Purpose: The Cylex score is a new test to detect immune responsiveness for heart transplant (HTx) patients (pts). A low Cylex score represents more intense immunosuppression and therefore a less responsive immune systemin general. Circulating antibodies (Ab) are seen in more than 50% of post-HTx pts. It is believed that more intense immunosuppression may decrease the risk of Ab production post-HTx. Although the Cylex score represents T cell immunoresponsiveness, it may also reflect a general immunosuppressive state and thereby may reflect the ability of the recipient to make Abs. Methods: Between 2007 and 2012 we evaluated 103 HTx pts who did not have circulating Abs pre-HTx. Post-HTx Ab levels were assayed at 1,3,6,12 months post-op and correlated to the Cylex score. Cylex scores were obtained routinely at the time of endomyocardial biopsy. Pts were divided into 3 Cylex score groups: <200, 200-500, >500. All pts were under tacrolimus and mycophenolate mofitel immunosuppression. Endpoints included: development of de novo Abs, 1-year freedom from cellular (CMR) and antibody-mediated rejection (AMR), 1-year survival, 1-year freedom from cardiac allograft vasculopathy (CAV) and 1-year freedom from Non-Fatal Major Adverse Cardiac Events (NF-MACE: Myocardial Infarction, Heart Failure, angioplasty, pacemaker/ICD, stroke). Results: There were 5.4 ± 2.9 first-year Cylex scores per pt. Pts with Cylex scores <200 had numerically more suppressed Ab responses compared to Cylex score 200-500 and >500 groups (4.8% vs 13.7% vs 22.2%), but numbers are small. However, there was no difference in 1-year freedom from CMR or AMR. There was also no significant difference in 1-year survival, 1-year freedom from CAV and 1-year freedom from NF-MACE among groups (see table).Table: No Caption available.Conclusion: Low Cylex score reflecting more intense immunosuppression may be a useful tool to suppress Ab response after HTx, but a larger number of pts are needed to confirm this observation. DISCLOSURES:Patel, J.: Grant/Research Support, Alexion Pharmaceuticals. Chang, D.: Stockholder, Abbot Pharmaceuticals, ABBV. Esmailian, F.: Grant/Research Support, Transmedics. Kobashigawa, J.: Grant/Research Support, XDx Inc, Novartis.