In human male testes, the regions outside the seminiferous tubules are called interstitial spaces, and they contain

a. Immunologically competent cells
b. Leydig cells
c. Sertoli cells

Seminiferous tubules are lined by two types of cells, the main spermatogonia i.e., mother cells that form the sperms and the Sertoli cells or nurse cells where the sperms mature. In between the seminiferous tubules is interstitial tissue that contains Leydig cells, blood vessels, immune cells etc.