Coeptis Therapeutics’ SNAP-CAR: Innovative, Dynamic, Cost-Effective. What’s Not To Like?

Chimeric antigen receptors are synthetic surface molecules that are usually expressed on immune cells and are designed to enhance their ability to find and kill diseased cells – the most common disease type is cancer but they can theoretically be employed against viral infections, bacterial infections, and even autoimmune disorders. I won’t go into too much detail here about the structure and function of a CAR – for that, I would direct you to my short article here – I will say this though: In its simplest form, all a CAR really does is “recognize something out there”, and tell the cell to do something in response. Usually the “something out there” is a protein on the surface of a diseased cell, and the cellular response is typically, “kill that thing!”.

Well, the brilliant scientists over at Coeptis Therapeutics in Pittsburgh have developed a unique type of CAR that has really caught my attention. It’s called SNAP-CAR and it is poised to blow the competition out of the water.

Why? Read on and you’ll see.

What is SNAP-CAR?

SNAP-CAR is a type of synthetic surface receptor that can be expressed within immune cells to elicit immunological effector functions in an antigen-dependent manner – just like CARs. Where SNAP-CARs differ is that they harbor a “SNAP-tag” ectodomain that has the capacity to covalently bind to monoclonal antibodies (mAbs) bearing a “benzylguanine” (BG) motif. See their paper in Nature Communications for a nice illustration, it’s in Figure 1. I have also provided my own diagram below.

Binding of the BG-tagged mAb to the SNAP-tag domain “transfers” the specificity of the mAb to the SNAP-CAR. Thus, SNAP-CARs are essentially CARs with a customizable antigen recognition domain. SNAP-CAR-expressing immune cells (NK or T) are co-administered with BG-tagged tumor antigen-specific mAbs. The mAbs bind to either the antigen target (via non-covalent recognition), or the SNAP-tag on the SNAP-CAR and directs the lymphocyte towards antigen-expressing cells.

So, that’s the basics, hopefully it’s making sense. Now to the important parts. There are several functional and manufacturing advantages of this platform over traditional CAR technologies. Understanding these advantages may enable a deeper understanding of the technology, so let’s dive in.

Advantages of SNAP-CAR over traditional CAR platforms

1. The ability to titrate the concentration of the “activating peptide” (the BG-conjugated antibody) limits toxicities associated with overstimulation of CAR cells and enhances therapeutic potency.

Titrating the concentration of the tumor antigen-specific BG-conjugated antibody allows for precise control over SNAP-CAR cell activity [1], enabling clinicians to easily “turn up” or “turn down” the immunological effect of the cells depending on the specific circumstance. This capability provides a solution to one of the most significant problems plaguing CAR T cell technology, cytokine-release syndrome (CRS). CRS occurs when CAR-T cells become overstimulated by tumor antigen and begin to release high concentrations of immunostimulatory cytokines causing inflammation, off-target tissue damage, and systemic toxicities [2]. Due to the relatively short half-life of an antibody within circulation – about a week to one month [3], which is much shorter than a live CAR T cell which can persist for several months to years – it is possible to “rapidly” alter the serum concentration and therefore SNAP-CAR activity. So, with SNAP-CAR, CRS-associated toxicities can be mitigated by simply lowering the dose of the BG-antibody. With other cell therapy platforms, if CRS toxicities begin to manifest, hampering cell activity is not an option because, by that point, the overstimulated cells are acting independent of outside influence [2].

Interestingly, on the opposite side of the coin, another major problem with CAR cell therapy is the emergence of antigen-positive resistant disease [4]. This is thought to be primarily due to a lack of persistence of the CAR cells as a result of poor antigen stimulation, poor health of cells (mainly associated with autologous platforms), or diminution of antigen expression allowing for evasion of CAR-mediated recognition [4, 5]. With SNAP-CAR, increasing the concentration of the BG-antibody will aid in CAR cell persistence and cancer cell recognition by enhancing engagement with tumor antigens.

Having such an easy way to control the activity of the therapeutic cells is a significant advantage of SNAP-CAR technology within this market.

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2. Flexible antigen specificity combats resistance to cell therapy.

One of the most common reasons that cell therapies struggle to effectively treat cancer is the fact that tumors (liquid and solid) do not typically express a single, homogeneous tumor-specific antigen at a high enough level. Then, as the cell therapy begins to kill the antigen-expressing cancer cells, the only cancer cells that are left alive are those that do not express a biologically relevant level of the correct antigen. The surviving cells may begin to express a slightly modified version of the target – one that is not recognized by the cell therapy – downregulate the antigen, or simply not express it at all. This phenomenon is known as “antigen drift/loss” and it is a very common resistance mechanism to antigen-dependent cell therapies [6].

SNAP-CAR technology provides a direct solution to this problem by allowing for the same CAR-expressing cell population to target a wide variety of antigens. This is achieved by simply co-administering a variety of BG-antibodies with different targets. Using traditional CAR approaches, in order to achieve “multi-targeting” of CAR cells, either a single cell population would have to express MULTIPLE DIFFERENT CAR constructs, or multiple different CAR-expressing cells would need to be pooled and co-administered [7, 8]. This is extremely difficult, complex, and expensive because for each additional target, a new CAR must be designed and a new batch of CAR cells engineered.

Furthermore, with SNAP-CAR, the CAR target(s) can be quickly rearranged by simply administering a different BG-conjugated antibody. So, when trying to treat rapidly evolving tumors, SNAP-CAR is a game-changer. The dynamic and flexible nature of this technology allows clinicians to “keep pace” with the tumor evolution, increasing the chances of eliminating a larger proportion of the tumor, improving overall efficacy.

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3. Flexible antigen specificity allows for diverse application of therapeutic cells.

CAR cell’s “anti-disease” activity is dictated by the antigen-specificity of the CAR receptor. For example, a population of CD-19 CAR-expressing T cells will be very effective at finding and killing CD-19-expressing leukemia cells, but they won’t be very effective against HER2-expressing breast tumors. So, typically, a single CAR-expressing cell is restricted to one, maybe two, targets. Using traditional CAR approaches, in order to develop a CAR cell therapy that can target multiple different diseases – for example, CD-19+ malignancies and HER2+ breast cancer – you would need to develop TWO UNIQUE cell therapy platforms – one expressing CD-19-specific CAR and another expressing a HER2-specific CAR. However, with SNAP-CAR, you can develop ONE cell platform and simply co-administer different BG-antibodies for the different disease types. This enables the same cells to be deployed against (basically) every disease for which an antigen is identified; this includes things like cancer, respiratory illnesses, and even autoimmune disorders.

SNAP-CAR cells, therefore, have the potential to be an extremely cost-effective, widely applicable cell therapy platform for a vast array of indications. Truly ingenious.

SNAP-CAR’s Competition: How Does it Stack Up?

There are several platforms that share a similar M.O.A. space as SNAP-CAR. Let’s delve into the various competitors, their technologies, and how SNAP-CAR compares in terms of mechanism and feasibility.

1. Switchable-CAR Ts by Calibr-Skaggs at Scripps Research [12, 13]

Switchable CAR-T or sCAR-T cells have been designed and developed by the Calibr-Skaggs Institute for Innovative Medicines at Scripps Research. These cells utilize a universal CAR construct that consists of an ectodomain capable of binding to antibody fragments that are co-administered with the CAR-expressing lymphocytes.

This is a direct competitor. Seems to operate according to, essentially the same mechanism of action. However, there are key differences that exist between the two platforms which may differentiate their effectiveness.

Firstly, the production of their PNE-Fab molecules relies on conventional protein production procedures – utilization of cell culture-mediated expression followed by protein purification techniques. This is far inferior to the method employed for the generation of BG-tagged mAbs making SNAP-CAR technology superior in terms of cost of production.

2. Multi-specific CAR constructs [8,9]

These are essentially chimeric antigen receptors that have affinity to more than one antigen target. These are inferior to SNAP-CAR for several reasons.

• They are difficult to design and manufacture – much more difficult than SNAP-CAR – and they only target a very limited number of antigens.
• These are also inflexible. If a bispecific CAR T cell loses potency due to antigen drift, well, go back to the drawing board. With SNAP-CAR, you can pop a BG linker onto a new target-specific antibody and inject that sucker. Relatively simple.

3. Bi-specific T cell Engagers (BiTEs) [10]

These are bispecific antibodies that bind to CD3 on T cells and a tumor-specific antigen. The problem with BiTEs is that they can’t be used with allogenic T cells because allogenic T cells have their TCR removed, they also don’t work in patients whose T cell population is already damaged (from chemotherapy) or exhausted due to persistent antigen stimulation – monotherapy BiTEs rely on the patient’s own T cells to carry out the anti-tumor activity. This is a risky business because it is likely that a cancer patient’s immune system not is not fully functional, limiting the immunogenicity of the BiTE.

Also, BiTEs engage an endogenous receptor on the T cell which restricts the intracellular signaling capacity to naturally occurring signaling domain configurations. With SNAP-CAR, highly potent intracellular signaling domains can be employed to ensure robust immunological activity in response to ligand engagement., enhancing efficacy and ensuring persistence.

4. FATE Therapeutics’ CD3 Fusion Surface Receptor (CD3-FR)

Some companies like FATE therapeutics have overcome some of the issues with BiTEs. They have developed a CD3-fusion protein called CD3-FR that is essentially a CAR with an extracellular domain that recognizes the CD3-binding portion of BiTEs. See my article on this technology here. So, the CD3-FS mimics naturally occurring CD3 and allows for BiTE engagement with TCR-negative immune cells.

This is inferior to SNAP-CAR for one major reason:

• BiTE manufacturing is less robust than commercially available antibodies giving SNAP-CAR access to a wider library of potential antigen targets.

5. Innate cell engagers/mAbs + haCD16-expressing immune cells

This system works essentially the same way as SNAP-CAR, kind of.

High-affinity CD16 receptors (haCD16) are synthetic receptors with a CD16 extracellular domain and variable intracellular signaling domains. These receptors bind to the Fc portion of Ig antibodies and are able to engage target cells via this interaction. So, several biotechnology companies have employed high-affinity CD16-expressing immune cells in combination with tumor-specific mAb administration.

SNAP-CAR are superior for several reasons:

• The interaction between mAb and CAR cell is covalent providing a more stable interaction.
• Also, when SNAP-CAR is expressed in an NK cell, the BG-tagged antibodies are not only able to engage with the SNAP-CAR and stimulate tumor cell immunity this way, but they can also engage the endogenous CD16 receptor on the same NK cell providing a co-stimulatory signal of sorts.
• Furthermore, CD16 receptors are subject to protease-mediated cleavage within the tumor microenvironment, rendering the CD16 receptor non-functional. SNAP-CAR is resistant to this intratumoral suppression. Companies like FATE are developing protease-resistant CD16 receptors so, there are ways to mitigate this other than SNAP-CAR technology.

References

1. Ruffo, E., et al., Post-translational covalent assembly of CAR and synNotch receptors for programmable antigen targeting. Nature Communications, 2023. 14(1): p. 2463.
2. Frey, N. and D. Porter, Cytokine Release Syndrome with Chimeric Antigen Receptor T Cell Therapy. Biol Blood Marrow Transplant, 2019. 25(4): p. e123-e127.
3. Booth, B.J., et al., Extending human IgG half-life using structure-guided design. MAbs, 2018. 10(7): p. 1098-1110.
4. Fry, T.J., et al., CD22-targeted CAR T cells induce remission in B-ALL that is naive or resistant to CD19-targeted CAR immunotherapy. Nat Med, 2018. 24(1): p. 20-28.
5. Shah, N.N. and T.J. Fry, Mechanisms of resistance to CAR T cell therapy. Nature Reviews Clinical Oncology, 2019. 16(6): p. 372-385.
6. Mishra, A., et al., Antigen loss following CAR-T cell therapy: Mechanisms, implications, and potential solutions. Eur J Haematol, 2024. 112(2): p. 211-222.
7. Pan, J., et al., CD22 CAR T-cell therapy in refractory or relapsed B acute lymphoblastic leukemia. Leukemia, 2019. 33(12): p. 2854-2866.
8. Bailey, S.R. and M.V. Maus, Gene editing for immune cell therapies. Nat Biotechnol, 2019. 37(12): p. 1425-1434.
9. Shah, N.N., et al., Bispecific anti-CD20, anti-CD19 CAR T cells for relapsed B cell malignancies: a phase 1 dose escalation and expansion trial. Nat Med, 2020. 26(10): p. 1569-1575.
10. Tian, Z., et al., Bispecific T cell engagers: an emerging therapy for management of hematologic malignancies. Journal of Hematology & Oncology, 2021. 14(1): p. 75.
11. Ajina, A. and J. Maher, Strategies to Address Chimeric Antigen Receptor Tonic Signaling. Mol Cancer Ther, 2018. 17(9): p. 1795-1815.
12. https://calibr.scripps.edu/our-pipeline/scar-t/
13. Rodgers, D.T., et al., Switch-mediated activation and retargeting of CAR-T cells for B-cell malignancies. Proc Natl Acad Sci U S A, 2016. 113(4): p. E459-68.