A method of modifying cells includes removing fluid including cells from a patient, contacting the removed fluid from the patient with at least one surface upon which at least one agent to interact at least one cell receptor is immobilized to modify cells in the fluid, and returning the fluid to the patient. The agent can, for example, be immobilized via covalent bonding or ionic bonding to the at least one surface. The fluid can, for example, be blood or a blood fraction. The agent can, for example, be an agonist, an antagonist or an inverse agonist.