Abstract: Surface-modified cell containing a cell and a conformal coating on the extracellular surface of the cell are described. The conformal coating contains two or more layers containing particles (e.g. nanoparticles) or macromolecules. The cell is an islet cell, a B cell, or a T cell. The macromolecules or particles are formed from zwitterionic polymers. Covalent linkages are employed to link the particles or macromolecules to a cell surface molecule containing an abiotic functional group, or between macromolecules and/or particles in adjacent layers. Also described are methods of making and using a surface-modified cell.