The CCR5 gene-modified cells are highly resistant to R5-tropic HIV-1 infection including transmitted founder (T/F) viruses (Fig. 3 and 6A and B) and exhibit a selective survival advantage over cells with unmodified CCR5 during R5-tropic HIV-1 infection (Fig. 6C and D). The gene discussed is CCR5; the disease is HIV-1 infection.