Next-generation CAR T cells

Dr John Maher

article

Next-generation CAR T cells

By Dr John Maher
Dr John Maher (Leucid Bio)

3 July 2023

Dr John Maher discusses the challenges associated with developing chimeric antigen receptor (CAR) T-cell therapy for solid tumours.

Dr John Maher, founder and Chief Scientific Officer of Leucid Bio, responds to questions about how to overcome the challenges associated with developing chimeric antigen receptor (CAR) T-cell therapy for solid tumours and how the clinical stage biotech company is making strides towards this goal.

Download

Read this article in full

To read this article in full please login or create an account. If you choose to create an account you'll gain access to our website content, as well as the opportunity to subscribe free-of-charge to Drug Target Review's journal and email communications.

Do you want to create an account?

Step 1 - Read this article in full

Please enter your email and choose a password for your account. Passwords must include at least 8 characters, a mixture of both uppercase and lowercase letters, at least one letter and number and at least one special character, e.g. ! @ # ? ]

Email address {{errors.email}}

Password {{errors.password}}

Confirm password {{errors.confirm_password}}

Step 2 - Subscription preferences

Please select whether you would like to receive Drug Target Review journal in printed and/or digital form, and choose which types of email communication you would like to receive.

Check all that apply:

Select all

Printed version of Drug Target Review journal (Sent free-of-charge by post 4 times a year)

Digital version of the Drug Target Review journal (Sent free-of-charge via email 4 times a year)

Step 3 - Personal details

Please enter your personal details.

Title

Title other

First name

Last name

Job title

Your employer

Telephone

Step 4 - Location details

Please enter your location details. We may use these details to personalise the content you see.

Address 1

Address 2

Town/City

Zip/Post code

Country

Step 5 - Areas of interest

Please select your areas of interest. We may use these details to personalise the content you see.

Tick all that apply:

Select all

Step 6 - Therapeutic areas of interest

Please select the therapeutic areas you are interested in. We may use these details to personalise the content you see.

Tick all that apply:

Select all

Please select whether you would like to receive relevant information and insights from Russell Publishing.

By completing this form you are agreeing to our terms and conditions and privacy policy. As part of your content download, and in compliance with GDPR, we will share your data with the specific sponsor(s)/partner(s) of this content who may wish to contact you. You may opt-out at any time by using the unsubscribe link in one of our, or our sponsor's, marketing emails, or by contacting [email protected].

Privacy policy / terms & conditions

Please review and accept Drug Target Review's privacy policy and terms & conditions

By completing this form you are agreeing to our terms and conditions and privacy policy. As part of your content download, and in compliance with GDPR, we will share your data with the specific sponsor(s)/partner(s) of this content as we believe you have a legitimate interest in this and other similar content. You may opt-out at any time by using the unsubscribe link in one of our, or our sponsor's, marketing emails, or by contacting [email protected].

Please tell us about your background and your work

I am a practising clinical immunologist. I spend most of my time divided between being an academic at King’s College London and working as the Chief Scientific Officer of Leucid Bio. My primary focus from the academic and commercial perspective is the development of CAR T-cell immunotherapies mainly, but not exclusively, for solid tumours. I have been working on CAR T cells since 1999 and it has been interesting because in the early days CAR T-cell therapy was quite a niche activity.

I started out in CAR T-cell research at Memorial Sloan Kettering Cancer Center, working in the laboratory of Michel Sadelain, who is a pioneer in the field. When I was there, I introduced second-generation CAR T-cell technology into the lab, benefitting from Michel’s ability to genetically engineer human T cells rather than immortalised cell lines. Second-generation CAR technology was invented here in the UK by Helene Finney and consists of a chimeric receptor in which you have both an activating unit and a co-stimulatory domain. This method creates T cells that not only kill tumour cells but can also proliferate following that encounter. I was enamoured with the potency of this approach, converting me to become a CAR T-cell scientist. Nonetheless, I was advised by several senior colleagues that I was wasting my time working in this particular arena. Hearteningly, however, when we fast forward to about 10 years later, we witnessed the tremendous impact that this technology has made in the context of treating patients with refractory blood cancers.

We spun Leucid Bio out at the end of 2014 and secured funding in 2017. That second-generation CAR T-cell technology is what we are currently using to treat head and neck cancer patients in an ongoing clinical trial.

Could you briefly outline how CAR T cells work and why they are effective?

T cells are key white blood cells of the immune system, which recognise foreign species called antigens. They are adapted to the individual in whom the T cells circulate. This is one of the reasons that organ transplantation is a problem, because if you take an organ from a donor and give it to a genetically unrelated recipient, their T cells will recognise it as a foreign invader, leading the T cells to attack it. This creates problems for new cancer immunotherapies because they must be designed with the patient in mind. A CAR is a synthetic solution to address this issue. The CAR allows the T cells to recognise tumours by virtue of a target molecule expressed on the surface of the tumour itself.

Provided the target is there, the CAR will enable the T cell to recognise that particular tumour cell. This means that the CAR does not need to be tailored to the patient, provided that their cancer expresses the target that it binds to.

The manner in which the CAR is introduced into the patient’s T cells most commonly involves the use of a disabled viral vector, which cannot replicate. It delivers the gene encoding for the CARs into the T cells and thereafter the virus no longer propagates itself. By contrast, the T cells can replicate and all the daughters of that population of T cells will continue to express the CAR. That gives you a large pool of T cells with the potential to target tumour cells.

Why have CAR T cells seen more success in haematological cancers and is it possible to target them towards solid tumours?

In the history of cancer medicine, it is traditionally easier to treat blood cancers than solid tumours. The reason that haematologists came out of the lab and into the clinic was that in the 1960s, they learned how to treat childhood leukaemia with chemotherapy drugs. Since then, we have seen the development of bone marrow transplantation as a very powerful, albeit intensive, treatment for patients with blood cancers who cannot achieve remission with traditional therapies. We have lagged behind in developing curative therapies for solid tumours but have developed therapies that can control these tumours for a period of time.

In general, however, common solid tumours are very difficult to cure once they have undergone metastasis. There are several hurdles to the development of effective CAR T-cell therapies for solid tumours. The first is selecting a suitable target antigen that is expressed on the malignant cells. When it comes to blood cancers, the top two targets are molecules known as CD19 and BCMA. These two molecules are expressed on the malignant cell population and also on some healthy cells. You can get away with depleting those healthy cells, which are generally B cells that make antibodies, since you can treat patients with immunoglobulin replacement. This effectively circumvents the issue of having no B cells present following CAR T-cell therapy. However, this approach cannot be easily employed in patients with solid tumours.

There are virtually no targets found on common solid tumours that are absolutely tumour specific or which are found on healthy, but dispensable, normal cells. Almost all the targets we look at in the context of solid tumours are found at lower levels on vital organs in the body, presenting significant risk of so-called “on-target off-tumour” toxicity. The second issue is that CAR T cells are generally administered intravenously. In the context of someone with a blood cancer, this provides direct access to the malignant cells. By contrast, solid tumours tend to originate and spread to various vital organs of the body. This presents a problem of how to get the CAR T cells to exit the bloodstream and access the sites where tumour deposits are located. This is something people are beginning to address by introducing homing receptors alongside the CAR, but it is not yet a perfect solution.

If you can manage to overcome these issues – ie, you have a safe target and can get your T cells into the tumour – you then have a third problem: the tumour microenvironment. There are a multitude of physical, chemical and biological obstacles which tumours establish within their local microenvironment, which turn off immune cell reactions. This includes acidosis, hypoxia and nutrient deprivation. Tumour cells produce a variety of immunosuppressive small molecules, like transforming growth factor (TGF) beta, IL10, prostaglandin E2, indoleamine dioxygenase – the list goes on.

Tumours also provide a physical barrier to the delivery of any kind of drug into the tumour, including CAR T cells. You also have a host of other cells in the tumour microenvironment that are immunosuppressive, such as regulatory T-cell macrophages, myeloid-derived suppressor cells, cancer-associated fibroblasts and mesenchymal stromal cells. All of these factors operate in the tumour microenvironment, preventing T cell activation and thus challenges for T-cell orchestrated immune responses.

How can we overcome some of those challenges?

If I had an answer to all of those problems, I would be a famous and wealthy man! However, if you break it down, starting with target selection, we now have very high‑end technologies available to us built around omics, which can help us to investigate new targets (eg, endogenous retroviral antigens) and target combinations in solid tumours.

Another tumour-associated target of particular interest are the NKG2D ligands. This is a family of eight ligands, upregulated by stress and recognised by cells such as natural killer (NK) cells, which express the NKG2D receptor. A cell that expresses an NKG2D ligand is, by definition, a stressed cell, so the immune system sees it as a threat. Owing to stress arising from DNA damage and the abnormal nature of the tumour microenvironment, over 80 percent of human cancers express NKG2D ligands. These ligands constitute the target of Leucid Bio’s lead clinical CAR T-cell asset (LEU-011) which we hope to evaluate in a clinical trial that Leucid Bio is looking to initiate next year. We have great hopes for this approach based on the pre-clinical data that we have generated.

Furthermore, the co-expression of a homing receptor can enable some degree of semi-selective trafficking of T cells into tumours. In the past, we have used CXCR2, a chemokine receptor, for this purpose. It has seven different ligands – CXCL1, 2, 3, 5, 6, 7 and 8, although CXCL8 is better known as IL8. Those ligands in particular tend to be produced by stress cells to flag the immune system and draw in cells like neutrophils. Many solid tumours overproduce CXCR2 ligands, particularly IL8. In pre-clinical models, we have found that you can improve the trafficking of CAR T cells into human tumours if you co-express CXCR2. Other groups have shown similar findings with different homing receptors so there is great scope for tailoring the approach here.

There are also immune checkpoints which are potentially important in the tumour microenvironment; eg, PD-L1, LAG-3, TIM-3 and CTLA‑4. Consequently, we can envision the treatment of patients with a CAR T-cell product in combination with an immune checkpoint inhibitor that is tailored for that particular tumour type. TGF beta is a well-recognised immunosuppressive factor within the tumour microenvironment and there are traps which can be used to deplete TGF beta to counteract this. Alternatively, a switch receptor may be expressed in the CAR T cell which binds TGF beta and delivers a positive signal to the T cells as a result.

There are also inhibitors of other potential checkpoints such as prostaglandin E2, IDO inhibitors and arginase which offer further opportunities to develop alternative hybrid approaches.

Another solid tumour-focused approach we were recently involved in was a collaboration with James Arnold at King’s College London in which we designed hypoxia‑sensing CARs. The CAR recognises a potentially dangerous target such as ErbB dimers, but since it only moves to the cell surface under conditions of hypoxia, it operates preferentially within the tumour to enhance safety.

Can you tell me about some of the work at Leucid Bio?

We are very interested in NKG2D ligands as a target family for CAR T-cell immunotherapy, building on the pioneering work of Charles Sentman. The rationale here is that these are natural targets for immune surveillance, so our hope is that by potentiating this system, we may see impact against solid tumours.

The other major thing we are doing at Leucid is redesigning CARs. Traditional CARs are linear fusion receptors, where you have a targeting moiety, a spacer domain, a transmembrane domain and a signalling domain – which often has two or three components to deliver activating and co-stimulatory signals to the T cells. However, we have found that there is only so far you can push that prototype or model before you start to lose functionality. This is a particular problem with the signalling domain, where if you have three units in the endo domain, by definition, two of them are away from their natural location in proximity to the plasma membrane. To address this, we are building out rather than building up – we call this a laterally configured CAR.

An example of this principle is called a parallel CAR. This consists of a traditional second‑generation CAR (eg, containing CD28) paired with a chimeric co-stimulatory receptor in which you have a different co‑stimulatory domain, such as 4-1BB. We found that this platform consistently outperforms traditional linear CARs. We are also working on an adapter CAR system, whereby the targeting moiety is separated from the signalling machinery. In nature, many receptors that operate in the immune system have this adapter-type structure, prompting us to take a leaf out of nature’s book by building CARs that exploit this configuration. LEU-011, our lead asset, is an adapter CAR targeting NKG2D ligands.

The final point is that we are interested in off-the-shelf allogeneic CAR T-cell solutions. We published a paper describing a method to expand gamma-delta T cells to enhance their intrinsic antitumour activity. We found that if these T cells are expanded in the presence of TGF beta – a prototypic immunosuppressive cytokine – you paradoxically achieve a better yield of gamma-delta T cells with enhanced intrinsic antitumour activity. Gamma-delta T cells are interesting in this regard because, in contrast to traditional alpha-beta T cells, they do not recognise antigen in a human leukocyte antigen (HLA)-dependent manner. As a result, they do not cause graft‑versus-host disease, unlike allogeneic alpha-beta T cells.

This makes it difficult to use alpha-beta T cells as an off-the-shelf therapy, unless you can neutralise the expression of the T-cell receptor (TCR) using genome editing. Gamma‑delta T cells are not hindered in this manner and therefore provide a ready to use off-the-shelf cellular chassis for CAR T-cell immunotherapy. For an off-the-shelf approach, you could therefore put a CAR into a gamma‑delta and if you expand the cells in TGF beta, you will also boost their intrinsic antitumour activity. That is something we are quite interested in developing at Leucid as well.

Author Bio:

Dr John Maher

Dr John Maher is the scientific founder and Chief Scientific Officer of Leucid Bio. He is also a clinical immunologist who leads the CAR Mechanics research group within King’s College London. He played a key role in the early development of second-generation (CD28) CAR technology while a visiting fellow at Memorial Sloan Kettering Cancer Center, an approach that has achieved clinical impact in haematological malignancies. His research group is focused on the development of adoptive immunotherapy using CAR-engineered and gamma-delta T cells, with a primary emphasis on solid tumour types. In addition, he is a consultant immunologist at Eastbourne Hospital.

Cookie	Type	Duration	Description
cookielawinfo-checkbox-advertising-targeting	persistent	1 year	The cookie is set by GDPR cookie consent to record the user consent for the cookies in the category "Advertising & Targeting".
cookielawinfo-checkbox-analytics	persistent	1 year	This cookie is set by GDPR Cookie Consent WordPress Plugin. The cookie is used to remember the user consent for the cookies under the category "Analytics".
cookielawinfo-checkbox-necessary	persistent	1 year	This cookie is set by GDPR Cookie Consent plugin. The cookie is used to store the user consent for the cookies in the category "Necessary".
cookielawinfo-checkbox-performance	persistent	1 year	This cookie is set by GDPR Cookie Consent WordPress Plugin. The cookie is used to remember the user consent for the cookies under the category "Performance".
PHPSESSID	session	1 year	This cookie is native to PHP applications. The cookie is used to store and identify a users' unique session ID for the purpose of managing user session on the website. The cookie is a session cookies and is deleted when all the browser windows are closed.
viewed_cookie_policy	persistent	1 year	The cookie is set by the GDPR Cookie Consent plugin and is used to store whether or not user has consented to the use of cookies. It does not store any personal data.
zmember_logged	session	1 year	This session cookie is served by our membership/subscription system and controls whether you are able to see content which is only available to logged in users.

Cookie	Type	Duration	Description
advanced_ads_browser_width	persistent	1 month	This cookie is set by Advanced Ads and measures the browser width.
advanced_ads_page_impressions	persistent	2 years	This cookie is set by Advanced Ads and measures the number of previous page impressions.
advanced_ads_pro_server_info	persistent	1 month	This cookie is set by Advanced Ads and sets geo-location, user role and user capabilities. It is used by cache busting in Advanced Ads Pro when the appropriate visitor conditions are used.
advanced_ads_pro_visitor_referrer	persistent	1 year	This cookie is set by Advanced Ads and sets the referrer URL.
bscookie	persistent	2 years	This cookie is a browser ID cookie set by LinkedIn share Buttons and ad tags.
IDE	persistent	2 years	This cookie is set by Google DoubleClick and stores information about how the user uses the website and any other advertisement before visiting the website. This is used to present users with ads that are relevant to them according to the user profile.
li_sugr	persistent	3 months	This cookie is set by LinkedIn and is used for tracking.
UserMatchHistory	persistent	1 month	This cookie is set by Linkedin and is used to track visitors on multiple websites, in order to present relevant advertisement based on the visitor's preferences.
VISITOR_INFO1_LIVE	persistent	5 months	This cookie is set by YouTube. Used to track the information of the embedded YouTube videos on a website.

Cookie	Type	Duration	Description
bcookie	persistent	2 years	This cookie is set by LinkedIn. The purpose of the cookie is to enable LinkedIn functionalities on the page.
GPS	persistent	30 minutes	This cookie is set by YouTube and registers a unique ID for tracking users based on their geographical location
lang	session	1 year	This cookie is set by LinkedIn and is used to store the language preferences of a user to serve up content in that stored language the next time user visit the website.
lidc	persistent	1 day	This cookie is set by LinkedIn and used for routing.
lissc	persistent	11 months	This cookie is set by LinkedIn share Buttons and ad tags.
vuid	persistent	2 years	We embed videos from our official Vimeo channel. When you press play, Vimeo will drop third party cookies to enable the video to play and to see how long a viewer has watched the video. This cookie does not track individuals.
wow.anonymousId	persistent	2 years	This cookie is set by Spotler and tracks an anonymous visitor ID.
wow.schedule	persistent	20 minutes	This cookie is set by Spotler and enables it to track the Load Balance Session Queue.
wow.session	persistent	20 minutes	This cookie is set by Spotler to track the Internet Information Services (IIS) session state.
wow.utmvalues	persistent	20 minutes	This cookie is set by Spotler and stores the UTM values for the session. UTM values are specific text strings that are appended to URLs that allow Communigator to track the URLs and the UTM values when they get clicked on.
_ga	persistent	2 years	This cookie is set by Google Analytics and is used to calculate visitor, session, campaign data and keep track of site usage for the site's analytics report. It stores information anonymously and assign a randomly generated number to identify unique visitors.
_gat	persistent	1 minute	This cookies is set by Google Universal Analytics to throttle the request rate to limit the collection of data on high traffic sites.
_gid	persistent	1 day	This cookie is set by Google Analytics and is used to store information of how visitors use a website and helps in creating an analytics report of how the website is doing. The data collected including the number visitors, the source where they have come from, and the pages visited in an anonymous form.

Cookie	Type	Duration	Description
cf_ob_info	persistent	1 minute	This cookie is set by Cloudflare content delivery network and, in conjunction with the cookie 'cf_use_ob', is used to determine whether it should continue serving “Always Online” until the cookie expires.
cf_use_ob	persistent	1 minute	This cookie is set by Cloudflare content delivery network and is used to determine whether it should continue serving “Always Online” until the cookie expires.
free_subscription_only	session	1 year	This session cookie is served by our membership/subscription system and controls which types of content you are able to access.
ls_smartpush	persistent	1 month	This cookie is set by Litespeed Server and allows the server to store settings to help improve performance of the site.
one_signal_sdk_db	persistent	Until cleared	This cookie is set by OneSignal push notifications and is used for storing user preferences in connection with their notification permission status.
YSC	session	1 year	This cookie is set by Youtube and is used to track the views of embedded videos.

Recommended

Next-generation CAR T cells

Shares

Share this post

Email preferences