When considering the mixed cellular composition of differentiated neurospheres, which clearly retained a distinct proportion of NPCs (Fig. 1d), we speculate that addition of IL-34, M-CSF, and TGFβ-1 induced these progenitor cells to differentiate in a myeloid/microglia phenotype that was more permissible to HIV-1 infection. Here, TGFB1 is linked to HIV-1 infection.