Arginase-1 specific CD8+ T cells react toward malignant and regulatory myeloid cells.

Arginase-1 (Arg1) is expressed by regulatory myeloid cells in the tumor microenvironment (TME), where they play a pro-tumorigenic and T-cell suppressive role. Arg1-specific CD4+ and CD8+ memory T cells have been observed in both healthy individuals and cancer patients. However, while the function of anti-regulatory Arg1-specific CD4+ T cells has been characterized, our knowledge of CD8+ Arg1-specific T cells is only scarce. In the current study, we describe the immune-modulatory capabilities of CD8+ Arg1-specific T cells. We generated CD8+ Arg1-specific T cell clones to target Arg1-expressing myeloid cells. Our results demonstrate that these T cells recognize both malignant and nonmalignant regulatory myeloid cells in an Arg1-expression-dependent manner. Notably, Arg1-specific CD8+ T cells possess cytolytic effector capabilities. Immune modulatory vaccines (IMVs) represent a novel treatment modality for cancer. The activation of Arg1-specific CD8+ T cells through Arg1-based IMVs can contribute to the modulatory effects of this treatment strategy.

Retroviral Transduction of Human Primary T Cells Followed by Real-Time T-Cell-Mediated Cancer Cell Cytolysis Analysis.

Retroviral transduction is a highly useful tool to genetically engineer hard-to-transfect human primary cells. Here, we transduce human primary T cells with a tumor-specific T cell receptor. This creates a useful tool to analyze T cell-cancer cell interactions, such as cytolysis analysis using xCELLigence technology.

Preferential Expansion of HPV16 E1-Specific T Cells from Healthy Donors' PBMCs after Ex Vivo Immunization with an E1E2E6E7 Fusion Antigen.

Persistent human papillomavirus (HPV) infection is responsible for practically all cervical and a high proportion of anogenital and oropharyngeal cancers. Therapeutic HPV vaccines in clinical development show great promise in improving outcomes for patients who mount an anti-HPV T-cell response; however, far from all patients elicit a sufficient immunological response. This demonstrates a translational gap between animal models and human patients. Here, we investigated the potential of a new assay consisting of co-culturing vaccine-transduced dendritic cells (DCs) with syngeneic, healthy, human peripheral blood mononuclear cells (PBMCs) to mimic a human in vivo immunization. This new promising human ex vivo PBMC assay was evaluated using an innovative therapeutic adenovirus (Adv)-based HPV vaccine encoding the E1, E2, E6, and E7 HPV16 genes. This new method allowed us to show that vaccine-transduced DCs yielded functional effector T cells and unveiled information on immunohierarchy, showing E1-specific T-cell immunodominance over time. We suggest that this assay can be a valuable translational tool to complement the known animal models, not only for HPV therapeutic vaccines, and supports the use of E1 as an immunotherapeutic target. Nevertheless, the findings reported here need to be validated in a larger number of donors and preferably in patient samples.

First in man study: Bcl-Xl_42-CAF®09b vaccines in patients with locally advanced prostate cancer.

Background: The B-cell lymphoma-extra-large (Bcl-XL) protein plays an important role in cancer cells' resistance to apoptosis. Pre-clinical studies have shown that vaccination with Bcl-XL-derived peptides can induce tumor-specific T cell responses that may lead to the elimination of cancer cells. Furthermore, pre-clinical studies of the novel adjuvant CAF®09b have shown that intraperitoneal (IP) injections of this adjuvant can improve the activation of the immune system. In this study, patients with hormone-sensitive prostate cancer (PC) received a vaccine consisting of Bcl-XL-peptide with CAF®09b as an adjuvant. The primary aim was to evaluate the tolerability and safety of IP and intramuscular (IM) administration, determine the optimal route of administration, and characterize vaccine immunogenicity. Patients and methods: Twenty patients were included. A total of six vaccinations were scheduled: in Group A (IM to IP injections), ten patients received three vaccines IM biweekly; after a three-week pause, patients then received three vaccines IP biweekly. In Group B (IP to IM injections), ten patients received IP vaccines first, followed by IM under a similar vaccination schedule. Safety was assessed by logging and evaluating adverse events (AE) according to Common Terminology Criteria for Adverse Events (CTCAE v. 4.0). Vaccines-induced immune responses were analyzed by Enzyme-Linked Immunospot and flow cytometry. Results: No serious AEs were reported. Although an increase in T cell response against the Bcl-XL-peptide was found in all patients, a larger proportion of patients in group B demonstrated earlier and stronger immune responses to the vaccine compared to patients in group A. Further, we demonstrated vaccine-induced immunity towards patient-specific CD4, and CD8 T cell epitopes embedded in Bcl-XL-peptide and an increase in CD4 and CD8 T cell activation markers CD107a and CD137 following vaccination. At a median follow-up of 21 months, no patients had experienced clinically significant disease progression. Conclusion: The Bcl-XL-peptide-CAF®09b vaccination was feasible and safe in patients with l hormone-sensitive PC. In addition, the vaccine was immunogenic and able to elicit CD4 and CD8 T cell responses with initial IP administration eliciting early and high levels of vaccine-specific responses in a higher number og patients. Clinical trial registration: https://clinicaltrials.gov, identifier NCT03412786.

Patients With Myeloproliferative Neoplasms Harbor High Frequencies of CD8 T Cell-Platelet Aggregates Associated With T Cell Suppression.

Myeloproliferative neoplasms (MPN) are chronic cancers of the hematopoietic stem cells in the bone marrow, and patients often harbor elevated numbers of circulating platelets (PLT). We investigated the frequencies of circulating PLT-lymphocyte aggregates in MPN patients and the effect of PLT-binding on CD8 T cell function. The phenotype of these aggregates was evaluated in 50 MPN patients and 24 controls, using flow cytometry. In vitro studies compared the proliferation, cytokine release, and cytoxicity of PLT-bound and PLT-free CD8 T cells. Frequencies of PLT-CD8 T cell aggregates, were significantly elevated in MPN patients. Advanced disease stage and CALR mutation associated with the highest aggregate frequencies with a predominance of PLT-binding to antigen-experienced CD8 T cells. PLT-bound CD8 T cells showed reduction in proliferation and cytotoxic capacity. Our data suggest that CD8 T cell responses are jeopardized in MPN patients. JAK2 and CALR exon 9 mutations - the two predominant driver mutations in MPN - are targets for natural T cell responses in MPN patients. Moreover, MPN patients have more infections compared to background. Thus, PLT binding to antigen experienced CD8 T cells could play a role in the inadequacy of the immune system to control MPN disease progression and prevent recurrent infections.

High Intensity Aerobic exercise training and Immune cell Mobilization in patients with lung cancer (HI AIM)-a randomized controlled trial.

BACKGROUND: The increasing role of exercise training in cancer care is built on evidence that exercise can reduce side effects of treatment, improve physical functioning and quality of life. We and others have shown in mouse tumor models, that exercise leads to an adrenalin-mediated increased influx of T and NK cells into the tumor, altering the tumor microenvironment (TME) and leading to reduced tumor growth. These data suggest that exercise could improve immune responses against cancer cells by increase immune cell infiltration to the tumor and potentially having an impact on disease progression. Additionally, there are data to suggest that infiltration of T and NK cells into the TME is correlates with response to immune checkpoint inhibitors in patients. We have therefore initiated the clinical trial HI AIM, to investigate if high intensity exercise can mobilize and increase infiltration of immune cells in the TME in patients with lung cancer. METHODS: HI AIM (NCT04263467) is a randomized controlled trial (70 patients, 1:1) for patients with non-small cell lung cancer. Patients in the treatment arm, receive an exercise-intervention consisting of supervised and group-based exercise training, comprising primarily intermediate to high intensity interval training three times per week over 6 weeks. All patients will also receive standard oncological treatments; checkpoint inhibitors, checkpoint inhibitors combined with chemotherapy or oncological surveillance. Blood samples and biopsies (ultrasound guided), harvested before, during and after the 6-week training program, will form basis for immunological measurements of an array of immune cells and markers. Primary outcome is circulating NK cells. Secondary outcome is other circulating immune cells, infiltration of immune cells in tumor, inflammatory markers, aerobic capacity measured by VO2 max test, physical activity levels and quality of life measured by questionnaires, and clinical outcomes. DISCUSSION: To our knowledge, HI AIM is the first project to combine supervised and monitored exercise in patients with lung cancer, with rigorous analyses of immune and cancer cell markers over the course of the trial. Data from the trial can potentially support exercise as a tool to mobilize cells of the immune system, which in turn could potentiate the effect of immunotherapy. TRIAL REGISTRATION: The study was prospectively registered at ClinicalTrials.gov on February 10th 2020, ID: NCT04263467. https://clinicaltrials.gov/ct2/show/NCT04263467.

Mitochondrial-Linked De Novo Pyrimidine Biosynthesis Dictates Human T-Cell Proliferation but Not Expression of Effector Molecules.

T-cell activation upon antigen stimulation is essential for the continuation of the adaptive immune response. Impairment of mitochondrial oxidative phosphorylation is a well-known disruptor of T-cell activation. Dihydroorotate dehydrogenase (DHODH) is a component of the de novo synthesis of pyrimidines, the activity of which depends on functional oxidative phosphorylation. Under circumstances of an inhibited oxidative phosphorylation, DHODH becomes rate-limiting. Inhibition of DHODH is known to block clonal expansion and expression of effector molecules of activated T cells. However, this effect has been suggested to be caused by downstream impairment of oxidative phosphorylation rather than a lower rate of pyrimidine synthesis. In this study, we successfully inhibit the DHODH of T cells with no residual effect on oxidative phosphorylation and demonstrate a dose-dependent inhibition of proliferation of activated CD3+ T cells. This block is fully rescued when uridine is supplemented. Inhibition of DHODH does not alter expression of effector molecules but results in decreased intracellular levels of deoxypyrimidines without decreasing cell viability. Our results clearly demonstrate the DHODH and mitochondrial linked pyrimidine synthesis as an independent and important cytostatic regulator of activated T cells.

Real-time Monitoring of Mitochondrial Respiration in Cytokine-differentiated Human Primary T Cells.

During activation, the metabolism of T cells adapts to changes that impact their fate. An increase in mitochondrial oxidative phosphorylation is indispensable for T cell activation, and the survival of memory T cells is dependent on mitochondrial remodeling. Consequently, this affects the long-term clinical outcome of cancer immunotherapies. Changes in T cell quality are often studied by flow cytometry using well-known surface markers and not directly by their metabolic state. This is an optimized protocol for measuring real-time mitochondrial respiration of primary human T cells using an Extracellular Flux Analyzer and the cytokines IL-2 and IL-15, which differently affect T cell metabolism. It is shown that the metabolic state of T cells can clearly be distinguished by measuring the oxygen consumption when inhibiting key complexes in the metabolic pathway and that the accuracy of these measurements is highly dependent on optimal inhibitor concentration and inhibitor injection strategy. This standardized protocol will help implement mitochondrial respiration as a standard for T cell fitness in monitoring and studying cancer immunotherapies.

Small Molecule Inhibitors of MERTK and FLT3 Induce Cell Cycle Arrest in Human CD8+ T Cells.

There is an increasing interest in the development of Receptor Tyrosine Kinases inhibitors (RTKIs) for cancer treatment, as dysregulation of RTK expression can govern oncogenesis. Among the newer generations of RTKIs, many target Mer Tyrosine Kinase (MERTK) and Fms related RTK 3 (FLT3). Next to being overexpressed in many cancers, MERTK and FLT3 have important roles in immune cell development and function. In this study, we address how the new generation and potent RTKIs of MERTK/FLT3 affect human primary CD8+ T cell function. Using ex vivo T cell receptor (TCR)-activated CD8+ T cells, we demonstrate that use of dual MERTK/FLT3 inhibitor UNC2025 restricts CD8+ T proliferation at the G2 phase, at least in part by modulation of mTOR signaling. Cytokine production and activation remain largely unaffected. Finally, we show that activated CD8+ T cells express FLT3 from day two post activation, and FLT3 inhibition with AC220 (quizartinib) or siRNA-mediated knockdown affects cell cycle kinetics. These results signify that caution is needed when using potent RTKIs in the context of antitumor immune responses.

Vγ9Vδ2 T Cells Concurrently Kill Cancer Cells and Cross-Present Tumor Antigens.

The human Vγ9Vδ2 T cell is a unique cell type that holds great potential in immunotherapy of cancer. In particular, the therapeutic potential of this cell type in adoptive cell therapy (ACT) has gained interest. In this regard optimization of in vitro expansion methods and functional characterization is desirable. We show that Vγ9Vδ2 T cells, expanded in vitro with zoledronic acid (Zometa or ZOL) and Interleukin-2 (IL-2), are efficient cancer cell killers with a trend towards increased killing efficacy after prolonged expansion time. Thus, Vγ9Vδ2 T cells expanded for 25 days in vitro killed prostate cancer cells more efficiently than Vγ9Vδ2 T cells expanded for 9 days. These data are supported by phenotype characteristics, showing increased expression of CD56 and NKG2D over time, reaching above 90% positive cells after 25 days of expansion. At the early stage of expansion, we demonstrate that Vγ9Vδ2 T cells are capable of cross-presenting tumor antigens. In this regard, our data show that Vγ9Vδ2 T cells can take up tumor-associated antigens (TAA) gp100, MART-1 and MAGE-A3 - either as long peptide or recombinant protein - and then present TAA-derived peptides on the cell surface in the context of HLA class I molecules, demonstrated by their recognition as targets by peptide-specific CD8 T cells. Importantly, we show that cross-presentation is impaired by the proteasome inhibitor lactacystin. In conclusion, our data indicate that Vγ9Vδ2 T cells are broadly tumor-specific killers with the additional ability to cross-present MHC class I-restricted peptides, thereby inducing or supporting tumor-specific αßTCR CD8 T cell responses. The dual functionality is dynamic during in vitro expansion, yet, both functions are of interest to explore in ACT for cancer therapy.

TAM Receptor Inhibition-Implications for Cancer and the Immune System.

Tyro3, Axl and MerTK (TAM) receptors are receptor tyrosine kinases which play important roles in efferocytosis and in the balancing of immune responses and inflammation. TAM receptor activation is induced upon binding of the ligands protein S (Pros1) or growth arrest-specific protein 6 (Gas6) which act as bridging molecules for binding of phosphatidyl serine (PtdSer) exposed on apoptotic cell membranes. Upon clearance of apoptotic cell material, TAM receptor activation on innate cells suppresses proinflammatory functions, thereby ensuring the immunologically silent removal of apoptotic material in the absence of deleterious immune responses. However, in T cells, MerTK signaling is costimulatory and promotes activation and functional output of the cell. MerTK and Axl are also aberrantly expressed in a range of both hematological and solid tumor malignancies, including breast, lung, melanoma and acute myeloid leukemia, where they have a role in oncogenic signaling. Consequently, TAM receptors are being investigated as therapeutic targets using small molecule inhibitors and have already demonstrated efficacy in mouse tumor models. Thus, inhibition of TAM signaling in cancer cells could have therapeutic value but given the opposing roles of TAM signaling in innate cells and T cells, TAM inhibition could also jeopardize anticancer immune responses. This conflict is discussed in this review, describing the effects of TAM inhibition on cancer cells as well as immune cells, while also examining the intricate interplay of cancer and immune cells in the tumor microenvironment.

The capacity of CD4+ Vγ9Vδ2 T cells to kill cancer cells correlates with co-expression of CD56.

Human Vγ9Vδ2 T cells are a unique T-cell type, and data from recent studies of Vγ9Vδ2 T cells emphasize their potential relevance to cancer immunotherapy. Vγ9Vδ2 T cells exhibit dual properties since they are both antigen-presenting cells and cytotoxic toward cancer cells. The majority of Vγ9Vδ2 T cells are double-negative for the co-receptors CD4 and CD8, and only 20-30% express CD8. Even though they are mostly neglected, a small fraction of Vγ9Vδ2 T cells also express the co-receptor CD4. Here the authors show that CD4+ Vγ9Vδ2 T cells comprise 0.1-7% of peripheral blood Vγ9Vδ2 T cells. These cells can be expanded in vitro using zoledronic acid, pamidronic acid or CD3 antibodies combined with IL-2 and feeder cells. Unlike most conventional CD4+ αß T cells, CD4+ Vγ9Vδ2 T cells are potently cytotoxic and can kill cancer cells, which is here shown by the killing of cancer cell lines of different histological origins, including breast cancer, prostate cancer and melanoma cell lines, upon treatment with zoledronic acid. Notably, the killing capacity of CD4+ Vγ9Vδ2 T cells correlates with co-expression of CD56.

Adrenergic Signaling in Immunotherapy of Cancer: Friend or Foe?

The incidence of cancer is increasing worldwide, which is to a large extent related to the population's increasing lifespan. However, lifestyle changes in the Western world are causative as well. Exercise is intrinsically associated with what one could call a "healthy life", and physical activity is associated with a lower risk of various types of cancer. Mouse models of exercise have shown therapeutic efficacy across numerous cancer models, at least in part due to the secretion of adrenaline, which mobilizes cells of the immune system, i.e., cytotoxic T and natural killer (NK) cells, through signaling of the ß-2 adrenergic receptor (ß2AR). Clinical trials aiming to investigate the clinical value of exercise are ongoing. Strikingly, however, the use of ß-blockers-antagonists of the very same signaling pathway-also shows signs of clinical potential in cancer therapy. Cancer cells also express ß-adrenergic receptors (ßARs) and signaling of the receptor is oncogenic. Moreover, there are data to suggest that ß2AR signaling in T cells renders the cell functionally suppressed. In this paper, we discuss these seemingly opposing mechanisms of cancer therapy-exercise, which leads to increased ß2AR signaling, and ß-blocker treatment, which antagonizes that same signaling-and suggest potential mechanisms and possibilities for their combination.

Vaccination against RhoC induces long-lasting immune responses in patients with prostate cancer: results from a phase I/II clinical trial.

BACKGROUND: Peptide-based vaccination is a rational option for immunotherapy of prostate cancer. In this first-in-man phase I/II study, we assessed the safety, tolerability and immunological impact of a synthetic long peptide vaccine targeting Ras homolog gene family member C (RhoC) in patients with prostate cancer. RhoC is a small GTPase overexpressed in advanced solid cancers, metastases and cancer stem cells. METHODS: Twenty-two patients who had previously undergone radical prostatectomy received subcutaneous injections of 0.1 mg of a single RhoC-derived 20mer peptide emulsified in Montanide ISA-51 every 2 weeks for the first six times, then five times every 4 weeks for a total treatment time of 30 weeks. The drug safety and vaccine-specific immune responses were assessed during treatment and thereafter within a 13-month follow-up period. Serum level of prostate-specific antigen was measured up to 26 months postvaccination. RESULTS: Most patients (18 of 21 evaluable) developed a strong CD4 T cell response against the vaccine, which lasted at least 10 months following the last vaccination. Three promiscuouslypresented HLA-class II epitopes were identified. Vaccine-specific CD4 T cells were polyfunctional and effector memory T cells that stably expressed PD-1 (CD279) and OX-40 (CD134), but not LAG-3 (CD223). One CD8 T cell response was detected in addition. The vaccine was well tolerated and no treatment-related adverse events of grade ≥3 were observed. CONCLUSION: Targeting of RhoC induced a potent and long-lasting T cell immunity in the majority of the patients. The study demonstrates an excellent safety and tolerability profile. Vaccination against RhoC could potentially delay or prevent tumor recurrence and metastasis formation. TRIAL REGISTRATION NUMBER: NCT03199872.

Expansion With IL-15 Increases Cytotoxicity of Vγ9Vδ2 T Cells and Is Associated With Higher Levels of Cytotoxic Molecules and T-bet.

Cancer immunotherapy has shown great advances during recent years, but it has yet to reach its full potential in all cancer types. Adoptive cell therapy (ACT) is now an approved treatment option for certain hematological cancers and has also shown success for some solid cancers. Still, benefit and eligibility do not extend to all patients. ACT with Vγ9Vδ2 T cells is a promising approach to overcome this hurdle. In this study, we aimed to explore the effect of different cytokine conditions on the expansion of Vγ9Vδ2 T cells in vitro. We could show that Vγ9Vδ2 T cell expansion is feasible with two different cytokine conditions: (a) 1,000 U/ml interleukin (IL)-2 and (b) 100 U/ml IL-2 + 100 U/ml IL-15. We did not observe differences in expansion rate or Vγ9Vδ2 T cell purity between the conditions; however, IL-2/IL-15-expanded Vγ9Vδ2 T cells displayed enhanced cytotoxicity against tumor cells, also in hypoxia. While this increase in killing capacity was not reflected in natural killer (NK) cell marker or activation marker expression, we demonstrated that IL-2/IL-15-expanded Vγ9Vδ2 T cells were characterized by an increased expression of perforin, granzyme B, and granulysin compared to IL-2-expanded cells. These cytotoxic molecules were not only increased in a resting state, but also released to a greater extent upon target recognition. In contrast, CD107a and cytokine expression did not differ between expansion conditions. However, IL-2/IL-15-expanded Vγ9Vδ2 T cells showed higher levels of transcription factor T-bet expression, which could indicate that T-bet and cytotoxic molecule levels confer the increased cytotoxicity. These results advocate the inclusion of IL-15 into ex vivo Vγ9Vδ2 T cell expansion protocols in future clinical studies.

Exercise Oncology and Immuno-Oncology; A (Future) Dynamic Duo.

Recent advances in clinical oncology is based on exploiting the capacity of the immune system to combat cancer: immuno-oncology. Thus, immunotherapy of cancer is now used to treat a variety of malignant diseases. A striking feature is that even patients with late-stage disease may experience curative responses. However, most patients still succumb to disease, and do not benefit from treatment. Exercise has gained attention in clinical oncology and has been used for many years to improve quality of life, as well as to counteract chemotherapy-related complications. However, more recently, exercise has garnered interest, largely due to data from animal studies suggesting a striking therapeutic effect in preclinical cancer models; an effect largely mediated by the immune system. In humans, physical activity is associated with a lower risk for a variety of malignancies, and some data suggest a positive clinical effect for cancer patients. Exercise leads to mobilization of cells of the immune system, resulting in redistribution to different body compartments, and in preclinical models, exercise has been shown to lead to immunological changes in the tumor microenvironment. This suggests that exercise and immunotherapy could have a synergistic effect if combined.

TAM-ing T cells in the tumor microenvironment: implications for TAM receptor targeting.

The TAM receptors-TYRO3, AXL, MERTK-are pleiotropically expressed receptors in both healthy and diseased tissue. A complex of the ligands Protein S (PROS1) or Growth Arrest-Specific 6 (GAS6) with apoptotic phosphatidylserine activates the TAM receptors. Hence, this receptor family is essential for the efferocytosis of apoptotic material by antigen-presenting cells. In addition, TAM receptors are expressed by virtually all cells of the tumor microenvironment. They are also potent oncogenes, frequently overexpressed in cancer and involved in survival and therapy resistance. Due to their pro-oncogenic and immune-inhibitory traits, TAM receptors have emerged as promising targets for cancer therapy. Recently, TAM receptors have been described to function as costimulatory molecules on human T cells. TAM receptors' ambivalent functions on many different cell types therefore make therapeutic targeting not straight-forward. In this review we summarize our current knowledge of the function of TAM receptors in the tumor microenvironment. We place particular focus on TAM receptors and the recently unraveled role of MERTK in activated T cells and potential consequences for anti-tumor immunity.

MERTK Acts as a Costimulatory Receptor on Human CD8+ T Cells.

The TAM family of receptor tyrosine kinases (TYRO3, AXL, and MERTK) is known to be expressed on antigen-presenting cells and function as oncogenic drivers and as inhibitors of inflammatory responses. Both human and mouse CD8+ T cells are thought to be negative for TAM receptor expression. In this study, we show that T-cell receptor (TCR)-activated human primary CD8+ T cells expressed MERTK and the ligand PROS1 from day 2 postactivation. PROS1-mediated MERTK signaling served as a late costimulatory signal, increasing proliferation and secretion of effector and memory-associated cytokines. Knockdown and inhibition studies confirmed that this costimulatory effect was mediated through MERTK. Transcriptomic and metabolic analyses of PROS1-blocked CD8+ T cells demonstrated a role of the PROS1-MERTK axis in differentiation of memory CD8+ T cells. Finally, using tumor-infiltrating lymphocytes (TIL) from melanoma patients, we show that MERTK signaling on T cells improved TIL expansion and TIL-mediated autologous cancer cell killing. We conclude that MERTK serves as a late costimulatory signal for CD8+ T cells. Identification of this costimulatory function of MERTK on human CD8+ T cells suggests caution in the development of MERTK inhibitors for hematologic or solid cancer treatment.

Identification of Tumor Antigens Among the HLA Peptidomes of Glioblastoma Tumors and Plasma.

Glioblastoma multiforme (GBM) is the most aggressive brain tumor with poor prognosis to most patients. Immunotherapy of GBM is a potentially beneficial treatment option, whose optimal implementation may depend on familiarity with tumor specific antigens, presented as HLA peptides by the GBM cells. Further, early detection of GBM, such as by a routine blood test, may improve survival, even with the current treatment modalities. This study includes large-scale analyses of the HLA peptidome (immunopeptidome) of the plasma-soluble HLA molecules (sHLA) of 142 plasma samples, and the membranal HLA of GBM tumors of 10 of these patients' tumor samples. Tumor samples were fresh-frozen immediately after surgery and the plasma samples were collected before, and at multiple visits after surgery. In total, this HLA peptidome analysis involved 52 different HLA allotypes and resulted in the identification of more than 35,000 different HLA peptides. Strong correlations were observed in the signal intensities and in the repertoires of identified peptides between the tumors and plasma-soluble HLA peptidomes of the individual patients, whereas low correlations were observed between these HLA peptidomes and the tumors' proteomes. HLA peptides derived from Cancer/Testis Antigens (CTAs) were selected based on their presence among the HLA peptidomes of the patients and absence of expression of their source genes from any healthy and essential human tissues, except from immune-privileged sites. Additionally, peptides were selected as potential biomarkers if their levels in the plasma-sHLA peptidome were significantly reduced after the removal of tumor mass. The CTAs identified among the analyzed HLA peptidomes provide new opportunities for personalized immunotherapy and for early diagnosis of GBM.