by Richard Boyd and Aleta Pupovac
A question which has long baffled scientists, frustrated clinicians and devastated patients is why does the immune system so effectively defend against infections but so poorly deal with cancer? What lessons can be learnt?
Thanks to a molecular biology-led revolution in immunotherapy, we are now beginning to strategically apply the immune defence rules that deal with micro-organisms, to attacking cancer. Importantly, no single cell type or molecule can provide effective protection against infections. It is therefore not surprising that targeting cancer cells with a single therapy has had limited success. Recently a highly innovative treatment approach has emerged, involving genetically modifying a patient’s own immune T cells in the laboratory, with a gene that codes for a chimeric antigen receptor (CAR); this CAR allows that T cell to find and bind to a cancer cell, triggering an activation cascade resulting in death of the cancer. Cancer reactive immune cells are naturally very rare; CAR technology enables a whole army of cancer fighting cells to be produced and injected back into the patient.
This CAR-mediated “seek and destroy” treatment has had stunning successes in blood cancers, with some patients actually cured. Despite this, such autologous (i.e. using the patient’s own cells) CAR-T cell therapy is limited by the number and quality of the patient’s T cells which can be obtained because of damage through e.g. chemotherapy, radiation, exhaustive exposure to the cancer, and natural ageing. It is also prohibitively expensive.
Furthermore, with these single antigen-specific CAR-T cells, relapses are now arising from cancer cells which have escaped by mutating off the nominal target antigen. In addition, such CAR-T cells have been largely ineffective against the biologically more complex solid tumours.
Why not apply multiple component parts of the immune system which successfully defeats infections, to targeting cancer cells?
In the response to infections, it is cells of the natural “innate” immune system which are first engaged. Of these, macrophages are particularly important because they not only engulf and destroy microbes but they can also activate other cells of the adaptive immune system to complete the elimination and also provide long term protection. Macrophages can also detect and eradicate abnormal cells, including cancer cells, before they grow and spread. While some macrophages are effective at killing, another form are immune suppressive and thrive in the solid tumour microenvironment (TME), promoting cancer growth. In the TME, the population of anti-tumour macrophages is relatively low. A key question is therefore can the immune suppressing macrophages be converted to those attacking cancer to improve a patient’s prognosis?
Recently, Natural Killer (NK) cells have emerged as very important anti-cancer killer cells. NK cells have multiple surface receptors that recognise cancer cells, and their activation does not require complex pre-stimulation signals. In terms of killing cancer cells, they are “alert and ready to go”. The primary targets of NK cells are so-called “cell stress molecules”, which are expressed on old and damaged cells, virally infected cells and cancer cells. Normal healthy cells escape this killing because they lack the “stress molecules” and in addition they have a parallel set of receptors that directly inhibit NK-cell function. When donor NK cells are transplanted into unmatched patients, there is no rejection, making them safer than T cells which can attack the patient’s cells.
However, as promising as NK cells are, there are three major problems thwarting their general utility: they do not divide so are numerically limited, they too are subject to the immunosuppressive TME and they are relatively resistant to gene editing.
Cancer cells can also actively evade the immune system by multiple mechanisms. They secrete potent immune suppressing molecules. They can also express so called “don’t eat me” receptors such as CD47. This has a natural role in protecting healthy cells from being destroyed by macrophages; when cells become damaged or aged, the levels of CD47 are reduced and the cells can then be removed by macrophages. Cancer cells have hijacked this system, by increasing their surface expression of CD47 to promote survival by inhibiting macrophages. Blocking CD47 on cancer cells allows macrophages to not only “eat” cancer but also converts them from being immune suppressive to pro-cancer killing in the TME. Our strategy here is to generate dual CARs: one specific to the cancer and the other to “smother” CD47 on the cancer cell, enabling its killing by engaging the patient’s own macrophages, in addition to the cancer-specific CAR on the NK cells.
Additionally, immunosuppressive checkpoint “handbrake” genes can prevent immune cells from functioning properly. In fighting infections this is normally a good thing because it prevents immune system burn out, however, it is the last thing a cancer patient needs. By removing these genes from NK cells and macrophages, the cancer killing becomes more potent and prolonged.
The challenge is clear: can we successfully manipulate and co-engage these different immune system components to synergistically remove cancer cells, hopefully permanently: 3D immunity?
Cartherics is pioneering innovative methods to undertake this. To address the limitations of autologous CAR therapy, Cartherics’ strategy involves genetic sculpturing of iPSC which grow indefinitely, enabling an endless supply of young, healthy immune cells to be produced. Cartherics has developed this sophisticated iPSC-based technology to generate large-scale, cost-effective, clinic-ready NK (iNK) cells. We can also differentiate iPSC into T cells and macrophages. Importantly, the iPSC can be gene-edited to incorporate a CAR genetic construct and deleted of immune “handbrake” genes. Being iPSC, means these functionally critical, cancer fighting genetic improvements will be transferred to all the immune killer cells they differentiate into.
Our current focus is to combine these genetic edits of the iPSC to produce “off-the-shelf” iNK cells with a CAR targeted to TAG-72, a tumour antigen present on all adenocarcinomas such as ovarian cancer. Ovarian cancer is especially challenging, with up to 85% of patients experiencing cancer recurrence despite undergoing surgery and chemotherapy. The 5 year survival for stage 3 and 4 patients being 41% and 31% respectively. These TAG-72 CAR-iNK cells have one or more “checkpoint” gene(s) deleted to further enhance function. A clinical trial is expected within 2-3 years.
Several companies have embraced iPSC technologies to produce gene-edited immune cells, with the aim of advancing immunotherapies and providing more effective treatments for cancer patients. These include Shoreline, Fate Therapeutics, and Century. Numerous research groups, both in universities and independent institutions, are also at the forefront of exploring the potential of iPSCs for immunotherapy including Stanford University, Harvard University and the University of California. Additionally, premier medical research institutions including the Memorial Sloan Kettering Cancer Center are engaged in refining gene-editing and optimisation of iPSC-derived immune cells for cancer treatment. The collective efforts of these companies and research groups contribute significantly to the advancement of iPSC technology, aiming to develop personalised and effective immunotherapies for cancer and other diseases.
The stage is now set for Cartherics to use its proprietary gene-edited iPSC-derived immune cell production platform to generate a functionally co-ordinated multicellular anti-cancer therapy. The future of “3D immunity” indeed looks promising.
Richard Boyd is the CSO and Aleta Pupovac is the Publications Officer at Cartherics, an Australian biotech company developing immune cell therapies for the treatment of cancers.