Introduction: Glioblastoma (GBM) immunotherapy is hampered by poorly characterized patient lymphopenia and T-cell dysfunction. Murine glioma models reveal CD4+ T-lymphocyte disappearance from blood / lymph nodes / spleens, as well as marked splenic and thymic retraction. Meanwhile, the bone marrow of glioma-bearing mice reveals 6-fold expansion of CD4+ T-lymphocytes (1-3). We hypothesized that the blood, spleen, and bone marrow of patients with GBM would demonstrate similar alterations to T-cell homeostasis, and we addressed mechanistic questions in the mouse.
Methods: Samples are analyzed by 8-color flow cytometry, luminex, IHC, ELISA, and functional assays. Retrospective patient studies included complete blood counts and 3D spleen/tumor volumetric assessments in 284 treatment-naïve GBM patients and 46 age-matched controls. Ongoing prospective studies examine T-cells in blood, tumor, and bone marrow of 20 newly diagnosed GBM patients and 10 age-matched spinal fusion controls.
Results: 23% of treatment-naïve GBM patients prove lymphopenic (ct<1000 cells/ul) at presentation. Mean patient CD4 counts thus far are 308 (control 849, p<0.001). 50% of patients present with CD4 counts < 200 (AIDS demarcation in HIV). Patients demonstrate 32% reductions in spleen volume versus controls (P<0.0001), with 1/3 exhibiting greater than 50% volume reduction. Decadron exacerbates lymphopenia but does not affect spleen volume. Increased ratios of bone marrow to blood CD4 T-cells have similarly been detected in patients. In mice, this bone marrow CD4 accumulation proves to be brain-tumor specific and abrogated by anti-TGFß.
Conclusions: Immunologically recapitulative murine glioma models demonstrate T-cell accumulation in bone marrow in association with disappearance from other immunologic compartments. Treatment-naïve GBM patients exhibit similar lymphopenia, dramatically low CD4 counts, shrunken spleens, and relative T-cell concentration in the bone marrow. In mice, these phenomena are glioma-specific and TGF-ß-influenced. This represents the first characterization of an unprecedented alteration to T-cell homeostasis in patients with GBM and has implications for GBM immunotherapy and immunology more broadly.
Patient Care: These data on lymphopenia and bone marrow T-cell “sequestration” offer a greater understanding of immune derangements in patients with GBM, the potential etiologies of our immunotherapeutic failures, and the requirements for side-stepping tumor adaptive mechanisms en route to more rational and targeted immunotherapeutic design. This work has prompted current investigation into means of reversing patient lymphopenia, liberating bone marrow T-cells into the periphery, and even harvesting and employing bone marrow T-cells directly in the next generation of glioma immunotherapy.
Learning Objectives: By the conclusion of this session, participants should be able to: 1) Discuss derangements to systemic immunity in patients and mice with GBM; 2) Identify implications for glioma immunotherapy; and 3) recognize the bone marrow as a potential site for T-cell sequestration in patients with GBM.
References: 1. Dunn GP, Fecci PE, Curry WT. 2012. Cancer immunoediting in malignant glioma. Neurosurgery 71: 201-23
2. Fecci PE, Mitchell DA, Whitesides JF, Xie W, Friedman AH, Archer GE, Herndon JE, 2nd, Bigner DD, Dranoff G, Sampson JH. 2006. Increased regulatory T-cell fraction amidst a diminished CD4 compartment explains cellular immune defects in patients with malignant glioma. Cancer Res 66: 3294-302
3. Fecci PE, Sweeney AE, Grossi PM, Nair SK, Learn CA, Mitchell DA, Cui X, Cummings TJ, Bigner DD, Gilboa E, Sampson JH. 2006. Systemic anti-CD25 monoclonal antibody administration safely enhances immunity in murine glioma without eliminating regulatory T cells. Clin Cancer Res 12: 4294-305