H3K27M+ Diffuse Intrinsic Pontine Gliomas Derive Benefit from GD2-Directed CAR T-cell Therapy

Children and young adults with H3K27M positive diffuse intrinsic pontine gliomas and spinal diffuse midline gliomas saw a clinical benefit in treatment with GD2-targeted chimeric antigen receptor T cell therapy.

A durable benefit was observed with GD2-targeted chimeric antigen receptor (CAR) T cells (GD2-CART) for children and young adults with H3K27M diffuse intrinsic pontine gliomas (DIPG) and spinal diffuse midline gliomas (DMG), according to a presentation of the American Association for Cancer Research (AACR) Annual Meeting 2022.1

“This is a really important series because it is one of the first to show sustained benefit in multiple individuals with solid tumors and clearly in incurable solid tumors,” said Robbie G. Mazner, MD, in his presentation at AACR. “We have identified the maximum tolerated dose of intravenously infused GD2 CAR T cells [as 1e6/kg]and that was around dose-limiting toxicities due to the high-grade cytokine release syndrome [CRS]†

DIPG and other H3K27M mutated DMGs are universally lethal pediatric tumors of the central nervous system. Disialoganglioside GD2 is specifically highly expressed on H3K27M mutated glioma cells and has demonstrated promising preclinical efficacy of GD2 CAR T cells.

A mouse model found that most subjects given GD2 CAR T cells survived compared to those given CD19 CAR T cells.2

“GD2 is identical between mouse and human and is expressed at low levels on neurons. Despite that, the neurons appear normal, and we have seen no evidence that the GD2 CAR T cells attacked normal nerve cells expressing low levels of GD2.”

In addition, GD2 CAR T cells are associated with fatal hydrocephalus in some models. The toxicity developed by the mice was due to the tumors and therefore the first-in-human phase I clinical trial (NCT04196413) was set up to test whether GD2 CAR T cells can be successfully made from immune cells collected from children. and young adults with H3K27M mutant DIPG or spinal H3K27M mutant DMG.

Eligibility to enroll was open to patients ages 2-30 who were located in the United States. Other requirements were a tissue diagnosis of H3K27M mutated DIPG with radiographically apparent tumor confined to the brainstem, or tissue diagnosis of H3K27M mutated DMG of the spinal cord, at least 6 weeks after completion of first-line radiation therapy, at least 3 weeks after chemotherapy or 5 half-lives, and an ECOG performance status of 0 or 1. H3K27M mutant testing will be conducted as part of standard care prior to enrollment.

A total of 13 subjects were enrolled and 11 were treated, including 4 in dose level 1 and 9 in dose level 2. Two subjects were removed prior to treatment due to rapid progression. The median number of intracerebroventricular (ICV) infusions between patients was 5 and the median month from diagnosis was also 5.

The study design was a standard 3+3 dose increase administered to subjects with DIPG testing GD2 CAR T cells in subjects with H3K27M mutant DIPG. Dose level 1 consisted of 1 x 10 6 CAR T cells/kg body weight, dose level 2 was 3 x 10 6 CAR T cells/kg body weight and dose level 3 was 10 x 10 6 CAR T cells/kg body weight.

Dose level 1 was studied if the first treated subject experienced dose-limiting toxicity (DLT) or if more than 2 of 6 treated subjects experienced DLT. Once the maximum tolerated dose or RP2D was determined in the dose extension of subjects with DIPG and spinal DMG, up to 20 evaluable subjects with H3K27M mutant DIPG and 10 evaluable subjects with H3K27M mutant spinal DMG would be treated at the RP2D. This includes subjects treated during dose escalation.

Primary endpoints include rate of successful production of GD2 CAR T, maximum tolerated dose, and safety with secondary endpoints including assessment of the clinical benefit of GD2 CAR T on RP2D in children and young adults with H3K27M gliomas and evaluation of safety and impact on the clinical benefit of repeated ICV administrations of GD2 CAR T

Although no DLTs were observed at dose level 1, 3 subjects received DLT at dose level 2 (2 DIPG/1 sDMG). This was due to grade 4 CRS successfully treated with tocilizumab (Actemra), anakinra, and corticosteroids. CRS occurred earlier at dose level 2 versus 1 (day 3 versus 7).

At both dose levels, all subjects showed transient symptoms related to inflammation on the tumor called Tumor Inflammation-Associated Neurotoxicity (TIAN), which was successfully treated with anakinra and, in some cases, CSF drainage and dexamethasone. No DLT occurred due to TIAN.

Ten patients reported adequate follow-up to assess benefit, with 9 patients having radiographic and/or clinical benefit after IV infusion. In addition, they received subsequent ICV GD2 CAR T infusions (median = 4 ICV infusions/pt, range 1-6). Although ICV infusions were not associated with high-grade CRS, some subjects developed transient fever, headache, meningismus, nausea and/or vomiting, and several subjects developed tumor inflammation associated with neurotoxicity.

A total of 4 patients continued to receive ICV infusions during the study and had sustained clinical and radiographic benefit at 11, 9.5, 8 and 7 months after enrollment. One participant, a 31-year-old with sDMG, experienced a near-complete (>95%) reduction in tumor volume and a 17-year-old with DIPG experienced a near-complete (>98%) reduction in the volume of a pontine tumor.

Toxicity was largely related to tumor location and was reversible with intensive supportive care. On-target, off-tumor toxicity was not observed. Overall, 3 out of 4 patients showed clinical and radiographic improvement. The pro-inflammatory cytokine levels were elevated in plasma and cerebrospinal fluid. Transcriptomic analyzes of 65,598 single cells of CAR T cell products and cerebrospinal fluid elucidate heterogeneity in response between participants and routes of administration.

“ICV treatment was tolerated at a flat dose of 30 million CAR T cells without lymphodepletion as a retreatment strategy. We are currently enrolling in an ICV arm without lymphodepletion,” added Mazner.

These early results underscore the promise of this therapeutic approach for patients with H3K27M mutated spinal cord DIPG or DMG.

References

Majzner RG, Mahdi J, Ramakrishna S, et al. Large tumor regressions in H3K27M-mutated diffuse midline glioma (DMG) after sequential intravenous (IV) and intracerebroventricular (ICV) delivery of GD2-CAR T cells. Presented at: 2022 AACR Annual Meeting; Apr 8-13, 2022; New Orleans, Louisiana. Accessed April 10, 2022. Summary CT001.GD2 CAR T cells in diffuse intrinsic pontine glioma (DIPG) and spinal diffuse midline glioma (DMG). Clinicaltrials.gov. Accessed April 10, 2022. https://bit.ly/3LPYjAA