pCAR technology: an interview with John Maher


We spoke with John Maher (Chief Scientific Officer at Leucid Bio, UK) about his research in CAR-T cell therapy. He updates us on Leucid Bio’s (London) development since 2018, when we last spoke to him, and discusses pCAR, a revolutionary kind of CAR therapy designed to combat solid tumors.

Please introduce yourself and your organization.

I am a clinical immunologist with an interest in the development of cancer immunotherapy utilizing genetically re-targeted CAR-T cells. In the early days, there was considerable cynicism from the oncology community about immunotherapy, given the preceding decades of failure in this approach. Fortunately, this landscape has altered radically in recent years.

A pivotal event in my own career development was the short period that I spent over 20 years ago as a visiting fellow in the laboratory of Michel Sadelain at Memorial Sloan Kettering Cancer Center (NY, USA). Michel was an early pioneer of CAR-T cell immunotherapy and, at that time, he had developed unique systems to enable the stable genetic modification of human T-cells. This provided a tremendous opportunity since it allowed me to test the second-generation CAR technology developed by Helene Finney in primary T-cells, rather than in cell line models. Second generation CARs provide both an activating and a co-stimulatory signal, meaning that the T-cells can kill and proliferate in a tumor-dependent manner.

When I tested this system in primary human T-cells, I was really struck by their superior potency when compared to first generation counterparts that provide an activating signal alone. This led me to develop an academic career in CAR-T cell research, and I set up my lab at Guy’s and St Thomas’ NHS Foundation Trust (London, UK) in 2004.

My first post-doctoral position christened our group “The CAR Mechanics Lab”, a name which has stuck over the years. Subsequently, second generation CARs have proven to be highly impactful in the treatment of blood cancers, a finding that has driven the mainstream adoption of this treatment approach. This success has also led to the commercialization of these technologies, prompting us to spin out Leucid Bio in order to develop CAR technologies produced in my lab. Leucid Bio commenced operations in 2017 at Guy’s and St Thomas’ NHS Foundation Trust and works very closely alongside my academic group.

We spoke with you in 2018, how has Leucid Bio developed since then?

When we last spoke, Leucid Bio had just secured seed investment and had commenced operations to secure its IP portfolio and develop new CAR technologies, including parallel (p) CAR. This activity led to the identification of our lead clinical asset, which is referred to as LEU-011. LEU-011 builds on Leucid’s pCAR platform and is targeted against a family of stress-induced molecules known as NKG2D ligands. Since tumors are sites of intense cell stress, NKG2D ligands are widely expressed on both solid and hematological cancers. This expression is not restricted to the malignant cells themselves, but also to stromal cells that are commonly found in cancer.

Leucid Bio raised a Series A funding round last summer under the leadership of our CEO, Dr Artin Moussavi. This allowed the company to expand to ten employees, with plans for further growth in the short term. We have secured a laboratory base at Guy’s and St Thomas’ NHS Foundation Trust and are currently making plans for Phase I clinical testing of LEU-011, working in partnership with Lonza (Switzerland).

What are the challenges in treating solid tumors and how does pCAR address this?

Solid tumors impose multiple obstacles to successful treatment with any approach, including CAR-T cells. The first issue is what we can safely target in a solid tumor. Second, CAR-T cells struggle to gain access to solid tumors. With blood cancers, the infusion of CAR-T cells into the bloodstream provides them with direct access to the malignant cells. In contrast, solid tumor deposits generally lie within tissues, so we need systems to enable the CAR-T cells to find those sites. Once they arrive, CAR-T cells encounter a myriad of physical, chemical and biological obstacles that hinder their function. As a result, they ultimately become exhausted and incapable of tumor cell killing.

Despite these obstacles, I have focused my research primarily on solid tumors, because these account for over 90% of human cancers. However, CAR-T cells haven’t proven to be effective in this arena thus far. In thinking through potential approaches that could help tip the balance in their favor, I kept coming back to the fact that the breakthrough achieved by CAR-T cells against blood cancers was dependent on the inclusion of co-stimulation. Accordingly, it seemed logical that if we could enable CARs to deliver more potent co-stimulatory signals, this might enhance impact against solid tumors.

To address this, we constructed pCARs in which two co-stimulatory modules, such as CD28 and 4-1BB, are physically separated in two different receptors, one of which also provides an activating signal. By this means, we retain specificity directed against a single target but amplify the co-stimulatory signal when both targets are present.

We have found that when pCAR-T cells are evaluated for their anti-tumor activity, they demonstrate enhanced functional persistence, indicating that they are more resistant to the induction of exhaustion. We believe this attribute of the pCAR platform is advantageous for maximizing the therapeutic impact against solid tumors.

Why is a more natural biological configuration of T-cells desirable and what are the complexities of achieving this?

CARs are synthetic molecules which don’t fully recapitulate the geographical and temporal organization of signals naturally delivered by the T-cell receptor, and co-stimulatory molecules such as CD28 and 4-1BB. In particular, linear fusions often place signaling units in positions at which they are not found naturally. This is especially important for co-stimulatory domains.

It has been known for over 20 years that CD28 must be in proximity to the plasma membrane in order to function properly. This raises the possibility that similar restrictions apply to other co-stimulatory units such as 4-1BB. Although it is straightforward to include two co-stimulatory domains such as CD28 and 4-1BB in a linear CAR fusion, Leucid Bio found that this architecture doesn’t deliver effective co-stimulation from the second or downstream unit. This constraint led us to develop the pCAR solution described above. Our experience has been that the pCAR architecture more effectively harnesses the co-stimulatory potential of both CD28 and 4-1BB.

Why is effective provision of dual co-stimulation important and how does pCAR achieve this?

The pCAR system is focused on how we can harness co-stimulation by two distinct pathways such as CD28 and 4-1BB. We know that these pathways synergize during naturally occurring immune responses- and pCAR presents a synthetic approach to achieve this. We have also exemplified the technology, utilizing alternative co-stimulatory domains such as ICOS, CD27 and OX40, in addition to a range of targeting moieties, such as single chain antibody fragments, poplypeptides and short peptides. Moreover, pCARs can be designed to co-target the same epitope, different epitopes in the same target antigen or two completely different targets. Consequently, pCAR provides a highly adaptable “plug and play” system for CAR-T cell immunotherapy.

How have T-cell exhaustion and senescence hindered T-cell therapy and how does pCAR overcome this?

As mentioned above, T-cells lose fitness owing to a range of countermeasures deployed by cancer cells and accompanying stroma within the tumor microenvironment. The list of obstacles encountered there is both long and varied, meaning that it is very difficult to know which specific checkpoints we should try to disable in any given tumor. The pCAR platform is a device to take what we know has worked in blood cancers, namely the integrated provision of co-stimulation, and potentiate this in an effort to bridge the gap to effective treatment of solid tumors. Co-stimulation by 4-1BB and CD28 is very different and can be compared to a tortoise and a hare respectively. While 4-1BB provides a slow burning co-stimulation that enhances T-cell fitness and persistence, CD28 co-stimulation leads to rapid enhancement of functionality of CAR-T cells. We are trying to integrate both pathways using the pCAR technology in an effort to achieve the best of both worlds.

What does the future hold for Leucid Bio?

Leucid Bio’s mission is to develop better CAR solutions for patients, especially those with solid tumors. That is our focus, and we aim to transition promising CAR assets into clinical tests as quickly as we can. To that end, our recently announced partnership with Lonza to develop improved manufacturing processes is a key milestone in our development. Our manufacturing capability is at the heart of our development.

We also have a vibrant R&D program that seeks to identify new CAR technologies and improved solutions for the scalable manufacture of off-the-shelf CAR-T cell products. Leucid Bio also aims to work closely with our academic partners to understand better how our CARs work since we view the deep mechanistic understanding of our CAR technologies as being crucial to their further optimization.

Disclaimer

The opinions expressed in this interview are those of the interviewee and do not necessarily reflect the views of RegMedNet or Future Science Group.