Disclosed herein are materials and methods for modulating an immunologically adverse response to an exogenous or endogenous immunogen, including a cell, tissue, or organ associated immunogen. An implantable material comprising cells, such as but not limited to endothelial cells, anchored or embedded in a biocompatible matrix can modulate an adverse immune or inflammatory reaction to exogenous or endogenous immunogens, including response to non-syngeneic or syngeneic cells, tissues or organs, exogenous immunogens or stimuli, as well as ameliorate an autoimmune condition. The implantable material can be provided prior to, coincident with, or subsequent to occurrence of the immune response or inflammatory reaction. The implantable material can induce immunological acceptance in a transplant patient, reduce graft rejection and reduce donor antigen immunogenicity.