Team:SYSU-CHINA/Applied Design







Applied Design


Overview

CAR T (chimeric antigen receptor T cell) therapy is one of the most promising treatment for cancer. However, without proper control after administration of CAR-T cells, severe adverse effects associated with CAR-T therapy may bring fatal risks to the patients, especially during the clinical trial stages. Thus we designed a universal add-on for all CAR-Ts and TCR-Ts to ensure safety.

While immunosuppressive drugs like Tocilizumab and corticosteroids are commonly used for such treatments, multiple research groups and companies have proposed different strategies to mitigate these toxic side effects, including suicide switches, inducible expression of receptors and receptors regulated by small molecules. We conducted exhaustive literature search to find these strategies and compared the pros and cons of our design to theirs, finding our own strengths and potential improvements in the future.

We also designed how to integrate our safe switch into the current CAR T therapy, and other potential applications of the unique properties of U24 protein in other aspects of immunotherapy.

Comparation of Different Strategies

A more detailed version of each method can be seen in Description(See Our Description)

Immunosuppressive Drugs vs Integrated Safe Switch in CAR T

To date the most common way in clinical practices is to use immunosuppressive drugs, including Tocilizumab and corticosteroids. These drugs is effective, exemplified by reversion of cytokine release syndrome (CRS) within hours. However, the global effects may increase the risk of opportunistic infection.

In contrast, integrating a safe switch in CAR T, by genetic modification limits the treatment effect specifically to engineered cell population alone. However, it remains to be seen whether the inhibition of CAR T alone is enough to counteract the adverse effects, since CRS and neurotoxicity is a collective result of several cell types and cytokines.

Suicide Genes vs On/Off-switch

Suicide genes are well-characterized and has seen applications in several clinical trials of cell transfer therapies. They are universal as they target common pathways to induce cell death. However, they irreversibly eradicate the infused cell population.

In contrast, on/off-switch strategies enable repeated on and off cycles by adding and removing of drugs. However, few strategies have been reported, possibly due to the difficulty in engineer receptor machinery that respond to both antigens and drugs. Strategies reported to date rely heavily on direct modification on CAR receptors, which may not be transferable from one type of CAR to another due to their structural difference.

On-switch vs Off-switch

On and off switch differ in their action in the presence of drugs, the former activating the T cells and the latter inhibiting them. Although they possess distinct response dynamics and could both serve as effective safe switch, On-switch has one limitation that it requires continual drug administration for CAR T’s antitumor functions. However, this may be expensive, especially when the controlling drugs are antibodies recognized by CARs (Rodgers et al., 2016) . In addition, the persistence of CAR T cells in patients are believed to keep cancer cells in check (Kalos et al., 2011) , and such benefit of “living drugs” is diminished without adding activating drugs.

Strategies to integrate our device into CAR T

To ensure safety, it is preferred that our device integrated into the same vector for T cells transduction and CAR expression. Thus, any T cell expressing CARs are likely to have a controlling machinery.

Possible Usage of Our Device

Since our device uses transcriptional-based regulation, a shortcoming is that it takes longer to respond after drug is added. In order to maximize the potential of our device, we proposed the following methods for usage.

First, drugs can be added before or at the same time of infusion, and slowly decrease the dose of drugs. Thus, the CAR T cells reactivity can increase steadily without causing an overreaction.

Second, drugs can be added prior to severe CRS development, in order to prevent severe CRS in the first place. Several markers have been used to grading the severity of CRS (Lee et al., 2014) , thus it is possible to give drugs accordingly.

Third, when CRS develops, both doxycycline and immunosuppressive drugs are given at the same time. Immunosuppressive drugs are given to reverse the syndrome subsequently removed to prevent prolonged inhibition of the immune system. Doxycycline is continued and adjusted according to the patients’ situation.

In addition, our method should be combined with other in order to ensure safety. For example, suicide genes are more suitable when the CAR T cells are fundamentally flawed, e.g. express a CAR that has strong cross-reactivity towards normal antigens. And thus a suicide gene is highly recommended for CAR T in the clinical trial stage in addition to our device.

Potential applications of U24 protein in other aspects of CAR T therapy

By combination of tet-ON promoter and U24 protein, we achieved controllable T cells activity by addition or removal of doxycycline. However, the modularity of our design enables us to switch promoters upstream of U24 to achieve distinct functions. For example, by expressing U24 under the control of IL-6 responsive promoter, we can construct self-regulating CAR T that downregulate its own activity when the serum cytokines level increases. For such purpose, promoters that respond to IL-2, interferon-γ, IL-1, C-reactive protein and others may be used, for these cytokines are common players in the cytokine release syndrome (Brentjens et al., 2013) .

Another possible function is that by switching to promoters that reacts to a tissue specific marker, e.g. a specific component in the cerebrospinal fluid, it is possible to engineer CAR T to shut down when infiltrating the central nervous system, possibly preventing some neurotoxicity.


While the full induction of U24 can potentially reduce all T cells activity, the sub-optimal induction may limit some functions of CAR T while leaving others unaffected. This notion is supported by findings that high level of CARs is required for IL-2 production (Walker et al., 2017) , and different level of PD-1, an inhibitory protein, is required to impair different T cell functions, including granule release, cytokines production, and proliferation (Wei et al., 2013) . It is also possible that reduced surface CAR level enhances discrimination of tumor cells and normal cells baring the same antigen at different level. (see our modeling)

Reference

Brentjens, R.J., Davila, M.L., Riviere, I., Park, J., Wang, X., Cowell, L.G., Bartido, S., Stefanski, J., Taylor, C., Olszewska, M., et al. (2013). CD19-targeted T cells rapidly induce molecular remissions in adults with chemotherapy-refractory acute lymphoblastic leukemia. Science translational medicine 5, 177ra138.
Kalos, M., Levine, B.L., Porter, D.L., Katz, S., Grupp, S.A., Bagg, A., and June, C.H. (2011). T cells with chimeric antigen receptors have potent antitumor effects and can establish memory in patients with advanced leukemia. Science translational medicine 3, 95ra73. Lee, D.W., Gardner, R., Porter, D.L., Louis, C.U., Ahmed, N., Jensen, M., Grupp, S.A., and Mackall, C.L. (2014). Current concepts in the diagnosis and management of cytokine release syndrome. Blood 124, 188-195.
Rodgers, D.T., Mazagova, M., Hampton, E.N., Cao, Y., Ramadoss, N.S., Hardy, I.R., Schulman, A., Du, J., Wang, F., Singer, O., et al. (2016). Switch-mediated activation and retargeting of CAR-T cells for B-cell malignancies. Proceedings of the National Academy of Sciences of the United States of America 113, E459-468.
Walker, A.J., Majzner, R.G., Zhang, L., Wanhainen, K., Long, A.H., Nguyen, S.M., Lopomo, P., Vigny, M., Fry, T.J., Orentas, R.J., et al. (2017). Tumor Antigen and Receptor Densities Regulate Efficacy of a Chimeric Antigen Receptor Targeting Anaplastic Lymphoma Kinase. Molecular therapy : the journal of the American Society of Gene Therapy 25, 2189-2201.
Wei, F., Zhong, S., Ma, Z., Kong, H., Medvec, A., Ahmed, R., Freeman, G.J., Krogsgaard, M., and Riley, J.L. (2013). Strength of PD-1 signaling differentially affects T-cell effector functions. Proceedings of the National Academy of Sciences of the United States of America 110, E2480-2489.