Of the 11 patients treated, 2 achieved a partial response, 1 of whom is now in complete remission (CR) after receiving the second dose of CAR-NKT cell infusion, according to Andras Heczey, MD, lead author of the study and an assistant professor in pediatrics. Oncology at Baylor College of Medicine. In addition, 4 patients had stable disease and 5 experienced disease progression.
“CAR NKTs can be effectively manufactured on a clinical scale,” said Heczey. “These cells are safe and there is evidence of in vivo expansion and localization to metastatic sites. Now we see tumor regression in 3 patients, including 1 durable CR. “
CAR T cell therapy has shown good clinical results in multiple lymphoid malignancies, and this modality has changed the standard of care for many patients with these cancers. However, regarding the treatment of solid tumors, strategies with these therapies have yet to be fine-tuned.
“Maybe a way to improve [these strategies] is by looking at specific subsets of lymphocytes that may have better anti-tumor properties for solid tumors than general bulk expansion of αβ-T cells, ”said Heczey. “We believe NKT cells are such a subset.”
T cells recognize peptides presented by the MHC class I and II molecules and they have a variety of T cell receptors that allow them to do this. In contrast to these T cells, NKT cells can recognize hydrophobic molecules, such as glycolipids, presented by the CD1d molecules. In addition, according to Heczey, they express an invariant T cell receptor (iTCR) containing the Vα24 chain, which is preferentially accompanied by the β11 chain.
“We all share this iTCR in our NKT cells, which is important because they can regulate the same processes in all of us,” Heczey explained. “As the field moves towards standard approaches, these NKTs have no potential for induced graft-vs-host disease.”
In terms of their potential efficacy, NKTs move in a chemokine-dependent manner to solid tumors, especially neuroblastoma, in a CCL2 / CCL20-dependent manner. More importantly, according to Heczey, once at the tumor site, the NKTs target tumor-associated macrophages (TAMs) via a CD1d / iTCR interaction; CD1d is expressed on TAMs. Through this indirect mechanism, the infiltration of NKTs into neuroblastoma tissues has been associated with improved outcomes.
In addition, preclinical data have shown that NKTs engineered with a CAR expressing GD2 can directly and indirectly target tumor cells by destroying tumor-supporting TAMs; this has been demonstrated in neuroblastoma models.
These results were the rationale for starting the first phase 1 study in humans, which aimed to investigate genetically engineered NKT cells expressing optimized GD2-CAR and IL-15 to treat relapsed / refractory neuroblastoma in children. treat the autologous setting. “IL-15 was included because this cytokine can enhance the persistence of expansion and, consequently, the anti-tumor properties of NKTs in the preclinical setting,” noted Heczey.
To be eligible for enrollment, patients had to have a confirmed recurrent / refractory high-risk neuroblastoma, a life expectancy of at least 12 weeks, and between 1 and 21 years of age.2
The study utilized a 3 + 3 dose escalation design and patients were treated with 4 dose levels: dose level 1 of 3 x 106, dose level 2 of 1 x 107, dose level 3 of 3 x 107, and dose level 4 of 1 x 108. In addition, a standard lymphodepletion regimen and this included cyclophosphamide given at a dose of 500 mg / m2 on days -4, -3 and -2, and intravenous fludarabine at a dose of 30 mg / m2 on days -4 and -3, prior to cell infusion .
On day 0, patients received the CAR-NKT cell infusion and were evaluated weekly in the outpatient setting. At week 2 after infusion, the patients were biopsied and at week 4, the patients underwent imaging and evaluation of response to therapy.
“The safety assessment focuses on the first 28 days after the infusion,” added Heczey.
The primary endpoint of the study is safety, while other clinical endpoints included CAR-NKT cell persistence and trafficking, as well as anti-tumor responses.
Of the 11 patients enrolled in the study and treated so far, the median age was 7 years (range 2-12) and all had relapsed / refractory, high-risk stage IV neuroblastoma. In addition, all patients were able to receive the full prescribed lymphodepletion regimen and the complete CAR-NKT cell infusion.
“NKTs are a small subset of peripheral lymphocytes … so there was the question of whether the right amount of NKTs could be generated ex vivo,” said Heczey. “So far we have been able to produce these products with a high purity, up to 98% and sometimes even higher, with a nice CAR transduction efficiency.”
With this, the absolute number of NKTs that has expanded, even in smaller children, is approaching about 1 billion cells, according to Heczey. In the beginning, researchers planned these expansions to account for approximately 21 days of production. “Now we are only 14 days or less and we are still generating a large amount of very powerful NKT cells,” said Heczey.
To measure the heterogeneity of products between patients and differences in anti-tumor properties, NKT cells were repeatedly exposed to tumor cells in a co-culture assay. The CAR-NKT cells were replated several times with neuroblasts during this process. Researchers then evaluated their ability to expand and maintain their cytolytic capabilities and measured the expression of depletion markers.
“Most CAR-NKT products can maintain their ability to kill even after 5 rounds of co-culture,” noted Heczey. “However, there are some where the ability to kill diminishes significantly by the fifth round. If you look at the fold extension, there are clear differences between these products. Perhaps the biggest fold extension, for our product, is at the beginning, as we would expect. “
In terms of depletion markers in the CAR-NKT products, differences were seen in the proportion of TIM-3 and PD-13 dual positive populations, suggesting that those cells may be more depleted than others, Heczey explained.
After infusion, CAR-NKT cells expanded in the peripheral blood of patients. In addition, the absolute number of CAR-NKT cells varied significantly from patient to patient and did not appear to be dose level dependent. In all but one of the patients enrolled in the study, the frequency of CAR-NKT cells according to Heczey was higher than before the infusion. In addition, CAR-NKT cells were detected in peripheral blood in all patients, peaking at around week 2 and week 3 after infusion. In addition, at all dose levels, CAR-NKT cells were found in the neuroblastoma tumor sites, as well as in bone marrow biopsies.
In terms of GD2 expression in the CAR-NKT cells, 2 patients were found to have down-regulated expression. Researchers believe this loss of expression could have occurred prior to enrollment to study, but there are no biopsies to confirm this, Heczey said.
In addition to CAR-NKT cell expansion, tumor burden, as measured by Curie scores, was also found to be associated with anti-tumor activity in patients; those with a high area under the curve / Curie score were those who experienced anti-tumor activity.
In terms of safety, no dose-limiting toxicities were observed in the first 28 days after CAR-NKT infusion. Most of the Grade 3 or 4 adverse reactions (AEs) reported were mostly haematological, which is consistent with what has been observed in patients who received a cyclophosphamide / fludarabine lymphodepletion regimen, according to Heczey. The most common Grade 4 adverse reactions were neutropenia (n = 10/11), lymphopenia (n = 6/11), leucopenia (n = 6/11), and thrombocytopenia (n = 2/11).
Heczey A, Courtney A, Lui K, et al. Natural killer T cells expressing GD2-CAR and IL-15 are safe and can cause complete remission in children with recurrent neuroblastoma – an initial phase 1 study in humans . Presented at: 2021 Annual Meeting of the American Society of Gene and Cell Therapy; May 11-14, 2021; Virtual. Summary 198.GD2-specific CAR and interleukin-15 expressing autologous NKT cells to treat neuroblastoma in children (GINAKIT2). ClinicalTrials.gov. Updated January 15, 2021. Accessed May 14, 2021. https://clinicaltrials.gov/ct2/show/NCT03294954