A pair of new studies from researchers at the Abramson Cancer Center of the University of Pennsylvania are shedding light on why patients with advanced chronic lymphocytic leukemia (CLL) respond or do not respond to chimeric antigen receptor (CAR) T-cell therapy. Although CAR T-cell therapy is showing impressive results in the treatment of most patients—over 90%¹—with advanced acute lymphoblastic leukemia (ALL), with overall remission rates of over 80% within the first 3 months of treatment,² just a quarter of patients with CLL experience a durable response to the therapy.³

In one study, the researchers analyzed data from 41 patients with advanced, heavily pretreated, and high-risk CLL who had received at least one dose of CD19-directed CAR T cells (CTL019). They found that CTL019 cells from complete responders to the therapy were enriched in early memory-related genes and possessed the interleukin-6 (IL-6)/STAT3 signature gene; and the CTL019 produced higher levels of STAT3-signaling cytokines. The researchers also identified a strong positive correlation between serum IL-6 levels and CAR T-cell expansion in the patients. Importantly, the expansion and persistence of CTL019 cells were predictors of therapeutic response and seemed to be responsible for tumor control.

Furthermore, the analysis of premanufacturing T cells from complete responders revealed a strong predictor of sustained remission, and these patients had healthier early memory killer T cells marked by the expression of CD27 as well as the absence of CD45RO. In contrast, T cells from nonresponders expressed genes involved in late T-cell effector differentiation, aerobic glycolysis, exhaustion, and apoptosis, diminishing the T cell’s ability to expand and “go after” the cancer.⁴

In the second study, the researchers analyzed data from a patient with advanced CLL who went into complete remission because of a single CAR T cell and the cells it produced as it multiplied. The patient, now 83, has remained in remission for 5 years.⁵

Jan Joseph Melenhorst, PhD

Over the past year, the U.S. Food and Drug Administration (FDA) has approved two CAR T-cell therapies: tisagenlecleucel (Kymriah) for the treatment of relapsed or refractory pediatric and young adult ALL and adult patients with relapsed or refractory large B-cell lymphoma after two or more lines of systemic therapy; and axicabtagene ciloleucel (Yescarta) for the treatment of several types of relapsed or refractory large B-cell non-Hodgkin lymphomas in patients who have not responded to or who have relapsed after at least two other types of treatment. The FDA has not yet approved this therapy for CLL.

The ASCO Post talked with the senior author of these studies, Jan Joseph Melenhorst, PhD, Director of Product Development and Correlative Sciences Laboratory and Adjunct Associate Professor of Pathology and Laboratory Medicine in the Department of Pathology and Laboratory Medicine at the Perelman School of Medicine as well as a member of the Center for Cellular Immunotherapies at the University of Pennsylvania, about the findings from his research and how they may inform patient selection for cellular therapy as well as improve survival outcomes for more patients.

Generating New Memory T Cells

Please talk about the role of the IL-6/STAT3 signaling pathway as a predictor of how well patients with CLL are likely to respond to CAR T-cell therapy.

We think the IL-6/STAT3 pathway is active in the generation and maintenance of memory T cells. An important feature of one of the two arms of our immune system, the adaptive arm, is that after an encounter with, say, a viral pathogen, a small portion of the immune cells that fought off the invaders will persist and, in essence, “remember” that it saw this bug. This means the next time the same pathogen tries to invade the body, the immune system “remembers” and attacks it before the person becomes very sick.

This principle also applies to CAR-engineered T cells, as we showed in our previous study.⁶ In our current study, we have now demonstrated that in patients whose CAR T cells are effective cancer killers, those cells exhibit the gene signature IL-6/STAT3 pathway. Our data, and those from others, suggest that this pathway is important for sustained tumor control. The induction of this statutory pathway not only might indicate a demarcation of less-differentiated cells in the CAR T-cell product, but it also may be functionally important for their expansion and persistence after infusion into a patient.

Maintaining Sustained Remissions

Of the patients in your study, 26% responded to the CAR T-cell therapy. How long did their remissions last?

Our study was launched in 2010. I’m writing a paper now with the principal investigator, Dr. David Porter, analyzing the response of the first two patients treated back then, and both still have detectable functional CAR T cells and no detectable leukemia. It is pretty amazing that CAR T-cell therapy is not like other drug therapies that eventually get washed out; it is a living drug that forms a memory pool and keeps depressing malignancies. I think this memory pool is the key to maintenance of sustained remissions.

Disrupting TET2 Gene Promotes Therapeutic Efficacy

Please talk about your patient with CLL who, unexpectedly, at the peak of his response to CAR T-cell therapy experienced complete remission. How surprising was that finding?

We treat so many patients with this therapy, and as we discussed about the findings from our study of response and resistance to CD19 CAR T-cell therapy, we now have a general picture of who is likely to respond and not respond and have learned about common patterns. We know what it takes for a patient to respond to this living drug therapy, and under what circumstances it is most likely to fail, but we also see instances of unusual cases, outliers, and this particular patient was interesting because he underwent two infusions of CTL019 cells and initially did not respond or had a partial response that didn’t persist. However, 2 months after the second infusion, there was antitumor activity in the peripheral blood, lymph nodes, and bone marrow, and he experienced a complete response. His most recent long-term follow-up evaluation showed the presence of CAR T cells in the peripheral blood, ongoing B-cell aplasia, and no evidence of circulating disease or bone marrow infiltration.

We learned that we need only one single cell to drive a durable response and that TET2 modification may be useful for improving cellular therapy as well as other immunotherapies.

— Jan Joseph Melenhorst, PhD

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To learn why he didn’t initially respond to the therapy, we did deep sequencing of the T-cell beta repertoire. Subsequent analysis revealed that 94% of the CD8-positive “killer” CAR T-cell repertoire consisted of a single clone in which lentiviral vector–mediated insertion of the CAR transgene disrupted the methylcytosine dioxygenase TET2 gene. We did more digging and found once the TET2 gene was disrupted, it enabled a single cell—only one, imagine that, David vs an army of Goliaths—to eradicate the tumor without ever running out of steam. Quite remarkable. The biology of this response is so rich that it will not only facilitate cell therapy innovation, but will also provide questions, answers, and many more questions to answer with translational relevance.

What did the experience with this patient tell you about how CAR T-cell therapy could be made more effective for more patients, especially those who have undergone multiple prior therapies and may not have enough of their own healthy T cells to kill their cancer?

We learned that we need only one single cell to drive a durable response and that TET2 modification may be useful for improving cellular therapy as well as other immunotherapies. The following questions we are now pursuing in the laboratory: What does modulation of the TET2 gene do? Does it actually reprogram the T cells or keep the good quality they have so they never get exhausted? What does this mean for nonresponding patients? At this point, we don’t have any answers, but we are close, very close. Of course, we are also looking for ways to translate these findings into a better therapy for all, which is the beauty of translational research: it always has the patient in mind. Imagine that this unique case, this outlier, becomes a paradigm in CAR T-cell manufacturing. That’s where our work is headed.

Determining Appropriate Dosing

Typical CAR T-cell therapy includes three infusions with increasing doses. Your patient went into complete remission after just two doses because of a single cell. How might the findings from your research inform CAR T-cell therapy approaches in the future, including dosing?

It is possible, and I think likely, that in the future we will be able to do what I like to call precision CAR T-cell manufacturing for patients with leukemias and for other diseases as well; we would take the patient’s T cells, add specific edits, and infuse the cells into the patient to enable better control over dosing, efficacy, side effects, and therapy predictability. And then the management of the cancer becomes easier, too, because we will have a better understanding of what to expect.

Using Gene Therapy to Treat Solid Tumors

How might your discovery of a biomarker approach to determining likely responders to CAR T-cell therapy inform how this therapy could be made effective in the treatment of solid tumors?

We haven’t explored that yet, but I have started collaborative talks with some of my colleagues here to investigate the

CAR T-cell therapy is a living drug that forms a memory pool. I think this memory pool is the key to maintenance of sustained remissions.

— Jan Joseph Melenhorst, PhD

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connection. What we are currently doing is looking at this biomarker in other hematologic cancers, including ALL, multiple myeloma, and non-Hodgkin lymphoma. Solid tumors present an additional challenge: the tumor microenvironment. Effective treatment of this group of cancers may require additional attention with combination chemotherapies and other therapies to boost T-cell efficacy.

Reducing the Cost of Cancer Care

Currently, CAR T-cell therapies such as tisagenlecleucel and axicabtagene ciloleucel are approved only in the third-line setting. Do you see a possibility that they could be moved to second-line therapy, thereby reducing overall costs and improving the potential for cure?

I can actually see CAR T-cell therapy becoming a first-line therapy for B-cell malignancies at some point. We are getting better

at treating patients at earlier stages of their disease, when the tumor has not evolved so much and cure is possible; this is the challenge in treating any cancer. We can only be more effective if we can also identify cancers at a much, much earlier stage; the synergy between advanced therapies and early detection is critical. If we can identify patients with early-stage disease and treat them, it will be possible to replace allogeneic transplantation with CAR T-cell therapy, but that is a long-term goal. ■

DISCLOSURE: Dr. Melenhorst holds patents related to CTL019 cell therapy.

REFERENCES

1. Maude SL, Frey N, Shaw PA, et al: Chimeric antigen receptor T cells for sustained remissions in leukemia. N Engl J Med 371:1507-1517, 2014.

2. Maude SL, Laetsch TW, Buechner J, et al: Tisagenlecleucel in children and young adults with B-cell lymphoblastic leukemia. N Engl J Med 378:439-448, 2018.

3. Porter DL, Hwang WT, Frey NV, et al: Chimeric antigen receptor T cells persist and induce sustained remissions in relapsed refractory chronic lymphocytic leukemia. Sci Transl Med 7:303ra139, 2015.

4. Fraietta JA, Lacey SF, Orlando EJ, et al: Determinants of response and resistance to CD19 chimeric antigen receptor (CAR) T cell therapy of chronic lymphocytic leukemia. Nat Med 24:563-571, 2018.

5. Fraietta JA, Nobles CL, Sammons MA, et al: Disruption of TET2 promotes the therapeutic efficacy of CD19-targeted T cells. Nature 558:307-312, 2018.

6. Kalos M, Levine BL, Porter DL, et al: T cells with chimeric antigen receptors have potent antitumor effects and can establish memory in patients with advanced leukemia. Sci Transl Med 3:95ra73, 2011.