Carl H. June, MD, professor of immunotherapy at the Perelman School of Medicine, University of Pennsylvania, is a pioneer in precision medicine and immunotherapy of human immunodeficiency virus and cancer. He was the driving force behind the first FDA-approved gene therapy product, Kymriah, which uses chimeric antigen receptor (CAR) T cells to treat B-cell acute lymphoblastic leukemia.
In 1998, June was recruited to the University of Pennsylvania, where the welcome committed included James M. Wilson, MD, PhD, head of the Institute for Human Gene Therapy. June’s new position allowed him to continue research he had been conducting in immunotherapy for human immunodeficiency virus (HIV) infection, and he also started carrying out adoptive immunotherapy experiments in cancer patients.
When Kymriah won approval in 2017, June had become director of the Center for Cellular Immunotherapies at the University of Pennsylvania’s Abramson Cancer Center. He stated, “We hope the momentum behind the technology builds as we continue to investigate the abilities of personalized cellular therapeutics in blood cancers and solid tumors to help patients with many other types of cancer.” In 2020, June’s team made news again by reporting on the first clinical genome editing program that employed both CAR T-cell and CRISPR technology.
In the interview that follows, we present some of June’s reflections on the growth and evolution of CAR T-cell technology and its applications in personalized immune therapies. (This interview, which was conducted by Wilson and originally published in GEN’s sister journal Human Gene Therapy Clinical Development,* has been edited for length and clarity.)
Carl, what were the key conceptual and technical challenges that you had to overcome to make CAR T-cell therapy a reality?
JUNE: It was a long and winding road. When you look at a CAR T-cell therapeutic, there are several components, although a key one is the cells themselves. One aspect that determines the function of CAR T cells is the actual function of the underlying subset of T cells that are harvested and amplified. There are a number of ways this could play out, since the diversity of T cells in humans is quite complex and includes helper cells, cytotoxic cells, and numerous subsets, such as Th1 cells.
How the cells are actually cultured can change their effector functions when they are infused back into a patient, and that was one issue that Bruce Levine and I researched early on while working to treat HIV infection. During this time in the 1990s, we developed methods to grow and then infuse memory T cells into patients who had HIV/acquired immune deficiency syndrome (AIDS).
It turns out that HIV phenocopies much of what cancer does to the immune system. For example, HIV kills helper cells, while cancer inactivates them in a number of different ways, meaning that in both diseases, the CD8 cytotoxic T cells do not work well. Therefore, restoring functional helper T cells with adoptive T-cell transfer in cancer patients and HIV/AIDS has benefit.
Another component of the CAR T-cell product approved by the FDA is the actual gene transfer methodology used to engineer the T cells. For a variety of reasons, we decided to use replication-defective versions of lentiviruses. Again, we were fortunate to be working in HIV, where it was ethically determined that the first gene transfer using lentiviruses would be in patients who already had HIV. Inder Verma, Luigi Naldini, and Didier Trono developed these vectors, and it was Inder who was chair of the Recombinant Advisory Committee when we first proposed this strategy.
There were a lot of questions as to whether the engineering of the vector was sufficient to prevent recombination and the emergence of a replication-competent HIV variant. It was thought that patients who already had HIV would be the most ethical starting place, and that we would later transfer the application to cancer patients.
Having discussed the cell type and the vector transfer technology, I would like to comment on the actual design of the CAR. Chimeric receptors were first described by Zelig Eshhar at the Weizmann Institute, where he grafted antibody domains onto T-cell receptors and was able to make T cells that could recognize targets and did not require major histocompatibility complex restriction.
Following that, there were a number of advancements in CAR designs beyond reprogramming the specificity of the T cell, and Michael Milone and Carmine Carpenito in my lab ended up comparing the CD28 signaling domain to 4-1BB signaling domains, and we found that the co-stimulation provided by a 4-1BB signaling domain led to enhanced persistence in our preclinical models.
During the 2000s, there was little support for those working in the cell and gene therapy space. Still, you made substantial strides toward the development of T-cell-based therapies. How were you able to make such progress during this difficult era?
JUNE: You and I both experienced the retraction of support from pharma and biotech for gene transfer technology, which really slowed progress for the entire field. We had ideas, but they could not be tested due to insufficient funding.
My laboratory had an advantage and benefitted in one major way because we were working in restoring immune function in HIV-infected patients as well as cancer immunotherapy. The National Cancer Institute had very little support for cancer immunotherapy, and I was unable to get funding from them during that time, but quite unexpectedly I was much more successful in obtaining funding for HIV immunotherapy research.
The National Institutes of Allergy and Infectious Disease has had an ongoing cell and gene therapy program for the better part of two decades, and that is where we were successful in acquiring ongoing funding. With philanthropy, we were able to leverage our experience in HIV and transition to cancer. We were then able to begin our first-in-human trial in 2010 with the CAR T cells in cancer patients with advanced leukemia.
However, our first CAR T-cell trial was in patients with HIV infection in the late 1990s, and without the HIV funding, we would have never advanced to testing in cancer patients. Fortunately, those days are behind us, and I think the field is much more vibrant, with governmental funding, philanthropy, and biotech and pharma alliances.
It has changed so quickly—from almost an aversion to supporting what we were doing to this incredible influx of support. How do you feel about that swing in interest?
JUNE: It was really astonishing for us. The field had this lukewarm reception when the first FDA-approved cell therapy for cancer came out. That was a dendritic cell vaccine that Dendreon had developed for prostate cancer. It did not have a successful commercial launch, primarily due to its very expensive cost of goods for manufacturing the cells. It was just not a home run.
Then we had our first three CAR T-cell patients published in August 2011. It was like the dam broke, and we had floods of requests and inquiries about funding, spinoff opportunities, and pharma alliances. The field was ready for immuno-oncology, in part because of checkpoint antibodies and the progress they had made where chemotherapy had not.
The CAR-T cells really provided the first demonstration that led to breakthrough status, because the cells were genetically marked, and we had striking on-target effects. The noninfectious cytokine release syndrome that was observed with very high fever was a syndrome never seen in medicine before. It was a striking toxicity that was on-target, and it allowed the mechanism of action of CAR T cell to be clearly ascertained.
The T cells actually proliferated when they encountered tumor targets and were easily measurable because of the genetic marking in patients. I think all that led to the realization that genetic programming of cells actually had merit beyond what people before previously thought was a dead end, and because there were so many years when it did not work.
What do you think the next generation of immune therapies will look like for cancer?
JUNE: I think it will be somewhat different for cancer than it will be for congenital disorders, which can be repaired and thus cured using many technologies, such as with genome editing, stem cells, in vivo gene delivery, and so on.
In the case of cancer, I think the next-generation therapies will be combinations. One orthogonal technology that really adds so much from a synthetic biology aspect is the ability to use the various genome editing technologies to engineer the T cells and make them resistant to toxic tumor microenvironments, provide for conditional expression, and so on.
Therein lies a huge opportunity to improve the immune system over the natural immune system response, where usually responses are shut down in the context of the tumor environment.
Another possibility is the evolution of using non-autologous cells. There have been examples from the Great Ormond Street Hospital in London, where they are testing third-party T cells and editing out the endogenous T-cell receptor. I think there will be many opportunities with induced pluripotent stem cells to make various immune cells such as T cells, natural killer cells, macrophages, and so on, and these will be genetically pliable and synthetically enhanced.
Additionally, there are already some interesting trials where oncolytic viruses have shown a strong synergy and potential with engineered T cells. I think various oncolytic viruses can be made and used in many applications in cancers.
It is really exciting in the field now, because T cells are pliable for genetic manipulation and yet they seem to have a special resistance to transformation so that they have been very, very safe for genetic modification. I think engineered T cells will lead the way in a number of approaches using other cell types that will later become in vivo direct approaches where there is no ex vivo cell culture.