Glioblastoma is a highly aggressive primary malignant tumor with a <4% 5-year survival rate. Standard treatment is surgery to remove as much of tumor as possible (surgical resection) followed by radiation and, a DNA methylating agent. Options are extremely limited for recurring tumors.
This answer highlights immunotherapies for glioblastoma. Don’t know about biggest but currently four major research approaches dominate glioblastoma immunotherapy and likely will do so in the near future.
- Heat shock protein vaccines
- Peptide immunotherapy
- Dendritic cell (DC) vaccines
- Oncolytic viruses
Heat shock protein vaccines
- Based on Pramod K. Srivastava’s novel finding that heat shock proteins drive tumor-specific immune responses (1).
- Heat shock proteins function as chaperones to proteins, helping in their proper folding and secretion.
- Heat shock proteins are also immunogenic, capable of driving immune responses against their cargo.
- Among the proteins expressed by tumors are tumor-specific proteins. Thus, heat shock proteins purified from tumor cells would be associated with tumor-specific antigens.
- Most commonly used heat shock protein in glioblastoma vaccines is HSP 96, a 96-kilodalton protein.
- Most prolific in this field are Andrew T. Parsa, his colleagues and collaborators.
- A Phase I trial (2) with HSP-96 glioblastoma vaccine (HSPPC-96; Prophage) showed it drove anti-glioblastoma immunity in 11/12 patients. Tumor biopsies showed T and NK cell infiltration.
- A Phase II trial (3) with 41 patients bolstered Phase I results with similar findings.
- Another HSP, HSP47, could be another glioblastoma target for two reasons (4).
- Expressed at high levels in glioblastoma but not in normal tissue.
- Patients with anti-HSP47 cytotoxic T cell response had better overall and progression-free survival.
Drawbacks of Heat shock protein vaccines (5)
- Surgery necessary. This is an individualized Rx approach. Need as much of the tumor as possible since each patient’s tumor itself is the source of their vaccine, HSPPC-96.
- Surgery being necessary means that only a small subset of patients with recurrent glioblastoma are eligible.
- If surgery yields insufficient tumor tissue, may not be possible to generate enough vaccine from it.
- Need to wait at least 1 month post-surgery to start vaccine Rx, time it takes to manufacture patient-specific vaccine.
- Survival outcomes currently not better than with standard anti-glioblastoma Rx, namely, lomustine or bevacizumab.
- Personalized vaccine, i.e., expensive.
This table summarizes Glioblastoma heat shock protein vaccines (6).
- Most prolific in this field are John H. Sampson, his colleagues and collaborators.
- Current approach capitalizes on the observation that >90% glioblastomas, and not normal brain tissue, express Cytomegalovirus phosphoprotein 65 (pp65) RNA (7, 8, 9, 10).
- In their latest study (11), they preconditioned glioblastoma patients with either autologous mature dendritic cells (DCs) or tetanus/diphtheria toxoid one day before vaccinating with autologous DCs pulsed with Cytomegalovirus phosphoprotein 65 (pp65) RNA.
- Improved survival in patients preconditioned with tetanus/diphtheria toxoid.
- Caveats of this study were two-fold
- Unclear why tetanus/diphtheria toxoid preconditioning was compared to unpulsed DCs.
- Paper was under review with Nature for >1 year. Typically such long reviews suggest considerable tweaks were necessary to make data publication-worthy, meaning that original study data were weak and that reviewers demanded further experiments and/or additional controls.
Drawbacks of Peptide immunotherapy
- Majority of glioblastoma peptide vaccines are restricted to the MHC haplotype, HLA-A*02 (12, 13). Won’t work with glioblastoma patients with other MHC haplotypes.
- There is need to identify glioblastoma peptides presented by other prevalent MHC haplotypes.
- If and when tumor recurs, need to use different Rx approach. For example, earlier approaches targeted EGFRvIII (Epidermal Growth Factor Receptor), highly expressed on glioblastoma, i.e., a quasi-tumor-specific antigen. After this immunotherapy, 82% of patients with recurrence lost EGFRvIII expression (14). Implies two things
- Peptide vaccine successfully targeted EGFRvIII+ tumor cells.
- Peptide vaccine drove selective expansion of EGFRvIII- tumor cells.
- Suggests this Rx has potential to drive expansion of tumor escapees.
- Personalized immunotherapy, i.e., expensive.
Dendritic cell (DC) vaccines
- In contrast to glioblastoma cells, which are poor at inducing immunity (15), DCs are antigen presenting cells necessary for fully activating CD4 and CD8 T cells.
- DCs shown to be excellent in presenting glioblastoma-derived antigens to T cells, activating anti-glioblastoma cytotoxic T cells and inducing tumor cell death (16, 17).
- Similar to heat shock protein vaccines and peptide immunotherapy, this is also personalized medicine.
- Purify patient’s DCs from circulating blood, culture them during which they are pulsed/loaded with tumor lysates or peptides and then re-injected back into the patient.
- DC vaccines are among the most prevalent glioblastoma investigational immunotherapies under development (18, 19).
- Years of fine-tuning later, a Phase I trial revealed what’s critical for DC vaccines to drive strong anti-glioblastoma immunity, namely, tumor lysates. Compared patients (n=28) treated with autologous DCs pulsed with autologous tumor lysates to those pulsed with synthetic glioblastoma antigen peptides (n=6). The former drove stronger anti-tumor immunity (20). This would fit with immunological predictions since tumor lysates would contain additional potential targets of strong anti-glioblastoma immunity, namely as-yet unidentified antigens,, i.e., a polyvalent response unlike defined peptides.
- Another line of investigation with DC vaccines. What are the biomarkers that correspond to effective anti-glioblastoma immunity? Phospho-STAT (21)? CTLA-4 (22)?
Common drawbacks to HSP, peptide and DC vaccines
- Need tumor MHC class I expression.
- 30 to 60% of glioblastoma population observed to be MHC class I- (23), i.e., potential that much of tumor won’t be targeted by such immunotherapy.
- Targeting a single antigen may lead to tumor escapees so multiple targets, even multiple approaches may be necessary (18).
- An oncolytic virus is capable of replicating (24, 25).
- Engineered to selectively target and replicate in tumor cells. How (26)?
- Strategic mutations or deletions in viral genome that enhance their capacity to replicate within tumor cells while inhibiting the same in normal cells.
- Engineer virus to express tumor-antigen specific receptor, taking advantage of tumor-specific antigens expressed on tumor cell surface.
- Engineer virus to express viral genes under the control of promoters that will only be functional within tumor cells.
- Cause tumor cell death, either directly or indirectly by making the virus-infected tumor cell a target of immune cell-mediated responses.
Drawbacks of Oncolytic viruses
- Once virus is delivered to tumor, usually by injecting directly into it, host immune response kicks in to rapidly inactivate it before it can trigger sufficient tumor cell death.
- In order for the virus to make the tumor an excellent target of the ensuing anti-virus immunity, it needs to spread uniformly throughout the tumor. However, tumor is not simply a homogeneous bag of cells. It has a complicated microenvironment consisting of areas of lower oxygen tension (hypoxia) and unique extracellular matrix, which act as barriers limiting spread of virus within tumor.
- Preclinical models used thus far have been poor in predicting what would happen in human. Why? They grafted human glioblastoma into mice that lacked CD4 T cells (immunodeficient). Since such models lack one of the most important arms of immune function, they couldn’t recapitulate likely scenario in human patients.
- Which virus to use? Answer not so easy (27). Need to be validated in preclinical models first but several problems ensue
- Species-specific virus effects. Virus may not have same effect in human as it does in mouse.
- HSV, Adeno, Polio are attenuated (weak) in mice but potent in humans.
- OTOH, Sindbis, pseudorabies and Vesicular Stomatitis viruses are pathogenic in mice, and not known to infect humans. When such viruses move to clinical trials after being engineered for anti-glioblastoma activity in mice, they create novel safety concerns.
HSV (Herpes Simplex virus) has progressed furthest as an anti-glioblastoma oncolytic virus Rx. The following figures (25, 26) summarize the what and how of anti-glioblastoma oncolytic HSV and other viruses.
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- Crane, Courtney A., et al. “Individual patient-specific immunity against high-grade glioma after vaccination with autologous tumor derived peptides bound to the 96 KD chaperone protein.” Clinical Cancer Research 19.1 (2013): 205-214.
- Bloch, Orin, et al. “Heat-shock protein peptide complex–96 vaccination for recurrent glioblastoma: a phase II, single-arm trial.” Neuro-oncology 16.2 (2014): 274-279.
- Wu, Zhe Bao, et al. “CTL responses to HSP47 associated with the prolonged survival of patients with glioblastomas.” Neurology 82.14 (2014): 1261-1265.
- Chamberlain, Marc C. “Is there a role for vaccine-based therapy in recurrent glioblastoma?.” Neuro-oncology 16.5 (2014): 757.
- See, Alfred P., et al. “Heat shock protein-peptide complex in the treatment of glioblastoma.” (2011): 721-731.
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- Mitchell, Duane A., et al. “Tetanus toxoid and CCL3 improve dendritic cell vaccines in mice and glioblastoma patients.” Nature 519.7543 (2015): 366-369.
- Phuphanich, Surasak, et al. “Phase I trial of a multi-epitope-pulsed dendritic cell vaccine for patients with newly diagnosed glioblastoma.” Cancer Immunology, Immunotherapy 62.1 (2013): 125-135.
- Neidert, Marian Christoph, et al. “Natural HLA class I ligands from glioblastoma: extending the options for immunotherapy.” Journal of neuro-oncology 111.3 (2013): 285-294.
- Sampson, John H., et al. “Immunologic escape after prolonged progression-free survival with epidermal growth factor receptor variant III peptide vaccination in patients with newly diagnosed glioblastoma.” Journal of Clinical Oncology 28.31 (2010): 4722-4729.
- Ishikawa, Eiichi, et al. “Clinical trial of autologous formalin‐fixed tumor vaccine for glioblastoma multiforme patients.” Cancer science 98.8 (2007): 1226-1233.
- Cohn, Lillian, and Lélia Delamarre. “Dendritic cell-targeted vaccines.” Frontiers in immunology 5 (2014).
- Anguille, Sébastien, et al. “Clinical use of dendritic cells for cancer therapy.” The lancet oncology 15.7 (2014): e257-e267.
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- Prins, Robert M., et al. “Comparison of glioma-associated antigen peptide-loaded versus autologous tumor lysate-loaded dendritic cell vaccination in malignant glioma patients.” Journal of immunotherapy (Hagerstown, Md.: 1997) 36.2 (2013): 152.
- Everson, Richard G., et al. “Cytokine responsiveness of CD8 (+) T cells is a reproducible biomarker for the clinical efficacy of dendritic cell vaccination in glioblastoma patients.” J Immunother Cancer 2.10 (2014).
- Fong, Brendan, et al. “Monitoring of regulatory T cell frequencies and expression of CTLA-4 on T cells, before and after DC vaccination, can predict survival in GBM patients.” PloS one 7.4 (2012): e32614-e32614.
- Yamanaka, Ryuya. “Cell-and peptide-based immunotherapeutic approaches for glioma.” Trends in molecular medicine 14.5 (2008): 228-235.
- Russell, Stephen J., Kah-Whye Peng, and John C. Bell. “Oncolytic virotherapy.” Nature biotechnology 30.7 (2012): 658-670.
- Ning, Jianfang, and Hiroaki Wakimoto. “Oncolytic herpes simplex virus-based strategies: toward a breakthrough in glioblastoma therapy.” Frontiers in microbiology 5 (2014).
- Dey, Mahua, et al. “Antiglioma oncolytic virotherapy: unattainable goal or a success story in the making?.” Future virology 8.7 (2013): 675-693.
- Wollmann, Guido, Koray Ozduman, and Anthony N. van den Pol. “Oncolytic Virus Therapy of Glioblastoma Multiforme–Concepts and Candidates.” Cancer journal (Sudbury, Mass.) 18.1 (2012): 69.