For example, HIV infection of resting CD-4+ T cells, monocyte-derived macrophages, and macrophages generated from inducible pluripotent stem cells have been observed to be biased towards defective proviral genomes [29,30], possibly reflecting the expression of Sterile Alpha Motif and HD-domain-containing protein 1, SAMHD1, a host viral restriction factor which reduces intracellular nucleotide concentrations, limiting the completion of reverse transcription in myeloid cells and resting CD4+ T cells [31,32,33,34,35,36,37,38]. Here, CD4 is linked to HIV infectious disease.