(Left) Injectable hydrogels (purple) are being explored to deliver immunomodulatory drugs to solid tumors.  These synthetic polysaccharide gels are infiltrated by immune cells (green) that subsequently attack the neighboring tumor.  (Right) Tumor-reactive “killer” T-cells (blue) decorated with drug-loaded nanoparticles (yellow) can be infused into tumor-bearing hosts, to hunt down and destroy tumors.  By providing supporting drugs carried by each individual cell, the T-cells’ ability to proliferate and kill tumor cells is enhanced while minimizing exposure of other cell types to potent adjuvant drugs.