A method of processing a fluid comprising a recombinant therapeutic protein, the method comprising: (a) providing a first circuit system comprising (i) a tangential flow filtration unit having first and second inlets, and (ii) a first conduit in fluid communication between the first and second inlets, comprising at least one port for flowing fluid into or out of, or both, of the first circuit system, wherein the first circuit system is configured such that fluid can be flowed through the first conduit and the TFF unit, and filtrate not comprising the recombinant therapeutic protein can be collected from the TFF unit; (b) providing a second circuit system comprising (i) a tangential flow virus filtration (TFVF) unit having first and second inlets, and (ii) a second conduit in fluid communication between the first and second inlets of the TFVF unit, comprising at least one port for flowing fluid into or out of, or both, of the second circuit system, wherein the second circuit system is configured such that fluid can be flowed through the second conduit and the TFVF unit, and filtrate comprising the recombinant therapeutic protein can be collected from the TFVF unit; (c) continuously flowing a fluid comprising a recombinant therapeutic protein into the circuit system through one of the at least one port, and discarding filtrate not comprising the recombinant therapeutic protein for a first period of time; (d) continuously flowing a diafiltration medium into the first circuit system through one of the at least one port, and discarding filtrate not comprising the recombinant therapeutic protein for a second period of time; and (e) collecting a fluid comprising the recombinant therapeutic protein that is present in the circuit system after the first and second time periods through one of the at least one port; and (f) flowing the collected fluid of step (e) into the second circuit system using a connecting conduit in fluid communication between a port in the first circuit system and a port in the second circuit system, recirculating retentate in the second circuit system, and collecting filtrate comprising the recombinant therapeutic protein from the TFVF unit for a third period of time wherein rate of recirculating retentate in the second circuit system and rate of flowing the collected fluid of step (e) into the second circuit system can be independently controlled. (a) providing a first circuit system comprising (i) a tangential flow filtration unit having first and second inlets, and (ii) a first conduit in fluid communication between the first and second inlets, comprising at least one port for flowing fluid into or out of, or both, of the first circuit system, wherein the first circuit system is configured such that fluid can be flowed through the first conduit and the TFF unit, and filtrate not comprising the recombinant therapeutic protein can be collected from the TFF unit; (b) providing a second circuit system comprising (i) a tangential flow virus filtration (TFVF) unit having first and second inlets, and (ii) a second conduit in fluid communication between the first and second inlets of the TFVF unit, comprising at least one port for flowing fluid into or out of, or both, of the second circuit system, wherein the second circuit system is configured such that fluid can be flowed through the second conduit and the TFVF unit, and filtrate comprising the recombinant therapeutic protein can be collected from the TFVF unit; (c) continuously flowing a fluid comprising a recombinant therapeutic protein into the circuit system through one of the at least one port, and discarding filtrate not comprising the recombinant therapeutic protein for a first period of time; (d) continuously flowing a diafiltration medium into the first circuit system through one of the at least one port, and discarding filtrate not comprising the recombinant therapeutic protein for a second period of time; and (e) collecting a fluid comprising the recombinant therapeutic protein that is present in the circuit system after the first and second time periods through one of the at least one port; and (f) flowing the collected fluid of step (e) into the second circuit system using a connecting conduit in fluid communication between a port in the first circuit system and a port in the second circuit system, recirculating retentate in the second circuit system, and collecting filtrate comprising the recombinant therapeutic protein from the TFVF unit for a third period of time