O-154 monitoring of peripheral blood natural killer cells to identify heart transplant recipients at risk of infection

Background: Infection remains a source of mortality in heart recipients. We assessed whether monitoring of NK-cells could prove useful when identifying patients at risk of infection. Methods: We prospectively studied 133 consecutive heart recipients over a 12-month period. Severe infections that required intravenous antimicrobial therapy was the primary outcome. Superficial incisional surgical site infection, catheter-related infections were not considered infectious episodes in this study. As for immunosuppressive treatment, patients received induction therapy with the interleukin (IL) 2 receptor antagonist daclizumab (n=108 [93.1%]) or basiliximab (n=5 [4.3%]). Maintenance immunosuppression included mycophenolate mofetil, prednisone, and either cyclosporine (n=35, 30.2%) or tacrolimus (n=79, 68.1%), depending on the side effects. Total counts and percentages of NK-lymphocyte subsets (CD3–CD56/CD16+) were analyzed by four-color flow cytometry whole blood. Results: Forty-eight patients had at least one episode of severe infection. Patients with severe infection (n=48) disclosed lower NK absolute counts (day7 after transplantation [28 vs 57, P=0.021]), 3 months [96 vs 168 cells/uL, P=0.002], 6 months [127 vs 183 cells/uL, P=0.011] and 1 year [154 vs 254 cells/uL, P=0.014]). Patients with bacterial infections (n=27) disclosed lower NK absolute counts (day-7 [22 vs 52 cells/uL, P=0.040]). Patients with CMV infection (n=22) disclosed lower NK percentages (1 year [7 vs 14, P=0.006]), lower NK-cell absolute counts (day-30 [80 vs 117 cells/uL, P=0.05], 3 months [96 vs 151 cells/uL, P=0.016] and 1 year [133 vs 234 cells/uL, P=0.043]). In Cox regression analysis we found an association between the risk of developing an infection and lower day-7 absolute NK-cell count (per decrease of 10 cells/uL, RH 1.24, P=0.011). Conclusion: Data suggest that monitoring including NK-cell testing is useful when attempting to identify the risk of infection in heart recipients.