Cytokine Dynamics During Ustekinumab Induction as Predictors of Treatment Response in Crohn’s Disease: An Observational Study

<b>Background/Objectives</b>: Crohn's disease (CD) is a chronic immune-mediated disorder with heterogeneous response to biologic therapies. Ustekinumab (UST), an anti-IL-12/23 monoclonal antibody, is effective in CD, but predictive biomarkers of treatment response remain lacking. This study aimed to investigate cytokine dynamics during UST induction and to evaluate their association with clinical and biochemical outcomes in an observational cohort of CD patients. <b>Methods</b>: We prospectively recruited 31 adult patients with moderate-to-severe active CD initiating UST therapy at a tertiary referral center. Peripheral blood and stool samples were collected at baseline and weeks 4, 8, and 16. UST trough concentrations, C-reactive protein (CRP), fecal calprotectin (FC), hemoglobin, albumin, and 13 serum cytokines (including IL-1β, IL-6, IL-8, IL-10, IL-12p70, IL-13, IL-17, IL-23, TNF-α, and OSM) were analyzed. Response was defined as a ≥70% reduction in FC at week 16, or, alternatively, CRP < 5 mg/L or a Harvey-Bradshaw Index < 3. <b>Results</b>: Eighteen patients (58%) achieved response at week 16. Responders showed significant reductions in FC, CRP, and disease activity, while non-responders exhibited limited biochemical improvement. Overall, UST induction was associated with a global decrease in proinflammatory cytokines, particularly TNF-α and IL-1β. Responders displayed distinct cytokine patterns, with higher IL-13 levels at week 8 and lower IL-8 concentrations at week 16 compared with non-responders. UST trough levels tended to be higher in responders, and inverse correlations were observed between drug concentrations and several cytokines, including IL-6, IL-8, IL-13, and IL-23. <b>Conclusions</b>: UST induction leads to measurable immunological changes in CD, with differential cytokine dynamics distinguishing responders from non-responders. These findings support the potential of cytokine signatures, in combination with therapeutic drug monitoring, as pharmacodynamic biomarkers to optimize personalized treatment strategies in CD.