CXCR4 and HIV infectious disease: While this strategy provided protection for mature CD4+ T cells against X4 tropic HIV infection, nevertheless, Anderson et al. suggested that CXCR4 knockout/down has altered HSPC growth, migration, and transformation into more mature hematopoietic cells since CXCR4 expression was noted to play an essential role in CD34 positive (CD34+) HSPCs in terms of differentiation, and quiescence [28,30].