Patients with Nijmegen Breakage Syndrome (NBS) suffer from recurrent infections due to humoral and cellular immune deficiency. Despite low number of T lymphocytes and their maturation defect, the clinical manifestations of cell-mediated deficiency are not as severe as in case of patients with other types of combined immune deficiencies and similar T cell lymphopenia. In this study, multicolor flow cytometry was used for evaluation of peripheral T lymphocyte maturation according to the currently known differentiation pathway, in 46 patients with genetically confirmed NBS and 46 sex and age-matched controls. Evaluation of differential expression of CD27, CD31, CD45RA, CD95, and CD197 revealed existence of cell subsets so far not described in NBS patients. Although recent thymic emigrants and naïve T lymphocyte cell populations were significantly lower, the generation of antigen-primed T cells was similar or even greater in NBS patients than in healthy controls. Moreover, the senescent and exhausted T cell populations defined by expression of CD57, KLRG1, and PD1 were more numerous than in healthy people. Although this hypothesis needs further investigations, such properties might be related to an increased susceptibility to malignancy and milder clinical course than expected in view of T cell lymphopenia in patients with NBS.

De novo Donor Specific Antibodies (dnDSA) are associated with inferior graft outcomes. Standard immunosuppression is expected to prevent dnDSA production in low-risk patients. We have evaluated a cumulative effect of a triple immunosuppression (CNI/MMF/Pred), as well as TAC concentration and coefficient of variation on the incidence of dnDSA production. Overall, 67 transplanted patients were evaluated in retrospective (dnDSA for-cause; n = 29) and prospective (dnDSA by protocol; n = 38) groups. In the retrospective group, the eGFR value at first dnDSA detection (median interval—4.0 years post-transplant) was 41 mL/min/1.73 m2; 55% of patients presented biopsy-proven cAMR, and 41% lost the graft within next 2.4 years. Patients from the prospective group presented 97% graft survival and eGFR of 76 mL/min/1.73 m2 at 2 years follow-up, an overall incidence of 21% of dnDSA and 18% of acute (T cell) rejection. None of the patients from the prospective group developed cAMR. Median value of Vasudev score within 2 years of follow-up was not significantly higher in dsDSA negative patients, while median value of TAC C0 > 1–24 months post-transplant was 7.9 in dnDSA negative vs. 7.1 ng/mL in dnDSA positive patients (p = 0.008). Conclusion: dnDSA-negative patients presented a higher exposure to tacrolimus, while not to the combined immunosuppression.