Different from conventional vaccines, in situ vaccination could conveniently convert established tumors into a "vaccine factory" to release various tumor antigens for stimulating and diversifying antitumor T-cell response. [3] Radiation therapy (RT) is a widely used local therapy of malignancies and exhibits great potential in inducing in situ tumor vaccine effect. [4] However, even potentiated by CBI, RT could only lead to mild to moderate immune response within nonirradiated tumors, which is far less than medical needs. [5] Therefore, it is quite meaningful to boost RT-mediated in situ vaccination to extend its therapeutic effect to the whole body.To achieve this goal, a possible way could be potentiating RT-induced immunogenic cell death (ICD). ICD is a death modality accompanied by releasing tumor antigens and damage-associated molecular patterns, including calreticulin (CRT), high mobility group protein B1 (HMGB1), etc., which could provide antigens and adjuvants for tumor vaccination. [6] Currently, some studies have indicated that oxidative stress and DNA damage within tumor cells could potentially result in ICD. [7] However, due to the insufficient deposition of X-ray within tumor tissues, only low level of reactive oxygen species (ROS) could be produced to induce oxidative stress upon the recommended radiation doses. To address this problem, radiosensitizers based on high-Z elements are being developed widely to deposit X-ray for amplifying RT-induced oxidative stress. Of note, HfO 2 nanoparticles (Hensify) have been approved in Europe for locally advanced soft tissue sarcoma treatment [8] and are confirmed to augment RT-mediated antitumor immunity effect in many clinical trials. However, their slight improvements suggest the room for optimization. [9] The pentose phosphate pathway (PPP) is a branch of glycolysis and hyperactive in most tumors, [10] which could provide abundant NADPH and ribose 5-phosphate to maintain redox and nucleotides homeostasis, respectively. [11] NADPH is a central player in cellular antioxidant system, which not only mediates GSH synthesis, [12] but also acts as an electron donor to reduce oxidized GSH and thioredoxin (Trx, an important In situ tumor vaccination is preliminarily pursued to strengthen antitumor immune response. Immunogenic tumor cell death spontaneously releases abundant antigens and adjuvants for activation of dendritic cells, providing a paragon opportunity for establishing efficient in situ vaccination. Herein, Phy@PLGdH nanosheets are constructed by integrating physcion (Phy, an inhibitor of the pentose phosphate pathway (PPP)) with layered gadolinium hydroxide (PLGdH) nanosheets to boost radiation-therapy (RT)-induced immunogenic cell death (ICD) for potent in situ tumor vaccination. It is first observed that sheet-like PLGdH can present superior X-ray deposition and tumor penetrability, exhibiting improved radiosensitization in vitro and in vivo. Moreover, the destruction of cellular nicotinamide adenine dinucleotide phosphate (NADPH) and nucleotide...