Negative effect of CTLA-4 on induction of T-cell immunity in vivo to B7-1+, but not B7-2+, murine myelogenous leukemia

A novel costimulatory molecule gene-modified leukemia cell-derived exosome enhances the anti-leukemia efficacy of DC vaccine in mouse models

OBJECTIVES

Leukemia cell-derived exosomes (LEXs), carrying leukemia cell-specific antigens, can serve as a source of antigen for dendritic cell (DC) vaccine loading. However, LEX-targeted DC-based vaccines have demonstrated limited antitumor immune effects in clinical trials, attributed to the low immunogenicity of LEXs and the scant levels of costimulatory molecules on DCs. The costimulatory molecules CD80 and CD86, which are crucial to DC function, play a significant role in enhancing immune efficacy. In this study, we explored the anti-leukemia immune response of costimulatory molecule gene-modified LEX-targeted DCs (LEX-8086) in vitro and in animal models.

METHODS

DCs were incubated with LEX-8086 to produce LEX-8086-targeted DCs (DCsLEX-8086). ELISA, cytotoxicity assays and flow cytometry utilized to assess the antitumor efficacy of DCsLEX8086 in vitro. Flow cytometry was used to evaluate the immunomodulatory function of DCsLEX8086 in animal models.

RESULTS

Our findings indicated that LEX-8086 enhanced the maturation and antigen-presenting ability of DCs. Immunization with DCsLEX8086 significantly activated CD8+ T cells and boosted the CTL response in vitro. More importantly, DCsLEX-8086 effectively suppressed tumor growth and exerted anti-leukemia effects in both prophylactic and therapeutic animal models. Furthermore, DCsLEX-8086 promoted the proportion of CD4+ T cells, CD8+ T cells and M1 macrophages in the tumor environments both prophylactically and therapeutically. Treatment with DCsLEX-8086 showed no significant difference in the levels of M2 macrophages but decreased the proportion of Tregs within the tumor bed during therapeutic experiments.

CONCLUSION

The results suggested that DCsLEX-8086 induces a more effective anti-leukemia immunity compared to DCsLEX-null in vivo and in vitro. DCsLEX-8086 might achieve antitumor effects by elevating the numbers of CD4+ T cells, CD8+ T cells, and M1 macrophages in tumors. Our findings indicate that DCsLEX-8086 could be leveraged to develop a new, highly effective vaccine for anti-leukemia immunity.

The prognostic signature based on glycolysis-immune related genes for acute myeloid leukemia patients

Acute myeloid leukemia (AML) is widely considered an immunoresponsive malignancy. However, potential association between glycolysis-immune related genes and AML patients' prognosis has been seldom studied. AML-related data was downloaded from TCGA and GEO databases. We grouped patients according to Glycolysis status, Immune Score and combination analysis, basing on which overlapped differentially expressed genes (DEGs) were identified. The Risk Score model was then established. The results showed that totally 142 overlapped genes were probably correlated with glycolysis-immunity in AML patients, among which 6 optimal genes were screened to construct Risk Score. High Risk Score was an independent poor prognostic factor for AML. In conclusion, we established a relatively reliable prognostic signature of AML based on glycolysis-immunity related genes, including METTL7B, HTR7, ITGAX, TNNI2, SIX3 and PURG.

Dendritic cells can prime anti-tumor CD8+ T cell responses through major histocompatibility complex cross-dressing

Antigen cross-presentation, wherein dendritic cells (DCs) present exogenous antigen on major histocompatibility class I (MHC-I) molecules, is considered the primary mechanism by which DCs initiate tumor-specific CD8+ T cell responses. Here, we demonstrate that MHC-I cross-dressing, an antigen presentation pathway in which DCs acquire and display intact tumor-derived peptide:MHC-I molecules, is also important in orchestrating anti-tumor immunity. Cancer cell MHC-I expression was required for optimal CD8+ T cell activation in two subcutaneous tumor models. In vivo acquisition of tumor-derived peptide:MHC-I molecules by DCs was sufficient to induce antigen-specific CD8+ T cell priming. Transfer of tumor-derived human leukocyte antigen (HLA) molecules to myeloid cells was detected in vitro and in human tumor xenografts. In conclusion, MHC-I cross-dressing is crucial for anti-tumor CD8+ T cell priming by DCs. In addition to quantitatively enhancing tumor antigen presentation, MHC cross-dressing might also enable DCs to more faithfully and efficiently mirror the cancer cell peptidome.

Immune-Based Therapeutic Interventions for Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is an aggressive, clonally heterogeneous, myeloid malignancy, with a 5-year overall survival of approximately 27%. It constitutes the most common acute leukemia in adults, with an incidence of 3-5 cases per 100,000 in the United States. Despite great advances in understanding the molecular mechanisms underpinning leukemogenesis, the past several decades had seen little change to the backbone of therapy, comprised of an anthracycline-based induction regimen for those who are fit enough to receive it, followed by risk-stratified post-remission therapy with consolidation cytarabine or allogeneic stem cell transplantation (allo-SCT). Allo-SCT is the most fundamental form of immunotherapy in which donor cytotoxic T and NK cells recognize and eradicate residual AML in the graft-versus-leukemia (GvL) effect. Building on that, several alternative or synergistic approaches to exploit both self and foreign immunity against AML have been developed. Checkpoint inhibitors, for example, CTLA-4 inhibitors, PD-1 inhibitors, and PD-L1 inhibitors block proteins found on T cells or cancer cells that stop the immune system from attacking the cancer cells. They have been used with limited success in both the AML relapsed/refractory (R/R) and post SCT settings. AML tumor mutational burden is low compared to solid tumors and thus, it is less likely to generate neoantigens and respond to antibody-mediated checkpoint blockade that has shown unprecedented results in solid tumors. Therefore, alternative therapeutic strategies that work independently of the T cell receptor (TCR) specificity have been developed. They include bispecific antibodies, which recruit T cells through CD3 engagement, and in AML have shown an overall response rate ranging between 14 and 30% in early phase trials. Chimeric Antigen Receptor (CAR) T cell therapy is a type of treatment in which T cells are genetically engineered to produce a recombinant receptor that redirects the specificity and function of T lymphocytes. However, lack of cell surface targets exclusively expressed on AML cells including Leukemic Stem Cells (LSCs) combined with clonal heterogeneity represents the biggest challenge in developing CAR therapy for AML. Antibody-Drug Conjugates (ADC) constitute the only FDA-approved immunotherapy to treat AML with Gemtuzumab Ozogamicin, a CD33-specific ADC used in CEBPα-mutated AML. The identification of additional cell surface targets is critical for the development of other ADC's potentially useful in the induction and maintenance regimens, given the ease at which these reagents can be generated and managed. Here, we will review those immune-based therapeutic interventions and highlight active areas of research investigations toward fulfillment of the great promise of immunotherapy to AML.

Immunosuppressive Cell Subsets and Factors in Myeloid Leukemias

Simple Summary

Effector immune system cells have the ability to kill tumor cells. However, as a cancer (such as leukemia) develops, it inhibits and evades the effector immune response. Such a state of immunosuppression can be driven by several factors – receptors, soluble cytokines, as well as by suppressive immune cells. In this review, we describe factors and cells that constitute immunosuppressive microenvironment of myeloid leukemias. We characterize factors of direct leukemic origin, such as inhibitory receptors, enzymes and extracellular vesicles. Furthermore, we describe suppressive immune cells, such as myeloid derived suppressor cells and regulatory T cells. Finally, we sum up changes in these drivers of immune evasion in myeloid leukemias during therapy.

Abstract

Both chronic myeloid leukemia and acute myeloid leukemia evade the immune response during their development and disease progression. As myeloid leukemia cells modify their bone marrow microenvironment, they lead to dysfunction of cytotoxic cells, such as CD8+ T cells or NK cells, simultaneously promoting development of immunosuppressive regulatory T cells and suppressive myeloid cells. This facilitates disease progression, spreading of leukemic blasts outside the bone marrow niche and therapy resistance. The following review focuses on main immunosuppressive features of myeloid leukemias. Firstly, factors derived directly from leukemic cells – inhibitory receptors, soluble factors and extracellular vesicles, are described. Further, we outline function, properties and origin of main immunosuppressive cells - regulatory T cells, myeloid derived suppressor cells and macrophages. Finally, we analyze interplay between recovery of effector immunity and therapeutic modalities, such as tyrosine kinase inhibitors and chemotherapy.

Emerging Immunotherapy for Acute Myeloid Leukemia

Several immune checkpoint molecules and immune targets in leukemic cells have been investigated. Recent studies have suggested the potential clinical benefits of immuno-oncology (IO) therapy against acute myeloid leukemia (AML), especially targeting CD33, CD123, and CLL-1, as well as immune checkpoint inhibitors (e.g., anti-PD (programmed cell death)-1 and anti-CTLA4 (cytotoxic T-lymphocyte-associated protein 4) antibodies) with or without conventional chemotherapy. Early-phase clinical trials of chimeric antigen receptor (CAR)-T or natural killer (NK) cells for relapsed/refractory AML showed complete remission (CR) or marked reduction of marrow blasts in a few enrolled patients. Bi-/tri-specific antibodies (e.g., bispecific T-cell engager (BiTE) and dual-affinity retargeting (DART)) exhibited 11-67% CR rates with 13-78% risk of cytokine-releasing syndrome (CRS). Conventional chemotherapy in combination with anti-PD-1/anti-CTLA4 antibody for relapsed/refractory AML showed 10-36% CR rates with 7-24 month-long median survival. The current advantages of IO therapy in the field of AML are summarized herein. However, although cancer vaccination should be included in the concept of IO therapy, it is not mentioned in this review because of the paucity of relevant evidence.

Immunotherapy and Immunomodulation in Myeloproliferative Neoplasms

Myeloproliferative neoplasms are characterized by chronic inflammation. The discovery of constitutively active JAK-STAT signaling associated with driver mutations has led to clinical and translational breakthroughs. Insights into the other pathways and novel factors of potential importance are being actively investigated. Various classes of agents with immunomodulating or immunosuppressive properties have been used with varying degrees of success in treating myeloproliferative neoplasms. Early clinical trials are investigating the feasibility, effectiveness, and safety of immune checkpoint inhibitors, cell-based immunotherapies, and SMAC mimetics. The dynamic landscape of immunotherapy and immunomodulation in myeloproliferative neoplasms is the topic of the present review.

Loss of BIM in T cells results in BCL-2 family BH3-member compensation but incomplete cell death sensitivity normalization

BIM is the master BH3-only BCL-2 family regulator of lymphocyte survival. To understand how long-term loss of BIM affects apoptotic resistance in T cells we studied animals with T cell-specific deletion of Bim. Unlike CD19^CREBim^fl/fl animals, LCK^CREBim^fl/fl mice have pronounced early lymphocytosis followed by normalization of lymphocyte counts over time. This normalization occurred in mature T cells, as thymocyte development and apoptotic sensitivity remained abnormal in LCK^CREBim^fl/fl mice. T cells from aged mice experienced normalization of their absolute cell numbers and responses against various apoptotic stimuli. mRNA expression levels of BCL-2 family proteins in CD4⁺ and CD8⁺ T cells from young and old mice revealed upregulation of several BH3-only proteins, including Puma, Noxa, and Bmf. Despite upregulation of various BH3 proteins, there were no differences in anti-apoptotic BCL-2 protein dependency in these cells. However, T cells had continued resistance to direct BIM BH3-induced mitochondrial depolarization. This study further highlights the importance of BIM in cell death maintenance in T cells and provides new insight into the dynamism underlying BH3-only regulation of T cell homeostasis versus induced cell death and suggests that CD4⁺ and CD8⁺ T cells compensate differently in response to loss of Bim.

Immune evasion mechanisms in acute myeloid leukemia: A focus on immune checkpoint pathways

Immune surveillance mechanisms comprising of adaptive and innate immune systems are naturally designed to eliminate AML development. However, leukemic cells apply various immune evasion mechanisms to deviate host immune responses resulting tumor progression. One of the recently well-known immune escape mechanisms is over-expression of immune checkpoint receptors and their ligands. Introduction of blocking antibodies targeting co-inhibitory molecules achieved invaluable success in tumor targeted therapy. Moreover, several new co-inhibitory pathways are currently studying for their potential impacts on improving anti-tumor immune responses. Although immunotherapeutic strategies based on the blockade of immune checkpoint molecules have shown promising results in a number of hematological malignances, their effectiveness in AML patients showed less remarkable success. This review discusses current knowledge about the involvement of co-inhibitory signaling pathways in immune evasion mechanisms of AML and potential application of immune checkpoint inhibitors for targeted immunotherapy of this malignancy.

Whole leukemia cell vaccines: Past progress and future directions

It has long been recognized that allogeneic hematopoietic stem cell transplantation can reduce the risk of leukemia relapse by inducing the graft-versus-leukemia effect. However, allogeneic stem cell transplantation is also known to be able to cause graft-versus-host disease, which can cause considerable morbidity and even mortality in patients receiving allogeneic hematopoietic stem cell transplantation. Therefore, to elicit leukemia-specific immune responses without alloimmune reaction, the possibilities of active immunotherapy methods such as leukemia vaccines have been studied for decades. Among various types of leukemia vaccines, whole leukemia cell vaccines are known to be able to induce immune responses against multiple unknown antigens without the need for adoptive transfer of dendritic cells. In this review, we will discuss the past progress of whole leukemia cell vaccines, with a focus on strategies to enhance their immunogenicity. We will also present the future directions of whole leukemia cell vaccines along with addressing newly emerging concepts, such as immunogenic cell death and necroptosis. We will not discuss in detail other factors that can reduce the therapeutic efficacy of whole leukemia cell vaccines such as various immunosuppressive mechanisms of leukemia.

Alterations of T-cell-mediated immunity in acute myeloid leukemia

Acute myeloid leukemia (AML) is a systemic, heterogeneous hematologic malignancy with poor overall survival. While some malignancies have seen improvements in clinical outcomes with immunotherapy, success of these agents in AML remains elusive. Despite limited progress, stem cell transplantation and donor lymphocyte infusions show that modulation of the immune system can improve overall survival of AML patients. Understanding the causes of immune evasion and disease progression will identify potential immune-mediated targets in AML. This review explores immunosuppressive mechanisms that alter T-cell-mediated immunity in AML.

Immune checkpoint blockade and CAR-T cell therapy in hematologic malignancies

Harnessing the power of the immune system to recognize and eliminate cancer cells is a longtime exploration. In the past decade, monoclonal antibody (mAb)-based immune checkpoint blockade (ICB) and chimeric antigen receptor T (CAR-T) cell therapy have proven to be safe and effective in hematologic malignancies. Despite the unprecedented success of ICB and CAR-T therapy, only a subset of patients can benefit partially due to immune dysfunction and lack of appropriate targets. Here, we review the preclinical and clinical advances of CTLA-4 and PD-L1/PD-1-based ICB and CD19-specific CAR-T cell therapy in hematologic malignancies. We also discuss the basic research and ongoing clinical trials on emerging immune checkpoints (Galectin-9/Tim-3, CD70/CD27, LAG-3, and LILRBs) and on new targets for CAR-T cell therapy (CD22, CD33, CD123, BCMA, CD38, and CD138) for the treatment of hematologic malignancies.

Immune checkpoint-based therapy in myeloid malignancies: a promise yet to be fulfilled

INTRODUCTION

Immune system evasion is essential for tumor cell survival and is mediated by the immunosuppressive tumor microenvironment and the activation of inhibitory immune checkpoints. While immune checkpoint-based therapy yielded impressive results in several advanced solid malignancies such as melanoma and non-small cell lung cancer, its role in acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS) is still evolving. Areas covered: Here we review the immunology in the tumor microenvironment in the bone marrow and discuss the current preclinical and clinical data for immune checkpoint-based therapy in myeloid neoplasms. Expert commentary: Clinical trials of immune checkpoint inhibitors (ICI) in AML and MDS are still in early stages and reported results so far have been modest especially for monotherapy use in the refractory settings. However, there are preliminary data for synergistic effects for combination of multiple ICI with hypomethylating agents and conventional chemotherapy. ICI might also be effective in eradicating minimal residual disease and to prevent relapse following induction chemotherapy or hematopoietic stem cell transplant. Additional trials to provide insight into the efficacy and safety profile of immune checkpoint-based therapy, its optimal timing and potential combination with other types of therapy as well as identification of predictive biomarkers are needed.

Inhibition of RON kinase potentiates anti-CTLA-4 immunotherapy to shrink breast tumors and prevent metastatic outgrowth

The advent of immune checkpoint blockade as a new strategy for immunotherapy has changed the outlook for many aggressive cancers. Although complete tumor eradication is attainable in some cases, durable clinical responses are observed only in a small fraction of patients, underlining urgent need for improvement. We previously showed that RON, a receptor tyrosine kinase expressed in macrophages, suppresses antitumor immune responses, and facilitates progression and metastasis of breast cancer. Here, we investigated the molecular changes that occur downstream of RON activation in macrophages, and whether inhibition of RON can cooperate with checkpoint immunotherapy to eradicate tumors. Activation of RON by its ligand, MSP, altered the gene expression profile of macrophages drastically and upregulated surface levels of CD80 and PD-L1, ligands for T-cell checkpoint receptors CTLA-4 and PD-1. Genetic deletion or pharmacological inhibition of RON in combination with anti-CTLA-4, but not with anti-PD-1, resulted in improved clinical responses against orthotopically transplanted tumors compared to single-agent treatment groups, resulting in complete tumor eradication in 46% of the animals. Positive responses to therapy were associated with higher levels of T-cell activation markers and tumor-infiltrating lymphocytes. Importantly, co-inhibition of RON and anti-CTLA-4 was also effective in clearing metastatic breast cancer cells in lungs, resulting in clinical responses in nearly 60% of the mice. These findings suggest that RON inhibition can be a novel approach to potentiate responses to checkpoint immunotherapy in breast cancer.

Targeting the Immune Microenvironment in Acute Myeloid Leukemia: A Focus on T Cell Immunity

Immunotherapies, such as chimeric antigen receptor T cells, bispecific antibodies, and immune checkpoint inhibitors, have emerged as promising modalities in multiple hematologic malignancies. Despite the excitement surrounding immunotherapy, it is currently not possible to predict which patients will respond. Within solid tumors, the status of the immune microenvironment provides valuable insight regarding potential responses to immune therapies. Much less is known about the immune microenvironment within hematologic malignancies but the characteristics of this environment are likely to serve a similar predictive role. Acute myeloid leukemia (AML) is the most common hematologic malignancy in adults, and only 25% of patients are alive 5 years following their diagnosis. There is evidence that manipulation of the immune microenvironment by leukemia cells may play a role in promoting therapy resistance and disease relapse. In addition, it has long been documented that through modulation of the immune system following allogeneic bone marrow transplant, AML can be cured, even in patients with the highest risk disease. These concepts, along with the poor prognosis associated with this disease, have encouraged many groups to start exploring the utility of novel immune therapies in AML. While the implementation of these therapies into clinical trials for AML has been supported by preclinical rationale, many questions still exist surrounding their efficacy, tolerability, and the overall optimal approach. In this review, we discuss what is known about the immune microenvironment within AML with a specific focus on T cells and checkpoints, along with their implications for immune therapies.

A Multi-center Phase I Trial of Ipilimumab in Patients with Myelodysplastic Syndromes following Hypomethylating Agent Failure

Purpose: After failure of hypomethylating agents (HMA), patients with myelodysplastic syndromes (MDS) have dismal survival and no approved treatment options.Patients and Methods: We conducted a phase 1b investigator-initiated trial of ipilimumab in patients with higher risk MDS who have failed HMAs. Patients received monotherapy at two dose levels (DL; 3 and 10 mg/kg) with an induction followed by a maintenance phase. Toxicities and responses were evaluated with CTCAE.4 and IWG-2006 criteria, respectively. We also performed immunologic assays and T-cell receptor sequencing on serial samples.Results: Twenty-nine patients from 7 centers were enrolled. In the initial DL1 (3 mg), 3 of 6 patients experienced grade 2-4 immune-related adverse events (IRAE) that were reversible with drug discontinuation and/or systemic steroids. In DL2, 4 of 5 patients experienced grade 2 or higher IRAE; thus, DL1 (3 mg/kg) was expanded with no grade 2-4 IRAEs reported in 18 additional patients. Best responses included marrow complete response (mCR) in one patient (3.4%). Prolonged stable disease (PSD) for ≥46 weeks occurred in 7 patients (24% of entire cohort and 29% of those treated with 3 mg/kg dose), including 3 patients with more than a year of SD. Five patients underwent allografting without excessive toxicity. Median survival for the group was 294 days (95% CI, 240-671+). Patients who achieved PSD or mCR had significantly higher frequency of T cells expressing ICOS (inducible T-cell co-stimulator).Conclusions: Our findings suggest that ipilimumab dosed at 3 mg/kg in patients with MDS after HMA failure is safe but has limited efficacy as a monotherapy. Increased frequency of ICOS-expressing T cells might predict clinical benefit. Clin Cancer Res; 24(15); 3519-27. ©2018 AACR.

The progress and current status of immunotherapy in acute myeloid leukemia

Recently, there has been remarkable progress in basic and preclinical studies of acute myeloid leukemia (AML). The improved outcomes of AML can largely be attributed to advances in supportive care and hematopoietic cell transplantation as opposed to conventional chemotherapy. However, as the 5-year survival rate remains low due to a high incidence of relapse, novel and effective treatments are urgently needed. Increasing attention is focusing on identifying suitable immunotherapeutic strategies for AML. Here, we describe the immunological features, mechanisms of immune escape, and recent progress in immunotherapy for AML. Problems encountered in the clinic will also be discussed. Although current outcomes may be limited, ongoing preclinical or clinical efforts are aimed at improving immunotherapy modalities and designing novel therapies, such as vaccines, monoclonal antibody therapy, chimeric antibody receptor-engineered T cells (CAR-T), TCR-engineered T cells (TCR-T), and checkpoint inhibitors, which may provide promising and effective therapies with higher specificity and efficacy for AML.

Immunomodulatory Drugs: Immune Checkpoint Agents in Acute Leukemia

Intrinsic immune responses to acute leukemia are inhibited by a variety of mechanisms, such as aberrant antigen expression by leukemia cells, secretion of immunosuppressive cytokines and expression of inhibitory enzymes in the tumor microenvironment, expansion of immunoregulatory cells, and activation of immune checkpoint pathways, all leading to T cell dysfunction and/or exhaustion. Leukemic cells, similar to other tumor cells, hijack these inhibitory pathways to evade immune recognition and destruction by cytotoxic T lymphocytes. Thus, blockade of immune checkpoints has emerged as a highly promising approach to augment innate anti-tumor immunity in order to treat malignancies. Most evidence for the clinical efficacy of this immunotherapeutic strategy has been seen in patients with metastatic melanoma, where anti-CTLA-4 and anti-PD-1 antibodies have recently revolutionized treatment of this lethal disease with otherwise limited treatment options. To meet the high demand for new treatment strategies in acute leukemia, clinical testing of these promising therapies is commencing. Herein, we review the biology of multiple inhibitory checkpoints (including CTLA-4, PD-1, TIM-3, LAG-3, BTLA, and CD200R) and their contribution to immune evasion by acute leukemias. In addition, we discuss the current state of preclinical and clinical studies of immune checkpoint inhibition in acute leukemia, which seek to harness the body's own immune system to fight leukemic cells.

Checkpoint inhibition in pediatric hematologic malignancies

Immune surveillance comprising of adaptive and innate immune systems is naturally designed to eliminate cancer development; overexpression of inhibitory receptors and their ligands prevent this check and lead to evasion and hence cancer progression and metastasis. The use of tumor-specific monoclonal antibodies (MAbs) targeting these checkpoint regulators is promising and has led to this novel field of cancer immunotherapy. The first antibody directed against cytotoxic T-lymphocyte associated protein 4 (CTLA-4), ipilimumab, showed promising results in clinical trials and was approved by the US Food and Drug Administration (FDA) for the treatment of metastatic melanoma in 2011. Since then, various other immune checkpoint inhibitors are being studied in preclinical and clinical trial phases, targeting programmed-death-1 (PD-1) and its ligand programmed death ligand 1 (PD-L1), T cell lymphocyte activation gene-3 (LAG-3), and others. Results from clinical trials are promising, and currently this approach has proven effective and safe in patients with solid tumors and some hematological malignancies in adults. In general, CTLA-4 and PD-1 inhibitors are well tolerated; however, the augmented immune response enabled by this class of agents is associated with a unique group of side effects called immune-related adverse events (irAEs). Experience in pediatrics using immune checkpoint inhibitors for hematological malignancies is limited to Hodgkin's disease and non-Hodgkin's lymphoma as in the ongoing Children's Oncology Group (COG) protocol ADVL1412. Therapeutic advances in childhood leukemia and lymphoma (TACL) consortium will initiate an early phase clinical trial with PD-1 inhibitor nivolumab in relapsed/refractory acute myeloid leukemia (AML) in the next few months.

Immunotherapy in adult acute leukemia

The treatment of acute myeloid leukemia (AML) did not evolve profoundly in the last decades. Some improvement has been made for acute lymphoblastic leukemia (ALL). Emerging new treatment modalities, such as immunotherapy, are now beginning to be available for acute leukemia, mostly for patients suffering from ALL. This review aims to give an overview of these new therapeutic approaches, especially those already available. The focus is on cell-based immunotherapy, or molecules using preexisting host cells. Underlying mechanisms are explained and an overview of clinical experience with phase 1-3 studies is given. Immunotherapies discussed are antibody-drug conjugates, bispecific T-cell engagers (BiTEs), chimeric antigen receptor T cells (CARTs) and immune checkpoint inhibitors (ICPIs). Most of the clinical studies reviewed are in ALL patients, usually in the relapse setting, but where available, studies on AML patients were also considered. This new general treatment approach offers hope to patients with until now dismal clinical outcome. Hopes are high that future developments, and moving these therapies to an earlier treatment phase, will improve the prognosis of patients suffering from acute leukemia.

Mechanisms of Immune Tolerance in Leukemia and Lymphoma

The mechanisms through which immune responses are generated against solid cancers are well characterized and knowledge of the immune evasion pathways exploited by these malignancies has grown considerably. However, for hematological cancers, which develop and disseminate quite differently than solid tumors, the pathways that regulate immune activation or tolerance are less clear. Growing evidence suggests that, while numerous immune escape pathways are shared between hematological and solid malignancies, several unique pathways are exploited by leukemia and lymphoma. Below we discuss immune evasion mechanisms in leukemia and lymphoma, highlighting key differences from solid tumors. A more complete characterization of the mechanisms of immune tolerance in hematological malignancies is critical to inform the development of future immunotherapeutic approaches.

Checkpoint inhibitors in hematological malignancies

Inhibitory molecules such as PD-1, CTLA-4, LAG-3, or TIM-3 play a role to keep a balance in immune function. However, many cancers exploit such molecules to escape immune surveillance. Accumulating data support that their functions are dysregulated in lymphoid neoplasms, including plasma cell myeloma, myelodysplastic syndrome, and acute myeloid leukemia. In lymphoid neoplasms, aberrations in 9p24.1 (PD-L1, PD-L2, and JAK2 locus), latent Epstein-Barr virus infection, PD-L1 3'-untranslated region disruption, and constitutive JAK-STAT pathway are known mechanisms to induce PD-L1 expression in lymphoma cells. Clinical trials demonstrated that PD-1 blockade is an attractive way to restore host's immune function in hematological malignancies, particularly classical Hodgkin lymphoma. Numerous clinical trials exploring PD-1 blockade as a single therapy or in combination with other immune checkpoint inhibitors in patients with hematologic cancers are under way. Although impressive clinical response is observed with immune checkpoint inhibitors in patients with certain cancers, not all patients respond to immune checkpoint inhibitors. Therefore, to identify best candidates who would have excellent response to checkpoint inhibitors is of utmost importance. Several possible biomarkers are available, but consensus has not been made and pursuit to discover the best biomarker is ongoing.

Novel therapeutic options in Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is a biologically complex and molecularly and clinically heterogeneous disease, and its incidence is increasing as the population ages. Cytogenetic anomalies and mutation testing remain important prognostic tools for tailoring treatment after induction therapy. Despite major advances in understanding the genetic landscape of AML and its impact on the pathophysiology and biology of the disease, as well as the rapid development of new drugs, standard treatment options have not experienced major changes during the past three decades. Especially for patients with intermediate or high-risk AML, which often show relapse. Allogeneic hematopoietic stem cell transplantation (HSCT) remains the best chance for cure. Here we review the state of the art therapy of AML, with special focus on new developments in immunotherapies and cellular therapies including HSCT and particularly discuss the impact of new conditioning and haplo-identical donor regimens for HSCT, post-transplant strategies for preventing and treating relapse, and emerging novel therapeutic options.

Novel immunotherapeutic approaches for the treatment of acute leukemia (myeloid and lymphoblastic)

There have been major advances in our understanding of the multiple interactions between malignant cells and the innate and adaptive immune system. While the attention of immunologists has hitherto focused on solid tumors, the specific immunobiology of acute leukemias is now becoming defined. These discoveries have pointed the way to immune interventions building on the established graft-versus-leukemia (GVL) effect from hematopoietic stem-cell transplant (HSCT) and extending immunotherapy beyond HSCT to individuals with acute leukemia with a diversity of immune manipulations early in the course of the leukemia. At present, clinical results are in their infancy. In the coming years larger studies will better define the place of immunotherapy in the management of acute leukemias and lead to treatment approaches that combine conventional chemotherapy, immunotherapy and HSCT to achieve durable cures.

Harnessing the power of alloreactivity without triggering graft-versus-host disease: how non-engrafting alloreactive cellular therapy might change the landscape of acute myeloid leukemia treatment

Human leukocyte antigen-mismatched leukocyte infusions outside of the context of transplantation are a promising strategy for acute myeloid leukemia. Recent studies using such non-engrafting alloreactive cellular therapy (NEACT) revealed that survival of elderly patients increased from 10% to 39% when NEACT was given following chemotherapy, and that durable complete remissions were achieved in about a third of patients with relapsed or chemorefractory disease. We review the clinical reports of different NEACT approaches to date and describe how although T-cell and NK alloreactivity could generate immediate anti-leukemic effects, long-term disease control may be achieved by stimulating recipient-derived T-cell responses against tumor-associated antigens. Other variables likely impacting NEACT such as the release of pro-inflammatory cytokines from donor-host bidirectional alloreactivity and the choice of chemotherapeutics as well as future avenues for improving NEACT, such as optimizing the cell dose and potential synergies with adjuvant pharmacologic immune checkpoint blockade, are discussed.

T cell receptor signaling can directly enhance the avidity of CD28 ligand binding

T cell activation takes place in the context of a spatial and kinetic reorganization of cell surface proteins and signaling molecules at the contact site with an antigen presenting cell, termed the immunological synapse. Coordination of the activation, recruitment, and signaling from T cell receptor (TCR) in conjunction with adhesion and costimulatory receptors regulates both the initiation and duration of signaling that is required for T cell activation. The costimulatory receptor, CD28, is an essential signaling molecule that determines the quality and quantity of T cell immune responses. Although the functional consequences of CD28 engagement are well described, the molecular mechanisms that regulate CD28 function are largely unknown. Using a micropipet adhesion frequency assay, we show that TCR signaling enhances the direct binding between CD28 and its ligand, CD80. Although CD28 is expressed as a homodimer, soluble recombinant CD28 can only bind ligand monovalently. Our data suggest that the increase in CD28-CD28 binding is mediated through a change in CD28 valency. Molecular dynamic simulations and in vitro mutagenesis indicate that mutations at the base of the CD28 homodimer interface, distal to the ligand-binding site, can induce a change in the orientation of the dimer that allows for bivalent ligand binding. When expressed in T cells, this mutation allows for high avidity CD28–CD80 interactions without TCR signaling. Molecular dynamic simulations also suggest that wild type CD28 can stably adopt a bivalent conformation. These results support a model whereby inside-out signaling from the TCR can enhance CD28 ligand interactions by inducing a change in the CD28 dimer interface to allow for bivalent ligand binding and ultimately the transduction of CD28 costimulatory signals that are required for T cell activation.

Immune evasion in acute myeloid leukemia: current concepts and future directions

Immune responses generated against malignant cells have the potential to inhibit tumor growth, or even eliminate transformed cells before a tumor forms. However, immune tolerance mechanisms that normally protect healthy tissues from autoimmune damage pose a formidable barrier to the development of effective anti-tumor immunity. Because malignant cells are derived from self-tissues, the majority of defined tumor antigens are either shared or aberrantly expressed self-proteins. Eliciting productive T cell responses against such proteins is challenging, as most high-affinity, self-reactive T cells are purged during thymic selection. Some T cells capable of tumor antigen recognition escape thymic deletion, but are functionally inhibited by peripheral tolerance mechanisms which limit their ability to attack a developing malignancy. Alternatively, some tumors express antigens derived from mutated self-proteins, viral proteins or self proteins expressed only during embryonic development. These antigens are recognized by the immune system as foreign and could be recognized by a relatively large number of peripheral T cells. Even in this scenario, tumors evade otherwise effective T cell responses by employing potent immunosuppressive mechanisms within their local environment. In the setting for solid malignancies, such as melanoma, a growing number of putative immune evasion mechanisms have been characterized. However, acute myeloid leukemia (AML) is a systemic disease, and the pathways it exploits to subvert the host immune response may be quite different than those of a solid tumor. Much remains unknown regarding the immune escape mechanisms promoted by AML, and whether efforts to thwart tolerance may influence the progression of this disease. Here, we review current concepts of immune evasion in AML, and speculate how potentially effective immunotherapeutic strategies might be developed to reverse immune tolerance in leukemia patients in the future.

Coinhibitory molecules in hematologic malignancies: targets for therapeutic intervention

The adaptive immune system can be a potent defense mechanism against cancer; however, it is often hampered by immune suppressive mechanisms in the tumor microenvironment. Coinhibitory molecules expressed by tumor cells, immune cells, and stromal cells in the tumor milieu can dominantly attenuate T-cell responses against cancer cells. Today, a variety of coinhibitory molecules, including cytotoxic T lymphocyte–associated antigen-4, programmed death-1, B and T lymphocyte attenuator, LAG3, T-cell immunoglobulin and mucin domain 3, and CD200 receptor, have been implicated in immune escape of cancer cells. Sustained signaling via these coinhibitory molecules results in functional exhaustion of T cells, during which the ability to proliferate, secrete cytokines, and mediate lysis of tumor cells is sequentially lost. In this review, we discuss the influence of coinhibitory pathways in suppressing autologous and allogeneic T cell–mediated immunity against hematologic malignancies. In addition, promising preclinical and clinical data of immunotherapeutic approaches interfering with negative cosignaling, either as monotherapy or in conjunction with vaccination strategies, are reviewed. Numerous studies indicate that coinhibitory signaling hampers the clinical benefit of current immunotherapies. Therefore, manipulation of coinhibitory networks is an attractive adjuvant immunotherapeutic intervention for hematologic cancers after standard treatment with chemotherapy and hematopoietic stem cell transplantation.

Enhancement of suboptimal CD8 cytotoxic T cell effector function in vivo using antigen-specific CD80 defective T cells

T cell upregulation of B7 molecules CD80 and CD86 limits T cell expansion in immunodeficient hosts; however, the relative roles of CD80 separate from CD86 on CD4 versus CD8 T cells in a normal immune system are not clear. To address this question, we used the parent-into-F1 (P→F1) murine model of graft-versus-host disease and transferred optimal and suboptimal doses of CD80 and/or CD86 knockout (KO) T cells into normal F1 hosts. Enhanced elimination of host B cells by KO T cells was observed only at suboptimal donor cell doses and was greatest for CD80 KO→F1 mice. Wild-type donor cells exhibited peak CD80 upregulation at day 10; CD80 KO donor cells exhibited greater peak (day 10) donor T cell proliferation and CD8 T cell effector CTL numbers versus wild-type→F1 mice. Fas or programmed cell death-1 upregulation was normal as was homeostatic contraction of CD80 KO donor cells from days 12-14. Mixing studies demonstrated that maximal host cell elimination was seen when both CD4 and CD8 T cells were CD80 deficient. These results indicate an important role for CD80 upregulation on Ag-activated CD4 and CD8 T cells in limiting expansion of CD8 CTL effectors as part of a normal immune response. Our results support further studies of therapeutic targeting of CD80 in conditions characterized by suboptimal CD8 effector responses.

The role of the CTLA4 blockade in the treatment of malignant melanoma

Metastatic melanoma remains a disease with few effective treatments. The anti-tumor immune response has long been felt to be important in the prognosis of melanoma, and much work has focused on harnessing the immune system to fight this disease. Tumor-specific vaccines, immunomodulatory cytokines and non-specific immunostimulants (such as Bacille Calmette Guerin/BCG) have all been investigated. A new strategy has been identified involving cytotoxic T-lymphocyte antigen-4 (CTLA4). This molecule is expressed on the surface of activated T-lymphocytes and exerts a suppressive effect on the induction of immune responses after interaction between T-cell receptor (TCR) and human lymphocyte antigen (HLA) molecules on the antigen-presenting cell (APC). Work in animal models demonstrated that antibody-mediated blockade of this target could lead to anti-tumor responses. Two fully human monoclonal antibodies, ipilimumab (MDX-010) and tremelimumab (CP-675, 206; formerly known as ticilimumab), are in clinical development. Both have demonstrated hints of clinical activity in metastatic melanoma. Both also have a toxicity profile consistent with their mechanism of action, involving inactivation of a normal immunosuppressive homeostatic mechanism: development of auto-immune breakthrough events (IBE). These include inflammatory bowel disease (IBD), uveitis, dermatitis, arthritis, and others. Generally, these events have been easily managed by cessation of therapy and intravenous or topical steroid therapy and supportive care in most patients, although colectomy had been required in several severe cases and there have been several deaths. Interestingly, patients who develop IBE seem to have the greatest likelihood of clinical benefit, but it is unclear whether clinical benefit and IBE are dissociable events. Other than IBE, no other pharmacodynamic measure has been able to predict response, although certain autoimmune antibody titers may have promise in this regard. Further research will confirm the clinical benefit of these agents alone and in combination with other agents, further define the safety profile and protocols for toxicity management, and identify pharmacodynamic parameters predicting clinical benefit and toxicity.

Reduced monocyte CD86 expression in postinflammatory immunodeficiency

OBJECTIVE

Major surgery, polytrauma, stroke, and pancreatitis frequently lead to a compensatory anti-inflammatory response syndrome that often predisposes patients to lethal infections. This temporary postinflammatory immunodeficiency is characterized by altered function of blood monocytes. These cells show strongly reduced inflammatory and antigen-presentation capacity. Diminished monocyte expression of the major histocompatibility complex class II molecule human leukocyte antigen (HLA)-DR is a well-established diagnostic marker of this immunodeficiency. To further characterize the monocytic cells in this clinical state, we analyzed their expression of CD86, the most important co-stimulatory molecule.

DESIGN

Analysis of blood samples that entered the clinical immunologic diagnostics and of cells from an in vitro model of postinflammatory immunodeficiency.

SETTING

University laboratory.

SUBJECTS

Healthy donors and intensive care unit (ICU) patients at the university hospital.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The expression of HLA-DR on monocytes and of CD86 and CD80 on monocytes and B cells was analyzed by flow cytometry. Messenger RNA expression of CD86 was analyzed in isolated monocytes by real-time polymerase chain reaction on reverse transcribed. The normal range of monocyte CD86 expression in healthy subjects was established to be from 2128 to 5102 surface molecules per cell and was independent of age, gender, and leukocyte and monocyte count. The CD86 expression on monocytes in ICU patients correlated with HLA-DR expression. Approximately 40% of the ICU patients with long-term reduced monocyte HLA-DR expression had a long-term reduction of CD86 expression. Patients in whom the expression of both molecules was diminished had an unfavorable prognosis. The diminished number of CD86 surface molecules on monocytes was associated with reduced CD86 messenger RNA levels in these cells. The expression of CD86 in B cells was not diminished in immunodeficient patients. The expression of CD80 in both monocytes and B-cells was minimal in healthy donors and not clearly changed in patients.

CONCLUSIONS

The monocyte CD86 expression may be a helpful diagnostic variable in ICU patients.

Ligation of CD80 is critical for high-level CD25 expression on CD8+ T lymphocytes

CD80 and CD86 have been shown to play a critical role in the optimal activation of T cells. Although these two molecules bind the same ligand, CD28, the question of whether CD80 and CD86 provide unique signals or serve redundant roles remains controversial. Previous studies have suggested that CD80 binding to CD28 may be superior to CD86 for the activation of naive CD8+ T cells. This study provides a potential mechanism to explain these observations. Our study demonstrates a previously unappreciated role for CD80, its superiority over CD86 in promoting CD25 expression, increasing both the number of cells that express CD25 and the level expressed on a per cell basis. These findings provide new insights into the role of CD80 vs CD86 and have important implications for the design of vaccines and immunotherapeutics aimed at the generation of a robust CD8+ T cell response in vivo.

CTLA-4 blockade by a human MAb enhances the capacity of AML-derived DC to induce T-cell responses against AML cells in an autologous culture system

BACKGROUND

Cells from AML patients can differentiate into the phenotype of DC when cultured with GM-CSF and IL-4. Such cytokine-treated AML-derived DC (AML-DC) can stimulate autologous T cells. In this study we examined whether an anti-CTLA-4 MAb (MDX-010) could enhance the generation of autologous anti-AML T cells.

METHODS

MAb MDX-010 was added to AML PBMC cultures in the presence of GM-CSF and IL-4, a previously reported AML-DC culture method of generating anti-AML T cells. T-cell activation and proliferation were examined thereafter.

RESULTS

Addition of MDX-010 to GM-CSF/IL-4-conditioned AML-DC cultures induced a mean seven-fold increase in the numbers of autologous T cells compared with cultures without MDX-010 (P < 0.007). T cells stimulated by AML-DC with CTLA-4 blockade were significantly more cytotoxic towards autologous AML cells than those without MDX-010 (42 +/- 23% vs. 26 +/- 15%, E:T ratio of 20). T cells stimulated by AML-DC with CTLA-4 blockade had significantly greater proportions of T cells producing IFN-gamma in response to autologous AML cells than those cultured with AML-DC alone (10.7 +/- 4.7% vs. 4.5 +/- 2.4% for CD4+ IFN-gamma+ CD69+ and 9.8 +/- 4.1% vs. 4 +/- 2.1% for CD8+ IFN-gamma+ CD69+ with or without MDX-010; n = 7; P < 0.007, P < 0.003, respectively).

DISCUSSION

CTLA-4 blockade enhances the activity and numbers of AML-reactive T cells that can be stimulated by autologous AML-DC and may enhance the efficacy of adoptive immunotherapy of AML.

Distinct effects of CD86-mediated costimulation on resting versus activated human CD4+ T cells

CD80 and CD86 are important in the initiation of T cell immunity. Although their costimulatory function has long been appreciated, it remains unclear whether the biological significance of the two B7 isoforms resides in their different patterns and kinetics of expression or whether differences exist in their function. We have addressed this issue using HLA-DR1 transfectants co-expressing CD80, CD86, or both molecules as stimulators for naïve, memory, and activated human CD4+ T cells. Both CD80 and CD86 efficiently costimulated alloresponses by unseparated peripheral blood CD4+ T cells; however, CD86 was substantially inferior in costimulating alloresponses by separated memory T cells, and completely incompetent in costimulating three human T cell clones. Furthermore, CD80/CD86 double transfectants stimulated lower responses by the clones than cells expressing CD80 alone. That CD86 was actively inhibitory rather than merely neutral was evidenced by the increase in response to the double CD80/CD86 APC when anti-CD86 antibody was added. Furthermore, addition of anti-CTLA-4 Fab to cultures of HLA-DR1 transfectants co-expressing CD86, fully restored the proliferative response. These results indicate that CD80 and CD86 mediate distinct signals in previously activated T cells, and demonstrate that CTLA-4 ligation may dominate the outcome of CD86-mediated costimulation of activated CD4+ T cells.

High-affinity small molecule inhibitors of T cell costimulation: compounds for immunotherapy

Costimulatory molecules are important regulators of T cell activation and thus favored targets for therapeutic manipulation of immune responses. One of the key costimulatory receptors is CD80, which binds the T cell ligands, CD28, and CTLA-4. We describe a set of small compounds that bind with high specificity and low nanomolar affinity to CD80. The compounds have relatively slow off-rates and block both CD28 and CTLA-4 binding, implying that they occlude the shared ligand binding site. The compounds inhibit proinflammatory cytokine release in T cell assays with submicromolar potency, and as such, they represent promising leads for the development of novel therapeutics for immune-mediated inflammatory disease. Our results also suggest that other predominantly beta proteins, such as those that dominate the cell surface, may also be accessible as potentially therapeutic targets.

CD86 and CD80 differentially modulate the suppressive function of human regulatory T cells

Regulatory T cells (Treg) are important in maintaining tolerance to self tissues. As both CD28 and CTLA-4 molecules are implicated in the function of Treg, we investigated the ability of their two natural ligands, CD80 and CD86, to influence the Treg-suppressive capacity. During T cell responses to alloantigens expressed on dendritic cells, we observed that Abs against CD86 potently enhanced suppression by CD4(+)CD25(+) Treg. In contrast, blocking CD80 enhanced proliferative responses by impairing Treg suppression. Intriguingly, the relative expression levels of CD80 and CD86 on dendritic cells are modulated during progression from an immature to a mature state, and this correlates with the ability of Treg to suppress responses. Our data show that CD80 and CD86 have opposing functions through CD28 and CTLA-4 on Treg, an observation that has significant implications for manipulation of immune responses and tolerance in vivo.

B7-2 expression above a threshold elicits anti-tumor immunity as effective as interleukin-12 and prolongs survival in murine B-cell lymphoma

The costimulatory molecule, B7-2, is expressed by various lymphomas, but this level of expression is not sufficient to generate effective anti-tumor immunity in vivo. To determine whether up-regulated expression of the costimulatory molecule, B7-2, leads to more effective anti-tumor immunity in vivo, the A20 murine model of B-cell lymphoma was used. A20 tumor cells express major histocompatibility complex (MHC) I and II molecules and moderate constitutive levels of B7-2. While B7-1 and B7-2 have been introduced into tumor cells lacking these molecules, studies have not been conducted to determine whether tumors that constitutively express B7-1 or B7-2 can be made more immunogenic by increasing the expression of these molecules. In this report, A20/B7-2 transfectants expressing greater levels of B7-2 were rejected in syngeneic mice, and systemic immunity against the A20 parental cells was generated. Treatment with the A20/B7-2 variant cells significantly improved the survival of tumor-bearing mice. Coinjection with IL-12 secreting variants did not further augment the anti-tumor immunity observed for B7-2 therapy alone. Both CD8(+) T cells and natural killer (NK) cells mediated the anti-tumor immune response observed in A20/B7-2 immunized mice. In mice that developed tumors after immunization with the A20/B7-2 variant cells, resected tumor cells were shown to express lower levels of B7-2 than the transfected variants. These results suggest that the level of costimulation is important for the generation of anti-tumor immunity and for host survival. In addition, tumors appear to be able to evade the immune response by downregulating the expression of B7-2 below a threshold level.

Expression of costimulatory molecules (CD80, CD86, CD28, CD152), accessory molecules (TCR αβ, TCR γδ) and T cell lineage molecules (CD4+, CD8+) in PBMC of leprosy patients using Mycobacterium leprae antigen (MLCWA) with murabutide and T cell peptide of Trat protein

In leprosy, cell-mediated immunity (CMI) is more significant than humoral response to eliminate intracellular pathogen. T cell defect is a common feature in lepromatous leprosy (LL) patients as compared to tuberculoid type (TT) patients. For efficient initiation of CD4+, T cell response requires T cell receptor (TCR) activation and costimulation provided by molecules on antigen-presenting cells (APC) and their counter receptors on T cells. In our previous study, the defective T cell function in LL patients was restored to a proliferating state with the release of TH1 type cytokines using mycobacterial antigen(s) with two immunomodulators (Murabutide (MDP-BE) and T cell epitope of Trat protein of Escherichia coli) by presenting the antigen in particulate form in vitro to PBMC derived from leprosy patients. This observation prompted us to study the expression of the costimulatory molecules (CD80, CD86, CD28, CD152), other accessory molecules (TCR alphabeta/gammadelta) and T cell lineage molecules (CD4+ and CD8+) during constitutive and activated state of peripheral blood mononuclear cells (PBMC) derived from normal and leprosy individuals using different formulations of Mycobacterium leprae total cell wall antigen (MLCWA), Trat and MDP-BE using flow cytometric analysis. An increased surface expression of CD80, CD86 and CD28 but decreased CD152 expression was observed when PBMC of normal, BT/TT (tuberculoid) and BL/LL (lepromatous) patients were stimulated in vitro with MLCWA+MDP-BE+Trat peptide using liposomal mode of antigen delivery, while opposite results were obtained with the antigen alone. Antibody inhibition study using antihuman CD80 or CD86 completely abolished the T cell lymphoproliferation, thereby reconfirming the importance of these costimulatory molecules during T cell activation/differentiation. Though the liposome-entrapped antigen formulation has no effect on expression of alphabeta/gammadelta T cell receptor, the constitutive levels of TCR gammadelta were high in lepromatous patients. Thus, TCR bearing gammadelta appears to have a negligible regulatory role in peripheral blood of leprosy patients. The percentage of cells positive for CD4+ are increased in inducible state in all the three groups, while CD8+-positive cells were decreased in LL patients, thereby reconfirming the fact that priming of CD4+ cells are necessary for producing final effector functions. Lastly, intracellular cytokine staining experiment indicated that CD4+ cells are the major producers of IFN-gamma but not NK cells. The study highlights the reversal of T cell anergy especially in lepromatous patients through the modulation of costimulatory molecule expression under the influence of Th1 cytokines, i.e., IL-2 and IFNgamma.

What's the difference between CD80 and CD86?

CD28 and CD152 have crucial yet opposing functions in T-cell stimulation, in which CD28 promotes but CD152 inhibits T-cell responses. Intriguingly, they share two ligands, CD80 and CD86, but at present there is no clear model for understanding whether a ligand will promote or inhibit responses. Current perceptions are based around the concept that CD86 is the initial co-stimulatory ligand based on its more abundant and earlier expression pattern; CD80 has a role following antigen-presenting-cell activation. We describe an alternative view in which CD80 is the initial ligand, responsible for maintaining aspects of immune tolerance through interactions with CD152. These inhibitory functions can then be over-ridden by the upregulation of CD86 on dendritic cells as a result of inflammatory stimuli, leading to immune activation.

Dual expression of CD80 and CD86 produces a tumor vaccine superior to single expression of either molecule

A murine model for neuroblastoma, Neuro-2a (N2a), was used to establish a model tumor vaccine. An aggressive subclone of N2a and the less aggressive parental line were transfected with CD80, CD86, or both molecules and stable lines were established. The less aggressive N2a expressing either CD80 or CD86 induced anti-tumor immunity. In contrast, dual expression of CD80 and CD86 was required to initiate a protective anti-tumor immune response against the aggressive subclone. Control of tumor growth was dependent on CD8+ lymphocytes that infiltrated dual-expressing (CD80 and CD86) lesions. These tumor-infiltrating lymphocytes (TIL) exhibited a non-classical mechanism of tumor cell lysis that may require both the up-regulation of cell surface molecules on the tumor and the subsequent lytic activity normally associated with CD8+ TIL. Although Fas was up-regulated by the tumor in the presence of IFN-gamma, N2a and transfected N2a cell lines were not sensitive to Fas-mediated lysis.