Lessons learned from phase 3 trials of immunotherapy for glioblastoma: Time for longitudinal sampling?

Abstract

Glioblastoma (GBM)'s median overall survival is almost 21 months. Six phase 3 immunotherapy clinical trials have recently been published, yet 5/6 did not meet approval by regulatory bodies. For the sixth, approval is uncertain. Trial failures result from multiple factors, ranging from intrinsic tumor biology to clinical trial design. Understanding the clinical and basic science of these 6 trials is compelled by other immunotherapies reaching the point of advanced phase 3 clinical trial testing. We need to understand more of the science in human GBMs in early trials: the "window of opportunity" design may not be best to understand complex changes brought about by immunotherapeutic perturbations of the GBM microenvironment. The convergence of increased safety of image-guided biopsies with "multi-omics" of small cell numbers now permits longitudinal sampling of tumor and biofluids to dissect the complex temporal changes in the GBM microenvironment as a function of the immunotherapy.

Keywords: image-guided biopsy; multi-omics; phase 0 clinical trial; tumor microenvironment; window of opportunity clinical trial.

Figure 1.

“Window of opportunity” (top row) versus “longitudinal sampling” clinical trial. In the window of opportunity trial (top row), a therapeutic intervention is performed before tumor resection or biopsy. The advantages of this approach are: 1—the therapy can be easily incorporated as part of standard surgery or biopsy; 2—if the surgery is a craniotomy, large amounts of tissue is available for analysis; and 3—relatively simple therapeutic questions can be answered, such as the presence or absence of target engagement. The disadvantages are: 1—only a single timepoint for tissue analyses is available; 2—this timepoint of analysis is early (days to weeks) after the therapeutic intervention; 3—correlations between the therapy’s effect on the GBM (1 timepoint) and biofluid assays (multiple timepoints) must be assumed. In the longitudinal sampling trial, multiple timepoint image-guided biopsies are performed before, during, and/or after the therapeutic intervention. The advantages of this approach are: 1—temporal analyses of therapeutic targets and/or of changes in the TME can be carried out over several weeks to months; 2—temporal correlations between changes in the tumor and in assayed biofluids can be carried out; 3—mechanisms of eventual tumor evasion from the therapy can be understood. The disadvantages of this approach are: 1—the image-guided biopsies are research and not standard interventions and thus the trial can be too expensive for the routine research-based funding mechanisms; 2—there is, albeit low, surgical risk with multiple timepoint biopsies; 3—there can be patient discomfort undergoing multiple procedures over time.

Figure 2.

Layers of “omics” analyses of small amounts of tissues available via an image-guided biopsy. A small amount of tumor tissues can now be analyzed via several layers of “omics.” At the DNA level, specific or whole exome sequencing, chromosomal alterations, and DNA methylation analyses are routinely performed. At the RNA level, whole and single-cell RNA sequencing and spatial transcriptomics can be utilized. At the protein level, proteome sequencing, phosphoproteomics, immunopeptidomics, and anatomical localization technologies (CODEX, CyCIF, and others) can be used. At the immune cell level, TCR sequencing can be used to understand the evolution of T-cell responses. Coupled with CITE-Seq this can also map the regional changes in T-cell clonotype evolution.