*Purpose: There is growing evidence that type 2 immune effectors (immunoglobulin E, eosinophils, mast cells/basophils) play a role in autoimmune disorders and solid organ transplantation. The aim of this study was to evaluate the impact of blood count eosinophils (BCEo) on immunological outcomes in kidney transplant recipients with stable graft function during follow-up after 3 months post transplant.

*Methods: We performed survival analysis on a prospective cohort of 1013 kidney transplant patients who experienced kidney allograft rejection and the appearance of de novo donor specific antibodies with time-dependent variation in BCEo after excluding common causes of an increase in BCEo. The cause-specific Cox model was performed considering BCEo and the use of calcineurin inhibitors and systemic corticoids as time-dependent explicative variables at each routine measurement during patient follow-up.

*Results: BCEo ≥ 0.3 G/L was associated with a 3-fold increased risk of rejection independent of immunosuppressive regimen after 3 months post-transplant in patients without pre-transplant DSAs and with CNI-based immunosuppression. No association between BCEo either with donor specific antibodies, eosinophil infiltration of the graft or graft survival was noticed.

*Conclusions: Our data revealed that a BCEo threshold of ≥ 0.3 G/L could be an add-on routine marker to other routine parameters, such as DSAdn, to better assess the risk of rejection after 3 months post transplantation after eliminating common causes of an increase in BCEo (PTLD, allergy/atopy, parasitic infections, and drug-induced hypersensitivity). These observations in this large cohort support the possible involvement of eosinophils and type 2 immunity in alloimmunity in humans.

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