patients who experience >10-fold increase in IFNγ expression, using a chi- squared test. Peak immune response will be correlated with clinical response in an exploratory fashion to assess the relationship between immune response and clinical response. 14.1.2 Secondary Immunologic Endpoints Additional exploratory analyses will be conducted in a similar fashion to examine a number of secondary immunologic endpoints, including: myeloma specific T cells in the bone marrow, antigen specific reactivity by tetramer analysis, and quantification of T-cell subsets and PD-1 expressing lymphocytes by flow cytometry. In each case, log transformations will be considered to induce normality, and if still non-normal then nonparametric tests will be used. Profiles of these secondary immunologic endpoints will be described at each time point. The DF/HCC Protocol #: 18-280 Protocol Version Date: 10.17.2020 38 correlation between the immune environment measures and the myeloma specific T-cell response will be assessed and reported using Spearman rank correlation at each time point. 14.1.3 Duration of follow-up Patients will be followed monthly for the first 6 months following the end of treatment and then every 3 months for 5 years to assess disease status. 15. PUBLICATION PLAN The results should be made public within 24 months of reaching the end of the study. The end of the study is the time point at which the last data items are to be reported, or after the outcome data are sufficiently mature for analysis, as defined in the section on Sample Size, Accrual Rate and Study Duration. If a report is planned to be published in a peer-reviewed journal, then that initial release may be an abstract that meets the requirements of the International Committee of Medical Journal Editors. A full report of the outcomes should be made public no later than three (3) years after the end of the study. DF/HCC Protocol #: 18-280 Protocol Version Date: 10.17.2020 39 REFERENCES 1. Moreau P, Attal M, Facon T. Frontline therapy of multiple myeloma. Blood. 2015;125(20):3076–84. 2.