JITC: Cowpea mosaic virus can also be used as an anti-cancer vaccine!

In recent years, tumor vaccines have gradually become one of the important immunotherapies, and in situ vaccines (ISVs) have become more and more widely used
.
ISV directly acts on the tumor site, exerts an immunostimulating effect, recruits immune cells to the tumor site, promotes tumor antigen presentation, and can even trigger a systemic anti-tumor immune response [1].

However, due to the presence of immunosuppressive tumor microenvironment, immune effector cells are difficult to infiltrate, and the efficacy of ISV alone is not ideal, insufficient to eradicate tumors, and rarely provoke systemic anti-tumor immune responses
.
How to combine ISV with other immunotherapies to trigger local and systemic anti-tumor immune responses is also a hot issue
for researchers.

Recently, a research team
led by Steven Fiering of Dartmouth College.
Published important research results in the journal Cancer Immunotherapy [2].

They found that treating tumors with cowpea mosaic virus (CPMV) as an ISV could elicit a T lymphocyte- and dendritic cell-dependent anti-tumor immune response
in some tumor models.
When CPMV is combined with anti-CD40 antibody or anti-PD-1 antibody, it can further induce systemic anti-tumor immune response and effectively inhibit tumor growth
.

Their study proves that CPMV can trigger a systemic anti-tumor immune response and provides a new combination therapy, namely CPMV in situ therapy + anti-CD40 antibody in situ therapy + anti-PD-1 antibody
.
This combination therapy modality helps to improve the tumor microenvironment, enhance antigen presentation, and overcome tumor resistance to immune checkpoint therapy, inducing long-acting anti-tumor effects
.

Screenshot of the first page of the paper

CPMV is a plant virus that cannot infect animal cells, but its capsid and single-stranded RNA can act as toll-like receptor (TLR) agonists [3-4], effectively activating antigen-presenting cells, inducing cytokine secretion, and remodeling the tumor microenvironment
.
CPMV has been shown to inhibit tumor metastasis in mice [5] and canine tumor growth [6].

Since in situ therapy for CPMV can promote antigen presentation and trigger an anti-tumor immune response, what is its potential to stimulate a systemic immune response? When combined with immune checkpoint therapy, can it achieve a strong combination effect for different cancers?

In response to these problems, the researchers carried out the following explorations
.

The researchers first established different mouse bilateral tumor models, including the mouse melanoma B16F10 model, colon cancer CT26 and MC38 models, and the mouse breast cancer 4T1 tumor model, and administered two CPMV in situ therapy (intratumoral injection)
to one side tumor of tumor-bearing mice.
In B16F10, CT26 and MC38 tumor models, bilateral tumor growth was significantly inhibited, indicating that CPMV in situ therapy brought systemic anti-tumor immune response
.
In 4T1 tumors with poor immunogenicity, bilateral tumor growth was not inhibited
.

Different cancers respond differently to CPMV therapy

As a kind of immunotherapy, the effect of tumor vaccine is naturally inseparable from the participation of immune cells, and next, researchers explored the mechanism
of CPMV in situ therapy triggering anti-tumor immune response.

The researchers found that B16F10-bearing mice that responded to in situ therapy for CPMV had a significant increase
in CD8+ T lymphocytes in the tumor-draining lymph nodes.
In Rag2-/- immunodeficient mice lacking T cells and B cells, in situ CPMV therapy can only inhibit tumor growth at the treatment site, but not distant untreated tumors
.
When antibodies were used to remove CD8+ T lymphocytes from tumor-bearing mice, a similar phenomenon
occurred in tumor-bearing mice.

The immune response to in situ CPMV therapy is partly CD8+ T lymphocytes

In the anti-tumor immune response, in addition to relying on CD8+ T lymphocytes to attack tumor cells, antigen-presenting cells (APCs) are also an important player
.
Studies have shown that the effectiveness of CPMV in situ therapy relies on phagocytic antigen-presenting cells [7], which play a key role
in processing and delivering antigens.
Therefore, the researchers also observed changes
in antigen-presenting cells after in situ treatment with CPMV.

Flow cytometry analysis showed that after in situ treatment with CPMV, the proportion of dendritic cells (DCs), especially cDC1 cells, in mouse tumors increased
significantly.
Moreover, in dendritic cell-deficient mice (Batf3-/-mice), in situ CPMV treatment can only delay tumor growth at the treatment site, and lose its inhibitory effect
on distant untreated tumors.
The above data indicate that cDC1 cells are involved in the systemic anti-tumor immune response
induced by in situ therapy for CPMV.

The above experiments have shown that dendritic cells play an important role
in the anti-tumor immune response induced by in situ treatment of CPMV.
Therefore, the researchers hypothesized that the use of agonists to further activate dendritic cells could further improve the therapeutic effect of CPMV and trigger a stronger anti-tumor immune response?

The researchers established melanoma B16F10 and breast cancer 4T1 tumor models, and administered CPMV in situ, anti-CD40 antibody in situ therapy or a combination of the two to mice
, respectively.
The results showed that the tumors receiving the combination therapy were significantly reduced, and the growth of distant untreated tumors was also significantly delayed
.
It is worth mentioning that 4T1 tumors with poor immunogenicity also responded to this combination therapy, once again demonstrating the potential of
this combination therapy.

CPMV and anti-CD40 antibodies combined with in situ therapy induced a systemic anti-tumor immune response

It can be said that CPMV combined with anti-CD40 antibody in situ therapy has a certain effect, but 4T1 tumors continue to grow
.
Therefore, the researchers introduced anti-PD-1 antibodies on this basis, hoping to inhibit tumor growth
to a greater extent.
Happily, for breast cancer 4T1 tumors, triple combination therapy has a stronger inhibitory effect
on bilateral tumors.

Triple immunotherapy was more effective in inhibiting bilateral 4T1 tumor growth

Immune checkpoint therapy tends to show some resistance in clinical treatment, and the researchers have also explored whether CPMV and anti-CD40 antibody combined with in situ therapy can help overcome tumor resistance to immune checkpoint therapy
.

After using four triple combination therapies, almost all bilateral B16F10 tumors disappeared, and the survival of mice was significantly prolonged, while the survival of 4T1 breast cancer-bearing mice was also improved
.
It can be said that CPMV and anti-CD40 antibody combined with in situ therapy have helped overcome the resistance of immune checkpoint therapy, bringing a more durable anti-tumor immune effect
.

Triple combination therapy effectively prolongs the survival of tumor-bearing mice

Overall, this study demonstrates that CPMV is effective in stimulating systemic anti-tumor immune responses
as an orthotopic tumor vaccine.
When combined with dendritic cell agonist anti-CD40 antibody, it can activate antigen-presenting cells, improve the tumor microenvironment, and promote the response of "cold" tumors to anti-PD-1 antibodies, and this triple combination therapy provides a new idea
for tumor treatment.

In situ treatment of CPMV has certain advantages: its use dose is lower, the production process is simple and fast, so it brings lower costs; In addition, with CPMV in situ therapy, there is no need to recognize and synthesize tumor-specific neoantigens, and during treatment, the tumor itself and any recognizable antigens it contains can be used as "targets" for the immune system to attack to bring a stronger anti-tumor immune response
.
If this strategy is safely and effectively translated into clinical use, it will bring hope
to more cancer patients.

References:

1.
Mao C, Gorbet MJ, Singh A, Ranjan A, Fiering S.
In situ vaccination with nanoparticles for cancer immunotherapy: understanding the immunology.
Int J Hyperthermia.
2020; 37(3):4-17.
doi:10.
1080/02656736.
2020.
1810333

2.
Mao C, Beiss V, Ho GW, Fields J, Steinmetz NF, Fiering S.
In situ vaccination with cowpea mosaic virus elicits systemic antitumor immunity and potentiates immune checkpoint blockade.
J Immunother Cancer.
2022; 10(12):e005834.
doi:10.
1136/jitc-2022-005834

3.
Mao C, Beiss V, Fields J, Steinmetz NF, Fiering S.
Cowpea mosaic virus stimulates antitumor immunity through recognition by multiple MYD88-dependent toll-like receptors.
Biomaterials.
2021; 275:120914.
doi:10.
1016/j.
biomaterials.
2021.
120914

4.
Albakri MM, Veliz FA, Fiering SN, Steinmetz NF, Sieg SF.
Endosomal toll-like receptors play a key role in activation of primary human monocytes by cowpea mosaic virus.
Immunology.
2020; 159(2):183-192.
doi:10.
1111/imm.
13135

5.
Lizotte PH, Wen AM, Sheen MR, et al.
In situ vaccination with cowpea mosaic virus nanoparticles suppresses metastatic cancer.
Nat Nanotechnol.
2016; 11(3):295-303.
doi:10.
1038/nnano.
2015.
292

6.
Alonso-Miguel D, Valdivia G, Guerrera D, et al.
Neoadjuvant in situ vaccination with cowpea mosaic virus as a novel therapy against canine inflammatory mammary cancer.
J Immunother Cancer.
2022; 10(3):e004044.
doi:10.
1136/jitc-2021-004044

7.
Wang C, Fiering SN, Steinmetz NF.
Cowpea Mosaic Virus Promotes Anti-Tumor Activity and Immune Memory in a Mouse Ovarian Tumor Model.
Adv Ther (Weinh).
2019; 2(5):1900003.
doi:10.
1002/adtp.
201900003