Characterization of myeloid cell populations in human testes collected after sex reassignment surgery

The testis has been described in animal models as a site of immune privilege, which protects spermatids against tissue damage during inflammation. Myeloid cells, including macrophages and dendritic cells (DC), are defined as key players in the testicular immune privilege in animal models. However, their distribution and frequency in human testis remain poorly described. To overcome the challenges related to tissue sampling, we obtained testicular tissue from men under hormonal therapy who elected to have sex reassignment surgery (SRS). We examined the distribution of myeloid cell populations in tissue sections using immunohistofluorescence and evaluated their relative frequencies in fresh testicular cell suspensions compared with matched blood using multi-parametric flow cytometry. We identified 4.9% of CD45⁺ leucocytes in testicular cell suspensions, of which 0.4% were B cells, demonstrating a low level of blood contamination. Myeloid cells (Lin^-HLA-DR⁺) were located in the testicular interstitium and represented a median of 23.4% of testicular leucocytes, displaying higher HLA-DR expression compared to their counterparts in blood (p=0.001). The frequency of testicular myeloid cells was not linked with the duration of hormonal therapy. Resident macrophages (CD14⁺CD163⁺) constituted the most frequent myeloid cell subset and expressed high levels of CD163. Elevated proportion of myeloid DC (CD14^-CD11c⁺) contrasted with the paucity of plasmacytoïd DC (CD14^-CD123⁺) in testis. Myeloid-derived suppressor cells (Lin^-HLA-DR^-CD33^hiCD11b^hi) were not detected in the testis while constituting 0.5% of blood leucocytes. For the first time, we characterized myeloid cell subsets in human testes collected after SRS, providing a basis to assess their contribution to immune privilege.