Cytokine Release and Adoptive Cellular Therapy

Chimeric antigen receptor T cell (CAR-T) therapy has revolutionized the treatment of hematologic malignancies. The success of CAR-T in relapsed or refractory B cell acute lymphoblastic leukemia has been particularly impressive, with rates of complete remission as high as 90%.¹ One-year event-free survival and overall survival in this patient group stands at 73% and 90%, respectively.

Based on an accumulation of data investigators are examining CAR-T treatments for solid tumors as well. The website ClinicalTrials.gov lists nearly 600 ongoing studies,² including many for cancers of the colon, ovaries, pancreas, liver, and lung.

Despite these highly encouraging results, regulators have been understandably cautious, at least to date, in defining the parameters for current and emerging CAR-T clinical development. One reason for circumspection is toxicity, specifically the emergence of cytokine release syndrome (CRS) in most patients undergoing these cell-based therapies.

CRS is arguably the reason the U.S. Food and Drug Administration (FDA) has approved just four CAR-T therapies, and only for specific blood cancers in narrowly defined patient populations. For example, the agency has approved Breyanzi (lisocabtagene maraleucel) in adults with specific types of recurring B cell lymphoma; Tecartus (brexucabtagene autoleucel) for adults with recurring mantle cell lymphoma; Kymriah (tisagenlecleucel) for patients under 25 years of age with leukemia and adults with recurring large B cell lymphoma; and Yescarta (axicabtagene ciloleucel) for adults with certain types of recurring B cell lymphoma.³

As with most relatively new therapies—CAR-T has only been approved since 2017—we can learn quite a bit from the success stories but one could reasonably argue that the most critical lessons are to be found in treatment failures.

Why treatment fails

Cancer drugs fail for a variety of reasons. For CAR-T, experience with large B cell lymphoma is illustrative. Assuming the therapy cells target an appropriate cell marker, the limiting factors for CAR-T include several related but distinct pathways involving the tumor itself, the patient’s immune status, and the therapy’s overall safety.

Tumor-intrinsic factors: Anti-CD19 CAR T cell therapy for lymphoma relies on binding to CD19 targets on the surfaces of tumor cells. Perhaps the best-understood resistance mechanism involves the loss of expression of the CD19 epitope, which can occur through several mechanisms.⁴ Alternately the appearance of T cell surface inhibitory receptors, including PD-1 and CTLA-4 may downregulate the immune response to treatment.⁵

T cell specific factors: The many factors related to innate deficiencies in the patient’s immune repertoire include inadequacies in quantity or activity of central memory or stem central memory cells, T cell dysfunction due to illness or prior therapy, inappropriate cytokine profile, an inadequate supply of innate CD4 CAR-T cells, and insufficient CAR-T cell expansion or persistence.⁴

Safety limitations cover a lot of ground, including direct/immediate toxicity, teratogenicity, carcinogenicity, cardiac or hepatic toxicology, and initiation of inflammatory responses leading to complications and further morbidity and mortality. Cytokine release syndrome (CRS), a serious and sometimes fatal adverse reaction to CAR-T treatments, falls into the last category.

Factors involved in the success of CAR-T, specifically rapid, potent, systemic immune system stimulation, are also responsible for driving CRS. Moreover, CRS progression correlates with factors involved in the success of CAR-T, including T cell expansion and the elevation of cytokines and other markers of inflammation.⁶

Numerous cytokines show elevated levels in CRS. The most significant are interleukin-6, interleukin-10, interferon-gamma, monocyte chemoattractant protein 1, and granulocyte-macrophage colony-stimulating factor. Researchers have noted a rise in others as well, including tumor necrosis factor, interleukins 1, 2, and 8, and IL-2–receptor-α.⁷

CRS typically appears in patients within two weeks of their infusion. Depending on the administered drug and patient population, anywhere from about one-third to 100% of patients will develop CRS. Severe cases amount to anywhere from 1% to about 25% of those affected.⁸ Symptoms, which include fever, myalgia, and fatigue, may escalate and progress to life-threatening vasodilatory shock, capillary leak, hypoxia, and end-organ failure. Treatment runs the gamut, from supportive-only care with fever-lowering medication and fluids, to anticytokine-directed therapy such as corticosteroids or tocilizumab.

Although deaths from CRS are rare, the condition does kill some patients, so clinical trials have focused on identifying risk factors that might be predictive of the CRS response, or perhaps provide guidance on therapy choices.

Risk factors, treatment, prevention

Risk factors for developing CRS include high disease burden, high infusional dose, concurrent infectious illness, and early cytokine elevations. These may be prevented to a degree through pretreatment cytoreduction, adjusting dosages according to disease burden, fractionated dosing schemes, and prophylactic anticytokine therapy.⁶

Attempts to grade the severity of CRS using conventional, symptom-based evaluation methods applied to protein therapeutics in oncology have not been successful, mainly due to the complexity of CAR-T treatments. Instead, investigators today use a “consensus” grading scale that better captures CAR-T-induced CRS, with the goal of maximizing the “chance for therapeutic benefit from the immunotherapy while minimizing the risk for life threatening complications of CRS.”⁹

Similarly, dosing strategies are designed to limit toxicity and thereby allow administration of clinically meaningful doses. For example, adaptive dosing, an interesting, albeit counter-intuitive approach to minimizing CRS, involves low initial dosing in patients with high disease burden, which allows patients to adapt to the treatment before receiving the fully therapeutic dose.10 Another approach involves “fractional” dosing, in which second or third dosages are delayed while investigators look for early signs of CRS. This allows for real-time dose modification to provide the greatest benefit for the lowest toxicity.¹¹

In addition to treatments mentioned earlier, clinicians have investigated the use of JAK/STAT inhibitors and lenlizumab, co-administered with CAR-T treatments, to prevent emergence of CRS. JAK/STAT inhibitors have been shown to reduce levels of inflammatory cytokines,¹² while lenlizumab appears to reduce neurotoxicity without affecting CAR-T activity, in vitro.¹³ Yet another approach involves insertion of suicide genes, which allow physicians to kill CAR-T cells in place when CRS-related safety signals arise.¹⁴

CRS is a serious, life-threatening complication of CAR-T therapy whose prevention and treatment will be essential for wide-scale application of cellular therapy to additional hematologic cancers, as well as solid tumors and autoimmune diseases. Diagnosing CRS is relatively straightforward, and treatments and preventive measures are available to minimize the sequelae of CRS. Ultimately, the answer to this treatment-limiting event may be to design cell-based therapies that are inherently less risky. For example, therapies targeting antigens other than CD19, or even shifting focus away from modified T cells to bi-specific T cell-engaging antibodies.¹⁵

References

1. Jacoby, E, Bielorai, B, Avigdor, A, et al. Locally produced CD19 CAR T cells leading to clinical remissions in medullary and extramedullary relapsed acute lymphoblastic leukemia. Am J Hematol. 2018; 93: 1485– 1492. 

2. ClinicalTrials.gov. Searched Oct 6, 2021. 

3. Barrell A. Everything to know about CAR T cell therapy. Medical News Today. March 2021. 

4. Byrne M et al. Understanding and Managing Large B Cell Lymphoma Relapses after Chimeric Antigen Receptor T Cell Therapy. Biology of Blood and Marrow Transplantation, Volume 25, Issue 11, e344 - e351. 

5. Bucktrout SL, Bluestone JA, Ramsdell F. Recent advances in immunotherapies: from infection and autoimmunity, to cancer, and back again. Genome Med. 2018 Oct 31;10(1):79. 

6. Frey, N et al. Cytokine Release Syndrome with Chimeric Antigen Receptor T Cell Therapy. Biology of Blood and Marrow Transplantation, Volume 25, Issue 4, e123 - e127. 

7. Murthy, Hemant et al. Cytokine Release Syndrome: Current Perspectives. ImmunoTargets and therapy vol. 8 43-52. 29 Oct. 2019. 

8. ASTCT Journal Table. Outcomes after Anti-CD 19 CAR-Ts. 

9. Lee DW, Gardner R, et al. Current concepts in the diagnosis and management of cytokine release syndrome. Blood. 2014 Jul 10;124(2):188-95.

10. Turtle CJ, Hanafi LA, et al. CD19 CAR-T cells of defined CD4+:CD8+ composition in adult B cell ALL patients. J Clin Invest. 2016 Jun 1;126(6):2123-38. 

11. Frey NV. et al. Optimizing chimeric antigen receptor (CAR) T cell therapy for adult patients with relapsed or refractory (r/r) acute lymphoblastic leukemia (ALL). Journal of Clinical Oncology 2016 34:15_suppl, 7002-7002.

12. Kenderian, Saad S. et al. Ruxolitinib Prevents Cytokine Release Syndrome after Car T-Cell Therapy Without Impairing the Anti-Tumor Effect in a Xenograft Model. Biology of Blood and Marrow Transplantation, Volume 23, Issue 3, S19 - S20. 

13. Sterner RM et al. GM-CSF inhibition reduces cytokine release syndrome and neuroinflammation but enhances CAR-T cell function in xenografts. Blood. 2019 Feb 14;133(7):697-709. 

14. Diaconu I et al. Inducible Caspase-9 Selectively Modulates the Toxicities of CD19-Specific Chimeric Antigen Receptor-Modified T Cells. Mol Ther. 2017 Mar 1;25(3):580-592. 

15. Topp MS et al. Safety and activity of blinatumomab for adult patients with relapsed or refractory B-precursor acute lymphoblastic leukaemia: a multicentre, single-arm, phase 2 study. Lancet Oncol. 2015 Jan;16(1):57-66.