Background: Most patients with high or very high risk localized prostate cancer (PCa) experience disease recurrence after radical prostatectomy (RP). Neoadjuvant androgen ablation has not improved high-risk pathological features or recurrence rates after RP.¹ We reported the association between high intratumoral CD8⁺ T lymphocyte (CTL) density and improved survival post-RP, suggesting clinical benefit from neoadjuvant immunomodulation (NI).² Analysis of the tumor immune microenvironment after NI may also provide key insights into potential therapeutic strategies in PCa. CTL/NK/Th1-recruiting chemokines (CCL5, CXCL9 and CXCL10) are downregulated while MDSC/Treg-attracting chemokines (CCL2, CCL22, and CXCL12) are upregulated in human PCa tissue.³ A large proportion of T cells in PCa are Tregs or dysfunctional CTLs and this immunosuppressive profile may be partly driven by COX-2 upregulation.^4,5 A chemokine modulating regimen (CKM) of rintatolimod (TLR-3 ligand), aspirin (COX-2 inhibitor), and IFN-α favorably reprogrammed the chemokine profile and CTL/Treg ratio in human PCa explants.³ This combination has demonstrated safety in phase I/II trials across other tumor types, though it is unclear if IFN-α can be omitted without compromising efficacy.^7-8Methods: This is a three-arm, phase II trial where patients with localized PCa scheduled to undergo RP are randomized in 1:1:1 ratio to a 2-week regimen of neoadjuvant CKM triplet (rintatolimod + aspirin + IFN-α) vs CKM doublet (rintatolimod + aspirin) vs no CKM. Thirty patients will be enrolled to assess CD8⁺ T cell density in the RP specimen as the primary endpoint. Pathological and PSA responses, surgical margin positivity, and safety/toxicity of the CKM combinations will be secondary endpoints. Pre- and post-treatment density of various infiltrating T cell subtypes, MDSCs, chemokine and chemokine receptor profiles, immune checkpoint expression, immune-regulatory gene expression signatures, and peripheral blood immune cell landscape will be key exploratory endpoints. The trial is currently open with 11 patients enrolled. Clinical trial ID: NCT03899987. References: 1) Scolieri MJ, J Urol 2000, 2) Clin Oncol 36, 2018: suppl; abstr 5068, 3) Muthuswamy R, Prostate 2016, 4) Sfanos KS, Prostate 2009, 5) Gupta S, Prostate 2000, 6) NCT01545141, 7) NCT02151448, 8) NCT02432378.