top of page


MIE-101: Lead immuno-oncology candidate
Key highlights
  • Intratumoral immunotherapy

  • Not an oncolytic virus

  • Based on a non-infectious plant virus (cowpea mosaic virus, CPMV) nanotechnology platform 

  • Recognized by Pattern Recognition Receptors (PRRs) that activate the innate immune system

  • Robust anti-tumor responses in preclinical studies across multiple tumor types

  • Activates innate immune cells including neutrophils and NK cells (tumor killing function, cytokine secretion) and cytotoxic and memory T cells (adaptive immune response)

  • Downregulates MDSCs and expands tumor-specific T-cells (as indicated by upregulation of MHC II and CD86) – and therefore is distinct from checkpoint inhibitors that are not tumor-specific

  • Not neutralized by anti-drug antibodies (ADA)

  • Single agent and combination therapy synergy in multiple preclinical tumor studies

  • Single agent and combination therapy activity in dogs with naturally occurring tumors

  • Human immune cell activation is consistent with immune activation in preclinical animal models

  • Preclinical study results support combination potential with current standard of care including checkpoint treatments, chemotherapy and radiation

  • Immune memory and protection from tumor rechallenge in preclinical studies

About Pattern Recognition Receptors (PRRs)
Synergistic immune activation of MIE-101
Our preclinical studies have demonstrated that the activation of multiple PRRs by a single agent provides increased immune stimulation versus targeting individual PRRs. MIE-101 has been shown to engage with a class of PRRs known as toll-like receptors (TLRs). MIE-101 has demonstrated engagement of TLRs 2,4 & 7. In addition to TLR signaling, other PRRs and features contribute to potent preclinical antitumor activity, including the multivalent, nanoscale organization and the presence of T helper epitopes.

 Pattern recognition receptors (PRRs) are found on the surface and the interior of multiple immune cell types. These receptors function as a first line of defense against foreign microbes. Once PRRs on or inside immune cells have recognized a foreign pathogen based on its exterior molecular patterns or interior nucleic acid, innate immune cells become activated, fighting the pathogen and secreting chemicals known to recruit and activate additional cells to support the fight to clear the foreign entity. In recent years, molecules that stimulate PRRs have demonstrated anti-tumor activity in multiple cancer models by activating immune cells to better recognize and fight cancer. The intratumoral administration of PRR agonists has become an active area of research and product development in oncology with several treatment candidates showing promise in clinical trials.

About MIE-101: First-in-class plant virus-based Immune stimulant
Most PRR activating treatment candidates in development for oncology indications engage a single target. MIE-101 engages multiple PRRs which has been shown to increase the breadth and potency of the immune response.  PRRs are highly conserved across mammalian species, which provides rationale for preclinical data that demonstrate consistent anti-tumor effects when MIE-101 is used to treat multiple tumor types, whether in established preclinical animal models or in naturally occurring cancers in canine companion animals. Supporting the consistency of these immune cell targets across species, our researchers have observed similar signs of immune activation when MIE-101 is assessed with human immune cells in vitro.

Activating the Immune System Through Multiple Signaling Pathways​
Combination of immune activation and blocking tumor-based immune inhibition

The illustration below outlines the breadth of immune activation and anti-tumor responses induced by our lead immuno-oncology candidate, MIE-101, observed in preclinical studies. Upon intratumoral administration, PRRs on the surface and inside of host immune cells are engaged by MIE-101. The cells become alerted to a foreign threat. These cells then recognize tumor antigens as foreign, fighting the tumor while also secreting cytokines and chemokines known to recruit and activate additional immune cells. The result is a broad innate and adaptive antitumor immune response. 
MIE-101 immune
stimulation effects
Immune activation through multiple PRRs

Mechanistic details

  • Neutrophil activation (tumor killing function, cytokine secretion) and cytotoxic and memory T cells (adaptive) ​

  • Downregulates MDSCs and expands tumor-specific T cells (as indicated by upregulation of MHC II and CD86) ​

  • Not cytolytic – and therefore distinct from oncolytic vectors

  • Distinct from checkpoint inhibitors

Intratumoral MIE-101 activates multiple innate immune responses and antitumor T cell responses. CPMV nanoparticles are recognized and taken up by innate immune cells including neutrophils. The subsequent early inflammation phase (upregulation of IL-12, IL-6 and IFN-γ) recruits, activates, and polarizes immune cells, e.g. switch from pro-tumor to anti-tumor macrophages (M2 to M1 switch). Reduced levels of IL-10 and TGF-β further promote infiltration by N1 and M1 anti-tumor neutrophils and macrophages amongst other immune cells. The populations of DCs, NK cells, and myeloid cells positive for MHC II/costimulatory molecules are increased by the pro-inflammatory tumor microenvironment. Naive tumor infiltrated T cells can then engage with MHC on those potent APCs presenting tumor antigens. These tumor-specific T cells can activate tumor cell cytotoxicity and further expand to effector memory T cells.
Illustration: Wang, Fiering and Steinmetz: Cowpea Mosaic Virus Promotes Anti-Tumor Activity and Immune Memory in a Mouse Ovarian Tumor Model. Advanced Therapeutics. 2019, 2, 1900003

Once MIE-101 is recognized by innate immune cells, systemic immunity is induced

•Activates innate immune system through TLRs 2, 4 and 7*​

•Activates and recruits innate immune cells through key cytokines (IFNy, type I IFN)

•Innate immune cells (M1 macrophages, neutrophils, NK cells) kill tumor cells releasing tumor-associated antigens / neo-antigens

•Innate immune cells become APCs; link to adaptive immunity

•Potent and durable anti-tumor immunity mediated by CD8+ T cells and memory cells

* Mao C, Beiss V, Fields J, Steinmetz NF, Fiering S. 2021, Cowpea mosaic virus stimulates antitumor immunity through recognition by multiple MYD88-dependent toll-like receptors. Biomaterials. 2021 May 25;275:120914.

The innate immune system is constantly looking for viral threats

  • Pattern Recognition Receptors (PRRs) on innate immune cells identify viruses through their pathogen-associated molecular patterns (PAMPs)​

  • Once a virus is recognized, a robust immune response occurs to eliminate the disease​

  • In the tumor microenvironment, a robust immune response can result in tumor recognition and an anti-tumor immune response

MIE-101 immune activation turns a cold tumor into a hot tumor and results in a robust anti-tumor response


Tumor microenvironment

Intratumoral administration

MIE-101 is a naturally occurring plant virus that does not replicate in mammals but contains features of foreign pathogens

Innate immune cells constantly looking for viral pathogens  immediately recognize MIE-101

Turning cold tumors hot

Checkpoint inhibitors as a stand-alone therapy can provide significant life changing benefit for many cancer patients, however the majority of patients have incomplete or even no response to therapy.  Why and how patients respond to checkpoint inhibitors appears to be determined by the immunological status of the environment within their cancer.  Scientists and clinicians in immunotherapy describe tumors as either immunologically “cold” meaning the immune system in the tumor is suppressed or they are immunologically “hot” indicating that the local tumor immune response is more active and thus can respond more readily to checkpoint inhibitor treatment.  

Mosaic’s MIE-101 program is based on a CPMV nanoparticle that was carefully selected because of its features that allow it to stimulate a particularly strong immune response when delivered into the tumor. Despite the fact that the nanoparticle is non-infectious, the immune cells inside the tumor immediately sees it as a foreign entity because of its structural characteristics and genetic material.  The approximately one trillion nanoparticles delivered with each injection cause the innate immune cells to immediately signal the local immune system into action resulting in what is effectively a call to arms. The activated immune response inside the tumor results in an attack on the nanoparticle but also results in the destruction of tumor cells leading to the release of tumor antigens that trigger a further anti-tumor immune response.    

More specifically, MIE-101 converts a “cold” tumor into a “hot” tumor via an intra-tumoral cytokine and chemokine response through activation of Pattern Recognition Receptors (PRRs), including Toll-Like Receptors (TLRs) on the resident innate immune cells, inducing activation of tumor-associated macrophages and neutrophils with recruitment of dendritic cells and natural killer cells.  In addition, it converts pre-existing immunosuppressive myeloid cells into activated antigen-presenting cells, improving effector and memory T cell responses thereby creating systemic tumor-specific cytotoxic CD8+ T cell activity.  The result is conversion of an immunosuppressive tumor microenvironment into an anti-tumor microenvironment with a systemic search and destroy function that attacks not only the local tumor but also other tumor sites through immune surveillance which is referred to as an “abscopal effect”.

In preclinical studies, MIE-101 has been combined with other current standard of care treatments including chemotherapy, radiation and checkpoint treatments to further boost the effect of treatment.  The studies have validated the potential of combination therapy that can result in complete destruction of the primary tumor, destruction of other tumors via the abscopal effect and even protection against re-challenge with the same tumor type. We expect to advance MIE-101 into human clinical studies in 2022.  

Preclinical data

Single agent and combination with anti-PD-1 enhance survival and immune activation in ovarian ID8 model

Anti-tumor efficacy​

  • Single agent anti-tumor effects​

  • aPD-1/MIE-101 combination is curative in the majority of animals​

  • Protective immune memory prevents tumor growth on rechallenge

Immune mediated mechanism​

  • Increased Pro-inflammatory cytokines ​

  • MIE-101/antiPD-1 combination significantly increases NK cells​

  • MIE-101/antiPD-1 combination significantly increases CD8+ memory T Cells

* p<0.05 vs PBS      * * p<0.01 vs PBS       * * * * p<.0001 vs PBS.      #### p<0.0001 vs CPMV​
Wang and Steinmetz: A Combination of Cowpea Mosaic Virus and Immune Checkpoint Therapy Synergistically Improves Therapeutic Efficacy in Three Tumor Models. Advanced  Functional  Materials 2020, 2002299

Preclinical data

CPMV in combination with cyclophosphamide (CPA) systemically reduces tumor burden and inhibits lung metastasis in breast 4T1 model
Cai et al 2019. Cowpea Mosaic Virus Immunotherapy Combined with Cyclophosphamide Reduces Breast Cancer Tumor Burden and Inhibits Lung Metastasis. Advanced Science 2019, 6, 1802281 ​
Antitumor efficacy
Immune activation

Preclinical data

CPMV in combination with radiation​ initiates immune-mediated
tumor regression in ovarian ID8 model 
Antitumor efficacy
Immune activation
Tumor sections stained for CD4 and CD8 lymphocytes ​10 days post  treatment​
Treatment regimen
Patel et al 2018. Radiation Therapy Combined with Cowpea Mosaic Virus Nanoparticle in Situ Vaccination Initiates Immune-Mediated Tumor Regression. ACS Omega 2018, 3, 3702−3707

Combination of the viral in situ vaccine with RT may be a particularly powerful strategy because RT debulks tumors, providing a burst of tumor antigens in the context of immunogenic cell death, therefore, synergizing with the CPMV in situ immune stimulation that further augments antitumor immunity.

Preclinical data

CPMV enhances hypofractionated radiation in a B16 murine melanoma model
Tumor Growth Curves 
Tumor growth curves for each animal with tumor volume on a logarithmic scale. Control and Cowpea mosaic virus (CPMV) tumor growth are exponential as the lines appear linear, whereas in the radiation cohorts there are several animals that do not follow exponential growth. Additionally, in the combinatorial CPMV and radiation cohorts there were a few animals whose tumor volumes decreased towards zero.
CPMV presents a unique and promising hypofractionated radiation adjuvant that leads to increased anti-tumor cytotoxic and immune signaling, especially with respect to the immune mediated cytotoxicity, immune signaling, and toll-like receptor signaling pathways. This improvement was greater with a single dose than with a fractionated dose.
Kaplan-Meier survival curve
Kaplan-Meier curve demonstrating the changes in fraction on study for each treatment as a function of days post- treatment. Control and Cowpea mosaic virus (CPMV) cohorts lack separation, whereas all of the radiation cohorts are separated from control and CPMV, but not from each other. Using the log-rank (Mantel-Cox) test, we determined that treatment did significantly change survival, however, using multiple comparison adjustment and comparing two curves to each other, only control versus 15 Gy and control versus 15 Gy + CPMV were statistically significantly different.
Duval, Hoopes et al 2020. Cowpea Mosaic Virus Nanoparticle Enhancement of Hypofractionated Radiation in a B16 Murine Melanoma Model. Frontiers in Oncology 10:594614
In the below studies, a single dose of CPMV was administered to evaluate the potential mechanistic synergy of combining CPMV with radiation.
bottom of page