Neoantigen immune responses in healthy volunteers: insights from multiple integrated keyhole limpet hemocyanin challenge studies on repeated immunization and response covariates

Micha N. Ronner^1,2*Marieke De Kam¹Silke van Reeuwijk¹Jacobus Burggraaf^1,2Manon AA Jansen^1,2Matthijs Moerland^1,2*

• ¹Centre for Human Drug Research, Leiden, Netherlands
• ²Leids Universitair Medisch Centrum, Leiden, Netherlands

Introduction Investigational immunomodulatory drugs are often initially investigated in healthy volunteers, which lack drug-target engagement biomarkers, hampering evaluation of pharmacodynamic effects. A model such as the Keyhole Limpet Hemocyanin (KLH) neoantigen challenge induces a well-controlled adaptive immune response and can be used to study pharmacodynamic effects in healthy volunteers. To increase our understanding of sources of variability in KLH-induced responses, we integrated KLH data from multiple studies executed at our research institute and investigated the contribution of covariates to KLH challenge responses. Methods We performed a pooled analysis of seven KLH trials with standardized methodology and design. Included trials immunized participants with KLH one, two or three times, with an interval of two weeks, followed by subsequent intradermal KLH administration 2-3 weeks after the final immunization. Differences and correlations were calculated between anti-KLH IgM and IgG and skin perfusion, flare, and erythema. A mixed effects model analysis was performed to estimate variances and determine the effect of the number of immunizations and the systemic and local biomarkers on the sample size. Finally, the effect of covariates age, sex, and body mass index was analyzed. Results A total of 68 participants were included: 42 participants were immunized with KLH once, 5 participants twice, and 21 participants three times. Three times immunization resulted in significantly higher antibody levels, cutaneous perfusion, and flare. A study design incorporating three immunizations and skin imaging at 24h was found to have the most robust statistical power. Lastly, the systemic KLH response correlated negatively with age and positively with local KLH responses. Conclusion This analysis provides a basis for the design of future clinical studies with KLH challenges. These data provide further insights into the performance of the human KLH challenge, which will facilitate the implementation of this immune challenge model in future clinical pharmacology studies.