Immunotherapy of Neuroblastoma: Facts and Hopes

While the adoption of multimodal therapy including surgery, radiation, and aggressive combination-chemotherapy has improved outcomes for many children with high-risk neuroblastoma, we appear to have reached a plateau in what can be achieved with cytotoxic therapies alone. Most children with cancer, including high-risk neuroblastoma, do not benefit from treatment with immune-checkpoint-inhibitors (ICI) that have revolutionized the treatment of many highly immunogenic adult solid tumors. This likely reflects the low tumor mutation burden as well as the downregulated MHC-I that characterizes most high-risk neuroblastomas. For these reasons, neuroblastoma represents an immunotherapeutic challenge that may be a model for the creation of effective immunotherapy for other "cold" tumors in children and adults that do not respond to ICI. The identification of strong expression of the disialoganglioside, GD2, on the surface of nearly all neuroblastoma cells provided a target for immune recognition by anti-GD2 mAbs which recruit Fc-receptor-expressing innate immune cells that mediate cytotoxicity or phagocytosis. Adoption of anti-GD2 antibodies into both upfront and relapse treatment protocols has dramatically increased survival rates and altered the landscape for children with high-risk neuroblastoma. This review describes how these approaches have been expanded to additional combinations and forms of immunotherapy that have already demonstrated clear clinical benefit. We also describe the efforts to identify additional immune targets for neuroblastoma. Finally we summarize newer approaches being pursued that may well help both innate and adaptive immune cells, endogenous or genetically engineered, to more effectively destroy neuroblastoma cells, in order to better induce complete remission and prevent recurrence

CAR T Cell Therapy for Neuroblastoma

Patients with high risk neuroblastoma have a poor prognosis and survivors are often left with debilitating long term sequelae from treatment. Even after integration of anti-GD2 monoclonal antibody therapy into standard, upftont protocols, 5-year overall survival rates are only about 50%. The success of anti-GD2 therapy has proven that immunotherapy can be effective in neuroblastoma. Adoptive transfer of chimeric antigen receptor (CAR) T cells has the potential to build on this success. In early phase clinical trials, CAR T cell therapy for neuroblastoma has proven safe and feasible, but significant barriers to efficacy remain. These include lack of T cell persistence and potency, difficulty in target identification, and an immunosuppressive tumor microenvironment. With recent advances in CAR T cell engineering, many of these issues are being addressed in the laboratory. In this review, we summarize the clinical trials that have been completed or are underway for CAR T cell therapy in neuroblastoma, discuss the conclusions and open questions derived from these trials, and consider potential strategies to improve CAR T cell therapy for patients with neuroblastoma

Potent antitumor efficacy of anti-GD2 CAR T cells in H3-K27M+ diffuse midline gliomas letter

Diffuse intrinsic pontine glioma (DIPG) and other diffuse midline gliomas (DMGs) with mutated histone H3 K27M (H3-K27M) 1-5 are aggressive and universally fatal pediatric brain cancers 6 . Chimeric antigen receptor (CAR)-expressing T cells have mediated impressive clinical activity in B cell malignancies 7-10, and recent results suggest benefit in central nervous system malignancies 11-13 . Here, we report that patient-derived H3-K27M-mutant glioma cell cultures exhibit uniform, high expression of the disialoganglioside GD2. Anti-GD2 CAR T cells incorporating a 4-1BBz costimulatory domain 14 demonstrated robust antigen-dependent cytokine generation and killing of DMG cells in vitro. In five independent patient-derived H3-K27M+ DMG orthotopic xenograft models, systemic administration of GD2-targeted CAR T cells cleared engrafted tumors except for a small number of residual GD2lo glioma cells. To date, GD2-targeted CAR T cells have been well tolerated in clinical trials 15-17 . Although GD2-targeted CAR T cell administration was tolerated in the majority of mice bearing orthotopic xenografts, peritumoral neuroinflammation during the acute phase of antitumor activity resulted in hydrocephalus that was lethal in a fraction of animals. Given the precarious neuroanatomical location of midline gliomas, careful monitoring and aggressive neurointensive care management will be required for human translation. With a cautious multidisciplinary clinical approach, GD2-targeted CAR T cell therapy for H3-K27M+ diffuse gliomas of pons, thalamus and spinal cord could prove transformative for these lethal childhood cancers

Tuning the Antigen Density Requirement for CAR T-cell Activity

Insufficient reactivity against cells with low antigen density has emerged as an important cause of chimeric antigen receptor (CAR) T-cell resistance. Little is known about factors that modulate the threshold for antigen recognition. We demonstrate that CD19 CAR activity is dependent upon antigen density and that the CAR construct in axicabtagene ciloleucel (CD19-CD28ζ) outperforms that in tisagenlecleucel (CD19-4-1BBζ) against antigen-low tumors. Enhancing signal strength by including additional immunoreceptor tyrosine-based activation motifs (ITAM) in the CAR enables recognition of low-antigen-density cells, whereas ITAM deletions blunt signal and increase the antigen density threshold. Furthermore, replacement of the CD8 hinge-transmembrane (H/T) region of a 4-1BBζ CAR with a CD28-H/T lowers the threshold for CAR reactivity despite identical signaling molecules. CARs incorporating a CD28-H/T demonstrate a more stable and efficient immunologic synapse. Precise design of CARs can tune the threshold for antigen recognition and endow 4-1BBζ-CARs with enhanced capacity to recognize antigen-low targets while retaining a superior capacity for persistence. SIGNIFICANCE: Optimal CAR T-cell activity is dependent on antigen density, which is variable in many cancers, including lymphoma and solid tumors. CD28ζ-CARs outperform 4-1BBζ-CARs when antigen density is low. However, 4-1BBζ-CARs can be reengineered to enhance activity against low-antigen-density tumors while maintaining their unique capacity for persistence.This article is highlighted in the In This Issue feature, p. 627

Supplemental Figure S1 from Reprogramming Cancer into Antigen-Presenting Cells as a Novel Immunotherapy

In vivo doxycycline administration results in significant TR-APC induction throughout tumors</p

Supplemental Figure S2 from Reprogramming Cancer into Antigen-Presenting Cells as a Novel Immunotherapy

In vivo TR-APC induction results in no observable off-target toxicity</p