CAR T Therapy and Toxic Side Effects

Chimeric Antigen Receptor T cell (CAR T) therapy entails extracting, modifying and increasing one’s own immune cells to counter cancer. While white blood cells cannot effectively attack cancer cells on their own, with genetic modification these T cells obtain a new receptor which can target antigen CD19, a biological tag found on the surface of cancerous and noncancerous B cells. The modified T cells, primed with new chimeric receptors and expanded to large numbers, can then bind and kill cancer cells once infused into the body (see Figure 1). Figure 2 describes the design of the CAR T cell in more detail.

The beauty of CAR T therapy lies in its ability to treat difficult blood cancers such as lymphoma, leukemia and multiple myeloma. These B cell cancers become resistant or unresponsive to previous lines of treatment—typically chemotherapy, targeted drug therapy, or radiation therapy. When these options are exhausted, CAR T cells attack the cancer anew and can even linger in the body to provide longer-term protection.

#1 Major Side Effect: Cytokine Release Syndrome (CRS) 

This health innovation can come with a price. Almost all CAR T patients experience a side effect known as cytokine release syndrome (CRS) or cytokine storm syndrome (CSS). As a result of CAR T cells continually stimulating the immune system, white blood cells may release inflammatory chemicals called cytokines. The cytokines can activate other white blood cells and perpetuate a cycle of inflammation.

The widespread inflammation manifests a gamut of symptoms ranging from mild to life-threatening. Mild to moderate symptoms include fluctuating fever, fatigue and muscle/joint pain. More severe cases experience low blood pressure and oxygen levels which can result in organ failure and death.

Cytokine release syndrome can usually be reversed within five to 17 days with treatments such as antihistamines, oxygen therapy or immunosuppressive medicines  as needed.

#2 Major Side Effect: Neurotoxicity 

CAR T therapy can also cause neurotoxic effects alongside cytokine release syndrome. Referred to as immune effector cell-associated neurotoxicity syndrome (ICANS), this potentially life-threatening complication impacts cognitive function—likely due to cytokines disrupting the blood-brain barrier.

Common symptoms include confusion, tremors, and hallucinations. Symptoms can escalate, albeit more rarely, to delirium, seizure or coma. Supportive care can resolve these neurotoxic side effects within 21 days of CAR T therapy.

Why and How to Make the “Switch”

Although the negative effects of CAR T therapy can be reversed, the risk of fatality raises questions on possible ways to control the treatment. If CAR T cells could pause or mobilize when prompted, this could prevent complications from worsening; once side effects have stabilized, cancer-fighting activity could restart again.

CAR T “Switch” Design 

Akin to a switchblade, researchers have developed a method to manipulate CAR T cells on and off to produce more precise results by using an antibody switch.

Traditional CAR T therapy alters T cells to detect the cancer cell directly. Rather than the cancer cell, switchable CAR T cells (sCAR T) target the antibody switch. As seen in Figure 3, the switch acts as a bridge, binding to the switchable CAR T cell on one side and the cancer cell on the other to trigger a cytotoxic response.

Figure 4 highlights the deviations from typical CAR T design. Researchers create the molecular switch by grafting a region called a peptide neoepitope (PNE) onto an anti-CD19 antibody clone; the protein neoepitope does not naturally occur in humans, making it a clear target for the therapy. Unlike traditional CAR T cells, sCAR T cells do not target CD19 but the peptide neoepitope on the switch. The desired response is therefore controlled in vivo by the presence and dosage of the switch.

Results 

Calibr, the nonprofit translational research institute of Scripps Research, recently reported preliminary results from their sCAR T clinical trial. The Phase I study tested the safety and optimal dosage of their sCAR T treatment on nine patients with B cell malignancies. The participants underwent a median of five prior treatments for their condition.

Of the nine participants, seven responded to the therapy (78%) and six experienced a complete response (67%), meaning all detectable signs of cancer disappeared. A single infusion of CAR T cells and a single injection of molecular switches elicited most responses in participants, while further switch injections hinted at deepening responses over time. The lower dosing seemed to achieve promising early results, with some doses reaching higher amounts of CAR T cell in the peripheral blood over the first 90 days than other approved CAR T therapies.

Importantly, the switchable therapy successfully minimized adverse side effects. Cytokine release syndrome and neurotoxicity associated with CAR T therapy typically resolves within five to 17 days when treated traditionally. However, by holding or reducing the switch dosage after observing early signs of side effects, the CAR T cells could essentially halt their activity; as a result, the patients experienced side effects for a shorter duration of time (between two to three days).

The Future of sCAR T 

The future of CAR T therapy continues to brighten. The early study result from Scripps Research suggests that switchable CAR T cells are not only safe to use for patients with B cell cancers, but comparatively safer and more effective than some CAR T therapies currently on the market. This also bolsters confidence in the universal molecular switch design. Using this basis, CAR T therapy could likely target any therapeutic antigen by altering the molecular switch. Further down the line, perhaps mRNA and sCAR T technology could combine to create the most ideal form of CAR T therapy—one that forgoes the lab entirely to create a potent and controllable “living drug” inside the body.

The post Researchers Control Cancer Treatment With New Innovation: CAR T Switch(Blade) appeared first on Medika Life.

CAR T therapy, a “living drug,” traditionally involves isolation and purification of T cells outside the body. The cells are then modified with a synthetic receptor and then re-infused into the body for treatment of cancers. Researchers have now successfully demonstrated that T cells can be modified in vivo by mRNA technology, bypassing the need for extraction, chemotherapy and re-infusion. Although this method proves effective in treating mice with scarred hearts, considering fibrosis contributes to over 800,000 deaths worldwide, the study contains great potential for human treatment.

A Damaged Heart 

The heart, flexible yet strong, circulates blood through the body by pumping blood through its chambers. Aging and injury tamper with this function, creating scarred and thickened tissue called fibrosis. Although fibrosis occurs normally when healing, a highly fibrotic heart loses its elasticity; the stiffened tissues and interrupted electrical signaling prevent proper contractions of the heart (see Figure 1). Cardiac fibrosis is highly associated with heart disease and heart failure.

Cardiac fibrosis has no “cure-all” treatment. Early detection improves prognosis, but options dwindle as damage progresses irreversibly. People with advanced cardiac fibrosis may take drugs which antagonize overstimulation of the heart or might even require heart valve replacement.

How CAR T Cells Work

In their study, Rurik et al. explore a new method to directly counter cardiac fibrosis. This method builds upon the basics of CAR T: the use of T cells with a synthetically engineered receptor to target and kill specific cells.

CAR T is approved to treat people with certain lymphomas, leukemias, and multiple myeloma. Figure 2 illustrates this process. In these cases, the desired T cells are extracted from the patient’s body. Synthetic mRNA is inserted into the cell with a retrovirus, a virus commonly used in gene therapy to permanently change other cells’ genomes. The altered and expanded cells are then infused back into the body after preparatory chemotherapy. These T cells target either CD19 or BCMA, two antigens found on malignant B cells.

The benefit of inserting genetic information with a retrovirus lies in its permanence. The CAR T cells can expand and persist in the body for a long time after infusion, continually fighting the cancerous cells they encounter. However, this is of no benefit to researchers hoping to fight cardiac fibrosis. If T cells continuously target fibrotic cells, they would impair normal healing processes and potentially induce autoimmunity. Rurik et al. employ an elegant solution which shortens the CAR T cells’ active duty, thereby circumventing the extraction process altogether.

 New CAR T Cell Design 

The team adapted mRNA delivery technology seen in current COVID-19 vaccines and applied it to basic Chimeric Antigen Receptor design. The mRNA does not integrate into the T cell genome, allowing for temporary transcription of the mRNA and transient expression of the new receptor.

CD5 Lipid Nanoparticles (LNP) 

The authors adopted a strategy to introduce the chimeric receptor to T cells in the body rather than extracting and purifying them outside the body. To accomplish this aim, they first synthesized mRNA that encodes a receptor against fibroblast activation protein (FAP), a protein expressed on activated fibroblasts responsible for fibrosis. They purified the mRNA and packaged the engineered mRNA into standard lipid nanoparticles (LNP).

The team then decorated the lipid nanoparticle surface with CD5 targeting antibodies to direct lipid uptake. The integration of CD5 antibodies allowed the lipid nanoparticles to target antigen CD5 naturally expressed by T cells once injected into the body; the CAR T cells are made after a single shot.

Chimeric Antigen Receptor 

The chimeric antigen receptor contains a single chain variable fragment (scFv) derived from fibroblast activation protein monoclonal antibodies; this recognition domain enables the CAR T cell to target cells which express fibroblast activation protein. The CAR design also includes CD28 and CD3z signaling domains in the cytoplasm. All three components are mouse-specific. Not illustrated in Figure 3 is an added small peptide which prevents immune suppression.

Genetic Integration In Vivo

The team found that lipid nanoparticles could successfully deliver the mRNA package to T cells, as seen in Figure 4. The killer T cell absorbs the lipid nanoparticle by endocytosis. The lipid particle then degrades and the synthetic mRNA releases into the cell. Finally, the cellular machinery reads the genetic instruction and briefly produces the receptor against fibroblast activation protein. This is possible with both animal and human T cell cultures.

Transitory CAR Expression 

Unlike traditional CAR T cells that carry a chimeric receptor encoded by DNA inserted into the genome, these CD5+ T cells carry mRNA only transiently. The mRNA is not integrated into the cell’s genome and remains stuck in the T cell cytoplasm before degrading. This is ideal; fibroblast activation protein receptors must be expressed briefly as longer expression may harm other tissues.

 Results 

The research team assessed the efficacy of the CAR T cells in different conditions. When they treated the cells in tissue culture, more than 80% of T cells expressed the chimeric antigen receptor and could effectively kill target cells with fibroblast activation protein.

The team then tested this model on mice with cardiac fibrosis. The mice received medication to injure the heart and induce scarring. After one week, the team administered the lipid-mRNA injection. Consistent CAR expression was noted 48 hours after injection, and disappeared after one week.

The results were impressive. The function of the heart’s largest chamber improved, in some cases returning to uninjured levels. Similarly, the amount of blood filling the heart normalized to safe volumes. The therapy notably reduced the thickness of the heart. Finally, although the mass of the largest chamber did not normalize, it trended towards improvement.

One caveat in lipid-CAR T cell delivery is that some cells, perivascular fibroblasts, do not express fibroblast activation protein. In consequence, these cells were not impacted by CAR T cells and some fibrosis persisted. No overly toxic side effects were noted.

Trogocytosis

A key observation of effective CAR T therapy is the ability of the modified T cells to take small bites of the target cell—a phenomenon known as trogocytosis. Deriving “trogo” from the Greek word “to bite,” trogocytosis entails one cell nibbling another and, in the process, transferring the surface molecules from one to the other. The researchers found evidence of CAR T cells “nibbling” the activated fibroblasts and retaining the stolen antigens (illustrated in Figure 5), suggesting that the T cells successfully adopted the chimeric antigen receptors in vivo.

Future Implications

CAR T therapy revolutionized cancer treatment with its efficacy and innovation. Combining mRNA technology to this therapy creates a temporary version of this “living drug” that does not sacrifice on quality. The therapy is well tailored to heal mice with damaged and scarred hearts, and widens the possibilities to treat other non-cancerous human ailments. If translated to clinical settings, transient CAR T therapy may be less expensive and more readily available than its traditional counterpart

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