Cytokine profile of sipuleucel-T (sip-T) in differentiating reactivation of latent immunity from de novo immune responses.

163Background: Sip-T is an FDA-approved immunotherapy for treating patients (pts) with asymptomatic or minimally symptomatic metastatic castration-resistant prostate cancer (mCRPC). It is manufactured from autologous peripheral blood mononuclear cells (PBMCs) cultured with PA2024, a fusion of prostatic acid phosphatase (PAP) and granulocyte macrophage colony-stimulating factor. Survival of sip-T–treated mCRPC pts correlates with immune responses to PA2024 and/or PAP. PA2024- or PAP-specific CD4+ and CD8+ T cell proliferation and cytokine production and release were assessed to better understand sip-T–induced T cell responses. Methods: Pts with biochemical recurrence or mCRPC were from sip-T trials (NCT01431391, NCT01981122). PBMCs collected at baseline through 6 mo post–sip-T were cultured in vitro and stimulated with PA2024 or PAP. CD4+ and CD8+ T cells were assessed (n=19) for proliferation and intracellular IL-2 and IFN-γ. The cytokine profile was confirmed in supernatant with a meso scale discovery as...