(Un)-Natural Born Killers

Human natural killer (NK) cell.
Add CAR for extra killing.

Cancer immunotherapy, although far from offering universal cure, continues to rack up some remarkable successes. Immune checkpoint inhibitor treatment has transformed expectation in metastatic melanoma, non-small cell lung cancer and other advanced solid tumours, with new agents and novel combination therapies likely to further improve outcomes.

Cell-based therapies in which patient T cells are genetically engineered to express a protein construct (“chimeric antigen receptor”, hence CAR-T) specific for a target cancer antigen, then expanded and infused to bring about tumour destruction and long-term anti-tumour immunity. CAR-T treatment has achieved unprecedented complete response rates in certain types of otherwise untreatable childhood and adult leukaemia, although not without the risk of life-threatening adverse events resulting from cytokine release and relapse through the escape of cancer cells that do not express the selected target antigen. 

Clinical experience with CAR-T therapies is limited and so far confined to haematological cancers (Kymriah® developed by Novartis and Yescarta®, developed by Kite Pharma and since aquired by Gilead, only received FDA approval in August 2017 and October 2017, respectively), but the potential of cell-based cancer treatment  is such that substantial industrial and academic effort is focused on development of next generation therapies capable of tackling solid tumours, and which do not require  complex and expensive patient-specific product manufacture.

T cells are not the only components of the immune system capable of tumour recognition and destruction. So-called “natural killer” (NK cells- there’s a clue to their purpose in the name) are part of the innate immune system, a first-line defence that does not require the recognition and processing of foreign antigens to function. NK cells possess a variety of tumour-recognising receptors with interaction resulting in cancer cell destruction and upregulation of innate and adaptive immune systems.

In contrast to donated T cells (even when matched by tissue type), donated NK cells are not identified as foreign, opening up the possibility of off-the-shelf (“allogeneic”) treatments. NK cells are readily isolated from cord or peripheral blood and can be maintained as a cell line. Human stem cell-derived NK cells might one day prove suitable for industrial scale production. Moreover, as with T cells, NK cells are amenable to transformation by viral vectors encoding chimeric antigen receptor DNA.

A number of CAR-NK clinical studies are underway, utilising NK cells from donors or cell lines modified to express different cancer antigen receptors specific for lymphoma and various forms of leukaemia; glioblastoma; non-small cell lung cancer, and other solid tumours. Notably, several of these studies are sponsored by Chinese clinical investigators and biopharma companies, echoing the country’s substantial efforts in CAR-T product development.

CAR-NK product development is not without problems, such as the efficiency of cell production and need to optimise CAR design to minimise toxicity through “off target” effects and to improve the specificity of intracellular signalling which kicks NK cells into fighting mode. It’s too early to determine which of the available sources of NK cells, if any, will result in superior outcomes. NK cells are relatively short-lived and products based on a subset of longer-lived NK cells may be required to induce lasting anti-tumour effects.

However, as regulatory and clinical acceptance of CAR-T cell products demonstrates, the complexities of cell-based therapy can be mastered: CAR-NK products will undoubtedly benefit from this expanding knowledge base and through entering an environment with growing payer acceptance of high-ticket cancer treatments.

Photo credit: NIAID

Melanoma immunotherapy: Can vaccines and cell therapies expand on immune checkpoint inhibitor successes?

Mestastatic melanoma cells

Tracking the major cancer meetings has kept me occupied throughout October and into November but left me with plenty of material for this, and future, blog articles. A presentation at the UK’s NCRI conference on the increasing mortality rate from melanoma in men (but not women, where mortality rates are generally declining or stabilising), while alarming, did remind me of just how far melanoma treatment has advanced in a few short years.  

Prior to the availability of anti-CLTA-4 and anti-PD-1 immune checkpoint inhibitors, overall survival from metastatic melanoma in developed countries was around 25% after three years: combination immune checkpoint inhibitor treatment has stretched this to over 60%, and use following surgery (“adjuvant” use) significantly improves recurrence free survival.

Despite these successes, a significant need remains for alternative treatments for those who fail, or are intolerant of, current immune inhibitor checkpoint regimens and a gamut of investigational immunotherapies including “personalized” or “individualised” peptide and mRNA therapeutic vaccines, cell therapies and oncolytic virus therapies are in active clinical development.

That the immune system recognises melanoma as being “not self” has been known for decades and means of usefully exploiting this distinction long precede the discovery of immune checkpoints. Attempts to effectively boost the anti-melanoma immune response through injection of the Bacille Calmette–Guérin (BCG) tuberculosis vaccine were made in the 1970s, with mixed success. The potent immunomodulators, interferon alpha (IFNα) and interleukin 2 (IL-2), were approved for use in melanoma in the 1990s and still have a role in the treatment of metastatic disease and adjuvant therapy.

Melanoma has long been an attractive target for cancer vaccine development. A variety of melanoma antigens common to a majority of tumours - “tumour-associated antigens” (TAAs), including gp100, GM2; tryosinase, MART-1 and MAGE-A3, have been exploited, either alone or in combination, in cell-based and peptide therapeutic vaccines.

Cell-based vaccines (as either intact or processed tumour cells or as cell-free lysates) offer the advantage of presenting a spectrum of TAAs, although neither patient-derived (autologous) nor cultured tumour cell-derived (allogeneic) cell-based melanoma vaccines, such as Melacine® (GSK/Schering) and Canvaxin® (CancerVax/Serono), have made it through pivotal studies. M-VAX (AVAX), a chemically-modified autologous cell vaccine, has been in late-stage development limbo for over a decade.

Historically, peptide vaccines have fared no better, with a pivotal study of Oncophage® (Antigenics), the manufacture of which involved isolation of heat shock protein-peptide complexes from autologous tumour cells, being abandoned, and a Phase III study of a MAGE-A3 peptide vaccine (GSK) being terminated due to lack of obvious efficacy over placebo.

Adoptive cell transfer (ACT) involves the collection, isolation, ex vivo expansion and (re)-infusion of autologous tumour-associated cytotoxic T-cells. ACT using tumour-infiltrating lymphocytes (TIL) has occasionally attained response rates of 40%-50% and complete remission in 10% to 25% of patients with extensive metastatic disease: however, the complexity of ACT has essentially confined it to clinical studies and compassionate use.

As is the case with other cancer indications, decades of disappointment and inconsistency have not curbed the academic and commercial pursuit of effective melanoma immunotherapies. Applying recent advances in technology- next generation sequencing; gene transfer and editing; nucleic acid delivery- to melanoma vaccine and cell therapy development might just make these old dogs capable of new tricks.

Cancer vaccine efficacy is blunted by the immunosuppressive tumour microenvironment: combination with immune checkpoint inhibitors is an obvious means of increasing the odds of success and a number of studies combining therapeutic vaccines with anti-PD-1 or anti-CTLA-4 immune checkpoint inhibitors are underway. These agents may eventually be joined or replaced, by one or more of the “next wave” of immune-oncology drugs directed at LAG3, CSF1-R, GITR or at targets in the innate immune systems which can fire up the immune response.

Imlygic® (T-VEC: Amgen), an oncolytic virus therapy is“vaccine-like” in effect, activating both the innate immune system and revealing hidden tumour antigens (“neoantigens”) to the adaptive immune system through tumour lysis. Combination with ipilimumab has shown improvement in response rates over Imlygic® alone, and a Phase III combination study with pembrolizumab (KEYNOTE-034) is ongoing. Early-stage studies of CAVATAK®, an investigational virotherapy acquired by Merck & Co from Viralytics earlier this year, has shown promise when combined with either pembrolizumab or ipilimumab.

The application of next generation sequencing technology and bioinformatics could offer a practical route to bespoke melanoma vaccines, with antigen selection and vaccine composition being determined by tumour and patient genetic makeup. Neon Therapeutics is currently trialling a synthetic peptide vaccine (NEO-PV-01) using sequencing of tumour biopsy material to formulate a selection of up to 20 peptide-mimicking patient-specific neoantigens. NantBioScience is pursuing a similar personalization strategy, with expression of patient-specific neoantigens in yeast cells (YE-NEO-001).

The in vivo expression of melanoma (and other cancer antigens) through the introduction of the corresponding mRNA sequence is receiving increasing attention. Lipid complex mRNA vaccines, encoding multiple melanoma TAAs or a personalised selection of antigens, are now in early clinical studies (Lipo-MERIT and RO7198457: BioNTech).

mRNA has brought a new twist to dendritic cell (DC) vaccination, where DCs isolated from the patient are loaded with melanoma antigens to optimise their processing and efficiency of presentation to the immune system. eTheRNA’s TriMix technology combines mRNA encoding melanoma antigens with mRNA encoding proteins known to enhance DC activation and maturation and to promote both helper and cytotoxic T cell production. Durable clinical responses have been achieved in melanoma patients who had failed previous treatments when the TriMix-DC-MEL vaccine was administered in combination with ipilimumab.

Gene transfer may open up additional ACT strategies for melanoma. T-cell receptor (TCR) gene transfer allows the generation of antigen-specific lymphocytes from patient T-cells Early studies with melanoma antigen-specific TCRs have shown modest response rates, although several have been marred by severe adverse events due to the “off-target” destruction of normal melanocytes.

The utility of ACT may be significantly improved through chimeric antigen receptor (CAR-T) technology, where T-cell antigen receptors are engineered to combine binding, signalling and co-stimulatory domains. Pilot CAR-T studies are underway. Improvements in TIL ACT may be possible by using CRISPR-CAS9 gene editing to increase the ability of T-cells to home in on tumours.

Next generation cell therapies, including DC vaccination, are likely to benefit from the broader expanding commercial interest in CAR-T and TCR therapies which will likely lead to further improvements in manufacture and assist in establishing the logistics necessary to delivery patient-specific treatments. Growing use of semi- or wholly-automated cell product processing will ultimately reduce costs and make the treatment of larger number of patients viable.

Effective melanoma immunotherapy had been a long time in coming, but as immune checkpoint inhibitor therapy has shown, revolution is possible. Experimental melanoma immunotherapies still have a lot to prove, but with the aid of across the board advances in immuno-oncology and other disciplines, we may finally see vaccine and cell-based approaches becoming practical and valuable treatment options.

Photo credit: Valencia, JC. NCI Center for Cancer Research

ASCO Clinical Cancer Advances 2018. And the winner is...

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

CAR-T: A wheel falls off, but still rolling

In the same week that Kite Pharma announced positive data from a pivotal study of its lead CAR-T candidate, KTE-C19 (easier to remember- and to spell- than the non-proprietary designation axicabtagene ciloleucel) in patients with B-cell non-Hodgkin lymphoma (NHL) refractory to other treatments, a one-time leader in the CAR-T race, Juno Therapeutics, pulled the plug on its lead candidate, JCAR015.

CAR-T (chimeric antigen receptor – the “T” is for T cell) is a form of adoptive cell transfer therapy which involves collection of T-cells from the patient and genetically engineering them to express receptors specific for a protein expressed on the tumour surface. After expansion in the laboratory, the transformed cells are infused back into the patient to seek and destroy tumour cells.

CAR-T therapy first made headlines by achieving unprecedented remission rates in patients with acute lymphoblastic leukaemia (ALL), chronic lymphocytic leukaemia (CLL) and NHL where all available treatments had failed to slow disease progression. The other side of the coin was the accompanying high incidence of life-threatening adverse events arising from the massive release of cytokines (part and parcel of the anti-tumour response) and from immune-related neurotoxicity.

Juno’s JCAR015 was placed on clinical hold early in development following a death attributed to cytokine release syndrome and again twice in 2016 following five deaths from cerebral oedema during a Phase II study in ALL patients.  The company initially speculated that the deaths might be related to changes in a pre-treatment regimen involving two chemotherapy drugs but the decision to halt further development suggests that JCAR015 itself is now thought be the culprit. 

CAR-T candidates from Kite Pharma and Novartis have also resulted in high rates of cytokine release and neurotoxicity-related adverse events, but, so far, these have proved to be more manageable or of lesser severity than those occurring during the JCAR015 studies. No cerebral oedema occurred in the Kite Pharma pivotal study, with two treatment-related deaths probably arising from cytokine release.

Juno hope to stay in the game with an earlier stage CAR-T candidate, JCAR017, which showed a relatively low incidence of severe adverse events  in a small study conducted in NHL patients, but the abandonment of JCAR015 puts Juno a long way behind Kite Pharma and Novartis, with both shooting for regulatory approval in 2017.

CAR-T treatment will probably never be a “safe” option, although adverse event management would be expected to improve with experience. If regulators can be convinced that the benefits of CAR-T therapy outweigh risk, safety is likely to be a secondary concern for individuals cursed with otherwise untreatable B-cell malignancies. 

An arguably bigger challenge facing Kite Pharma, Novartis and other CAR-T contenders is whether individualised adoptive cell transfer therapies can be reliably scaled up and delivered at a cost that healthcare systems are able and willing to meet.

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Kite Announces Positive Topline Primary Results of Axicabtagene Ciloleucel from First Pivotal CAR-T Trial in Patients with Aggressive Non-Hodgkin Lymphoma. Company press release online 28^th February 2017. http://tinyurl.com/js7293j

Juno Therapeutics Reports Fourth Quarter and 2016 Financial Results. Company press release online 1^st March 2017. http://tinyurl.com/hunp9uh