T7 endonuclease 1 analysis of amplicons of CXCR4 and CCR5 was performed using DNA extracted from all four groups at 0, 9, 18 days post-infection, and the result showed that the modified groups (#1 and #2) exhibited an obvious increase of lower migrating bands corresponding to cleavage products, but the unmodified groups (mock, control) had no cleavage products (Fig. 4b). Here, CXCR4 is linked to infection.