Systems and methods for returning treated mononuclear cells to a blood source

A method for treating mononuclear cells for an extracorporeal photopheresis procedure, driven and adjusted by a microprocessor-based controller, comprising the steps of:

• priming a fluid circuit with priming fluid;
• directing whole blood derived from a blood source into the fluid circuit;
• separating the whole blood in a separation chamber of the fluid circuit into a red blood cell component, a mononuclear cell component, and a platelet/plasma component;
• returning a first portion of the red blood cell component and a first portion of the platelet/plasma component to the whole blood at the same time as the mononuclear cell component is accumulating in the separation chamber;
• adding a biological agent to the mononuclear cell component in an illumination container fluidically connected to the separation chamber to create an agent-added mononuclear cell component;
• irradiating the agent-added mononuclear cell component in an illumination container of the fluid circuit;
• and
• after irradiation of the agent-added mononuclear cell component has ended, incubating for a period of time a first portion of the agent-added mononuclear cell component in the illumination container to create an incubated agent-added mononuclear cell component, with the blood source being disconnected from the fluid circuit for at least a portion of the period of time, wherein
• the period of time is sufficiently long to allow for apoptotic T-cells generated in the agent-added mononuclear cell component by irradiation to induce differentiation of monocytes in the first portion of the agent-added mononuclear cell component into dendritic cells, and
• a single fluid circuit is used for both separating the whole blood and incubating the first portion of the agent-added mononuclear cell component.