The present disclosure provides compositions and methods for the delivery of immune cells to treat un-resectable or non-resected tumor cells and tumor relapse. The compositions comprise (i) a structure comprising an injectable polymer or scaffold comprising pores; (ii) lymphocytes disposed within the structure, (iii) at least one lymphocyte-adhesion moiety associated with the structure; and (iv) at least one lymphocyte-activating moiety associated with the structure, and optionally an immune stimulant.