Tumor-specific CD8 ⁺ T cells in stable tumor-draining lymph node reservoir are clonally and developmentally related to those in tumors.

Interferon-γ (IFN-γ) is a potent cytokine critical for response to immunotherapy, yet conventional methods to systemically deliver this cytokine have been hindered by severe dose-limiting toxicities. Here, we engineered a strain of probiotic bacteria that home to tumors and locally release IFN-γ. A single intratumoral injection of these IFN-γ–producing bacteria was sufficient to drive systemic tumor antigen–specific antitumor immunity, without observable toxicity. Although cancer cells use various resistance mechanisms to evade immune responses, bacteria-derived IFN-γ overcame primary resistance to programmed cell death 1 (PD-1) blockade via activation of cytotoxic Foxp3 ⁻ CD4 ⁺ and CD8 ⁺ T cells. Moreover, by activating natural killer (NK) cells, bacteria-derived IFN-γ also overcame acquired resistance mechanisms to PD-1 blockade, specifically loss-of-function mutations in IFN-γ signaling and antigen presentation pathways. Collectively, these results demonstrate the promise of combining IFN-γ–producing bacteria with PD-1 blockade as a therapeutic strategy for overcoming immunotherapy-resistant, locally advanced, and metastatic disease.

Kras-driven lung adenocarcinoma (LUAD) is the most common lung cancer. A significant fraction of patients with Kras-driven LUAD respond to immunotherapy, but mechanistic studies of immune responses against LUAD have been limited because of a lack of immunotherapy-responsive models. We report the development of the immunogenic KP × NINJA (inversion inducible joined neoantigen) (KP-NINJA) LUAD model. This model allows temporal uncoupling of antigen and tumor induction, which allows one to wait until after infection-induced inflammation has subsided to induce neoantigen expression by tumors. Neoantigen expression is restricted to EPCAM+ cells in the lung and expression of neoantigen was more consistent between tumors than when neoantigens were encoded on lentiviruses. Moreover, tumors were infiltrated by tumor-specific CD8 T cells. Finally, LUAD cell lines derived from KP-NINJA mice were immunogenic and responded to immune checkpoint therapy (anti-PD1 and anti-CTLA4), providing means for future studies into the immunobiology of therapeutic responses in LUAD.

The intratumoral microbiome has recently emerged as a potential hallmark of cancer, with implications for response or resistance to therapy. Bacteria can either promote or inhibit cancer growth. However, intratumoral bacteria can also be engineered using synthetic biology to remodel the tumor microenvironment. Here, we engineered the probiotic bacterium Escherichia coli Nissle 1917 (EcN) to express the human chemokine CXCL13 (C-X-C motif chemokine ligand 13), a critical component of germinal center (GC) formation. Antibody affinity maturation and class switching are fundamental aspects of adaptive immune response. Both occur primarily in the GCs of secondary lymphoid organs for defense against pathogens. Immune checkpoint blockade (ICB) efficacy is primarily driven by T cells; however, recent studies in mice and humans have shown that humoral immune responses act as critical partners for ICB-mediated antitumor activity. Using orthotopic models of bladder cancer, intravesically delivered engineered CXCL13-expressing EcN colonized bladder tumors and elicited GC responses in bladder tumor–draining lymph nodes after intravesical delivery. When combined with programmed cell death protein 1 (PD-1) blockade, engineered EcN improved antitumor activity in two aggressive, fast-growing, and immunologically cold orthotopic mouse models of bladder cancer. Mechanistically, this antitumor effect was dependent on the presence of CD8 ⁺ T cells and CD4 ⁺ T follicular helper cells; combination therapy increased tumor-specific antibody responses and promoted long-term survival and protective immunity upon tumor rechallenge. Thus, we demonstrate that synthetically engineered CXCL13-expressing EcN can enhance the efficacy of PD-1 checkpoint blockade immunotherapy by amplifying tumor-specific humoral immunity.

Achieving tumor-specific delivery and sustained activation of both cytotoxic and immune-modulating agents remains a critical challenge in chemoimmunotherapy. Here, a bacterial platform was engineered to combine enzyme/prodrug chemotherapy with immunotherapy, in which tumor-homing Escherichia coli Nissle 1917 expressed cytosine deaminase to convert the prodrug 5-fluorocytosine into the cytotoxic drug 5-fluorouracil and concurrently produced an IL-15 superagonist and a PD-L1 blocking nanobody in tumors. This platform demonstrated potent antitumor effects in murine MC38 and B16-F10 solid tumor models. Mechanistic analyses showed that bacterial enzyme/prodrug therapy alone elicited both immune activation and compensatory immunosuppressive responses, whereas inclusion of IL-15 superagonist and PD-L1 blockade enhanced activation of antigen-presenting cells, T cells, and natural killer cells and attenuated immunosuppressive pathways. Abscopal and rechallenge experiments indicated that this bacterial chemoimmunotherapy strategy induces systemic antitumor immunity and durable immune memory. In summary, our approach integrates enzyme/prodrug therapy and immunotherapy into a single bacterial delivery system, overcoming key limitations of conventional therapies by providing a rationally designed framework for spatially controlled chemoimmunotherapy.