Profiling a Neo-Antigen-Driven Immune Response in Healthy Volunteers: A Randomized, Double-Blind, Placebo-Controlled Study of the KLH Challenge Model.

Novel compounds targeting the adaptive immune system are commonly initially investigated in healthy volunteers (HV). HV frequently lack constitutively expressed drug-target engagement biomarkers, complicating the evaluation of pharmacological activity. The keyhole limpet hemocyanin (KLH) neo-antigen challenge elicits a controlled immune response in HV and is a potential model for investigating compounds targeting the adaptive immune system. A randomized, double-blind, placebo-controlled study in HV was conducted, investigating the effects of repeated immunizations with KLH on Days 1, 15, and 29, followed by intradermal KLH administration on Day 50. Systemically, KLH-specific antibodies were evaluated. Leukocytes were stimulated ex vivo to determine KLH-specific responses using ELISpot. Locally, KLH skin response was evaluated 0-48 hours post intradermal administration, using imaging, suction blister fluid analysis, and biopsy analysis. Twelve male HV aged 18-42 years completed the study. KLH antibody levels increased incrementally. ELISpot analyses demonstrated KLH-specific IFN-γ and IL-13 responses. Intradermal KLH injection drove a peak response 24 h after administration, observed as erythema and increased perfusion. Blister fluid analysis showed cell influx (T cells; B cells; monocytes; dendritic cells) at 24 h, largely decreasing at 48 h, as confirmed by immunofluorescent staining of skin biopsies. These findings demonstrate a T-cell-mediated response to intradermal KLH that is more rapid than the classical delayed-type hypersensitivity response. This study highlights the importance of the timing of measurements and combining non-invasive and invasive biomarkers. The KLH neo-antigen challenge model presented in this study offers a framework to study the effect of novel immunomodulatory compounds on the adaptive immune system early in clinical development.