Hydrogel materials have emerged as versatile platforms for various biomedical applications. Notably, the engineered nanofiber-hydrogel composite (NHC) has proven effective in mimicking the soft tissue extracellular matrix, facilitating substantial recruitment of host immune cells and the formation of a local immunostimulatory microenvironment. Leveraging this feature, here we report an mRNA lipid nanoparticle (LNP)-incorporated NHC microgel matrix, termed LiNx, by incorporating LNPs loaded with mRNA encoding tumour antigens. Harnessing the high transfection efficiency of LNPs in antigen-presenting cells, LiNx demonstrates substantial levels of immune cell recruitment, antigen expression and presentation, and cellular interaction. These attributes collectively create an immunostimulating microenvironment and yield a potent immune response with a single dose at a level comparable to the conventional three-dose LNP immunization protocol. Further investigation reveals that the LiNx generates not only high levels of Th1 and Th2 responses, but also a distinct Type 17 T helper cell response critical for bolstering antitumour efficacy. Our findings elucidate the mechanism underlying LiNx's role in potentiating antigen-specific immune responses, presenting a strategy for cancer immunotherapy.