Multiparamter MRI Investigation of High-Grade Glioma Response to CAR T Cell Immunotherapy
Harshan Ravi1, Olya Stringfield2, Gustavo De Leon3, Sandra Johnston4, Christine E Brown5, Kristin R Swanson3, Robert A Gatenby6, and Natarajan Raghunand1

1Department of cancer physiology, Moffitt Cancer research center, Tampa, FL, United States, 2Irat Shared service, Moffitt Cancer research center, Tampa, FL, United States, 3Mathematical NeuroOncology Lab Precision Neurotherapeutics innovation program, Mayo clinic, Phoenix, AZ, United States, 4Department of Radiology, University of Washington, Seattle, WA, United States, 5Department of Cancer Immunotherapy and Tumor Immunology, City of Hope Beckman Research Institute and Medical Center, Duarte, CA, United States, 6Department diagnostic and interventional radiology, Moffitt Cancer research center, Tampa, FL, United States


Immunotherapy is gaining interest for treatment of even poorly immunogenic cancers like gliomas. Pseudo-progression and pseudo-response are frequently noted on standard of care MRI in glioma patients receiving immunotherapy. We present a "Habitat" imaging approach to objectively follow response to CAR T cell therapy of glioma.


Glioblastoma (GBM) is a disease of complex etiology and dismal prognosis, with median survival reported to be between 12-18 months post-diagnosis (1, 2). Even with aggressive standard-of-care therapies that include maximal safe resection, concurrent radiotherapy, chemotherapy and adjuvant chemotherapy, estimated 5-year survival rates are only around 10% (3). Failure of disease control in GBM stems from persistence of therapy-resistant infiltrative malignant cells. Anti-tumor immunotherapy is showing promise in a variety of solid and hematological cancers (4). While the central nervous system (CNS) is immune privileged, parts of the CNS are able to induce robust immune responses (5). Personalized tumor antigen recognition by T cells can be increased by genetic modification of harvested T cells to express chimeric antigen receptors (CAR) and subsequent reinjection back into the patient. Brown et al. (6) are investigating the safety and efficacy of CAR T cell therapy engineered to target IL13 receptor a2 (IL13Ra2) in human subjects with recurrent GBM. The most common imaging biomarker used in assessing treatment response is tumor size, wherein decrease in tumor size is associated with disease regression. In the context of cancer immunotherapy, an initial increase in radiologic size of the tumor is often observed that is associated with treatment response rather than true tumor progression. Monitoring of the tumor on subsequent follow-up scans is required to differentiate such pseudo-progression from true tumor progression, potentially delaying changes to the therapeutic regimen of the patient (7, 8). Recent studies have shown the feasibility of multispectral clustering of standard of care (SOC) MR Images for quantifying tumor heterogeneity (9-14). Stringfield et al. extended this concept to identify intratumoral clusters that they termed “habitats”, one of which was correlated with survival in high-grade glioma (15-17). We have applied their method to investigate intratumoral “habitat” composition of recurrent glioma tumors before and after treatment with CAR T cells engineered to target IL13Ra2. In this study we are investigating longitudinal changes in the habitat composition of tumors over the course of CAR T cell therapy. Our hypothesis is that "Habitat 6", which represents voxels with both high FLAIR signal and high contrast enhancement (17), is associated with immune infiltrates in the tumor.


Patients with recurrent or refractory grade III or IV glioma were accrued to an IRB-approved single-institution study (ClinicalTrials.gov ID: NCT00730613). Standard-of-care MRI scans of the brain were acquired at 1.5 T at baseline and various times after initiation of CAR T cell therapy (6). Fluid-attenuated inversion recovery (FLAIR), T1W pre-contrast (T1Wpre) and T1W post-contrast (T1Wpost) images were first registered to T2-weighted (T2W) images. The mean intensities of two reference regions, cerebrospinal fluid (CSF) and white matter (WM), were used to linearly calibrate voxel intensities on FLAIR, T2W, T1Wpre and T1Wpost images (15-17). T1Wpost images were calibrated using the same linear transformation as the associated T1Wpre images. Previously identified intensity thresholds on calibrated FLAIR and calibrated (T1Wpost - T1Wpre) difference images (17) were applied to objectively generate a total of six intratumoral “habitats”: Habitat 1 (low Flair, low contrast enhancement), Habitat 2 (high Flair, low contrast enhancement), Habitat 3 (low Flair, medium contrast enhancement), Habitat 4 (high Flair, medium contrast enhancement), Habitat 5 (low Flair, high contrast enhancement), and Habitat 6 (high Flair, high contrast enhancement).

Results and Discussion:

Figure 1 depicts changes in "Habitat 6" pre- and post-treatment in three subjects who received CAR T cell therapy as described previously (6).In all 3 subjects we observed a significant increase in "Habitat 6" after treatment (Figure 2, and Table 1). Qualitative changes in FLAIR signal and contrast enhancement following immunotherapy of gliomas is frequently noted (7,8). Our approach of using image intensity calibration followed by multispectral clustering allows the application of standardized thresholds across subjects and scan dates. This permits a consistent and quantitative analysis of changes on MRI in gliomas post-immunotherapy with engineered CAR T cells. Validation of these preliminary "habitat" analysis results on additional glioma subjects receiving CAR T cell therapy is ongoing.


Recently, it was shown that tumor fractional volume of "Habitat 6" is a significant predictor of long-term survival in GBM patients. In this pilot study, we investigated the changes in "Habitat 6" in recurrent or refractory grade III or IV glioma patients treated with CAR T cell therapy. Our initial findings suggest that tumor volume fraction of "Habitat 6" increases post-treatment. Validation of these initial findings will provide a non-invasive response biomarker to guide immunotherapy of gliomas.


No acknowledgement found.


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Habitat 6 maps post and pre-treatment are shown above. A representative slice was to depict the changes in 3 subjects post-treatment. The black arrow shows the area where changes occur post-treatment. Normal brain parenchyma is shown in shades of blue. "Habitat 6" content is indicated in yellow through dark red.

Barplot showing the difference in total "Habitat 6" volume pre and post-treatment. In all three subjects, there was a significant increase in "Habitat 6" with treatment.

Table 1: Absolute volume (mm3) of "Habitat 6" in glioma tumors of 3 subjects.

Proc. Intl. Soc. Mag. Reson. Med. 27 (2019)