Alternating tangential flow fast harvesting

The invention relates to alternating tangential flow fast harvesting. Methods and systems are disclosed for harvesting cell products from a cell culture by culturing cells in a fluid medium until the cells have produced a harvested concentration of cell products. The cells are cultured in a cell culture system that includes a bioreactor connected to an ATF device. The method includes discharging the fluid medium from the bioreactor through the outlet and the ATF device until the bioreactor volume reaches a predetermined volume, and the ATF column produces a liquid containing the cellular product at the ATF outlet and returns the fluid medium having the cellular product at a concentration lower than the harvest concentration into the bioreactor, the liquid containing the cell product is withdrawn from the ATF outlet, the bioreactor is refilled with a sterile phosphate buffered brine or a fluid medium that does not contain any cell product, and the steps are repeated until the desired amount of cell product is