Lentiviral vector particles (HIV-1) display recombinant membrane envelope proteins containing stem cell factor (SCF) and TPO that can specifically target the vector particles to hematopoietic stem cells (HSCs) expressing the c-kit and c-mpl receptors for SCF and TPO, respectively. All vector particles contain the VSV-G envelope protein, which binds to phospholipids in cellular membranes. Illustration by Marie Dauenheimer.