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 
  • TLR Tri-agonist that activates the innate immune system through TLRs 2, 4 and 7
  • Robust anti-tumor responses in preclinical studies across multiple tumor types
  • Activates neutrophils (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 chemotherapy, radiation and checkpoint inhibitors
  • Immune memory and protection from tumor rechallenge in preclinical studies
Synergistic TLR activation of MIE-101
Our preclinical studies have demonstrated that the activation of multiple TLRs by a single agent provides increased immune stimulation versus targeting individual TLRs. Results of MIE-101 targeting TLRs 2,4 &7 together versus individually include:
  • More recruited and activated dendritic cells​

  • Stronger inhibition of T-regulatory cells​

  • Bridging of innate and adaptive immunity​

  • Increased T-effector cells​

  • Broad and consistent anti-tumor effects

About toll-like receptors (TLRs)
Discovered in the 1980's, TLRs make up a class of evolutionary conserved pattern recognition receptors 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 TLRs 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 TLRs have demonstrated anti-tumor efficacy in multiple cancer models by activating immune cells to better recognize and fight cancer. The intratumoral administration of TLR 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 TLR tri-agonist
Most TLR activating treatment candidates in development for oncology indications target a single TLR. MIE-101 engages multiple TLRs which has been shown to increase the breadth and potency of the immune response.  TLRs are highly conserved across mammalian species, which provides rationale for preclinical data that demonstrate consistent anti-tumor effects when CPMV 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 TLRs across species, our researchers have observed similar signs of immune activation when CPMV is assessed with human immune cells in vitro.

Activating the Immune System Through Multiple 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, TLRs 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 attract and activate additional immune cells. The result is a broad innate and adaptive antitumor immune response. 
MIE-101 immune
stimulation effects
Immune activation through TLRs 2,4,7

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

CPMV in situ vaccination activates multiple innate immune responses and antitumor T cell responses. CPMV nanoparticles are recognized and taken up by tumor-associated neutrophils and macrophages. The subsequent early inflammation phase (upregulation of IL-12, IL-6 and IFN-γ ) recruits G-MDSCs and MDSCs which may be converted to immunostimulatory myeloid cells. Reduced levels of IL-10 and TGF-β promotes infiltration by N1 and M1 anti-tumor neutrophils and macrophages and supports their immunostimulatory phenotype. 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

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 IE’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 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 inhibitors 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.  

Tumor residence time
The molecular weight of our MIE-101 nanoparticle is roughly 5.6 million Daltons. In comparison, small molecule TLR agonists typically have a molecular weight in the hundreds to thousands of Daltons.  This difference provides rationale for the long residence time inside tumors observed with MIE-101. 
Czapar, Steinmetz et al: Slow-Release Formulation of Cowpea Mosaic Virus for In Situ Vaccine Delivery to Treat Ovarian Cancer. Advanced Science 2018, 5, 1700991

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.