A single-use fluid circuit for recovering leukocytes in conjunction with separation of biological fluid into two or more components, comprising: a separator having an inlet for receiving the biological fluid, a first outlet for a separated first component, and a second outlet for a separated second component; a leukocyte reduction filter having an inlet and an outlet; a first fluid flow path in fluid communication with the inlet of the separator and configured to be connected to a source of biological fluid; a second fluid flow path connecting the first outlet of the separator to the inlet of the leukocyte reduction filter; a first collection container for receiving leukocyte-reduced first component; a third fluid flow path connecting the outlet of the leukocyte reduction filter to the first collection container; a source of additive solution; a fourth fluid flow path between the first fluid flow path and the source of additive solution; wherein the fluid circuit further comprises: a fifth fluid flow path between the source of additive solution and the second fluid flow path leading to the leukocyte filter; a source of eluate; a sixth fluid flow path between the source of eluate and the third fluid flow path, so as to permit eluate to flow to the outlet of the leukocyte filter to backwash the filter; a second collection container for receipt of recovered leukocytes, and a seventh fluid flow path between the second collection container and the fifth fluid flow path, so as to permit the recovered leukocytes and eluate to flow out of the inlet of the leukocyte filter and sequentially through the second fluid flow path, the fifth fluid flow path and the seventh fluid flow path and into the second collection container. a separator having an inlet for receiving the biological fluid, a first outlet for a separated first component, and a second outlet for a separated second component; a leukocyte reduction filter having an inlet and an outlet; a first fluid flow path in fluid communication with the inlet of the separator and configured to be connected to a source of biological fluid; a second fluid flow path connecting the first outlet of the separator to the inlet of the leukocyte reduction filter; a first collection container for receiving leukocyte-reduced first component; a third fluid flow path connecting the outlet of the leukocyte reduction filter to the first collection container; a source of additive solution; a fourth fluid flow path between the first fluid flow path and the source of additive solution; a fifth fluid flow path between the source of additive solution and the second fluid flow path leading to the leukocyte filter; a source of eluate; a sixth fluid flow path between the source of eluate and the third fluid flow path, so as to permit eluate to flow to the outlet of the leukocyte filter to backwash the filter; a second collection container for receipt of recovered leukocytes, and a seventh fluid flow path between the second collection container and the fifth fluid flow path, so as to permit the recovered leukocytes and eluate to flow out of the inlet of the leukocyte filter and sequentially through the second fluid flow path, the fifth fluid flow path and the seventh fluid flow path and into the second collection container.