Allospecific CD154 + T‐cytotoxic memory cells as potential surrogate for rejection risk in pediatric intestine transplantation

Clinical end-points dictate large trial enrollments and exclude children with the rare intestine transplant procedure (ITx), who experience higher drug-related morbidity. We evaluate the novel rejection-risk parameter, allo-(antigen)-specific CD154 + TcMs (i) as surrogates for ACR using Prentice's criteria, (ii) for association with immunosuppression targets to determine Fleming's surrogate end-point designation, and (iii) as time-to-event end-point in a simulated comparison of alemtuzumab (NCT#01208337, n = 14) and rabbit anti-human thymocyte globulin (rATG, n = 16) among 30 children with ITx. CD154 + TcM were measured in MLR before, and at 1-60 and 61-200 days after ITx (NCT#01163578). CD154 + TcM correlate significantly with rejection severity (Spearman r = 0.685, p = 2.03E-5) and associate with biopsy-proven ITx rejection with sensitivity/specificity of 94%/84% [corrected] independent of immunosuppressant. Previously stated sensitivity of 90% is incorrect. [corrected]. The rejection-risk threshold of CD154 + TcM resolves rapidly in 200-day follow-up (46 ± 20 vs. 158 ± 59 days, p = 0.009, K-M) with alemtuzumab, which demonstrates lower 90-day ACR incidence (50% vs. 69%, p=NS, Fisher's exact), and is associated with accelerated prednisone minimization to ≤2.5 mg/day, compared with rATG (120 ± 28 vs. 180 ± 30 days, p = 0.027, K-M). As a surrogate end-point, time-to-rejection-risk resolution measured with CD154 + TcM portends 50% reduction in sample sizes in a simulated trial of alemtuzumab vs. rATG. Rejection-risk assessment with CD154 + TcM may enable informed immunosuppression minimization, and preliminary efficacy comparisons in pediatric ITx.