A prospective non-randomized phase I trial of dendritic cell-based cryoimmunotherapy combined with checkpoint inhibitors in mCRPC

e14708 Background: Despite improvements, metastatic castration-resistant prostate cancer (mCRPC) still has dismal overall survival (OS). We treated 18 mCRPC patients with dendritic cell (DC)-based cryoimmunotherapy (CryoIT) as monotherapy or combined with checkpoint inhibitors to determine safety and immune response. Methods: mCRPC patients were biopsied before cryoablation, and subsequently injected intratumorally with autologous immature DCs. DC doses were escalated in a 3+3 design (n=9) followed by dose expansion combined with either ipilimumab (n=6) or pembrolizumab (n=3). The disease burden was assessed by PSA values, iRECISTv1.1 (PET/CT, MRI and bone scintigraphy at baseline, 14, 22 and 46 weeks) and circulating tumor cells (CTC; CellSearch). Immune response was monitored by ultradeep T-cell receptor sequencing. Results: The patients had aggressive cancer, with ISUP grade group 4 and 5 in 72% (13/18) at diagnosis and in 100% at inclusion. At baseline, higher ALP correlated with higher regulatory T cells (p=0.047), FoxP3+/CD3+ratios (p=0.014) and FoxP3+/CD8+ratios (p=0.004) in tissues. Median OS and progression-free survival (PFS) were 40.7 and 10.5 months, respectively. Of the 8 patients alive 43 to 85 months post-CryoIT, 7 had progressed and received other treatment. Early decreases in PSA (p=0.002) and LDH (p=0.01) levels 6 weeks after CryoIT indicated better outcomes at 22 weeks. Longer OS correlated with lower tissue ratios of CD4+/CD3+cells (p=0.002) and CD4+/CD8+cells (p=0.007). All patients with increased numbers of new T-cell clonotypes after CryoIT and CTC at the pretreatment level of 1-4 cells/ 7.5 mL blood changed to negative during follow-up up to 72 weeks. Conclusions: CryoIT demonstrates non-inferior OS and PFS compared to other mCRPC trials, and therapy response was suggested by decreased CTCs and induction of new T-cell clonotypes post-CryoIT. Lower CD4 + cell fractions of lymphocytes in the TME indicate better OS after CryoIT. CryoIT appears not to decrease effects of post-treatment recurrence therapies. Clinical trial information: NCT02423928 . [Table: see text]