|T cells ganging up on a tumour cell|
The American Society of Clinical Oncology’s (ASCO) annual review always makes for interesting reading. Immunotherapy continues to feature large [ASCO 2017 Annual Report again picks immunotherapy as “Advance of the Year"] , with adoptive cell immunotherapy being named “Advance of the Year”.
This bespoke treatment involves genetic manipulation of the patient’s own T-cells, in which an engineered virus is used to insert DNA encoding a protein capable of recognising unique molecules present on the surface of tumour cells. Transformed cells expressing chimeric antigen receptors (CAR) are cultured in the laboratory and then infused back into the donating patient. CAR-T cells then seek and destroy cancer cells. Being a “living therapy”, CAR-T cells continue to multiply to exert a persistent anti-tumour effect.
While the number of patients who have received CAR-T therapy to date is still in only in the hundreds and largely limited to certain haematological cancers, clinical response results certainly justify the ASCO accolade. Kymriah® (Novartis), the first adoptive cell immunotherapy to receive FDA approval, achieved unprecedented response rates in children and young adults suffering from relapsed or refractory acute lymphoblastic leukaemia (ALL). Over 80% of Kymriah® treated patients went into remission within 3 months, with 75% remaining still in remission after 6 months.
Impressive study results have been reported for another hard-to-treat blood cancer, relapsed or refractory diffuse large B-cell lymphoma (DLBCL). Response rates to available treatments are less 10%, with survival measured in months. Complete response rates were 40% and 30% after 1 and 6 months, respectively. Moreover, treatment raised the probability of being relapse-free at 6 months to almost 74%. Another FDA approved CAR-T therapy, Yescarta® (Kite Pharma, recently acquired by Gilead) has also shown achieved complete and durable complete responses in DLBCL and other forms of B-cell lymphoma.
The major challenge of CAR-T treatment is management of potentially life-threatening adverse effects, which are a direct consequence of the engineered anti-tumour response, with the most serious being “cytokine storms” resulting from release of potent inflammatory molecules (including IFN-γ, IL-10 and IL-6). Some degree of neurotoxicity is common in recipients, although the long-term consequences of this are unknown.
Other significant challenges are logistics and cost: as personalized living therapies, cell collection, transformation, expansion and delivery to the patient is a complex series of steps, with consistent manufacture of a safe and reliable product being the most demanding. While the list prices of Kymriah® and Yescarta® are $475,000 and $373,000, respectively (Novartis offers a rebate where patients do not respond to treatment), side effect management and other support costs can bring the total medical bill close to $1.5 million per patient. This, and complex reimbursement issues, are at least in part, factors in the low uptake of CAR-T therapy. Better definition of cost-effectiveness is needed.
Despite these challenges, a variety of investigational adoptive cell immunotherapies is in the works for cancers other than B-cell malignancies, with studies underway in multiple myeloma (Bluebird Bio, Kite Pharma); ovarian cancer (Juno Therapeutics), and glioblastoma (Mustang Bio, Aurora Biopharma). Several “next generation” candidates incorporate drug-sensitive “safety switches” that allow the anti-tumour response to be turned on or off.
Moving from bespoke to “off the peg” therapy using cells collected from healthy donors (“allogeneic” cell therapy) could substantially reduce the overall cost of cellular immunotherapy. Early clinical studies with an allogeneic CAR-T cell product developed by Cellectis are underway.
Cellular immunotherapy development has proved to be a rocky road. Clinical study deaths have resulted in the abandonment of a CAR-T candidate by Juno Therapeutics [CAR-T: A wheel falls off, but still rolling], and clinical trial holds imposed on Cellectis (although recently lifted) and as of this week, Bellicum Therapeutics, with three unexpected deaths occurring in subjects under treatment for haematological cancers. Growing experience may allow early identification of study subjects at increased risk of severe adverse events or development of safer investigational treatment regimens.
Commercial success could prove elusive for several developers with high product cost, small addressable patient populations, safety issues, and competition from both cellular and non-cellular immunotherapies, particularly in the B-cell malignancy segment, constraining uptake. Giants such as Novartis can afford the necessary infrastructure, flexible pricing and slow rate of uptake, but smaller players may join Kite Pharma and Juno Therapeutics in being acquired by companies with deep pockets.
Photo credit: NCI/NIH, Alex Ritter, Jennifer Lippincott Schwartz, and Gillian Griffiths
I can recommend a short perspective piece on the human side of adoptive cell immunotherapy that appeared in New England Journal of Medicine last year.
Tragedy, Perseverance, and Chance — The Story of CAR-T Therapy. Lisa Rosenbaum.
N Engl J Med 2017; 377:1313-1315. Online October 5, 2017. http://tinyurl.com/y9vpgch9