Decade-long leukaemia remissions with persistence of CD4+ CAR T cells.

The adoptive transfer of T lymphocytes reprogrammed to target tumour cells has demonstrated potential for treatment of various cancers1-7. However, little is known about the long-term potential and clonal stability of the infused cells. Here we studied long-lasting CD19-redirected chimeric antigen receptor (CAR) T cells in two patients with chronic lymphocytic leukaemia1-4 who achieved a complete remission in 2010. CAR T cells remained detectable more than ten years after infusion, with sustained remission in both patients. Notably, a highly activated CD4+ population emerged in both patients, dominating the CAR T cell population at the later time points. This transition was reflected in the stabilization of the clonal make-up of CAR T cells with a repertoire dominated by a small number of clones. Single-cell profiling demonstrated that these long-persisting CD4+ CAR T cells exhibited cytotoxic characteristics along with ongoing functional activation and proliferation. In addition, longitudinal profiling revealed a population of gamma delta CAR T cells that prominently expanded in one patient concomitant with CD8+ CAR T cells during the initial response phase. Our identification and characterization of these unexpected CAR T cell populations provide novel insight into the CAR T cell characteristics associated with anti-cancer response and long-term remission in leukaemia.

Two cases of severe pulmonary toxicity from highly active mesothelin-directed CAR T cells.

Multiple clinical studies have treated mesothelin (MSLN)-positive solid tumors by administering MSLN-directed chimeric antigen receptor (CAR) T cells. Although these products are generally safe, efficacy is limited. Therefore, we generated and characterized a potent, fully human anti-MSLN CAR. In a phase 1 dose-escalation study of patients with solid tumors, we observed two cases of severe pulmonary toxicity following intravenous infusion of this product in the high-dose cohort (1-3 × 108 T cells per m2). Both patients demonstrated progressive hypoxemia within 48 h of infusion with clinical and laboratory findings consistent with cytokine release syndrome. One patient ultimately progressed to grade 5 respiratory failure. An autopsy revealed acute lung injury, extensive T cell infiltration, and accumulation of CAR T cells in the lungs. RNA and protein detection techniques confirmed low levels of MSLN expression by benign pulmonary epithelial cells in affected lung and lung samples obtained from other inflammatory or fibrotic conditions, indicating that pulmonary pneumocyte and not pleural expression of mesothelin may lead to dose-limiting toxicity. We suggest patient enrollment criteria and dosing regimens of MSLN-directed therapies consider the possibility of dynamic expression of mesothelin in benign lung with a special concern for patients with underlying inflammatory or fibrotic conditions.

Chimeric Antigen Receptor T Cells in Refractory B-Cell Lymphomas.

BACKGROUND: Patients with diffuse large B-cell lymphoma or follicular lymphoma that is refractory to or that relapses after immunochemotherapy and transplantation have a poor prognosis. High response rates have been reported with the use of T cells modified by chimeric antigen receptor (CAR) that target CD19 in B-cell cancers, although data regarding B-cell lymphomas are limited. METHODS: We used autologous T cells that express a CD19-directed CAR (CTL019) to treat patients with diffuse large B-cell lymphoma or follicular lymphoma that had relapsed or was refractory to previous treatments. Patients were monitored for response to treatment, toxic effects, the expansion and persistence of CTL019 cells in vivo, and immune recovery. RESULTS: A total of 28 adult patients with lymphoma received CTL019 cells, and 18 of 28 had a response (64%; 95% confidence interval [CI], 44 to 81). Complete remission occurred in 6 of 14 patients with diffuse large B-cell lymphoma (43%; 95% CI, 18 to 71) and 10 of 14 patients with follicular lymphoma (71%; 95% CI, 42 to 92). CTL019 cells proliferated in vivo and were detectable in the blood and bone marrow of patients who had a response and patients who did not have a response. Sustained remissions were achieved, and at a median follow-up of 28.6 months, 86% of patients with diffuse large B-cell lymphoma who had a response (95% CI, 33 to 98) and 89% of patients with follicular lymphoma who had a response (95% CI, 43 to 98) had maintained the response. Severe cytokine-release syndrome occurred in 5 patients (18%). Serious encephalopathy occurred in 3 patients (11%); 2 cases were self-limiting and 1 case was fatal. All patients in complete remission by 6 months remained in remission at 7.7 to 37.9 months (median, 29.3 months) after induction, with a sustained reappearance of B cells in 8 of 16 patients and with improvement in levels of IgG in 4 of 10 patients and of IgM in 6 of 10 patients at 6 months or later and in levels of IgA in 3 of 10 patients at 18 months or later. CONCLUSIONS: CTL019 cells can be effective in the treatment of relapsed or refractory diffuse large B-cell lymphoma and follicular lymphoma. High rates of durable remission were observed, with recovery of B cells and immunoglobulins in some patients. Transient encephalopathy developed in approximately one in three patients and severe cytokine-release syndrome developed in one in five patients. (Funded by Novartis and others; ClinicalTrials.gov number, NCT02030834 .).

OX40 engagement depletes intratumoral Tregs via activating FcγRs, leading to antitumor efficacy.

Antibodies targeting checkpoint inhibitors or co-stimulatory receptors on T cells have shown significant antitumor efficacy in preclinical and clinical studies. In mouse tumor models, engagement of activating Fcγ receptor (FcγR)-expressing immune cells was recently shown to be required for the tumoricidal activity of antibodies recognizing the tumor necrosis factor superfamily receptor (TNFR) GITR (CD357) and CTLA-4 (CD152). In particular, activating FcγRs facilitated the selective elimination of intratumoral T-cell populations. However, it remains unclear whether FcγRs contribute to the antitumor efficacy of other immunomodulatory antibodies. Here, we explored the mechanism of antitumor activity mediated by an agonistic antibody (clone OX86) to the co-stimulatory TNFR OX40 (CD134). OX40 was highly expressed by intratumoral T cells, particularly those of the FoxP3(+) regulatory T-cell (Treg) lineage. OX86 administration resulted in the depletion of intratumoral regulatory T cells in an activating FcγR-dependent manner, which correlated with tumor regression. Together with previous data from our group and others, these findings support a mechanism whereby antibodies targeting antigens highly expressed by intratumoral T cells can mediate their elimination by FcγR-expressing immune cells, and facilitate subsequent antitumor immunity.

Cytokine-mediated CAR T therapy resistance in AML.

Acute myeloid leukemia (AML) is a rapidly progressive malignancy without effective therapies for refractory disease. So far, chimeric antigen receptor (CAR) T cell therapy in AML has not recapitulated the efficacy seen in B cell malignancies. Here we report a pilot study of autologous anti-CD123 CAR T cells in 12 adults with relapsed or refractory AML. CAR T cells targeting CD123+ cells were successfully manufactured in 90.4% of runs. Cytokine release syndrome was observed in 10 of 12 infused individuals (83.3%, 90% confidence interval 0.5-0.97). Three individuals achieved clinical response (25%, 90% confidence interval 0.07-0.53). We found that myeloid-supporting cytokines are secreted during cell therapy and support AML blast survival via kinase signaling, leading to CAR T cell exhaustion. The prosurvival effect of therapy-induced cytokines presents a unique resistance mechanism in AML that is distinct from any observed in B cell malignancies. Our findings suggest that autologous CART manufacturing is feasible in AML, but treatment is associated with high rates of cytokine release syndrome and relatively poor clinical efficacy. Combining CAR T cell therapies with cytokine signaling inhibitors could enhance immunotherapy efficacy in AML and achieve improved outcomes (ClinicalTrials.gov identifier: NCT03766126 ).

Repeated peripheral infusions of anti-EGFRvIII CAR T cells in combination with pembrolizumab show no efficacy in glioblastoma: a phase 1 trial.

We previously showed that chimeric antigen receptor (CAR) T-cell therapy targeting epidermal growth factor receptor variant III (EGFRvIII) produces upregulation of programmed death-ligand 1 (PD-L1) in the tumor microenvironment (TME). Here we conducted a phase 1 trial (NCT03726515) of CAR T-EGFRvIII cells administered concomitantly with the anti-PD1 (aPD1) monoclonal antibody pembrolizumab in patients with newly diagnosed, EGFRvIII+ glioblastoma (GBM) (n = 7). The primary outcome was safety, and no dose-limiting toxicity was observed. Secondary outcomes included median progression-free survival (5.2 months; 90% confidence interval (CI), 2.9-6.0 months) and median overall survival (11.8 months; 90% CI, 9.2-14.2 months). In exploratory analyses, comparison of the TME in tumors harvested before versus after CAR + aPD1 administration demonstrated substantial evolution of the infiltrating myeloid and T cells, with more exhausted, regulatory, and interferon (IFN)-stimulated T cells at relapse. Our study suggests that the combination of CAR T cells and PD-1 inhibition in GBM is safe and biologically active but, given the lack of efficacy, also indicates a need to consider alternative strategies.

A Novel Autologous CAR-T Therapy, YTB323, with Preserved T-cell Stemness Shows Enhanced CAR T-cell Efficacy in Preclinical and Early Clinical Development.

CAR T-cell product quality and stemness (Tstem) are major determinants of in vivo expansion, efficacy, and clinical response. Prolonged ex vivo culturing is known to deplete Tstem, affecting clinical outcome. YTB323, a novel autologous CD19-directed CAR T-cell therapy expressing the same validated CAR as tisagenlecleucel, is manufactured using a next-generation platform in <2 days. Here, we report the preclinical development and preliminary clinical data of YTB323 in adults with relapsed/refractory diffuse large B-cell lymphoma (r/r DLBCL; NCT03960840). In preclinical mouse models, YTB323 exhibited enhanced in vivo expansion and antitumor activity at lower doses than traditionally manufactured CAR T cells. Clinically, at doses 25-fold lower than tisagenlecleucel, YTB323 showed (i) promising overall safety [cytokine release syndrome (any grade, 35%; grade ≥3, 6%), neurotoxicity (any grade, 25%; grade ≥3, 6%)]; (ii) overall response rates of 75% and 80% for DL1 and DL2, respectively; (iii) comparable CAR T-cell expansion; and (iv) preservation of T-cell phenotype. Current data support the continued development of YTB323 for r/r DLBCL. SIGNIFICANCE: Traditional CAR T-cell manufacturing requires extended ex vivo cell culture, reducing naive and stem cell memory T-cell populations and diminishing antitumor activity. YTB323, which expresses the same validated CAR as tisagenlecleucel, can be manufactured in <2 days while retaining T-cell stemness and enhancing clinical activity at a 25-fold lower dose. See related commentary by Wang, p. 1961. This article is featured in Selected Articles from This Issue, p. 1949.

Anti-BCMA/CD19 CAR T Cells with Early Immunomodulatory Maintenance for Multiple Myeloma Responding to Initial or Later-Line Therapy.

We conducted a phase I clinical trial of anti-BCMA chimeric antigen receptor T cells (CART-BCMA) with or without anti-CD19 CAR T cells (huCART19) in multiple myeloma (MM) patients responding to third- or later-line therapy (phase A, N = 10) or high-risk patients responding to first-line therapy (phase B, N = 20), followed by early lenalidomide or pomalidomide maintenance. We observed no high-grade cytokine release syndrome (CRS) and only one instance of low-grade neurologic toxicity. Among 15 subjects with measurable disease, 10 exhibited partial response (PR) or better; among 26 subjects responding to prior therapy, 9 improved their response category and 4 converted to minimal residual disease (MRD)-negative complete response/stringent complete response. Early maintenance therapy was safe, feasible, and coincided in some patients with CAR T-cell reexpansion and late-onset, durable clinical response. Outcomes with CART-BCMA + huCART19 were similar to CART-BCMA alone. Collectively, our results demonstrate favorable safety, pharmacokinetics, and antimyeloma activity of dual-target CAR T-cell therapy in early lines of MM treatment. SIGNIFICANCE: CAR T cells in early lines of MM therapy could be safer and more effective than in the advanced setting, where prior studies have focused. We evaluated the safety, pharmacokinetics, and efficacy of CAR T cells in patients with low disease burden, responding to current therapy, combined with standard maintenance therapy. This article is highlighted in the In This Issue feature, p. 101.

Anti-CD19 CAR T cells in combination with ibrutinib for the treatment of chronic lymphocytic leukemia.

In chronic lymphocytic leukemia (CLL) patients who achieve a complete remission (CR) to anti-CD19 chimeric antigen receptor T cells (CART-19), remissions are remarkably durable. Preclinical data suggesting synergy between CART-19 and the Bruton's tyrosine kinase (BTK) inhibitor ibrutinib prompted us to conduct a prospective single-center phase 2 trial in which we added autologous anti-CD19 humanized binding domain T cells (huCART-19) to ibrutinib in patients with CLL not in CR despite ≥6 months of ibrutinib. The primary endpoints were safety, feasibility, and achievement of a CR within 3 months. Of 20 enrolled patients, 19 received huCART-19. The median follow-up for all infused patients was 41 months (range, 0.25-58 months). Eighteen patients developed cytokine release syndrome (CRS; grade 1-2 in 15 of 18 subjects), and 5 developed neurotoxicity (grade 1-2 in 4 patients, grade 4 in 1 patient). While the 3-month CR rate among International Working Group on CLL (iwCLL)-evaluable patients was 44% (90% confidence interval [CI], 23-67%), at 12 months, 72% of patients tested had no measurable residual disease (MRD). The estimated overall and progression-free survival at 48 months were 84% and 70%, respectively. Of 15 patients with undetectable MRD at 3 or 6 months, 13 remain in ongoing CR at the last follow-up. In patients with CLL not achieving a CR despite ≥6 months of ibrutinib, adding huCART-19 mediated a high rate of deep and durable remissions. ClinicalTrials.gov number, NCT02640209.

Monitoring of tisagenlecleucel transgene DNA using a quantitative polymerase chain reaction assay.

Chimeric antigen receptor (CAR)-T cell therapies reprogram T cells to engage and eliminate cancer cells. Patients' T cells are transduced in vitro using lentiviral or retroviral vectors containing a CAR transgene. Following infusion, CAR-T cells expand in vivo and may persist in the peripheral blood and bone marrow for years. Therefore, monitoring in vivo copies of the CAR transgene requires highly sensitive, validated analytical methods. Herein, we describe the validation of a qPCR assay to detect tisagenlecleucel transgene in patient samples. The limit of detection and lower limit of quantitation were 3.1 and 10 copies/200 ng genomic DNA, respectively, equivalent to ∼50 copies/µg genomic DNA and in alignment with US Food and Drug Administration guidance on bioanalytical method validation. The assay allowed quantitation of the tisagenlecleucel transgene over a wide dynamic range with a high degree of linearity, that is, 101-106 copies/200 ng genomic DNA (R2 ≥ 0.9988). Coefficients of variation of measured transgene copies ranged from 0.2% to 12.8%. A droplet digital PCR assay was performed as a method of validation and showed a strong correlation with the qPCR assay (R2 = 0.9980, p < 0.0001). This qPCR assay is being utilized to monitor tisagenlecleucel expansion and persistence in clinical trials.

An IMiD-inducible degron provides reversible regulation for chimeric antigen receptor expression and activity.

The recent development of successful CAR (chimeric antigen receptor) T cell therapies has been accompanied by a need to better control potentially fatal toxicities that can arise from adverse immune reactions. Here we present a ligand-controlled CAR system, based on the IKZF3 ZF2 ß-hairpin IMiD-inducible degron, which allows for the reversible control of expression levels of type I membrane proteins, including CARs. Testing this system in an established mouse xenotransplantation model for acute lymphoblastic leukemia, we validate the ability of the CAR19-degron to target and kill CD19-positive cells displaying complete control/clearance of the tumor. We also demonstrate that the activity of CAR19-degron can be regulated in vivo when dosing a US Food and Drug Administration-approved drug, lenalidomide.

Humanized CD19-Targeted Chimeric Antigen Receptor (CAR) T Cells in CAR-Naive and CAR-Exposed Children and Young Adults With Relapsed or Refractory Acute Lymphoblastic Leukemia.

PURPOSE: CD19-targeted chimeric antigen receptor (CAR)-modified T cells demonstrate unprecedented responses in B-cell acute lymphoblastic leukemia (B-ALL); however, relapse remains a substantial challenge. Short CAR T-cell persistence contributes to this risk; therefore, strategies to improve persistence are needed. METHODS: We conducted a pilot clinical trial of a humanized CD19 CAR T-cell product (huCART19) in children and young adults with relapsed or refractory B-ALL (n = 72) or B-lymphoblastic lymphoma (n = 2), treated in two cohorts: with (retreatment, n = 33) or without (CAR-naive, n = 41) prior CAR exposure. Patients were monitored for toxicity, response, and persistence of huCART19. RESULTS: Seventy-four patients 1-29 years of age received huCART19. Cytokine release syndrome developed in 62 (84%) patients and was grade 4 in five (6.8%). Neurologic toxicities were reported in 29 (39%), three (4%) grade 3 or 4, and fully resolved in all cases. The overall response rate at 1 month after infusion was 98% (100% in B-ALL) in the CAR-naive cohort and 64% in the retreatment cohort. At 6 months, the probability of losing huCART19 persistence was 27% (95% CI, 14 to 41) for CAR-naive and 48% (95% CI, 30 to 64) for retreatment patients, whereas the incidence of B-cell recovery was 15% (95% CI, 6 to 28) and 58% (95% CI, 33 to 77), respectively. Relapse-free survival at 12 and 24 months, respectively, was 84% (95% CI, 72 to 97) and 74% (95% CI, 60 to 90) in CAR-naive and 74% (95% CI, 56 to 97) and 58% (95% CI, 37 to 90) in retreatment cohorts. CONCLUSION: HuCART19 achieved durable remissions with long-term persistence in children and young adults with relapsed or refractory B-ALL, including after failure of prior CAR T-cell therapy.

Antigen-independent activation enhances the efficacy of 4-1BB-costimulated CD22 CAR T cells.

While CD19-directed chimeric antigen receptor (CAR) T cells can induce remission in patients with B cell acute lymphoblastic leukemia (ALL), a large subset relapse with CD19- disease. Like CD19, CD22 is broadly expressed by B-lineage cells and thus serves as an alternative immunotherapy target in ALL. Here we present the composite outcomes of two pilot clinical trials ( NCT02588456 and NCT02650414 ) of T cells bearing a 4-1BB-based, CD22-targeting CAR in patients with relapsed or refractory ALL. The primary end point of these studies was to assess safety, and the secondary end point was antileukemic efficacy. We observed unexpectedly low response rates, prompting us to perform detailed interrogation of the responsible CAR biology. We found that shortening of the amino acid linker connecting the variable heavy and light chains of the CAR antigen-binding domain drove receptor homodimerization and antigen-independent signaling. In contrast to CD28-based CARs, autonomously signaling 4-1BB-based CARs demonstrated enhanced immune synapse formation, activation of pro-inflammatory genes and superior effector function. We validated this association between autonomous signaling and enhanced function in several CAR constructs and, on the basis of these observations, designed a new short-linker CD22 single-chain variable fragment for clinical evaluation. Our findings both suggest that tonic 4-1BB-based signaling is beneficial to CAR function and demonstrate the utility of bedside-to-bench-to-bedside translation in the design and implementation of CAR T cell therapies.

B cell maturation antigen-specific CAR T cells are clinically active in multiple myeloma.

BACKGROUND: Chimeric antigen receptor (CAR) T cells are a promising therapy for hematologic malignancies. B-cell maturation antigen (BCMA) is a rational target in multiple myeloma (MM). METHODS: We conducted a phase I study of autologous T cells lentivirally-transduced with a fully-human, BCMA-specific CAR containing CD3ζ and 4-1BB signaling domains (CART-BCMA), in subjects with relapsed/refractory MM. Twenty-five subjects were treated in 3 cohorts: 1) 1-5 x 108 CART-BCMA cells alone; 2) Cyclophosphamide (Cy) 1.5 g/m2 + 1-5 x 107 CART-BCMA cells; and 3) Cy 1.5 g/m2 + 1-5 x 108 CART-BCMA cells. No pre-specified BCMA expression level was required. RESULTS: CART-BCMA cells were manufactured and expanded in all subjects. Toxicities included cytokine release syndrome and neurotoxicity, which were grade 3-4 in 8 (32%) and 3 (12%) subjects, respectively, and reversible. One subject died at day 24 from candidemia and progressive myeloma, following treatment for severe CRS and encephalopathy. Responses (based on treated subjects) were seen in 4/9 (44%) in cohort 1, 1/5 (20%) in cohort 2, and 7/11 (64%) in cohort 3, including 5 partial, 5 very good partial, and 2 complete responses, 3 of which were ongoing at 11, 14, and 32 months. Decreased BCMA expression on residual MM cells was noted in responders; expression increased at progression in most. Responses and CART-BCMA expansion were associated with CD4:CD8 T cell ratio and frequency of CD45RO-CD27+CD8+ T cells in the pre-manufacturing leukapheresis product. CONCLUSION: CART-BCMA infusions with or without lymphodepleting chemotherapy are clinically active in heavily-pretreated MM patients. TRIAL REGISTRATION: NCT02546167. FUNDING: University of Pennsylvania-Novartis Alliance and NIH.

Genetic mechanisms of target antigen loss in CAR19 therapy of acute lymphoblastic leukemia.

We identified genetic mutations in CD19 and loss of heterozygosity at the time of CD19- relapse to chimeric antigen receptor (CAR) therapy. The mutations are present in the vast majority of resistant tumor cells and are predicted to lead to a truncated protein with a nonfunctional or absent transmembrane domain and consequently to a loss of surface antigen. This irreversible loss of CD19 advocates for an alternative targeting or combination CAR approach.

Determinants of response and resistance to CD19 chimeric antigen receptor (CAR) T cell therapy of chronic lymphocytic leukemia.

Tolerance to self-antigens prevents the elimination of cancer by the immune system1,2. We used synthetic chimeric antigen receptors (CARs) to overcome immunological tolerance and mediate tumor rejection in patients with chronic lymphocytic leukemia (CLL). Remission was induced in a subset of subjects, but most did not respond. Comprehensive assessment of patient-derived CAR T cells to identify mechanisms of therapeutic success and failure has not been explored. We performed genomic, phenotypic and functional evaluations to identify determinants of response. Transcriptomic profiling revealed that CAR T cells from complete-responding patients with CLL were enriched in memory-related genes, including IL-6/STAT3 signatures, whereas T cells from nonresponders upregulated programs involved in effector differentiation, glycolysis, exhaustion and apoptosis. Sustained remission was associated with an elevated frequency of CD27+CD45RO-CD8+ T cells before CAR T cell generation, and these lymphocytes possessed memory-like characteristics. Highly functional CAR T cells from patients produced STAT3-related cytokines, and serum IL-6 correlated with CAR T cell expansion. IL-6/STAT3 blockade diminished CAR T cell proliferation. Furthermore, a mechanistically relevant population of CD27+PD-1-CD8+ CAR T cells expressing high levels of the IL-6 receptor predicts therapeutic response and is responsible for tumor control. These findings uncover new features of CAR T cell biology and underscore the potential of using pretreatment biomarkers of response to advance immunotherapies.

Resident lung antigen-presenting cells have the capacity to promote Th2 T cell differentiation in situ.

Antigen exposure via airway epithelia is often associated with a failure to prime or with the preferential priming of Th2 cells. We previously reported that the intranasal delivery of a Th1-inducing antigen promoted Th2-dominated responses, rather than the expected Th1 responses. Thus, we proposed that when pulmonary T cell priming is induced, the lung microenvironment might intrinsically favor the generation of Th2 types of responses. To establish a potential mechanism for such preferential priming, we examined the initial interactions between antigens and resident antigen-presenting cells (APCs) within the lung. We show that intranasally delivered antigens are preferentially taken up and can be presented to antigen-specific T cells by a resident population of CD11c(bright) APCs. Most of these antigen-loaded APCs remained within lung tissues, and migration into secondary lymphoid organs was not crucial for T cell priming to occur within the pulmonary tract. Furthermore, these pulmonary APCs demonstrated a marked expression of IL-6 and IL-10 within hours of antigen uptake, suggesting that resident tissue APCs have the capacity to promote Th2 T cell differentiation in situ.

A single dose of peripherally infused EGFRvIII-directed CAR T cells mediates antigen loss and induces adaptive resistance in patients with recurrent glioblastoma.

We conducted a first-in-human study of intravenous delivery of a single dose of autologous T cells redirected to the epidermal growth factor receptor variant III (EGFRvIII) mutation by a chimeric antigen receptor (CAR). We report our findings on the first 10 recurrent glioblastoma (GBM) patients treated. We found that manufacturing and infusion of CAR-modified T cell (CART)-EGFRvIII cells are feasible and safe, without evidence of off-tumor toxicity or cytokine release syndrome. One patient has had residual stable disease for over 18 months of follow-up. All patients demonstrated detectable transient expansion of CART-EGFRvIII cells in peripheral blood. Seven patients had post-CART-EGFRvIII surgical intervention, which allowed for tissue-specific analysis of CART-EGFRvIII trafficking to the tumor, phenotyping of tumor-infiltrating T cells and the tumor microenvironment in situ, and analysis of post-therapy EGFRvIII target antigen expression. Imaging findings after CART immunotherapy were complex to interpret, further reinforcing the need for pathologic sampling in infused patients. We found trafficking of CART-EGFRvIII cells to regions of active GBM, with antigen decrease in five of these seven patients. In situ evaluation of the tumor environment demonstrated increased and robust expression of inhibitory molecules and infiltration by regulatory T cells after CART-EGFRvIII infusion, compared to pre-CART-EGFRvIII infusion tumor specimens. Our initial experience with CAR T cells in recurrent GBM suggests that although intravenous infusion results in on-target activity in the brain, overcoming the adaptive changes in the local tumor microenvironment and addressing the antigen heterogeneity may improve the efficacy of EGFRvIII-directed strategies in GBM.

Rationale for anti-GITR cancer immunotherapy.

Over the past decade, our understanding of cancer immunotherapy has evolved from assessing peripheral responses in the blood to monitoring changes in the tumour microenvironment. Both preclinical and clinical experience has taught us that modulation of the tumour microenvironment has significant implications to generating robust antitumour immunity. Clinical benefit has been well documented to correlate with a tumour microenvironment that contains a dense infiltration of CD8+CD45RO+ T effectors and a high ratio of CD8+ T cells to FoxP3+ regulatory T cells (Tregs). In preclinical tumour models, modulation of the Glucocorticoid induced TNF receptor (GITR)/GITR ligand (GITRL) axis suggests this pathway may provide the desired biological outcome of inhibiting Treg function while activating CD8+ T effector cells. This review will focus on the scientific rationale and considerations for the therapeutic targeting of GITR for cancer immunotherapy and will discuss possible combination strategies to enhance clinical benefit.