Engineered Bifidobacterium Shows Dual Promise: Oral Vaccine Boosts Anti-Tumor Immunity in Phase I Trial as NCI Funds Systemic Delivery Platform for Pancreatic Cancer
Key Insights
A phase I trial of B440 (search), an oral Bifidobacterium-based WT1 cancer vaccine, showed tolerability and immune enhancement in 12 metastatic urothelial cancer (search) patients, with six demonstrating WT1-specific cellular immune responses.
Three of seven patients who received pembrolizumab rechallenge after B440 (search) treatment showed tumor shrinkage, though causality could not be established in the small, non-randomized setting.
The University of Chicago received a $1.75 million NCI R01 award to develop engineered Bifidobacterium longum as a systemic delivery vehicle for IL-2 immunotherapy targeting metastatic pancreatic ductal adenocarcinoma (search).
Two independent research programs are advancing genetically engineered Bifidobacterium longum as a novel platform for cancer immunotherapy, with one reporting early clinical data from an oral vaccine approach and the other securing major federal funding for a systemic delivery strategy targeting pancreatic tumors.
A Kobe University-led team has published results from an exploratory phase I clinical trial of B440 (search), an oral vaccine based on genetically engineered Bifidobacterium longum designed to display a modified Wilms tumor 1 (WT1) (search) protein. Simultaneously, the University of Chicago has received a $1.75 million National Cancer Institute (NCI) R01 award under the "Bugs as Drugs" program to develop Bifidobacterium as a systemic delivery vehicle for interleukin-2 (IL-2) immunotherapy in metastatic pancreatic ductal adenocarcinoma (search) (PDAC).
Oral Vaccine Platform: Early Clinical Signals
The Kobe University study, published in JCO Oncology Advances, enrolled 12 patients with metastatic urothelial cancer (search) who had exhausted standard treatment options. The only treatment-related adverse event was a transient increase in interleukin-6 (IL-6), observed in three patients; all cases were mild and non-serious.
WT1-specific cellular immune responses were detected in six of the 12 patients, all of whom already had weak preexisting responses before treatment. These patients remained progression-free for longer than those without detectable responses. In the remaining six patients, who had no detectable preexisting WT1 response, B440 (search) did not appear to induce a new WT1-specific immune response.
"This suggests that B440 (search) may act more as an immune enhancer than as an initiator of immunity," the researchers noted. If confirmed in future studies, a low-level preexisting immune response to WT1 could serve as a candidate biomarker for identifying patients most likely to benefit from B440 or similar cancer immunotherapies.
After completing the trial, seven patients received pembrolizumab rechallenge at their physicians' discretion. Tumor shrinkage was observed in three of these patients, all of whom had detectable WT1-specific cellular immune responses after B440 (search) treatment. However, because of the small number of patients and the post-trial, non-randomized nature of the observation, the researchers caution that it is not possible to determine whether B440 contributed to these responses.
Shirakawa Toshiro, a translational cancer researcher at Kobe University's Department of Urology, explained the rationale: "When patients no longer respond to immune checkpoint inhibitors, effective treatment options are often limited. We need new approaches that can safely enhance anti-tumor immunity and complement immune checkpoint inhibitors."
The Kobe University-led team is now conducting a phase I/II clinical trial of B440 (search) in combination with the immune checkpoint inhibitors nivolumab and ipilimumab in patients with non-removable malignant pleural mesothelioma (search). "We believe this represents an important next step toward evaluating orally administered cancer vaccines as a new component of combination cancer immunotherapy," Shirakawa said.
Systemic Delivery for Pancreatic Cancer: NCI-Funded Program
The University of Chicago program, led by co-investigators Mark Mimee and Ralph Weichselbaum and funded through June 2029, targets PDAC—one of the cancers least responsive to existing treatments. Checkpoint immunotherapy and radiotherapy have demonstrated limited efficacy in this disease, partly due to an immunosuppressive tumor microenvironment dominated by tumor-associated macrophages and depleted of T cells.
The strategy exploits Bifidobacterium longum's natural ability to preferentially colonize hypoxic tumor regions following intravenous administration. The team has developed genetic tools to engineer the bacterium to secrete a modified interleukin-2 variant (SumIL2) directly within the tumor microenvironment, with a built-in gene circuit controlling both cytokine release and bacterial self-destruction.
The IL-2 delivery angle addresses a long-standing clinical problem: systemic IL-2 administration carries significant toxicity that has constrained its use in oncology. By restricting cytokine secretion to the tumor site through bacterial colonization, the approach aims to preserve efficacy while reducing off-target effects. The self-destruction circuit adds a further safety mechanism not present in earlier bacterial vector platforms.
Preliminary data indicated that systemic Bifidobacterium administration converted non-responding mice into responders to anti-CD47 (search) immunotherapy and radiotherapy, providing preclinical proof-of-concept for the combination approach.
A Favorable Translational Path
Both programs benefit from Bifidobacterium's status as a human commensal, which distinguishes it from competing microbial cancer therapy approaches. Attenuated Salmonella and Clostridium-based vectors have been explored in earlier-stage work but carry greater safety concerns given their pathogenic profiles. Bifidobacterium's established safety record—it is commonly used in probiotic yogurts—gives these programs a potentially more tractable translational path, though clinical validation remains a future step for the systemic delivery approach.
The NCI's continued investment in the "Bugs as Drugs" mechanism signals sustained institutional interest in microbial platforms as adjuncts to established immuno-oncology modalities.