In contrast to different blood cancers, the effectiveness of adoptive T cell therapies in the treatment of solid tumors, which comprise about 90% of all tumors, has been very limited because of several formidable barriers. Now immune-engineers have developed a novel biomaterials-based immunotherapy approach named SIVET that has the potential to break down these barriers. The injectable biomaterial enables both: the local delivery of antigen-specific adoptively transferred T cells directly to tumor sites and their prolonged activation, as well as a broader engagement of the host immune system to provide much longer-lasting anti-tumor effects against tumor cells carrying new antigens. Validated in mice carrying melanomas, a particularly aggressive type of solid tumor, SIVET enabled the fast shrinking of tumors and long-term protection against them.