A Large Number of CD52 Negative Natural Killer Cells in Liver Grafts: Role for Infections after Liver Transplantation with Alemtuzumab Induction

ackground: T cell depleting strategies have become an integral part of immunosuppressive regimens widely used for induction in solid organ transplantation. Alemtuzumab (AL) is a recombinant humanized monoclonal antibody against human CD52, a cell surface antigen expressed on B and T cells, monocytes, and natural killer (NK) cells. Although the depletion of lymphocytes would be expected to result in an increased risk of infections, some studies reported not to increase the incidence of infections. We observed early large granulocyte reconstitution in liver transplantation (LT) with AL. However, information is limited regarding the phenotype and function of liver NK cells in T cell depletion using AL. Methods: Absolute counts and proportion of NK and T cells were measured after LT with AL. We collected the mononuclear cells from the liver (LMC), peripheral blood (PBMC), spleen (SP), and lymph nodes (LN) from the donor in LT patients. Phenotype and functional differences were examined by flow cytometry and in vitro cytotoxicity assays. Anti- CD3, CD16, TRAIL, NKp30, NKp44, NKp46, NKG2D, CD52, CD56, CD94, CD117, and CD158b mAbs are used for phenotyping lymphocyte and NK cells. Results: Absolute counts of T cells remained low for 6 months. In contrast, those of NK cells had emerged with larger number since early days after LT (Fig 1A). LMC (n=7) contained high percentage of CD52- CD56+ NK cells (54.2±9.0 % especially CD56 bright 81.2±5.7 %, Fig 1B). It was statistically significant higher percentage than that of PBMC, SP, and LN (25.1%, 28.4%, and 9.3 % respectively, P< 0.05). The phenotype of almost liver NK cells showed mature type (stage5; CD94+CD117-: 99.1%). The expressions of other markers had not any differences between CD52-CD56+ and CD52+CD56+ NK cells. On the other hand, PBMC contained high percentage of CD52+CD56+ NK cells (99.3%). Donor liver NK cells had stronger cytotoxicity after IL-2 stimulation in the presence of AL. These data indicated that NK cells in PBMC were depleted but NK cells in LMC remained alive and active in LT patient with AL induction.[Figure 1]Conclusions: The liver contains high percentage of CD52-CD56+ NK cells which are mature type. The function of CD52-CD56+ NK cells had stronger cytotoxicity even in the presence of AL. These results suggest that the functionally maintained CD52-CD56+ NK cells contribute to protect the recipients from severe infections even after T cell depletion therapy such as AL induction.