P0878 Early lymphocytosis is a novel predictor of response to rescue infliximab in acute severe ulcerative colitis: results from PREDICT-UC
Authors: Con D , Choy M , Li Wai Suen C , Boyd K , Pena R , Burrell K , Rosella O , Proud D , Brouwer R , Gorelik A , Liew D , Connell W , Wright E , Taylor K , Pudipeddi A , Sawers M , Christensen B , Ng W , Begun J , Radford-Smith G , Garg M , Martin N , van Langenberg D , Ding N , Beswick L , Leong R , Sparrow M , De Cruz P 
Published: January 2025

Abstract

Background
The ability to predict failure of infliximab (IFX) in acute severe ulcerative colitis (ASUC) is crucial to identify patients who may benefit from dose-escalation, sequential rescue or early colectomy.

Methods
PREDICT-UC (NCT02770040) was a randomised controlled trial that compared IFX dosing strategies in ASUC.1 Clinical factors and biomarkers were collected daily between day 0 to 3 post-IFX and assessed on their ability to predict IFX failure (Lichtiger score ≥10 on day 14) and 3-month colectomy. Stepwise logistic regression was used to develop a Risk of IFX Failure (RIF) index, which was calibrated against the observed risk of IFX failure. The RIF index represents the predicted probability of IFX failure and takes on values between 0 and 1. Internal validation was performed using bootstrap validation.

Results
Of 138 patients, 46 received a first IFX dose of 10mg/kg and 92 received 5mg/kg; 39 (28%) experienced IFX failure and 17 (12%) required colectomy by 3 months.
There was no difference in lymphocyte count (LC, ×109/L) on day 0 (prior to IFX) in patients who failed or responded to IFX (median [IQR] 1.1 [0.9–1.6] vs 1.3 [0.9–1.8], P=0.47). LC rose by day 3 in both groups, though to a lesser degree in patients who failed IFX (median [IQR] 1.9 [1.4–2.8]) compared to responders (3.3 [2.1–4.9]; P=0.004), and lower in patients requiring colectomy (median [IQR] 1.4 [1.1–1.9] vs 3.0 [2.0–4.8]; P&lt;0.001).
A lower day 3 LC was predictive of IFX failure (AUC 0.71, 95% CI 0.60–0.81) and colectomy (AUC 0.83, 95% CI 0.74–0.92). A higher CRP was predictive of both IFX failure and colectomy at all time-points from days 0 to 3 (day 3 CRP AUC 0.68, P=0.003 and 0.70, P=0.019 respectively). A lower day 3 albumin predicted IFX failure (AUC 0.63, P=0.039) while a lower day 2 albumin predicted colectomy (AUC 0.66, P=0.042).
The final RIF index comprised day 3 stool frequency, rectal bleeding score, CRP and LC. The RIF index had a naïve AUC of 0.80 and an optimism-adjusted AUC of 0.73 (95% CI 0.65–0.80) for predicting IFX failure, and a naïve AUC of 0.90 and an optimism-adjusted AUC of 0.88 (95% CI 0.81–0.94) for predicting colectomy. A RIF index threshold of ≥0.15 had an 85% sensitivity and 90% negative predictive value (NPV) for IFX failure and a 94% sensitivity and 98% NPV for colectomy, while a threshold of ≥0.50 had a 92% specificity and 69% positive predictive value (PPV) for IFX failure, and an 88% specificity and 42% PPV for colectomy.

Conclusion
Lymphocytosis by day 3 is a novel predictor of response to IFX rescue in ASUC. The RIF index is a simple on-treatment risk index that predicts IFX failure and colectomy, and may be used to inform IFX dose-optimisation or switch to alternate therapies.

References
1Choy MC, Li Wai Suen CFD, Con D, et al. Intensified versus standard dose infliximab induction therapy for steroid-refractory acute severe ulcerative colitis (PREDICT-UC): an open-label, multicentre, randomised controlled trial. Lancet Gastroenterol Hepatol 2024; 9(11): 981-96.