CD34 and head and neck squamous cell carcinoma: It is widely accepted that the exposure of the CD34+ cells to the human GM-CSF cytokine produced by the NOG-EXL mouse does result in the engraftment and development of CD33+ myeloid cells; however, it cannot be excluded that the HNSCC indication, which is often characterized by an abundance of immunosuppressive myeloid populations, including myeloid-derived suppressor cells (MDSCs) and tumor-associated macrophages (TAMs), plays a critical role in the presence and function of these CD33+ cells in immune evasion and therapeutic resistance.