Background: AMG 160 is an HLE BiTE immune therapy that binds prostate-specific membrane antigen (PSMA) on tumor cells and CD3 on T cells, leading to T cell activation, cytokine production, and tumor cell lysis. A phase 1 study of AMG 160 in patients with metastatic castration-resistant PCa is ongoing (NCT03792841). We investigated whether the combination of AMG 160 and an anti-PD-1 antibody could increase AMG 160 cytotoxicity against PCa cells in vitro and ex vivo. Methods: C4-2B human PCa cells engineered to overexpress PD-L1 were treated with a range of AMG 160 doses (0.144–30,000 pM) +/– a fixed dose of anti-PD-1 in the presence of activated human T cells. Cell viability was assessed by Steady-Glo after 1 day. PD-1 expression on T cells was evaluated by flow cytometry. A human tumor explant model consisting of thin sections of fresh surgically resected human PCa tumors was also used to evaluate the AMG 160 + anti-PD-1 combination. Explants were incubated in media over 2 days and treated with buffer alone, AMG 160, or AMG 160 + anti-PD-1 at fixed doses. Activation of autologous T cells within the tumor slices was assayed by flow cytometry, and secretion of cytokines into culture supernatants was measured by Meso Scale Discovery (MSD). Immune-response profiles of the culture tissues were assessed by NanoString. Results: In the PCa in vitro study, AMG 160 treatment induced upregulation of PD-1 on T cells. Cotreatment with AMG 160 + anti-PD-1 increased the potency of cell killing by 2–5x and killed a greater percentage of cells than AMG 160 alone. In the tumor explant model, which preserves tumor architecture and microenvironment, AMG 160 treatment induced activation of the autologous infiltrating T cells, and this activation was increased by cotreatment with anti-PD-1. AMG 160 treatment increased cytokine production, and cotreatment of tumor explants with AMG 160 + anti-PD-1 increased cytokine production further. Conclusions: Together these data suggest that antitumor efficacy of the AMG 160 HLE BiTE immune therapy can be increased by co-treatment with anti-PD-1. These data provide a rationale for evaluating this combination in future clinical studies.