Immune Function Testing and Long-Term Immune-Related Outcomes among Heart Transplant Recipients

Purpose The Cylex ImmuKnow (IK) assay, a rapid quantitative assessment of T-cell-mediated function, is used to monitor immunosuppression among heart transplant (HT) recipients. It is unclear whether the IK assay can aid in characterizing the long-term risk of adverse immune-related events among HT recipients. Methods We conducted a single-center, retrospective, cohort study of all single organ HT recipients from 2014 to 2018. The IK assay divided subjects into low, moderate, or high immune response categories at 6-month, 1-, and 2-year intervals. IK assay categorization was correlated to the primary composite outcome which included acute cellular rejection, antibody-mediated rejection, development of donor-specific antibodies, coronary allograft vasculopathy, and death over 2 years of follow-up. Results 134 single organ HT recipients were included (median age 56.5 years, 70% male). On an immunosuppressive regimen of tacrolimus, prednisone, and mycophenolate mofetil, most subjects had low and moderate immune response levels at 6 months (53% low vs 37% moderate vs 10% high). A higher proportion of subjects exhibited moderate immune response at 1 (44% low vs 47% moderate vs 9% high) and 2 years (29% vs 60% vs 11%). The composite outcome occurred in 14% of subjects by 6 months, 35% by 1 year, and 36% by 2 years. There was no difference in the rate of the composite outcome or its individual components between the immune response groups at any of the time points (Fig. 1B). The relative change in an individual's IK score between timepoints was not associated with the composite outcome. Conclusion On standard immunosuppression, a majority of HT recipients exhibit low to moderate immune response per the IK assay. The IK assay reflects expected increases in immune function with reduced immunosuppression. IK assay-based immune response categorization does not appear to aid in identifying HT recipients at risk for adverse immune-related events in the long-term. The results are limited by the sample size and low event rates.