Abstract The Cylex ImmuKnow assay measures the amount of stimulated ATP production by CD4+ T-cells, and has been used clinically, trying to predict rejection and infection episodes. However, predictive values of this assay after induction therapy with steroid-sparing maintenance protocols are unclear. In this single-center cohort study, we analyzed renal transplant recipients who received T-cell depleting+/−anti-IL2 receptor antibodies and tacrolimus/mycophenolate maintenance without steroids. A total of 4224 ImmuKnow levels in 306 patients were available for analysis. ImmuKnow levels (Mean±SE) changed over time after induction therapy with a paradoxical initial increase: 419±23, 461±32, 519±14, 411±10, 344±6, and 405±3 for pre-transplant, 0–1wk, 1wk–1mo, 1–3mos, 3mos–1yr, and thereafter. This change was parallel to the evolution of peripheral WBC counts and ImmuKnow levels had weak but significant correlation with WBC counts (R2=0.264, P<0.0001). The levels for biopsy-proven rejection (389±56) and borderline/clinical rejection (254±41) were not significantly higher than the levels of quiescent patients. The levels for opportunistic infection (349±48) and other infections (345±27) were not significantly lower than the levels of quiescent patients. The longitudinal changes in ImmuKnow levels were not predictive of rejection or infection. In conclusion, ImmuKnow levels can vary after T-cell depleting induction therapies at various time points, even without significant clinical events. Since ImmuKnow levels seem to be affected by WBC counts, ImmuKnow results need to be interpreted with caution. The effects of leukocytosis or leukopenia caused by immunosuppressive medication on the ImmuKnow assay need further investigation.