In cancer therapy research, scientists harness viruses and gene transfer to trigger immune-driven tumor destruction, offering hope against hard-to-treat melanoma.
Study: A virus based vaccine combined with IL12 gene therapy eradicates aggressive melanoma. Image credit: shoma81/Shutterstock.com
Melanoma is among the most aggressive and common cancers. Surgery, chemotherapy, and radiation therapy have been the mainstay of melanoma treatment, but they fail to control aggressive tumors, especially when resistance develops. A new study published in the journal Scientific Reports explored the effectiveness of combined bacteriophage-gene therapy in a mouse melanoma model.
Each year, there are more than 132,000 new melanoma cases globally. Research has uncovered much of the biology of the tumor, leading to the development of effective immunotherapies, including gene therapy and anti-cancer vaccines.
The latter stimulates a tumor-antigen-directed, specific immune response that involves both innate and adaptive immunity, targeting tumor cells. Nanotechnology has revolutionized the anti-tumor vaccine field.
Among the most reliable agents in this area are bacteriophages (phages), the most abundant life forms in many environments, including the human body. Filamentous M13 bacteriophages have a simple, easily engineered structure, enabling them to display multiple tumor-associated antigens simultaneously to stimulate the immune response.
They also carry single-stranded DNA-rich CpG motifs that induce an intense immune response and thus act as adjuvants to the cancer vaccine, enhancing the anti-tumor response. They rarely infect mammalian cells and cannot replicate inside them, making them safe for use as medical interventions.
“These developments position bacteriophage-based immunotherapy at the forefront of next-generation cancer treatment strategies.”
Such vaccines may be combined with other immunotherapies. Similar approaches, using immune checkpoint inhibitors or anti-PD-1 inhibitors, have been explored in earlier research. For instance, the tumor microenvironment induces immunosuppression and inhibits T cell function, often causing T cell exhaustion.
Interleukin-12 (IL-12) is an immunomodulatory cytokine that may enhance the immune reaction, partially reversing tumor-associated immunosuppression.
The current study tested the bacteriophage M13, which expresses three tumor-associated antigens (MAGE-A1, gp100, and MART-1), for its impact on mouse melanoma growth and survival. Multiple antigens were used to prevent the development of tumor resistance, often by reducing or eliminating the expression of tumor antigens on the cell surface targeted by the host immune system.
Secondly, the vaccine was combined with IL-12 stimulation. An IL-12-encoding plasmid was inserted into the tumor by electroporation-gene electrotransfer (GET)-IL-12 to achieve this. This method is designed to achieve sustained local production of IL-12 within the tumor microenvironment and minimize the serious adverse effects caused by excessive levels of recombinant cytokines introduced by other routes. However, GET-IL-12 is still investigational.
The aim was to evaluate the difference in antitumor activity with the combined approach. The study used the highly aggressive B16 F10 melanoma model with few tumor-infiltrating lymphocytes (immunologically cold). This presents a challenging benchmark for cancer immunotherapy.
Compared to other tumor models like CT26, which are more immunogenic, B16 F10 tumors tend to be resistant to monotherapy and less responsive to immune activation.
Study findings
Mice were injected with melanoma cells to induce tumor growth. They were treated with wild-type or engineered phages, as monotherapy or in combination with GET-IL-12.
The engineered phages suppressed tumor growth and thus prolonged mouse survival until the tumor was large enough for GET-IL-12. GET-IL-12 further increased the survival period and activated the immune response, as expected from current literature.
It also enhanced immune cell infiltration into the tumor microenvironment, including macrophages and T lymphocytes.
All groups failed to show any evidence of harm in terms of behavioral changes or reduced body weight.
Tumors proliferated in the control group, reaching a volume of 10 mm³ within the ten-day study period. With engineered phage therapy, this volume was reached in 21.3 days. Wild-type phages were less effective, as the tumor volume reached 10 mm³ in 14.3 days.
The experiment was terminated once the tumor reached 400 mm³. This occurred in a median of 17 days in the control group vs 26 days with the wild-type phages.
Engineered phage monotherapy prolonged this period to a median of 40.5 days, prolonging survival by 23.5 days.
When GET-IL-12 monotherapy was used (without phage), the median survival was also increased, and a complete response was observed in 10% of mice.
When wild-type phages were combined with GET-IL-12, median survival rose to 57 days. The highest survival was with the engineered phage-GET-IL12 combination, at 96.5 days.
Interestingly, 30% of the mice showed complete disappearance of cancer. The area of the primary tumor became depigmented, both skin and hair, with the appearance of vitiligo.
In contrast, phage monotherapy did not produce complete resolution in any group, probably because the tumor in this case was so aggressive.
With engineered phage monotherapy, the tumor was infiltrated by immune cells like macrophages, CD8, and CD4 tumor cells, compared to the minimal infiltrate seen in the control group. Phage therapy led to widespread areas of tumor necrosis, releasing tumor antigens and promoting tumor antigen presentation to host immune cells.
Combined treatment induced much greater antitumor activity compared to monotherapy. Intense lymphocytic infiltration shrank the tumors to small volumes. Only very small tumors were left behind at autopsy; most of the tumor was replaced by lymphocytic infiltrate.
The authors noted that phages activate immune responses through multiple mechanisms, including toll-like receptor signaling via their single-stranded DNA, uptake by antigen-presenting cells, and contribution to both innate and adaptive immunity.
They also noted that phages facilitate cross-presentation of tumor antigens by dendritic cells, further enhancing CD8+ T-cell activation.
A limitation of phage-IL-12 therapy is its failure to induce long-term immunity. To compensate, boosters may be required, or other immunotherapies, like checkpoint inhibitors, may be added.
This aligns with the broader literature on cold tumors, where immunotherapy often fails to sustain memory responses.
Conclusions
This in vivo experiment demonstrates the safety and effectiveness of a combined engineered M13 phage-GET-IL-12 cancer vaccine.
It produced an effective anti-tumor immune response, eliminating the tumor in almost a third of cases and drastically shrinking the tumor in the rest by promoting immune cell-mediated tumor destruction.
Wild-type phages were less effective than engineered phages, whether used alone or with IL-12. Combining GET-IL-12 with engineered phages expressing different tumor peptides on their capsids considerably increased survival time compared to controls or wild-type phage monotherapy.
This combination enhanced tumor infiltration by immune cells, primarily T lymphocytes, showing synergistic effects with phage therapy.
The authors emphasized the need for careful regulation, standardization of phage production, and biosafety oversight before advancing to human trials. The translation of phage-based cancer vaccines to clinical use will require further studies to confirm safety, optimal dosing, and efficacy, as well as addressing regulatory challenges.
Meanwhile, further studies are needed to confirm the safety and efficacy of monotherapy or combined therapies, as well as the optimal treatment strategies.
Notably, this research remains preclinical and investigational, and although promising, the results in mice will require substantial validation before being applied to humans.
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