Disclosed herein are methods for maintaining a population of therapeutic cells administered to a treatment site in a subject in need of cell therapy for a period of time. The methods include administering a therapeutically-effective amount of therapeutic cells and an effective amount of a biodegradable material to the treatment site. The biodegradable material includes a hyaluronan compound and has an in vivo degradation profile similar to that of a hyaluronic acid having a molecular weight of 20 kDa to 2,000 kDa.
