Cancer vaccine strategies for the treatment of diffusely infiltrating gliomas

Diffusely infiltrating gliomas - including glioblastoma (GBM), isocitrate dehydrogenase (IDH) mutant gliomas, and histone 3 (H3) altered gliomas - are primary brain tumors with an invariably fatal outcome. Despite advances in the understanding of their biology, standard, targeted and immune checkpoint inhibitor immunotherapies have proven ineffective in arresting their inexorable progression and associated morbidity and mortality. Recognizing the unique aspects of the immunogenicity of cancer cells, the last decade has seen the development and evaluation of vaccine-based therapies for the treatment of solid tumors, including gliomas. Here we review the current vaccine strategies for the treatment of GBM, IDH-mutant gliomas and diffuse midline glioma H3 K27M-altered. We discuss potential benefits and challenges of vaccine therapies in these specific patient populations.

PATH-15. THE PROGNOSTIC IMPLICATION OF MGMT PROMOTER METHYLATION IN IDH-MUTANT GLIOMAS

BACKGROUND

MGMT promoter methylation in IDH-mutant gliomas was associated with improved survival in a recent study (PMID 35386566) but did not account for the updated WHO classification of CNS tumors. We evaluated the prognostic value of MGMT methylation in IDH-mutant gliomas incorporating the 2021 WHO classification.

METHODS

We retrospectively identified 431 patients with IDH-mutant gliomas treated at a single institution from 2010-2020. Kaplan-Meier method was used to estimate OS and PFS rates. Log-Rank test was used to evaluate differences between groups.

RESULTS

Median age was 36.2 years. MGMT promoter was methylated in 49.6%, unmethylated in 17.2%, partially methylated in 6.7%, and untested in 26.5%. Histological diagnosis was consistent with astrocytoma in 45.7%, oligodendroglioma in 33.9%, glioblastoma in 16.4%, and oligoastrocytoma in 4%. After accounting for 1p/19q and CDKN2A statuses, 190 patients had an integrated diagnosis of astrocytoma, grade 2 or 3; 94 had astrocytoma, grade 4; and 147 had oligodendroglioma, grade 2 or 3. There were 101 death events. Median OS was 33.36 years and median PFS was 5.67 years in MGMT methylated gliomas, compared to median OS of 12.54 years (p=0.0064) and median PFS of 3.91 years (p=0.0034) in unmethylated tumors. Upon univariate subgroup analysis, MGMT methylation was associated with significantly longer OS in histological astrocytomas, grade 2 or 4. However, when stratifying patients according to 2021 WHO classification of CNS tumors, there was no significant difference in OS between MGMT methylated and unmethylated astrocytomas or oligodendrogliomas, irrespective of WHO grade.

CONCLUSION

MGMT promoter methylation was associated with prolonged OS in histological astrocytomas, IDH-mutant. However, MGMT status did not impact survival after incorporating 2021 WHO classification of CNS tumors, suggesting that 1p/19q co-deletion and CDKN2A homozygous deletion are stronger prognostic factors in our cohort. The number of survival events was limited; larger datasets are required for more definitive conclusions.

NIMG-59. EVALUATION OF THE RESPONSE ASSESSMENT CRITERIA IN NEWLY DIAGNOSED AND RECURRENT GLIOBLASTOMA

BACKGROUND

We sought to compare the Response Assessment in Neuro-Oncology (RANO), modified RANO (mRANO), and immunotherapy RANO (iRANO) in a large population of patients with newly diagnosed (nGBM) and recurrent (rGBM) glioblastoma.

METHODS

Bidimensional measurements of enhancing disease and FLAIR sequence evaluation were performed by two independent readers on brain MRIs of consecutive patients with IDH-wildtype nGBM and rGBM treated at a single institution. Discrepancies were evaluated by a third reader. Dates of disease progression (PD) were identified using RANO, mRANO, iRANO, and other response assessment criteria variations. Spearman’s correlations between PFS and OS were calculated using iterative multiple imputations for censored observations.

RESULTS

526 nGBM and 580 rGBM cases were included. Spearman’s correlations were not significantly different between RANO and mRANO in nGBM (0.69 [95% CI 0.62 to 0.75] vs. 0.67 [0.60, 0.73]) and rGBM (0.48 [0.40, 0.55] vs. 0.50 [0.42, 0.57]). Evaluation of FLAIR did not improve the correlation in patients who received antiangiogenic therapy. Acquisition of confirmation scans was associated with increased correlation only when PD was identified within 12 weeks of completion of radiation in nGBM. The use of the post-radiation MRI as a baseline was associated with increased correlation compared to use of the pre-radiation MRI in nGBM (0.67 [0.60, 0.73] vs. 0.53 [0.42, 0.62]). The correlation with iRANO was similar to RANO and mRANO among 98 patients with nGBM and 175 patients with rGBM who received immunotherapy.

CONCLUSIONS

RANO and mRANO demonstrated similar correlations between PFS and OS. The evaluation of FLAIR can be omitted, while confirmation scans were only beneficial in nGBM in the first 12 weeks after completion of radiation. There was a trend in favor of the post-radiation MRI as the baseline scan in nGBM. The use of iRANO criteria did not add a significant benefit in patients who received immunotherapy.

Evaluation of the response assessment criteria in newly diagnosed and recurrent glioblastoma

2020

Background: The Response Assessment in Neuro-Oncology (RANO) and modified RANO (mRANO) criteria are the two most widely used criteria to evaluate treatment response in glioblastoma (GBM) clinical trials. Unlike RANO, mRANO omits the evaluation of FLAIR sequence and requires a repeat scan to confirm responses. It also uses the post-radiation (RT) MRI as a baseline MRI in the newly diagnosed setting instead of the pre-RT MRI used in RANO. We sought to compare the 2 response assessment criteria and evaluate the differences between them in a large patient population. We also sought to compare them to immunotherapy RANO (iRANO) in patients who received immunotherapy. Methods: We conducted a retrospective review of consecutive patients with newly diagnosed (nGBM) and recurrent (rGBM) IDH wild-type GBM treated at Dana-Farber Cancer Institute from 2014 to 2020. Bidimensional measurements of enhancing disease and evaluation of FLAIR sequences were performed by two independent readers on patients’ brain MRIs obtained before change of treatment, and discrepancies were evaluated by a third reader. Dates of disease progression (PD) were identified using RANO, mRANO, iRANO, and other response assessment criteria variations. Spearman’s correlations between PFS and OS were calculated using an iterative multiple imputation method to account for any right-censoring. Results: 526 and 580 patients were included in the newly diagnosed and recurrent cohorts, respectively. Spearman’s correlations were not significantly different between RANO and mRANO in the nGBM (0.69 [95% CI 0.62 to 0.75] vs. 0.67 [0.60, 0.73]) and rGBM (0.45 [0.37, 0.52] vs. 0.50 [0.42, 0.57]) cohorts. Evaluation of FLAIR sequences did not improve the correlation between PFS and OS in patients who received antiangiogenic therapy. Addition of confirmation scans was associated with stronger Spearman’s correlations only when PD was identified within 12 weeks of completion of RT in the nGBM cohort, but did not affect the Spearman’s correlations in the rGBM cohort. The use of the post-RT MRI as a baseline was associated with a higher Spearman’s correlation in nGBM than the use of pre-RT MRI (0.67 [0.60, 0.73] vs. 0.53 [0.42, 0.62]). Among 98 patients with nGBM and 175 patients with rGBM who received immunotherapy, the Spearman’s correlations (nGBM and rGBM) with iRANO (0.63 [0.44, 0.76] and 0.34 [0.17, 0.49]) were similar to RANO (0.73 [0.60, 0.82] and 0.42 [0.28, 0.54]) and mRANO (0.65 [0.48, 0.77] and 0.43 [0.28, 0.56]). Conclusions: RANO and mRANO demonstrated similar correlation between PFS and OS. The evaluation of FLAIR can be omitted, while confirmation scans appear to be only beneficial in the nGBM settings during the first 12 weeks of completion of RT. There was a nonsignificant trend in favor of the use of post-RT MRI as the baseline scan in the nGBM setting. The application of iRANO criteria did not add significant benefit in patients who received immunotherapy.

Glioblastoma with Gliomatosis Cerebri Growth Pattern Presenting as Rapidly Progressive Dementia

The differential diagnosis of rapidly progressive dementia includes neurodegenerative, toxic/metabolic, infectious, inflammatory, vascular, and malignant etiologies. This case highlights a patient with rapidly progressive cognitive decline that remained a diagnostic dilemma due to nonspecific symptoms of disorientation that progressed to persistent alteration in mental status over the span of three months. Routine laboratory testing did not help clarify the diagnosis and initial brain imaging showed only subtle abnormalities that were not commensurate with the patient’s neurologic examination. As imaging findings evolved over time to reveal a multifocal process, a biopsy was pursued, with histology consistent with infiltrating glioma and molecular testing consistent with glioblastoma. Glioblastoma with gliomatosis cerebri growth pattern should be considered on the differential diagnosis of rapidly progressive dementia in patients with multifocal imaging findings.

Evaluation and management of chimeric antigen receptor (CAR) T-cell-associated neurotoxicity

Adoptive cell therapies are a group of cancer immunotherapies that involve the infusion of engineered immune cells targeting specific tumor antigens, with chimeric antigen receptor (CAR) T cells at the vanguard of this revolution in cancer therapy. Several CAR T-cell products have been approved for the treatment of leukemia and lymphoma and many more are currently undergoing evaluation in clinical trials for the treatment of other liquid and solid malignancies. Despite their remarkable effectiveness, as with other immunotherapies, CAR T cells are frequently associated with systemic and neurologic toxicity. There has been a major effort by many institutions to develop specific protocols to guide the management of treatment-associated toxicities (eg, cytokine release syndrome [CRS]). However, neurotoxic effects of CAR T-cell therapies are more difficult to evaluate and treat, not easily lending themselves to an algorithmic approach to diagnosis and management. Given the steadily expanding use of CAR T-cell therapies for various malignancies, it is of critical importance for neuro-oncologists to be familiar with the clinical presentation and management principles of CAR T-cell-associated neurotoxicity. Here, we present key principles for the evaluation and management of patients affected by CAR T-cell-associated neurotoxicity based on the most recent evidence.

Environmental consistency determines the rate of motor adaptation

BACKGROUND

The motor system has the remarkable ability not only to learn but also to learn how fast it should learn. However, the mechanisms behind this ability are not well understood. Previous studies have posited that the rate of adaptation in a given environment is determined by Bayesian sensorimotor integration based on the amount of variability in the state of the environment. However, experimental results have failed to support several predictions of this theory.

RESULTS

We show that the rate at which the motor system adapts to changes in the environment is primarily determined not by the degree to which environmental change occurs but by the degree to which the changes that do occur persist from one movement to the next, i.e., the consistency of the environment. We demonstrate a striking double dissociation whereby feedback response strength is predicted by environmental variability rather than consistency, whereas adaptation rate is predicted by environmental consistency rather than variability. We proceed to elucidate the role of stimulus repetition in speeding up adaptation and find that repetition can greatly potentiate the effect of consistency, although unlike consistency, repetition alone does not increase adaptation rate. By leveraging this understanding, we demonstrate that the rate of motor adaptation can be modulated over a range that encompasses a 20-fold increase from lowest to highest.

CONCLUSIONS

Understanding the mechanisms that determine the rate of motor adaptation could lead to the principled design of improved procedures for motor training and rehabilitation. Regimens designed to control environmental consistency and repetition during training might yield faster, more robust motor learning.

Temporal structure of motor variability is dynamically regulated and predicts motor learning ability

Individual differences in motor learning ability are widely acknowledged, yet little is known about the factors that underlie them. Here we explore whether movement-to-movement variability in motor output, a ubiquitous if often unwanted characteristic of motor performance, predicts motor learning ability. Surprisingly, we found that higher levels of task-relevant motor variability predicted faster learning both across individuals and across tasks in two different paradigms, one relying on reward-based learning to shape specific arm movement trajectories and the other relying on error-based learning to adapt movements in novel physical environments. We proceeded to show that training can reshape the temporal structure of motor variability, aligning it with the trained task to improve learning. These results provide experimental support for the importance of action exploration, a key idea from reinforcement learning theory, showing that motor variability facilitates motor learning in humans and that our nervous systems actively regulate it to improve learning.

The binding of learning to action in motor adaptation

In motor tasks, errors between planned and actual movements generally result in adaptive changes which reduce the occurrence of similar errors in the future. It has commonly been assumed that the motor adaptation arising from an error occurring on a particular movement is specifically associated with the motion that was planned. Here we show that this is not the case. Instead, we demonstrate the binding of the adaptation arising from an error on a particular trial to the motion experienced on that same trial. The formation of this association means that future movements planned to resemble the motion experienced on a given trial benefit maximally from the adaptation arising from it. This reflects the idea that actual rather than planned motions are assigned 'credit' for motor errors because, in a computational sense, the maximal adaptive response would be associated with the condition credited with the error. We studied this process by examining the patterns of generalization associated with motor adaptation to novel dynamic environments during reaching arm movements in humans. We found that these patterns consistently matched those predicted by adaptation associated with the actual rather than the planned motion, with maximal generalization observed where actual motions were clustered. We followed up these findings by showing that a novel training procedure designed to leverage this newfound understanding of the binding of learning to action, can improve adaptation rates by greater than 50%. Our results provide a mechanistic framework for understanding the effects of partial assistance and error augmentation during neurologic rehabilitation, and they suggest ways to optimize their use.