Morphological characteristics of the spermatogonial stem cells in man.

The present investigation is concerned with establishing morphological criteria of spermatogonial stem cells in man. Testicular biopsies from patients having undergone semicastration for malignant tumors and radio- and chemotherapy for one year following the operation were studied light and electron microscopically. Those spermatogonial types that survived the treatment were regarded as stem cells in view of the fact that the stem cells, in contrast to the more differentiated spermatogonia, are radiation resistant and less sensitive to various noxious agents. In 7 out of 28 cases examined, a small number of spermatogonia was found adjacent to the basement membrane. The majority of these cells show the characteristic features of pale type A spermatogonia, while a few cells may represent variants of this cell type. The dark type A spermatogonia are almost completely eliminated from the seminiferous tubules. A concept is proposed that the stem cells of the human testis may be derived from the pale type A spermatogonia or the variants of this cell type.