CXCR4 and infection: It has been repeatedly shown that various SIV isolates can infect primary human Δ32 homozygous PBMC independent of both CCR5 and CXCR4, indicating that alternative coreceptors are expressed in a manner that supports infection in primary lymphocytes ex vivo, at least in cells of human origin [51], [52], [53], [54], [55], [56].