High PD-1 expression and suppressed cytokine signaling distinguish T cells infiltrating follicular lymphoma tumors from peripheral T cells

Immune checkpoint blockade: Releasing the brake towards hematological malignancies

Tumor cells utilize co-inhibitory molecules to avoid host immune destruction. Checkpoint blockade has emerged as a promising approach to treat cancer by restoring T cell effector function and breaking a tumor permissive microenvironment. Patients with hematological malignancies often have immune dysregulation, thus the role of checkpoint blockade in treatment of these neoplasms is particularly intriguing. In early trials, antibodies targeting cytotoxic T lymphocyte antigen 4 (CTLA-4) or the programmed death 1 (PD-1) signaling pathway have displayed significant efficacy with minimal toxicity in patients with relapsed and refractory hematological neoplasms. In this review, we provide evidence of dysregulation of CTLA-4 and PD-1/PD-Ls in the context of several major types of hematological neoplasms and summarize relevant clinical practice points for checkpoint blockade. The preclinical rationale and preliminary clinical data of potential combination approaches designed to optimize checkpoint antagonists are well presented.

Signaling pathway and dysregulation of PD1 and its ligands in lymphoid malignancies

Tumor cells evade immune destruction, at least partially, by upregulating inhibitory signals to limit effector T cell activation. Programmed death 1 (PD-1) is one of the most critical co-inhibitory molecules limiting the T-cell antitumor response. PD-1 and its ligands, PD-L1 and PD-L2, are overexpressed by various types of tumors as well as reactive cells in the tumor microenvironment. A growing body of evidence has shown the clinical efficiency and minimal toxicity of PD-1 pathway inhibitors in patients with solid tumors, but the role of these inhibitors in lymphoid malignancies is much less well studied. In this review, we analyze the pathologic role of the PD-1 pathway in most common lymphoid malignancies and we organize the clinical data from clinical trials of PD-1 pathway inhibitors. Several anti-PD-1 regimens have shown encouraging therapeutic effects in patients with relapsed or refractory Hodgkin lymphoma, follicular lymphoma, and diffuse large B-cell lymphoma. Additional progress is needed to foster an improved understanding of the role of anti-PD-1 therapy in reconstituting antitumor immunity in patients with lymphoid malignancies. Upcoming trials will explore the clinical efficiency of combining PD-1 pathway inhibitors and various agents with diverse mechanisms of action and create more therapeutic possibilities for afflicted patients.

Current status of checkpoint inhibitors in lymphoma

Cancer immunotherapy is evolving very fast. With understanding of tumor and immune system interactions, two pathways have been identified through which tumor cells evade and escape immune system. Blocking these pathways by monoclonal antibodies has shown promising results in wide variety of tumors. The treatment of lymphomas have been evolving with various new molecules ranging from monoclonal antibodies, antibody–drug conjugates to small molecule inhibitors. Here, we review the activity of immune checkpoint inhibitors in various lymphomas. These agents have shown very promising activity in Hodgkin lymphoma and other B-cell lymphomas in early-phase clinical trials.

Rational combination therapies targeting survival signaling in aggressive B-cell leukemia/lymphoma

PURPOSE OF REVIEW

The identification of oncogenic 'driver' mutations and activated survival pathways in selected aggressive B-cell malignancies directs the development of novel adjunctive therapies using targeted small molecule inhibitors. With a focus on diffuse large B-cell lymphoma 'not otherwise specified', Hodgkin lymphoma and childhood B-cell precursor acute lymphoblastic leukemia, this review will provide an up-to-date account of the current literature on the development of new molecularly targeted treatment modalities for aggressive B-cell malignancies.

RECENT FINDINGS

Subclassification of B-cell malignancies depending on their particular genetic 'driver' lesions and transcriptional and/or signaling signatures has led to the development of targeted therapeutic approaches using small molecule inhibitors to amend current combination chemotherapy.

SUMMARY

Treatment outcome with current combination chemotherapy is still poor for subsets of aggressive B-cell malignancies, and demands development of targeted therapeutic approaches. Advanced gene expression profiling and genomic sequencing have revealed a more detailed landscape of recurrent alterations, allowing a better subclassification of B-cell lymphomas and leukemias. Many alterations directly or indirectly lead to activation of survival signaling pathways and expression of key oncoproteins and prosurvival molecules, including Janus kinase-signal transducer and activator of transcription (JAK-STAT), phosphatidylinositol-3 kinase/protein kinase B/mammalian target of rapamycin (PI3K/AKT/mTOR), avian myelocytomatosis viral oncogene homolog (MYC) and B-cell lymphoma 2 (BCLl-2). Small molecule inhibitors targeting these proteins and pathways are currently being tested in clinical trials and preclinically to improve chemotherapeutic regimes and treatment outcomes.

Microenvironment abnormalities and lymphomagenesis: Immunological aspects

Innate and adaptive immune cells within the microenvironment identify and eliminate cells displaying signs of malignant potential. Immunosurveillance effector Natural Killer (NK) cells and Cytotoxic T Lymphocytes (CTL) identify malignant cells through germline receptors such as NKG2D and in the case of CTLs, presentation of antigen through the T cell receptor. Manipulation of immunosurveillance through altered tumor-identifying ligand expression or secretion, resistance to cytotoxicity, or compromised cytotoxic cell activity through immune tolerance mechanisms all contribute to failure of these systems to prevent cancer development. This review examines the diverse mechanisms by which alterations in the immune microenvironment can promote lymphomagenesis.

Programmed cell death-1 inhibition in lymphoma

Cancers can evade the host immune system by inducing upregulation of immune inhibitory signals. Anti-programmed cell death-1 (PD-1) monoclonal antibodies block these inhibitory signals allowing the host to mount an immune response against malignant cells. This class of drugs is active in solid tumours, where upregulation of cell-surface PD-1 ligand proteins is nearly uniform. Because lymphoma is a malignancy of immune system cells, the role of the PD-1 pathway in these neoplasms is more complex. However, early clinical trials using PD-1 inhibitors have shown significant clinical activity in various subtypes of relapsed lymphoma. In this Review, we assess the scientific literature on the role of the PD-1 pathway in lymphoma, the relevant clinical data for PD-1 inhibition, and future strategies for this next generation of anticancer agents.

Are we nearing an era of chemotherapy-free management of indolent lymphoma?

Indolent B-cell lymphomas are heterogeneous, comprising three grades of follicular lymphoma, small lymphocytic lymphoma, Waldenstöm macroglobulinemia, marginal zone lymphoma, and most recently, possibly low proliferative mantle cell lymphoma. These lymphomas are characterized by a high responsiveness to chemotherapy or immunochemotherapy; however, in most cases, conventional therapy might not offer a cure. Furthermore, the patient's age at diagnosis, at time to first or subsequent relapses, as well as potential comorbidities often preclude the use of chemotherapy. Recent progress has been made in our understanding of dysregulated pathways and immunologic antitumor responses in indolent lymphoma. Major therapeutic advances have been achieved in the development of nonchemotherapeutic agents, making "chemo-free" treatment a near-future reality. In this article, we highlight these promising approaches, such as the combination of anti-CD20 antibodies with immunomodulatory drugs, with mAbs directed against other surface antigens such as CD22, with immunomodulatory antibodies such as PD-1, or with inhibitors of key steps in the B-cell receptor pathway signaling. However, the cost of such therapies and potential, albeit manageable, toxicity should be considered. Phase III trials will confirm the benefit of these new treatment strategies that do not require a chemotherapeutic drug and help us identify their exact place in the therapeutic armamentarium for indolent lymphoma. Here we focus on follicular lymphoma, which is the most frequent subtype of indolent lymphoma and for which an increasing body of evidence has emerged that supports the dawn of a new era of chemotherapy-free treatment. See all articles in this CCR Focus section, "Paradigm Shifts in Lymphoma."

Anergic bone marrow Vγ9Vδ2 T cells as early and long-lasting markers of PD-1-targetable microenvironment-induced immune suppression in human myeloma

Vγ9Vδ2 T cells have a natural inclination to recognize malignant B cells in vitro via receptors for stress-induced self-ligands and TCR-dependent recognition of phosphoantigens (pAgs) generated in the mevalonate (Mev) pathway. This inclination is continuously challenged in vivo by the immune suppression operated by tumor cells. Multiple myeloma (MM) is a prototypic B-cell malignancy in which myeloma cells subvert the local microenvironment to reshape antitumor immune responses. In this study, we have investigated the immune competence of bone marrow (BM) Vγ9Vδ2 T cells in a large series of MM patients. We have found that the BM microenvironment significantly hampers the pAg-reactivity of BM Vγ9Vδ2 T cells, which become largely PD-1⁺ and are surrounded by PD-L1⁺ myeloma cells and increased numbers of PD-L1⁺ myeloid-derived suppressor cells (MDSC). Vγ9Vδ2 T-cell dysfunction is an early event that can be already detected in individuals with monoclonal gammopathy of undetermined significance (MGUS) and not fully reverted even when MM patients achieve clinical remission. Anti-PD-1 treatment increases the cytotoxic potential of Vγ9Vδ2 T cells by almost 5-fold after pAg stimulation, and appears to be a promising strategy for effective immune interventions in MM.

Several immune escape patterns in non-Hodgkin's lymphomas

Follicular Lymphomas (FL) and diffuse large B cell lymphomas (DLBCL) must evolve some immune escape strategy to develop from lymphoid organs, but their immune evasion pathways remain poorly characterized. We investigated this issue by transcriptome data mining and immunohistochemistry (IHC) of FL and DLBCL lymphoma biopsies. A set of genes involved in cancer immune-evasion pathways (Immune Escape Gene Set, IEGS) was defined and the distribution of the expression levels of these genes was compared in FL, DLBCL and normal B cell transcriptomes downloaded from the GEO database. The whole IEGS was significantly upregulated in all the lymphoma samples but not in B cells or other control tissues, as shown by the overexpression of the PD-1, PD-L1, PD-L2 and LAG3 genes. Tissue microarray immunostainings for PD-1, PD-L1, PD-L2 and LAG3 proteins on additional biopsies from 27 FL and 27 DLBCL patients confirmed the expression of these proteins. The immune infiltrates were more abundant in FL than DLBCL samples, and the microenvironment of FL comprised higher rates of PD-1⁺ lymphocytes. Further, DLBCL tumor cells comprised a higher proportion of PD-1+, PD-L1⁺, PD-L2⁺ and LAG3⁺ lymphoma cells than the FL tumor cells, confirming that DLBCL mount immune escape strategies distinct from FL. In addition, some cases of DLBCL had tumor cells co-expressing both PD-1, PD-L1 and PD-L2. Among the DLBCLs, the activated B cell (ABC) subtype comprised more PD-L1⁺ and PD-L2⁺ lymphoma cells than the GC subtype. Thus, we infer that FL and DLBCL evolved several pathways of immune escape.

Immune checkpoint blockade in hematologic malignancies

Therapeutic blockade of immune checkpoint pathways, in particular cytotoxic T-lymphocyte associated protein 4 and programmed-death 1 (PD-1), has become a paradigm-shifting treatment in solid tumor oncology. Hematologic malignancies (HMs), many of which are known to have clinically exploitable immune sensitivity, are a natural target for this type of treatment. Several clinical trials of checkpoint blockade have been conducted in HM, with preliminary results suggesting the therapeutic usefulness of this approach across several tumor types. In particular, the results of PD-1 blockade in Hodgkin lymphoma (HL) are remarkable, and raise hope that it may alter the treatment landscape in this disease. However, numerous questions remain about the optimal role of checkpoint blockade both in HL and beyond. Those questions are the focus of this review, in the hope that, if we are at the dawn of a new day in HM immunotherapy, we may begin to envision its morning.

Current state of anti-PD-L1 and anti-PD-1 agents in cancer therapy

Immunotherapy for the treatment of cancer is rapidly evolving from therapies that globally and non-specifically simulate the immune system to more targeted activation of individual components of the immune system. The net result of this targeted approach is decreased toxicity and increased efficacy of immunotherapy. More specifically, therapies that inhibit the interaction between programmed death ligand 1 (PD-L1), present on the surface of tumor or antigen-presenting cells, and programmed death 1 (PD-1), present on the surface of activated lymphocytes, are generating much excitement and enthusiasm, even in malignancies that are not traditionally considered to be immunogenic. Herein, we review the current landscape of anti-PD-1 and anti-PD-L1 therapies in the world of oncology. We have performed a comprehensive literature search on the data available through PubMed, Medline, Scopus, the ClinicalTrials.gov registry, and abstracts from major oncology meetings in order to summarize the clinical data of anti-PD-1/PD-L1 therapies.

CD10 delineates a subset of human IL-4 producing follicular helper T cells involved in the survival of follicular lymphoma B cells

In follicular lymphoma (FL), follicular helper T cells (TFH) have been depicted as one of the main components of the malignant B-cell niche and a promising therapeutic target. Although defined by their capacity to sustain FL B-cell growth together with specific gene expression and cytokine secretion profiles, FL-TFH constitute a heterogeneous cell population. However, specific markers reflecting such functional heterogeneity are still lacking. In this study, we demonstrate that CD10 identifies a subset of fully functional germinal center TFH in normal secondary lymphoid organs. Importantly, this subset is amplified in the FL context, unlike in other B-cell lymphomas with a follicular growth pattern. Furthermore, whereas FL-TFH produce high levels of interleukin (IL)-21 and low levels of IL-17 irrespectively of their CD10 expression, CD10(pos) FL-TFH specifically exhibit an IL-4(hi)IFN-γ(lo)TNF-α(hi) cytokine profile associated with a high capacity to sustain directly and indirectly malignant B-cell survival. Altogether, our results highlight the important role of this novel functional subset in the FL cell niche.

PD-1 expression defines two distinct T-cell sub-populations in follicular lymphoma that differentially impact patient survival

To determine the biological and clinical relevance of programmed death 1 (PD-1) in follicular lymphoma (FL), we characterized PD-1⁺ T-cell subsets and assessed their biological function as well as potential clinical impact. We found that PD-1 is expressed on intratumoral CD4⁺ T cells with both bright and dim intensity, representing two different sub-populations of cells. By immunohistochemistry, we found that CD4⁺PD-1^high T cells predominantly reside in the lymph node follicles, while PD-1^low T cells are mainly located in an interfollicular pattern. Intratumoral CD4⁺PD-1^high T cells have a T_FH cell phenotype, express CXCR5, secrete IL-21 and are BCL-6 positive with no TIM-3 expression. In contrast, CD4⁺PD-1^low T cells have an exhausted phenotype, express TIM-3 and do not express BCL-6 and CXCR5. Functionally, CD4⁺PD-1^high T cells actively supported B-cell growth, while CD4⁺PD-1^low T cells displayed a reduced cytokine production and cell-signal transduction. Clinically, we observed that the numbers of CD4⁺ or CD8⁺PD-1^low T cells significantly correlate with a reduced overall survival in FL patients (P=0.007 and 0.04 respectively; n=32). In contrast, the number of CD4⁺PD-1^high T cells was not associated with patient outcome. Taken together, these results indicated that PD-1 expression defines two sub-populations with distinct functions that differentially impact patient outcome in FL.

Chemotherapy-free treatment in patients with follicular lymphoma

The outcome of patients with follicular lymphoma (FL) has improved over the last two decades through the introduction of anti-CD20 monoclonal antibodies, usually used in combination with chemotherapy. However, patients with FL still experience multiple relapses, requiring several lines of treatment. Early toxicity of chemotherapy is a significant concern and as the life expectancy of patients with FL is increasing, late toxicities become an increasingly important concern. Progress made in understanding the biology of FL, especially dysregulation of intracellular pathways and immunological antitumor responses, recently allowed for the development of innovative chemo-free therapeutic approaches. In this report, different options such as new anti-CD20 antibodies, antibodies targeting other cell surface antigens, bi-specific antibodies, immunomodulation, idiotype vaccine and other targeted therapies are presented. The article also highlights how, although promising in early phase studies, the cost-effectiveness of new agents will have to be justified in Phase III trials. Furthermore, chemo-free regimen might not mean toxicity-free treatment and monitoring of early and late toxicities is required.

Checkpoint blockade in lymphoma

Immune checkpoint blockade therapy (CBT) was born of the combination of several elements: the understanding of some of the important immune regulation pathways in humans; the recognition that tumors can engage those pathways to evade immune responses; and the clinical development of monoclonal antibodies targeting checkpoint receptors to restore effective anti-tumor immunity. This form of therapy, focused to date mostly on the cytotoxic T-lymphocyte associated protein 4 (CTLA-4) and programmed-death 1 (PD-1) pathways, has already revolutionized the treatment of several solid tumors. Hematologic malignancies (HMs) offer a promising testing ground for this strategy, and several trials have already demonstrated evidence of therapeutic activity with checkpoint blockade, especially in lymphoma. This review will discuss the current clinical results of CBT in lymphoma in the context of their scientific underpinning, and build from this summary a projection of how the field may evolve in the near future.

Indolent lymphoma: follicular lymphoma and the microenvironment-insights from the microscope

Follicular lymphomas (FLs) are neoplasms of germinal center (GC) B cells, which retain many of the morphologic, immunophenotypic, genetic, and functional features of normal GC B cells. Both normal GCs and neoplastic follicles of FL also contain non-neoplastic cells (microenvironment) that influence and are influenced by the GC and FL B cells and are likely important for tumor cell survival. Many insights into the nature of the GC/FL microenvironment have come from morphologic and immunophenotypic analysis, both before and after the discoveries from gene expression profiling. This chapter reviews what we have learned from the microscope and highlights the pitfalls involved in trying to enumerate cells in the microenvironment for clinical prognostication.

Elevated serum levels of IL-2R, IL-1RA, and CXCL9 are associated with a poor prognosis in follicular lymphoma

Serum cytokines and chemokines may reflect tumor biology and host response in follicular lymphoma (FL). To determine whether the addition of these biological factors may further refine prognostication, 30 cytokines and chemokines were measured in pretreatment serum specimens from newly diagnosed FL patients (n = 209) and from 400 matched controls. Cytokine levels were correlated with clinical outcome in patients who were observed or received single agent rituximab, or those who received chemotherapy. Correlations with outcome in chemotherapy treated patients were further examined in a separate cohort of 183 South West Oncology Group (SWOG) patients and all patients were then included in a meta-analysis. Six cytokines were associated with outcome in the Molecular Epidemiology Resource (MER) after adjusting for the FL international prognostic index. In patients who were observed or treated with rituximab alone, increased serum IL-12 and interleukin 1 receptor antagonist (IL-1RA) (P = .005 and .02) were associated with a shorter event-free survival. In patients receiving chemotherapy, hepatocyte growth factor, IL-8, IL-1RA, and CXCL9 (P = .015, .048, .004, and .0005) predicted a shorter EFS. When the MER chemotherapy treated patients and SWOG patients were combined in a meta-analysis, IL-2R, IL-1RA, and CXCL9 (P = .013, .042, and .0012) were associated with a poor EFS.

The perspective of immunotherapy: new molecules and new mechanisms of action in immune modulation

PURPOSE OF REVIEW

Targeting CTLA-4, the patriarch of immune checkpoint modulators, is currently the only immunotherapeutic approach that has achieved significant clinical benefit in melanoma phase III trials. In this review, recent new ideas about the mechanism of action of anti-CTLA antibodies, other new molecules to target, and rationales for combination therapies will be discussed.

RECENT FINDINGS

Although the clinical efficacy of the anti-CTLA-4 monoclonal antibody (mAb) ipilimumab is meanwhile without doubt, its mechanism of action is still not fully understood. Recent data indicate that, besides modulation of the TCR signal, CTLA-4 mAbs can mediate regulatory T-cell depletion in an Fc gamma receptor dependent manner.Blockade of the molecules PD-1 and PD-L1 has given promising clinical responses (and this beyond melanoma), whereas their complex expression and interaction pattern makes a clear statement about the mechanism of action challenging.Additional other co-inhibitory and co-stimulatory molecules have been identified recently. Combinations of immune checkpoint modulators themselves or with other therapies, such as adoptive cell therapy, targeted therapy or radiotherapy, will improve the outcomes further.

SUMMARY

Immune checkpoint blockade is currently the most promising systemic therapeutic approach to achieve long-lasting responses or even cure in melanoma and other malignancies.

New antibody approaches to lymphoma therapy

The CD20-directed monoclonal antibody rituximab established a new era in lymphoma therapy. Since then other epitopes on the lymphoma surface have been identified as potential targets for monoclonal antibodies (mAb). While most mAbs eliminate lymphoma cells mainly by antibody-dependent cellular cytotoxicity, complement-dependent cytotoxicity or direct cell death, others counter mechanisms utilized by malignant cells to evade immune surveillance. Expression of PD-L1 on malignant or stromal cells in the tumor environment for example leads to T-cell anergy. Targeting either PD-1 or PD-L1 via mAbs can indirectly eliminate cancer cells by unblocking the host intrinsic immune response. Yet another mechanism of targeted therapy with mAbs are bi-specific T-cell engagers (BiTE) such as blinatumomab, which directly engages the host immune cells. These examples highlight the broad spectrum of available therapies targeting the lymphoma surface with mAbs utilizing both passive and active immune pathways. Many of these agents have already demonstrated significant activity in clinical trials. In this review we will focus on novel CD20-directed antibodies as well as mAbs directed against newer targets like CD19, CD22, CD40, CD52 and CCR4. In addition we will review mAbs unblocking immune checkpoints and the BiTE blinatumomab. Given the success of mAbs and the expansion in active and passive immunotherapies, these agents will play an increasing role in the treatment of lymphomas.

High-dimensional single-cell cancer biology

Cancer cells are distinguished from each other and from healthy cells by features that drive clonal evolution and therapy resistance. New advances in high-dimensional flow cytometry make it possible to systematically measure mechanisms of tumor initiation, progression, and therapy resistance on millions of cells from human tumors. Here we describe flow cytometry techniques that enable a "single-cell " view of cancer. High-dimensional techniques like mass cytometry enable multiplexed single-cell analysis of cell identity, clinical biomarkers, signaling network phospho-proteins, transcription factors, and functional readouts of proliferation, cell cycle status, and apoptosis. This capability pairs well with a signaling profiles approach that dissects mechanism by systematically perturbing and measuring many nodes in a signaling network. Single-cell approaches enable study of cellular heterogeneity of primary tissues and turn cell subsets into experimental controls or opportunities for new discovery. Rare populations of stem cells or therapy-resistant cancer cells can be identified and compared to other types of cells within the same sample. In the long term, these techniques will enable tracking of minimal residual disease (MRD) and disease progression. By better understanding biological systems that control development and cell-cell interactions in healthy and diseased contexts, we can learn to program cells to become therapeutic agents or target malignant signaling events to specifically kill cancer cells. Single-cell approaches that provide deep insight into cell signaling and fate decisions will be critical to optimizing the next generation of cancer treatments combining targeted approaches and immunotherapy.

Safety and activity of PD1 blockade by pidilizumab in combination with rituximab in patients with relapsed follicular lymphoma: a single group, open-label, phase 2 trial

BACKGROUND

Endogenous or iatrogenic antitumour immune responses can improve the course of follicular lymphoma, but might be diminished by immune checkpoints in the tumour microenvironment. These checkpoints might include effects of programmed cell death 1 (PD1), a co-inhibitory receptor that impairs T-cell function and is highly expressed on intratumoral T cells. We did this phase 2 trial to investigate the activity of pidilizumab, a humanised anti-PD1 monoclonal antibody, with rituximab in patients with relapsed follicular lymphoma.

METHODS

We did this open-label, non-randomised trial at the University of Texas MD Anderson Cancer Center (Houston, TX, USA). Adult (≥18 years) patients with rituximab-sensitive follicular lymphoma relapsing after one to four previous therapies were eligible. Pidilizumab was administered at 3 mg/kg intravenously every 4 weeks for four infusions, plus eight optional infusions every 4 weeks for patients with stable disease or better. Starting 17 days after the first infusion of pidilizumab, rituximab was given at 375 mg/m(2) intravenously weekly for 4 weeks. The primary endpoint was the proportion of patients who achieved an objective response (complete response plus partial response according to Revised Response Criteria for Malignant Lymphoma). Analysis was by intention to treat. This trial is registered with ClinicalTrials.gov, number NCT00904722.

FINDINGS

We enrolled 32 patients between Jan 13, 2010, and Jan 20, 2012. Median follow-up was 15.4 months (IQR 10.1-21.0). The combination of pidilizumab and rituximab was well tolerated, with no autoimmune or treatment-related adverse events of grade 3 or 4. The most common adverse events of grade 1 were anaemia (14 patients) and fatigue (13 patients), and the most common adverse event of grade 2 was respiratory infection (five patients). Of the 29 patients evaluable for activity, 19 (66%) achieved an objective response: complete responses were noted in 15 (52%) patients and partial responses in four (14%).

INTERPRETATION

The combination of pidilizumab plus rituximab is well tolerated and active in patients with relapsed follicular lymphoma. Our results suggest that immune checkpoint blockade is worthy of further study in follicular lymphoma.

FUNDING

National Institutes of Health, Leukemia and Lymphoma Society, Cure Tech, and University of Texas MD Anderson Cancer Center.

Radioimmunotherapy combined with maintenance anti-CD20 antibody may trigger long-term protective T cell immunity in follicular lymphoma patients

Growing evidence suggests that the patient's immune response may play a major role in the long-term efficacy of antibody therapies of follicular lymphoma (FL). Particular long-lasting recurrence free survivals have been observed after first line, single agent rituximab or after radioimmunotherapy (RIT). Rituximab maintenance, furthermore, has a major efficacy in prolonging recurrence free survival after chemotherapy. On the other hand, RIT as a single step treatment showed a remarkable capacity to induce complete and partial remissions when applied in recurrence and as initial treatment of FL or given for consolidation. These clinical results strongly suggest that RIT combined with rituximab maintenance could stabilize the high percentages of patients with CR and PR induced by RIT. While the precise mechanisms of the long-term efficacy of these 2 treatments are not elucidated, different observations suggest that the patient's T cell immune response could be decisive. With this review, we discuss the potential role of the patient's immune system under rituximab and RIT and argue that the T cell immunity might be particularly promoted when combining the 2 antibody treatments in the early therapy of FL.

The yin and the yang of follicular lymphoma cell niches: role of microenvironment heterogeneity and plasticity

Follicular lymphoma (FL) results from the malignant transformation of germinal center B cells and is characterized by recurrent genetic alterations providing a direct growth advantage or facilitating interaction with tumor microenvironment. In agreement, accumulating evidences suggest a dynamic bidirectional crosstalk between FL B cells and surrounding non-malignant cells within specialized tumor niches in both invaded lymph nodes and bone marrow. Infiltrating stromal cells, macrophages, and T/NK cell subsets either contribute to anti-tumor immune response, or conversely form a tumor supportive network promoting FL B cell survival, growth, and drug resistance. This review depicts the phenotypic heterogeneity and functional plasticity of the most important FL cell partners and describes their complex interplay. We also unravel how malignant B cells recruit and subvert accessory immune and stromal cells to trigger their polarization toward a supportive phenotype. Based on these observations, innovative therapeutic approaches have been recently proposed, in order to benefit from local anti-tumor immunity and/or to selectively target the protective cell niche.

Immune checkpoint blockade immunotherapy to activate anti-tumour T-cell immunity

The tumour microenvironment plays a dual role in cancer: it can promote tumour progression by establishing pro-tumour survival conditions but can also suppress tumour progression by killing cancer cells or inhibiting their outgrowth. These dynamically interconnected processes are under intense investigation to better understand cancer pathophysiology and allow identification of new therapeutic approaches. The ability of cancer cells to evade anti-tumour T-cell activity in the microenvironment has recently been accepted as a hallmark of cancer progression. This review will highlight the most promising therapeutic approach aimed at activating anti-tumour T-cell immunity in the cancer microenvironment: blocking inhibitory immune regulatory proteins (immune checkpoint ligands and receptors). There is emerging evidence that haematological tumours co-opt immune checkpoints as a major immune resistance mechanism. Pre-clinical findings indicate that targeted therapies and blockade of immune checkpoints could be combined to promote therapeutic synergy and long-term anti-tumour immunity to improve clinical outcomes for cancer patients.