Chemo- and protein-based therapeutics are two major modalities for the treatment of malignant tumors with drastically different therapeutic indices, toxicity, and other pharmacological properties. For intended in vivo applications, they also have distinctly different formulation challenges to be addressed separately. In this study, we attempt to overcome the formulation barriers of chemo- and protein-based therapeutics, and report the development of injectable nanogels, a class of crosslinked physical and chemical composite gels (nPCGs), for the joint delivery of doxorubicin (DOX), protein cytokines recombinant human interleukin-2 (IL-2), and recombinant human interferon-gamma (IFN-gamma). The nPCGs are designed through a quick gelation induced by ionic crosslinking of 4-arm poly(ethylene glycol)-b-poly(L-glutamic acid) (PPLG) and hydroxypropyl chitosan/4-arm poly(ethylene glycol)-b-poly(L-lysine) (HPCS/PPLL), followed by the formation of covalent bonds via a Schiff-base reaction of the oxidized, cholesterol-bearing dextran (OCDEX) nanogels with HPCS/PPLL, which results in increased hydrogel moduli (G' around 13.8 kPa) and improved stability. This nPCG, which contains DOX, IL-2, and IFN-gamma, shows a synergistic anticancer efficacy through the regulation of apoptosis-related genes in Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathways and mitochondrial pathways in xenograft tumor-bearing mice.