A 2-year-old child has a history of multiple bone fractures with minor trauma. On examination, he has hepatosplenomegaly and palsies involving cranial nerves II, VII, and VIII. Laboratory studies show pancytopenia. Radiographs reveal diffusely and symmetrically sclerotic bones with poorly formed metaphyses. Molecular analysis of his bone reveals a defect in the production of carbonic anhydrase to solubilize hydroxyapatite crystal. He is treated with hematopoietic stem cell transplantation. Which of the following cells in his bones was most likely functionally deficient and replaced following transplantation?