P1013 Aim: To analyse the lymphocytic (Ly) and dendritic cell (DC) reconstitution after liver (LT) and kidney transplants (KT). Methods: Fifty-eight patients (pts) 23 LT and 35 KT were entered in the study. Immunosuppresive induction therapy was Thymoglobulin for LT and Dacluzimab for KT. Maintenance immunosuppression consisted of Tacrolimus. Steroids were tapered off at 3 mos after transplant (TX). The absolute number of T-helper, T-cytotoxic, T-regulatory, NK, B and myeloid and plasmacytoid DC (mDC and pDC) was analyzed before, 1 and 6 mos after TX, and at acute rejection (ACR). T cell subsets were identified by flow cytometry by double staining with an anti-CD3 and anti-CD4 or anti-CD8 monoclonal antibody (mAb), or by triple staining with anti-CD3, anti-CD4 and anti-CD25 mAb (T regulatory cells), NK cells and B cells with anti-CD56 and anti-CD19 mAbs, while mDC were defined as BDCA1+CD19- and pDC as BDCA2+. Results: Before TX, LT pts had 5-8 fold lower median levels of circulating immune cells than KT pts. Median numbers of CD4+ and CD8+ cells in LT vs KT patients were 86/μl vs 719/μl (p<0.00001) and 83/μl vs 464/μl (p=0.00004), respectively, and median numbers of CD4+CD25+ T-regulatory cells, BDCA1+CD19- mDC and BDCA2+ pDC were 13/μl vs 105/μl (p=0.00008), 5/μl vs 27/μl (p=0.00003) and 2/μl vs 15/μl (p=0.0014), respectively. However, 1 mos after TX the levels of Ly and mDC in KT pts were only 2-fold greater than in LT, whereas pDC levels were similar, whereas six mos after TX, LT pts had a significantly higher median number of CD3+CD8+ cells (623/μl vs 169/μl) (p=0.04), CD56+ cells (103/μl vs 37/μl) (p=0.007) and mDC (65/μl vs 21/μl) (p=0.07). ACR occurred in 4 KT. At ACR both Ly and DC numbers dropped. Interestingly, one month after ACR the CD4+ and CD8+ cell and mDC numbers recovered to levels of pts without ACR, whereas CD4+CD25+ cell and pDC numbers remained much smaller (p=0.01 and p=0.09, respectively). Conclusions: While the immunological status of LT pts is significantly impaired compared to KT pts, at 6 mos after TX blood levels of cytotoxic lymphocytes and mDC are greater in LT than in KT pts. Moreover, the observation of a profound and sustained depletion of T regulatoty cells (CD4+CD25+) and pDC in KT with ACR indirectly supports the role of these cells in tolerance induction after TX.