Unleashing Our Immune Response to Quash Cancer

An array of diverse and potent therapies to turbocharge our immune system

It’s astounding how devious cancer cells and tumor tissue can be. This week in Science we learned how certain lung cancer cells can function like ”Catch Me If You Can”—changing their driver mutation and cell identity to escape targeted therapy. This histologic transformation, as seen in an experimental model, is just one of so many cancer tricks that we are learning about.

Recently, as shown by single-cell sequencing, cancer cells can steal the mitochondria from T cells, a double whammy that turbocharges cancer cells with the hijacked fuel supply and, at the same time, dismantles the immune response.

Last week, we saw how tumor cells can release a virus-like protein that unleashes a vicious autoimmune response.

And then there’s the finding that cancer cell spread predominantly is occurring while we sleep.

As I previously reviewed, the ability for cancer cells to hijack neurons and neural circuits is now well established, no less their ability to reprogram neurons to become adrenergic and stimulate tumor progression, and interfere with the immune response. Stay tuned on that for a new Ground Truths podcast with Prof Michelle Monje, a leader in cancer neuroscience, which will post soon.

Add advancing age’s immunosenescence as yet another challenge to the long and growing list of formidable ways that cancer cells, and the tumor microenvironment, evade our immune response.

An Ever-Expanding Armamentarium

All of this is telling us how we need to ramp up our game if we are going to be able to use our immune system to quash a cancer. Fortunately, we have abundant and ever-growing capabilities for doing just that.

Immune Checkpoint Inhibitors

The field of immunotherapies took off with the immune checkpoint inhibitors, first approved by the FDA in 2011, that take the brakes off of T cells, with the programmed death-1 (PD-1), PD-ligand1, and anti-CTLA-4 monoclonal antibodies (3 Figures below from Oula Dagher and colleagues).

But we’re clearly learning they are not enough to prevail over cancer with common recurrences, only short term success in most patients, with some notable exceptions. Adding other immune response strategies, such as a vaccine, or antibody-drug conjugates, or engineered T cells, are showing improved chances for success.

Therapeutic Cancer Vaccines

There are many therapeutic cancer vaccines in the works, as depicted below, and reviewed in depth here.

Here’s a Table of ongoing clinical trials of cancer vaccines. You’ll note most of these are on top of a checkpoint inhibitor and use personalized neoantigens (cancer cell surface proteins) derived from sequencing (whole-exome or whole genome, RNA-sequencing and HLA-profiling) the patient’s tumor.

An example of positive findings is with the combination of an mRNA-nanoparticle vaccine with up to 34 personalized neoantigens and pembrolizumab (Keytruda) vs pembrolizumab alone in advanced melanoma after resection, with improved outcomes at 3-year follow-up, cutting death or relapse rate in half.

Antibody-Drug Conjugates (ADC)

There is considerable excitement about antibody-drug conjugates (ADC) whereby a linker is used to attach a chemotherapy agent to the checkpoint inhibitor antibody, specifically targeting the cancer cell and facilitating entry of the chemotherapy into the cell. Akin to these are bispecific antibodies (BiTEs, binding to a tumor antigen and T cell receptor simultaneously, Figure below), both of these conjugates acting as “biologic” or “guided” missiles.

Here’s a schematic of how they work to destroy the cancer cell (apoptosis), now with over 20 ADCs approved and more than 100 in ongoing clinical trials

A very good example of the potency of an ADC was seen in a “HER2- low” breast cancer randomized trial. The absence or very low expression or amplification of the HER2 receptor is common in breast cancer and successful treatment has been elusive. A randomized trial of an ADC (trastuzumab deruxtecan) compared to physician’s choice therapy demonstrated a marked success for progression-free survival in HER2- low patients, which was characterized as “unheard-of success” by media coverage.

This strategy is being used to target some of the most difficult cancer driver mutations such as TP53 and KRAS.

Oncolytic Viruses

Modifying viruses to infect the tumor and make it more visible to the immune system, potentiating anti-tumor responses, known as oncolytic viruses, have been proposed as a way to rev up the immune response for a long time but without positive Phase 3 clinical trials.

After decades of failure, a recent trial in refractory bladder cancer showed marked success, along with others, summarized here, now providing very encouraging results. It looks like oncolytic viruses are on a comeback path.

Engineering T cells (Chimeric Antigen Receptor (CAR- T)

As I recently reviewed, there are over 500 ongoing clinical trials to build on the success of the first CAR-T approval for leukemia 7 years ago. I won’t go through that all again here, but to reiterate most of the success to date has been in “liquid” blood (leukemia and lymphoma) cancer tumors. This week in Nature is the discovery of a T cell cancer mutation, a gene fusion CARD11-PIK3R3, from a T cell lymphoma that can potentially be used to augment CAR-T efficacy. It has pronounced and prolonged effects in the experimental model. Instead of 1 million cells needed for treatment, even 20,000 were enough to melt the tumor. This is a noteworthy discovery since CAR-T work to date has largely not exploited such naturally occurring mutations, while instead concentrating on those seen in the patient’s set of key tumor mutations.

As currently conceived, CAR-T, and what is being referred to more broadly as adoptive cell therapies, involves removing T cells from the patient’s body and engineering their activation, then reintroducing them back to the patient. This is laborious, technically difficult, and very expensive. Recently, the idea of achieving all of this via an injection of virus that specifically infects T cells and inserts the genes needed, was advanced by two biotech companies with preclinical results, one in non-human primates.

Gearing up to meet the challenge of solid tumor CAR-T intervention, there’s more work using CRISPR genome editing of T cell receptors. A.I. is increasingly being exploited to process the data from sequencing and identify optimal neoantigens.

Instead of just CAR-T, we’re seeing the emergence of CAR-macrophage and CAR-natural killer (NK) cells strategies, and rapidly expanding potential combinations of all the strategies I’ve mentioned. No less, there’s been maturation of on-off suicide switches programmed in, to limit cytokine release and promote safety of these interventions. Overall, major side effects of immunotherapies are not only cytokine release syndromes, but also include interstitial pneumonitis and neurotoxicity.

Summary

Given the multitude of ways cancer cells and tumor tissue can evade our immune response, durably successful treatment remains a daunting challenge. But the ingenuity of so many different approaches to unleash our immune response, and their combinations, provides considerable hope that we’ll increasingly meet the challenge in the years ahead. We have clearly learned that combining different immunotherapy strategies will be essential for many patients with the most resilient solid tumors.

Of concern, as noted by a recent editorial in The Lancet, entitled “Cancer Research Equity: Innovations For The Many, Not The Few,” is that these individualized, sophisticated strategies are not scalable; they will have limited reach and benefit. The movement towards “off the shelf” CAR-T and inexpensive, orally active checkpoint inhibitors may help mitigate this issue.

Notwithstanding this important concern, we’re seeing an array of diverse and potent immunotherapy strategies that are providing highly encouraging results, engendering more excitement than we’ve seen in this space for some time. These should propel substantial improvements in outcomes for patients in the years ahead. It can’t happen soon enough.

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