It is generally believed that the peak of lentivirus production is between 24 ~ 24 ~ 48h after transfection, when the virus production rate is higher than the degradation rate. At this time, the first batch of lentiviruses can be harvested, which is also the time with the highest titer. After 48~72 h, the packaging continued, but the titer decreased (the production capacity decreased, but the degradation rate remained unchanged). In terms of yield, 1~2 lentivirus can be harvested with a small amount of culture medium within these 24 hours and fused with the lentivirus harvested for the first time. But if you simply pursue high titer, you can harvest it at once. In fact, the lentivirus harvested for the first time can meet the needs of many experiments.