Responses to human CD40 ligand/human interleukin-2 autologous cell vaccine in patients with B-cell chronic lymphocytic leukemia

Potential role of immune cell therapy in gynecological cancer and future promises: a comprehensive review

Gynecological malignancies are most leading causes of death among women worldwide. The high prevalence of gynecologic malignancies remains significant, necessitating to turn the novel treatment approach like immunotherapy, wherein cancer cells are killed by the invasion of immune system. In recent year, immunotherapy has mostly an advanced treatment approach to repressing the tumor cells survival, proliferation, and invasion via the activation of immune systems. Moreover, various types of immune cells including T-cells, B-cells, and dendritic cells are associated with the immunotherapeutic strategy in cancer treatment. Although the significant role of T-cells against cancer is well established, while B-cells and dendritic cells also play an important role against different gynecological cancer by regulating the immune system. This review focuses on that arena and highlight the role of immune cells in the treatment of gynaecological cancer. Various immune cell-based anticancer therapies such as T-cell therapies, Adoptive Cellular transfer, B-cell therapies as well as approaches to Dendritic Cell therapies have been discussed in detail. Furthermore, the clinical settings and future avenues regarding immunotherapy on gynecological cancer have also been reviewed and illuminated in the recent study.

Cancer immunotherapies: advances and bottlenecks

Immunotherapy has ushered in a new era in cancer treatment, and cancer immunotherapy continues to be rejuvenated. The clinical goal of cancer immunotherapy is to prime host immune system to provide passive or active immunity against malignant tumors. Tumor infiltrating leukocytes (TILs) play an immunomodulatory role in tumor microenvironment (TME) which is closely related to immune escape of tumor cells, thus influence tumor progress. Several cancer immunotherapies, include immune checkpoint inhibitors (ICIs), cancer vaccine, adoptive cell transfer (ACT), have shown great efficacy and promise. In this review, we will summarize the recent research advances in tumor immunotherapy, including the molecular mechanisms and clinical effects as well as limitations of immunotherapy.

Safety and efficacy of autologous cell vaccines in solid tumors: a systematic review and meta-analysis of randomized control trials

We conducted a systematic review and meta-analysis of randomized control trials to formally assess the safety and efficacy of autologous whole cell vaccines as immunotherapies for solid tumors. Our primary safety outcome was number, and grade of adverse events. Our primary efficacy outcome was clinical responses. Secondary outcomes included survival metrics and correlative immune assays. We searched MEDLINE, Embase, and the Cochrane Central Register of Controlled Trials for studies published between 1946 and August 2020 using any autologous whole cell product in the treatment of any solid tumor. The Cochrane Randomized Controlled Trial risk of bias tool was used to assess risk of bias. Eighteen manuscripts were identified with a total of 714 patients enrolled in control and 808 in vaccine arms. In 698 patients receiving at least one dose of vaccine, treatment was well tolerated with a total of 5 grade III or higher adverse events. Clinical response was reported in a minority (n = 2, 14%) of studies. Autologous cell vaccines were associated with improved overall (HR 1.28, 95% CI 1.01-1.63) and disease-free survival (HR 1.33, 95% CI 1.05-1.67) over thirteen and ten trials respectively. Where reported, immune assays correlated well with clinical outcomes. Our results suggest that autologous whole cell vaccination is safe and efficacious in increasing survival in patients undergoing treatment for solid tumors.Registration: PROSPERO CRD42019140187.

Role of B cells as antigen presenting cells

B cells have been long studied for their role and function in the humoral immune system. Apart from generating antibodies and an antibody-mediated memory response against pathogens, B cells are also capable of generating cell-mediated immunity. It has been demonstrated by several groups that B cells can activate antigen-specific CD4 and CD8 T cells, and can have regulatory and cytotoxic effects. The function of B cells as professional antigen presenting cells (APCs) to activate T cells has been largely understudied. This, however, requires attention as several recent reports have demonstrated the importance of B cells within the tumor microenvironment, and B cells are increasingly being evaluated as cellular therapies. Antigen presentation through B cells can be through antigen-specific (B cell receptor (BCR) dependent) or antigen non-specific (BCR independent) mechanisms and can be modulated by a variety of intrinsic and external factors. This review will discuss the pathways and mechanisms by which B cells present antigens, and how B cells differ from other professional APCs.

Enhanced Costimulatory Signaling Improves CAR T-cell Effector Responses in CLL

CD19-redirected chimeric antigen receptor (CAR) T cells have shown remarkable activity against B-cell cancers. While second-generation CARs induce complete remission in >80% of patients with acute lymphoblastic leukemia, similar monotherapy induces long-term remissions in only 26% of patients with chronic lymphocytic leukemia (CLL). This disparity is attributed to cell-intrinsic effector defects in autologous CLL-derived T cells. However, the mechanisms by which leukemic cells impact CAR T-cell potency are poorly understood. Herein we describe an in vitro assay that recapitulates endogenous CLL-mediated T-cell defects in healthy donor CAR T cells. Contact with CLL cells insufficiently activates, but does not irreversibly impair, CAR T-cell function. This state is rescuable by strong antigenic stimulation or IL2, and is not driven by immune suppression. Rather, this activation defect is attributable to low levels of costimulatory molecules on CLL cells, and exogenous costimulation enhanced CAR T-cell activation. We next assessed the stimulatory phenotype of CLL cells derived from different niches within the same patient. Lymph node (LN)-derived CLL cells had a strong costimulatory phenotype and promoted better CAR T-cell degranulation and cytokine production than matched peripheral blood CLL cells. Finally, in vitro CD40L-activated CLL cells acquired a costimulatory phenotype similar to the LN-derived tumor and stimulated improved CAR T-cell proliferation, cytokine production, and cytotoxicity. Together, these data identify insufficient activation as a driver of poor CAR T-cell responses in CLL. The costimulatory phenotype of CLL cells drives differential CAR T-cell responses, and can be augmented by improving costimulatory signaling.

Significance

CLL cells insufficiently activate CAR T cells, driven by low levels of costimulatory molecules on the tumor. LN-derived CLL cells are more costimulatory and mediate enhanced CAR T-cell killing. This costimulatory phenotype can be modeled via CD40 L activation, and the activated tumor promotes stronger CAR T-cell responses.

B-Cell-Based Immunotherapy: A Promising New Alternative

The field of immunotherapy has undergone radical conceptual changes over the last decade. There are various examples of immunotherapy, including the use of monoclonal antibodies, cancer vaccines, tumor-infecting viruses, cytokines, adjuvants, and autologous T cells carrying chimeric antigen receptors (CARs) that can bind cancer-specific antigens known as adoptive immunotherapy. While a lot has been achieved in the field of T-cell immunotherapy, only a fraction of patients (20%) see lasting benefits from this mode of treatment, which is why there is a critical need to turn our attention to other immune cells. B cells have been shown to play both anti- and pro-tumorigenic roles in tumor tissue. In this review, we shed light on the dual nature of B cells in the tumor microenvironment. Furthermore, we discussed the different factors affecting the biology and function of B cells in tumors. In the third section, we described B-cell-based immunotherapies and their clinical applications and challenges. These current studies provide a springboard for carrying out future mechanistic studies to help us unleash the full potential of B cells in immunotherapy.

Current challenges in the manufacture of clinical-grade autologous whole cell vaccines for hematological malignancies

Autologous whole cell vaccines use a patient's own tumor cells as a source of antigen to elicit an anti-tumor immune response in vivo. Recently, the authors conducted a systematic review of clinical trials employing these products in hematological cancers that showed a favorable safety profile and trend toward efficacy. However, it was noted that manufacturing challenges limit both the efficacy and clinical implementation of these vaccine products. In the current literature review, the authors sought to define the issues surrounding the manufacture of autologous whole cell products for hematological cancers. The authors describe key factors, including the acquisition, culture, cryopreservation and transduction of malignant cells, that require optimization for further advancement of the field. Furthermore, the authors provide a summary of pre-clinical work that informs how the identified challenges may be overcome. The authors also highlight areas in which future basic research would be of benefit to the field. The goal of this review is to provide a roadmap for investigators seeking to advance the field of autologous cell vaccines as it applies to hematological malignancies.

Safety and efficacy of autologous whole cell vaccines in hematologic malignancies: A systematic review and meta-analysis

Autologous cell vaccines use a patient's tumor cells to stimulate a broad antitumor response in vivo. This approach shows promise for treating hematologic cancers in early phase clinical trials, but overall safety and efficacy remain poorly described. We conducted a systematic review assessing the use of autologous cell vaccination in treating hematologic cancers. Primary outcomes of interest were safety and clinical response, with secondary outcomes including survival, relapse rate, correlative immune assays and health-quality related metrics. We performed a search of MEDLINE, Embase and the Cochrane Register of Controlled Trials including any interventional trial employing an autologous, whole cell product in any hematologic malignancy. Risk of bias was assessed using a modified Institute of Health Economics tool. Across 20 single arm studies, only 341 of 592 enrolled participants received one or more vaccinations. Primary reasons for not receiving vaccination included rapid disease progression/death and manufacturing challenges. Overall, few high-grade adverse events were observed. One death was reported and attributed to a GM-CSF producing allogeneic cell line co-administered with the autologous vaccine. Of 58 evaluable patients, the complete response rate was 21.0% [95% CI, 10.4%-37.8%)] and overall response rate was 35.8% (95% CI, 24.4%-49.0%). Of 97 evaluable patients for survival, the 5-years overall survival rate was 64.9% (95% CI, 52.6%-77.2%) and disease-free survival was 59.7% (95% CI, 47.7%-71.7%). We conclude that, in hematologic malignancies, based on limited available data, autologous cell vaccines are safe and display a trend towards efficacy but that challenges exist in vaccine manufacture and administration.

Tumor cell-derived autophagosomes (DRibbles)-activated B cells induce specific naïve CD8+ T cell response and exhibit antitumor effect

Dendritic cell (DC) vaccine has been proved to be an effective way in cancer immunotherapy in both preclinical and clinical studies. However, limitations in DC isolation and culture have hampered its practice and promoted the development of other antigen-presenting cells (APCs) sources to fulfill that role. Our previous studies have shown that B cells loaded by tumor cell-derived autophagosomes, which we named as DRibbles (defective ribosomal products-containing blebs), could reactivate DC-induced effector T cell response. In this study, the roles of DRibble-loaded B cells in priming naïve CD8+ T cell responses and controlling tumors were investigated. We found that high-mobility group box 1 protein (HMGB1) on DRibbles was involved in DRibble-induced B cell activation, and the DRibble-triggered B cell phagocytosis via the caveolae-mediated endocytosis pathway. By using OT-I mouse-derived T cells, we demonstrated that DRibble-loaded B cells could activate specific naïve CD8+ T cells in vitro and ex vivo. In a tumor-bearing mouse model, DRibble-loaded B cells elicited systemic antitumor immunity and significantly suppressed the tumor growth. Moreover, the antitumor efficacy of DRibble-loaded B cells was enhanced when they were combined with CpG and anti-CD40 stimulation. These results suggest that DRibble-loaded B cells represent a viable and practical therapeutic vaccination strategy that might have important clinical implications for tumor immunotherapy.

Immunoinformatics design of multiepitopes peptide-based universal cancer vaccine using matrix metalloproteinase-9 protein as a target

A new approach toward cancer therapy is the use of cancer vaccine, yet the different molecular bases of cancers, reduce the effectiveness of this approach. In this article, we aim to use matrix metalloproteinase-9 protein (MMP9) which is an essential molecule in the survival and metastasis of all types of cancers as a target for universal cancer vaccine design. The reference sequence of MMP9 protein was obtained from NCBI databases. Furthermore, the B-cell and T cell-related peptides were analyzed using the IEDB website and other related soft wares. The best candidate peptides were then visualized using chimera software. Three peptides were found to be good candidates for interactions with B cells (SLPE, RLYT, and PALPR), while 10 peptides were found as good targets for interactions with MHC1 and another 10 peptides founded suitable for interactions with MHC2 with population coverages of 94.77 and 90.67%, respectively. Finally, the immune response simulation and molecular docking were done using the C-IMMSIM simulator and AutoDock Vina to confirm the effectiveness of the proposed vaccine. By the end of this project: twenty-three peptide-based vaccine was designed for use as a universal cancer vaccine which has a high world population coverage for MHC1 (94.77%) and MHC2 (90.67%) related alleles.

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.

Engineering extracellular vesicles as novel treatment options: exploiting herpesviral immunity in CLL

Extracellular vesicles (EVs) are important mediators of cell–cell communication. Intriguingly, EVs can be engineered and thus exploited for the targeted transfer of functional proteins of interest. Thus, engineered EVs may constitute attractive tools for the development of novel therapeutic interventions, like cancer immunotherapies, vaccinations or targeted drug delivery. Here, we describe a novel experimental immunotherapeutic approach for the adjuvant treatment of chronic lymphocytic leukaemia (CLL) based on engineered EVs carrying gp350, the major glycoprotein of Epstein–Barr virus (EBV), CD40L, a central immune accessory molecule and pp65, an immunodominant antigen of the human cytomegalovirus (CMV). We show that these engineered EVs specifically interact with malignant B cells from CLL patients and render these cells immunogenic to allogeneic and autologous EBV- and CMV-specific CD4+ and CD8+ T cells. Collectively, co-opting engineered EVs to re-target the strong herpesviral immunity in CLL patients to malignant cells constitutes an attractive strategy for the adjuvant treatment of a still incurable disease.

Abbreviations: CLL: chronic lymphocytic leukaemia; EBV: Epstein-Barr virus; CMV: cytomegalovirus

B Cell-Based Cancer Immunotherapy

B cells are not only producers of antibodies, but also contribute to immune regulation or act as potent antigen-presenting cells. The potential of B cells for cellular therapy is still largely underestimated, despite their multiple diverse effector functions. The CD40L/CD40 signaling pathway is the most potent activator of antigen presentation capacity in B lymphocytes. CD40-activated B cells are potent antigen-presenting cells that induce specific T-cell responses in vitro and in vivo. In preclinical cancer models in mice and dogs, CD40-activated B cell-based cancer immunotherapy was able to induce effective antitumor immunity. So far, there have been only few early-stage clinical studies involving B cell-based cancer vaccines. These trials indicate that B cell-based immunotherapy is generally safe and associated with little toxicity. Furthermore, these studies suggest that B-cell immunotherapy can elicit antitumor T-cell responses. Alongside the recent advances in cellular therapies in general, major obstacles for generation of good manufacturing practice-manufactured B-cell immunotherapies have been overcome. Thus, a first clinical trial involving CD40-activated B cells might be in reach.

An autologous tumor vaccine for CLL

Chronic Lymphocytic Leukemia B cells (CLL) are malignant cells which retain at least some functions of normal B cells. Paramount amongst the latter is that when such cells are appropriately stimulated, they are able to present antigens, including any potential tumor antigens, making them excellent choices as a candidate tumor vaccine. We show that following stimulation of CLL cells with Phorbol myristic acetate, IL-2, the TLR7 agonist imiquimod (P2I) and ionomycin (P2Iio), markedly increased expression of CD54 and CD83 was seen, indicative of B cell activation and a transition to antigen-presenting cells. However, this occurred in the context of augmented expression of the known immunoregulatory molecule, CD200. Accordingly we explored the effect of stimulation of CLL cells with P2Iio, followed by coating of cells with a non-depleting anti-CD200mAb, on the ability of those cells to immunize PBL in vitro to become cytotoxic to CLL cells, or to protect NOD-SCIDγc^null (NSG) mice from subsequent CLL tumor challenge. Our data indicate that this protocol is effective in inducing CD8⁺ CTL able to lyse CLL cells in vitro, and decrease tumor burden in vivo in spleen and marrow of mice injected with CLL cells. Pre-treatment of mice with a CD8 depleting antibody before vaccination with P2Iio/anti-CD200 coated cells abolished any protection seen. These data suggest a potential role for blockade of CD200 expression on CLL cells as a component of a tumor vaccination strategy.

New developments in immunotherapy for lymphoma

The development of immunotherapies for lymphoma has undergone a revolutionary evolution over the past decades. Since the advent of rituximab as the first successful immunotherapy for B-cell non-Hodgkin lymphoma over two decades ago, a plethora of new immunotherapeutic approaches to treat lymphoma has ensued. Four of the most exciting classes of immunotherapies include: chimeric antigen receptor T-cells, bispecific antibodies, immune checkpoint inhibitors, and vaccines. However, with addition of these novel therapies the appropriate timing of treatment, optimal patient population, duration of therapy, toxicity, and cost must be considered. In this review, we describe the most-promising immunotherapeutic approaches for the treatment of lymphoma in clinical development, specifically focusing on clinical trials performed to date and strategies for improvement.

K562-Derived Whole-Cell Vaccine Enhances Antitumor Responses of CAR-Redirected Virus-Specific Cytotoxic T Lymphocytes In Vivo

PURPOSE

Adoptive transfer of Epstein-Barr virus (EBV)-specific and cytomegalovirus (CMV)-specific cytotoxic T cells (CTL) genetically modified to express a chimeric antigen receptor (CAR) induces objective tumor responses in clinical trials. In vivo expansion and persistence of these cells are crucial to achieve sustained clinical responses. We aimed to develop an off-the-shelf whole-cell vaccine to boost CAR-redirected virus-specific CTLs in vivo after adoptive transfer. As proof of principle, we validated our vaccine approach by boosting CMV-specific CTLs (CMV-CTLs) engineered with a CAR that targets the GD2 antigen.

EXPERIMENTAL DESIGN

We generated the whole-cell vaccine by engineering the K562 cell line to express the CMV-pp65 protein and the immune stimulatory molecules CD40L and OX40L. Single-cell-derived clones were used to stimulate CMV-CTLs in vitro and in vivo in a xenograft model. We also assessed whether the in vivo boosting of CAR-redirected CMV-CTLs with the whole-cell vaccine enhances the antitumor responses. Finally, we addressed potential safety concerns by including the inducible safety switch caspase9 (iC9) gene in the whole-cell vaccine.

RESULTS

We found that K562-expressing CMV-pp65, CD40L, and OX40L effectively stimulate CMV-specific responses in vitro by promoting antigen cross-presentation to professional antigen-presenting cells (APCs). Vaccination also enhances antitumor effects of CAR-redirected CMV-CTLs in xenograft tumor models. Activation of the iC9 gene successfully induces growth arrest of engineered K562 implanted in mice.

CONCLUSIONS

Vaccination with a whole-cell vaccine obtained from K562 engineered to express CMV-pp65, CD40L, OX40L and iC9 can safely enhance the antitumor effects of CAR-redirected CMV-CTLs.

Paradigm shifts in the management of poor-risk chronic lymphocytic leukemia

With the growing complexity of treatment options for chronic lymphocytic leukemia (CLL) and variables that influence the underlying biology of this disease, providing allogeneic stem cell transplant (alloSCT) to appropriate candidates poses a challenge for transplant physicians. Novel small molecule inhibitors hold unprecedented promise for poor-risk subgroups, which will likely alter decision-making and referral patterns for transplant. In this review, we analyze what is known and may still remain true about indications for transplant based on outcomes reported in the literature recently and over the last decade.

Multifunctional CD40L: pro- and anti-neoplastic activity

The CD40 ligand is a type I transmembrane protein that belongs to a tumor necrosis factor (TNF) superfamily. It is present not only on the surface of activated CD4+ T cells, B cells, blood platelets, monocytes, and natural killer (NK) cells but also on cancer cells. The receptor for ligand is constitutively expressed on cells, TNF family protein: CD40. The role of the CD40/CD40L pathway in the induction of body immunity, in inflammation, or in hemostasis has been well documented, whereas its involvement in neoplastic disease is still under investigation. CD40L ligand may potentiate apoptosis of tumor cells by activation of nuclear factor-κB (NF-κB), AP-1, CD95, or caspase-depended pathways and stimulate host immunity to defend against cancer. Although CD40L has a major contribution to anti-cancer activity, many reports point at its ambivalent nature. CD40L enhance release of strongly pro-angiogenic factor, vascular endothelial growth factor (VEGF), and activator of coagulation, TF, the level of which is correlated with tumor metastasis. CD40L involvement in the inhibition of tumor progression has led to the emergence of not only therapy using recombinant forms of the ligand and vaccines in the treatment of cancer but also therapy consisting of inhibiting platelets-main source of CD40L. This article is a review of studies on the ambivalent role of CD40L in neoplastic diseases.

Breaking immunotolerance of tumors: a new perspective for dendritic cell therapy

The use of dendritic cells (DC) in cancer immunotherapy is based on their potent abilities to present antigens, so they can act as 'natural adjuvants' to enhance immunogenicity of tumor antigens and stimulate specific cytotoxic T-cells. Large amounts of DC can be generated from bone marrow, neonatal cord blood, and peripheral blood CD34(+) hematopoietic stem cells, or from peripheral blood monocytes. The DC can then be pulsed with tumor antigens and re-infused. In vitro, antigen-pulsed DC can stimulate allogeneic T-cell proliferation and induction of autologous specific cytotoxic T-cells; in vivo, the cells inhibit the growth of tumors or protect hosts (i.e. mice) from development of inoculated tumors. The results of preliminary clinical trials have shown that DC vaccines are safe and elicit immune responses; however, the rates of clinical responses are low. It has become quite clear that one key reason for unsatisfactory clinical results is tumor-induced immunosuppression. Among the factors contributing to this type of immunosuppression are populations of regulatory cells including: T-regulatory (T(reg)) cells, myeloid-derived suppressor cells (MDSC), tumor-associated macrophages (TAM), and DC expressing 2,3-dioxygenase indoleamine (IDO-DC). This review presents an overview of the current understanding about populations of regulatory cells and the most current research efforts directed to overcome immunosuppressive activity due to the tumor microenvironment.

Is cancer gene therapy an empty suit?

Gene therapy as a treatment for cancer is regarded as high in promise, but low in delivery, a deficiency that has become more obvious with ever-increasing reports of the successful correction of monogenic disorders by this approach. We review the commercial and scientific obstacles that have led to these delays and describe how they are progressively being overcome. Recent and striking successes and correspondingly increased commercial involvement suggest that gene transfer could finally become a powerful method for development of safe and effective cancer therapeutic drugs.

Targeting of the tumor necrosis factor receptor superfamily for cancer immunotherapy

The tumor necrosis factor (TNF) ligand and cognate TNF receptor superfamilies constitute an important regulatory axis that is pivotal for immune homeostasis and correct execution of immune responses. TNF ligands and receptors are involved in diverse biological processes ranging from the selective induction of cell death in potentially dangerous and superfluous cells to providing costimulatory signals that help mount an effective immune response. This diverse and important regulatory role in immunity has sparked great interest in the development of TNFL/TNFR-targeted cancer immunotherapeutics. In this review, I will discuss the biology of the most prominent proapoptotic and co-stimulatory TNF ligands and review their current status in cancer immunotherapy.

AdCD40L--crossing the valley of death?

CD40-mediated cancer therapy has been under development since it became clear that CD40 plays a profound role in the stimulation of adaptive immune responses. Further, CD40 signaling on tumor cells may lead to growth arrest or even apoptosis that improves therapy outcome. The therapeutic window is appealing since the immune system is selective and normal cells do not apoptose upon CD40 signaling. AdCD40L is an adenoviral-based immunostimulatory gene therapy under evaluation for its efficacy to treat cancer. Because of its nature, the adenoviral backbone will stimulate TLRs while CD40L potentiates the shifts toward Th1 type of immunity. AdCD40L has shown efficacy in various murine models, and safety studies have been performed on dog patients and in human clinical trials. AdCD40L has been used for both ex vivo gene modification of tumor cell vaccines as well as for direct intratumoral injections. Lately, an oncolytic vector has been used to further increase the eradication of solid tumors that as a consequence further boosts the release of tumor antigens and creates danger signaling in the tumor micro milieu. This review discusses the currently unfolding mechanisms of action of AdCD40L gene therapy and its possibilities to reach clinical care.

Immunomodulatory drugs and active immunotherapy for chronic lymphocytic leukemia

BACKGROUND

The last decade witnessed the emergence of several therapeutic options for patients with chronic lymphocytic leukemia (CLL) for first-line and relapsed settings. The vast majority of patients with relapsed or refractory CLL carry poor prognostic features, which are strong predictors of shorter overall survival and resistance to first-line treatment, particularly fludarabine-based regimens.

METHODS

This article highlights the current role of immunomodulatory drugs (IMiDs) and active immunotherapy as treatment options for this select group. The rationale of using IMiDs is discussed from the perspective of lenalidomide as a novel active agent. Relevant clinical trials using IMiDs alone or in combinations are discussed. New immunotherapeutic experimental approaches are also described.

RESULTS

As a single agent, lenalidomide offers an overall response rate of 32% to 47% in patients with relapsed/refractory disease. Recent studies have shown promising activity as a single agent in treatment-naive patients. The combination of lenalidomide with immunotherapy (rituximab and ofatumumab) has also shown clinical responses. Encouraging preclinical and early clinical data have been observed with different immunotherapeutic approaches.

CONCLUSIONS

The use of IMiDs alone or in combination with immunotherapy represents a treatment option for relapsed/refractory or treatment-naive patients. Mature data and further studies are needed to validate overall and progression-free survival. The toxicity profile of lenalidomide might limit its use and delay further studies. Immunotherapy offers another potential alternative, but further understanding of the immunogenicity of CLL cells and the mechanisms of tumor fl are reaction is needed to improve the outcomes in this field.

In vitro-activated tumor-bearing host T cells and the effectiveness of tumor vaccine immunotherapy

BACKGROUND AND OBJECTIVE

Vaccination during periods of lymphopenia may facilitate immune responses to weak self-antigens and enhance antitumor immunity. The objective of this study was to determine the effectiveness of tumor vaccine immunotherapy combined with immune reconstruction using tumor-bearing host immune cells in lymphopenia, and to investigate the role of tumor-bearing host T cells activated in vitro during immunotherapy.

DESIGN AND SETTING

Animal study conducted in the First Affiliated Hospital of Xi'an Jiaotong University from January 2009 to January 2010.

PATIENTS AND METHODS

Lymphopenia was induced by cyclophosphamide. A reconstituted immune system with different syngeneic lymphocytes was employed, including lymphocytes from naïve rats (unsensitized group), tumor-bearing rats (tumor-bearing group), and tumor-bearing rats activated in vitro (activated group). All rats were immunized with granulocyte-macrophage colony-stimulating factor (GM-CSF)-modified NuTu-19 ovarian cancer (GM-CSF/NuTu-19) cells. Tumor vaccine-draining lymph nodes (TVDLNs) were harvested, and then stimulated to induce effector T cells (T(E)). T(E) were then adoptively transferred to rats bearing a 3-day pre-established abdominal tumor (NuTu-19), and the survival rate was calculated.

RESULTS

Compared with the unsensitized group, the levels of interleukin-2 (IL-2) were significantly lower in the tumor-bearing group, whereas that of IL-4 were significantly higher (P<.05). The number of CD4+ T cells secreting interferon-γ and the specific cytotoxicity of CD8+ cytotoxic T lymphocytes were significantly lower (P<.05). The survival was significantly higher in the activated group compared with the other groups.

CONCLUSIONS

Lymphocytes from tumor-bearing rats activated in vitro can effectively reverse the immunosuppressive effects of tumor-bearing hosts.

Immunotherapy for B-cell lymphoma: current status and prospective advances

Therapy for non-Hodgkin's lymphoma has progressed significantly over the last decades. However, the majority of patients remain incurable, and novel therapies are needed. Because immunotherapy ideally offers target selectivity, an ever increasing number of immunotherapies, both passive and active, are undergoing development. The champion of passive immunotherapy to date is the anti-CD20 monoclonal antibody rituximab that revolutionized the standard of care for lymphoma. The great success of rituximab catalyzed the development of new passive immunotherapy strategies that are currently undergoing clinical evaluation. These include improvement of rituximab efficacy, newer generation anti-CD20 antibodies, drug-conjugated and radio labeled anti-CD20 antibodies, monoclonal antibodies targeting non-CD20 lymphoma antigens, and bispecific antibodies. Active immunotherapy aims at inducing long-lasting antitumor immunity, thereby limiting the likelihood of relapse. Current clinical studies of active immunotherapy for lymphoma consist largely of vaccination and immune checkpoint blockade. A variety of protein- and cell-based vaccines are being tested in ongoing clinical studies. Recently completed phase III clinical trials of an idiotype protein vaccine suggest that the vaccine may have clinical activity in a subset of patients. Efforts to enhance the efficacy of active immunotherapy are ongoing with an emphasis on optimization of antigen delivery and presentation of vaccines and modulation of the immune system toward counteracting immunosuppression, using antibodies against immune regulatory checkpoints. This article discusses results of the various immunotherapy approaches applied to date for B-cell lymphoma and the ongoing trials to improve their effect.

EBV-gp350 confers B-cell tropism to tailored exosomes and is a neo-antigen in normal and malignant B cells--a new option for the treatment of B-CLL

gp350, the major envelope protein of Epstein-Barr-Virus, confers B-cell tropism to the virus by interacting with the B lineage marker CD21. Here we utilize gp350 to generate tailored exosomes with an identical tropism. These exosomes can be used for the targeted co-transfer of functional proteins to normal and malignant human B cells. We demonstrate here the co-transfer of functional CD154 protein on tailored gp350+ exosomes to malignant B blasts from patients with B chronic lymphocytic leukemia (B-CLL), rendering B blasts immunogenic to tumor-reactive autologous T cells. Intriguingly, engulfment of gp350+ exosomes by B-CLL cells and presentation of gp350-derived peptides also re-stimulated EBV-specific T cells and redirected the strong antiviral cellular immune response in patients to leukemic B cells. In essence, we show that gp350 alone confers B-cell tropism to exosomes and that these exosomes can be further engineered to simultaneously trigger virus- and tumor-specific immune responses. The simultaneous exploitation of gp350 as a tropism molecule for tailored exosomes and as a neo-antigen in malignant B cells provides a novel attractive strategy for immunotherapy of B-CLL and other B-cell malignancies.

Comparison of two CD40-ligand/interleukin-2 vaccines in patients with chronic lymphocytic leukemia

BACKGROUND AIMS

Several studies have demonstrated that the immunogenicity of chronic lymphocytic leukemia (CLL) cells can be increased by manipulation of the CD40/CD40-ligand (CD40L) pathway. Although immunologic, and perhaps clinical, benefits have been obtained with an autologous CLL tumor vaccine obtained by transgenic expression of CD40L and interleukin (IL)-2, there is little information about the optimal gene transfer strategies.

METHODS

We compared two different CLL vaccines prepared by adenoviral gene transfer and plasmid electroporation, analyzing their phenotype and immunostimulatory activity.

RESULTS

We found that higher expression of transgenic CD40L was mediated by adenoviral gene transfer than by plasmid transduction, and that adenoviral transfer of CD40L was associated with up-regulation of the co-stimulatory molecules CD80 and CD86 and adhesion molecule CD54. In contrast, transgenic IL-2 secretion was greater following plasmid transduction. These phenotypic differences in the vaccines were associated with different functionality, both ex vivo and following administration to patients. Thus adenoviral vaccines induced greater activation of leukemia-reactive T cells ex vivo than plasmid vaccines. In treated patients, specific T-cell (T helper 1 (Th1) and T helper 2 (Th2)) and humoral anti-leukemia responses were detected following administration of the adenoviral vaccine (n = 15), while recipients of the plasmid vaccine (n = 9) manifested only a low-level Th2 response. Progression-free survival at 2 years was 46.7% in the adenoviral vaccine recipients, versus 11.1 % in those receiving plasmid vaccine.

CONCLUSIONS

CLL vaccines expressing the same transgenes but produced by distinct methods of gene transfer may differ in the polarity of the immune response they induce in patients.

Engineered T cells for the adoptive therapy of B-cell chronic lymphocytic leukaemia

B-cell chronic lymphocytic leukaemia (B-CLL) remains an incurable disease due to the high risk of relapse, even after complete remission, raising the need to control and eliminate residual tumor cells in long term. Adoptive T cell therapy with genetically engineered specificity is thought to fulfil expectations, and clinical trials for the treatment of CLL are initiated. Cytolytic T cells from patients are redirected towards CLL cells by ex vivo engineering with a chimeric antigen receptor (CAR) which binds to CD19 on CLL cells through an antibody-derived domain and triggers T cell activation through CD3ζ upon tumor cell engagement. Redirected T cells thereby target CLL cells in an MHC-unrestricted fashion, secret proinflammatory cytokines, and eliminate CD19(+) leukaemia cells with high efficiency. Cytolysis of autologous CLL cells by patient's engineered T cells is effective, however, accompanied by lasting elimination of healthy CD19(+) B-cells. In this paper we discuss the potential of the strategy in the treatment of CLL, the currently ongoing trials, and the future challenges in the adoptive therapy with CAR-engineered T cells.

Active and passive immunotherapy for lymphoma: proving principles and improving results

Conventional chemotherapy for lymphoma has advanced greatly over the past 50 years, changing some lymphoma subtypes from uniformly lethal to curable; however, the majority of lymphomas in patients remain incurable, and there is a need for novel therapies with less toxicity and more specific targeting of tumor cells. The vertebrate immune system has evolved the capacity for such specific targeting through the B-cell and T-cell receptors; passive immunotherapies utilizing these receptors, such as monoclonal antibodies (mAbs) or T cells, have shown efficacy in treating lymphomas. The first generation of mAb-based therapies has transformed the standard of care for lymphoma, and newer antibodies may improve on this approach. Clinical activity has been shown by T cells bearing receptors that target viral antigens as well as T cells bearing re-engineered receptors that target antigens recognized by antibodies. Active immunotherapies, such as vaccines and immune checkpoint blockades, have prolonged survival in certain solid tumors and are being actively pursued to treat lymphoma. A variety of vaccines (eg, protein- and cell-based vaccines) are being tested in ongoing trials, and the most recent iterations show therapeutic activity. Newer trials are addressing the problem of tumor-induced immunosuppression by the use of antibodies against immunologic checkpoints or by the reinfusion of primed T cells after lymphodepletion, a process we refer to as immunotransplantation. Herein, we discuss results of the various immunotherapy strategies applied to lymphoma and the ongoing approaches for their improvement.

Definition of a target for immunotherapy and results of the first Peptide vaccination study in chronic lymphocytic leukemia

Results of bone marrow transplantation, as well as remission phenomena after viral infections, suggest that chronic lymphocytic leukemia (CLL) might be targeted effectively by T-cell-based immunotherapy. Antigen-targeted immunotherapies represent novel treatments for CLL patients. Earlier, we screened the mRNA expression of several tumor associated antigens (TAAs), observing the presence of RHAMM/CD168, fibromodulin, syntaxin, and NY-Ren60 in 55%-90% of CLL patients. RHAMM/CD168, fibromodulin, PRAME, and MPP11 were expressed in CLL patients but not in healthy volunteers. Quantitative reverse transcriptase polymerase chain reaction revealed higher RHAMM expression in high-risk CLL patients as well as in advanced stages of the disease. CLL cases with higher RHAMM expressions showed significantly shorter median treatment-free survivals. Among patients with mutated IgVH genes, an analysis of RHAMM expression enabled us to distinguish a subgroup of patients with a favorable prognosis. In lymph nodes, RHAMM staining correlated with a higher Ki-67 index and CD40L expression. Functionally, stimulation with CD40L enhanced RHAMM expression in CLL. Because of the exquisite tissue expression of RHAMM and its high expression frequency in CLL patients, we further characterized RHAMM-specific CD8+ T cells in these patients. CD8+ T cells primed with the RHAMM-derived epitope R3, which is restricted by human leukocyte antigen (HLA)A2, lysed RHAMM+ CLL cells. Therefore, we initiated a Phase I clinical trial of R3 peptide vaccination. Four patients exhibited reduced white blood cell counts during the vaccination process. In 5/6 patients, R3-specific CD8+ T cells were detected with the corresponding peptide/HLA-A2 tetrameric complex; these populations were verified functionally in 4/5 patients using ELISpot assays. In conclusion, RHAMM expression seems to be of prognostic value, and may reflect the proliferative capacity of CLL cells; it may therefore represent an interesting target for immunotherapy. Peptide vaccination in CLL patients was safe eliciting specific CD8+ T-cell responses against the tumor antigen RHAMM.

In vitro and in vivo model of a novel immunotherapy approach for chronic lymphocytic leukemia by anti-CD23 chimeric antigen receptor

Chronic lymphocytic leukemia (CLL) is characterized by an accumulation of mature CD19(+)CD5(+)CD20(dim) B lymphocytes that typically express the B-cell activation marker CD23. In the present study, we cloned and expressed in T lymphocytes a novel chimeric antigen receptor (CAR) targeting the CD23 antigen (CD23.CAR). CD23.CAR(+) T cells showed specific cytotoxic activity against CD23(+) tumor cell lines (average lysis 42%) and primary CD23(+) CLL cells (average lysis 58%). This effect was obtained without significant toxicity against normal B lymphocytes, in contrast to CARs targeting CD19 or CD20 antigens, which are also expressed physiologically by normal B lymphocytes. Moreover, CLL-derived CD23.CAR(+) T cells released inflammatory cytokines (1445-fold more TNF-β, 20-fold more TNF-α, and 4-fold more IFN-γ). IL-2 was also produced (average release 2681 pg/mL) and sustained the antigen-dependent proliferation of CD23.CAR(+) T cells. Redirected T cells were also effective in vivo in a CLL Rag2(-/-)γ(c)(-/-) xenograft mouse model. Compared with mice treated with control T cells, the infusion of CD23.CAR(+) T cells resulted in a significant delay in the growth of the MEC-1 CLL cell line. These data suggest that CD23.CAR(+) T cells represent a selective immunotherapy for the elimination of CD23(+) leukemic cells in patients with CLL.

The microenvironment differentially impairs passive and active immunotherapy in chronic lymphocytic leukaemia - CXCR4 antagonists as potential adjuvants for monoclonal antibodies

Direct contact with stromal cells protects chronic lymphocytic leukaemia (CLL) B cells from chemotherapy-induced apoptosis in vitro. Blockade of CXCR4 signalling antagonizes stroma-mediated interactions and restores CLL chemosensitivity. In vivo, administration of CXCR4 antagonists effectively mobilizes haematopoietic progenitor cells. Therefore, combinations of CXCR4 blockade and cytoreductive treatment with selective activity on CLL cells may avoid potential haematotoxicity. Hence, we tested CXCR4 antagonists in the context of passive and active immunotherapeutic approaches. We evaluated how efficiently rituximab, alemtuzumab and cytotoxic T cells killed CLL cells cocultured with stromal cells in the presence and absence of a CXCR4 antagonist. Stromal cell contact attenuated rituximab- and alemtuzumab-induced complement-dependent cytotoxicity of CLL cells. Addition of CXCR4 antagonists abrogated the protective effect of stroma. In contrast, stromal cells did not impair antibody-dependent cell-mediated cytotoxicity and cytotoxicity induced by activated T cells. Destruction of microtubules in CLL target cells restored the protective effect of stroma coculture for CLL cells during Natural Killer cell attack by preventing mitochondrial relocalization towards the immunological synapse. Our data identify the combination of CXCR4 antagonists with passive - but not active - immunotherapy as a promising potential treatment concept in CLL.

AdCD40L immunogene therapy for bladder carcinoma--the first phase I/IIa trial

PURPOSE

Immunotherapy with Bacillus Calmette-Guerin (BCG) instillation is recommended for high-risk, non-muscle invasive bladder cancer. Bacillus Calmette-Guerin is not effective in advanced tumors, and better alternatives are warranted. Immunostimulating gene therapy with adenoviral vectors expressing CD40 ligand (AdCD40L) has shown efficacy in tumor models. CD40 ligand stimulates systemic immunity and may be effective in local and invasive human disease.

EXPERIMENTAL DESIGN

Patients with invasive bladder cancer scheduled for cystectomy or patients with T(a) tumors were enrolled in a phase I/IIa trial. Patients were treated with three cycles of intrabladder Clorpactin WCS-90 prewash, followed by AdCD40L instillation 1 week apart. Safety, gene transfer, immune effects, and antitumor responses were monitored.

RESULTS

All eight recruited patients were treated as scheduled, and therapy was well tolerated. The main adverse effect was transient local pain during prewash. Postoperatively, urinary tract infections and one case of late septicemia with elevated potassium were reported. No adverse events were ascribed to vector therapy. Gene transfer was detected in biopsies, and bladders were heavily infiltrated with T cells. The effector marker IFN-gamma increased in biopsies, whereas levels of circulating T regulatory cells were reduced. Histologic evaluation indicated that AdCD40L therapy reduced the load of malignant cells.

CONCLUSIONS

To our knowledge, this is the first report on immunogene therapy in bladder cancer and the first using AdCD40L in vivo. Local AdCD40L gene therapy was safe, boosted immune activation, and should be further evaluated as a single or an adjuvant therapy for urothelial malignancies.

Gamma-ray resistance of regulatory CD4+CD25+Foxp3+ T cells in mice

Abstract CD4(+)CD25(+) regulatory T cells (Treg cells) are an important subset of T cells for keeping proper immune responses and tolerance. However, the effects of gamma radiation on CD4(+)CD25(high) Foxp3(+) Treg cells have not been examined previously. In the present study, we compared the sensitivity of mouse CD4(+)CD25(high) Foxp3(+) Treg cells and CD4(+)CD25(-) T cells to gamma radiation in vitro and in vivo. After C57BL/6 mice received a whole-body dose of 5 Gy gamma rays, the numbers of lymphocyte subsets in blood, lymph nodes, spleens and thymuses clearly decreased. However, gamma radiation significantly enhanced the ratios of CD4(+)CD25(high) Treg cells and CD4(+)CD25(high) Foxp3(+) Treg cells to CD4(+) T cells in the blood, lymph nodes, spleens and thymuses of mice. More dead cells were observed in CD4(+)CD25(-) T cells than in CD4(+)CD25(high) Treg cells or CD4(+)CD25(high) Foxp3(+) Treg cells when the cells were irradiated in vitro, indicating that CD4(+)CD25(high) Foxp3(+) Treg cells are more resistant to gamma radiation than other T cells. Moreover, a higher expression of Bcl-2 in CD4(+)CD25(high) Treg cells was detected compared with that in CD4(+)CD25(-) T cells. CD4(+)CD25(+) Treg cells from irradiated mice were functional, though their immunosuppressive ability was somewhat impaired compared to those from nonirradiated mice as determined by an in vitro assay. These results indicate that mouse CD4(+)CD25(+) Treg cells and CD4(+)CD25(-) T effector cells have different sensitivities to gamma radiation in mice.

Selective elimination of a chemoresistant side population of B-CLL cells by cytotoxic T lymphocytes in subjects receiving an autologous hCD40L/IL-2 tumor vaccine

Side-population (SP) analysis identifies precursor cells in normal and malignant tissues. Cells with this phenotype have increased resistance to many cytotoxic agents, and in malignant disease may represent a primary drug resistant population. To discover whether drug resistant malignant SP cells are nonetheless sensitive to immune-mediated killing, we first established the presence of a malignant CD5⁺CD19⁺ SP subset in the blood of 18/21 subjects with B-CLL. We examined the fate of these cells in 6 of these individuals who received autologous hCD40L/IL-2 gene-modified tumor cells as part of a tumor vaccine study. Vaccinated patients showed an increase in B-CLL-reactive T cells followed by a corresponding decline in circulating CD5⁺CD19⁺ SP cells. T cell lines and clones generated from vaccinated patients specifically recognized B-CLL SP tumor cells. Elimination of SP cells is likely triggered by their increased expression of target antigens such as RHAMM following stimulation of the malignant cells by hCD40L, since CD8⁺ RHAMM-specific T cells could be detected in the peripheral blood of immunized patients and were associated with the decline in B-CLL SP cells. Hence malignant B cells with a primary drug resistant phenotype can be targeted by T cell mediated effector activity following immunization of human subjects.

Cellular immunotherapy of cancer

Standard therapies for many common cancers remain toxic and are often ineffective. Cellular immunotherapy has the potential to be a highly targeted alternative, with low toxicity to normal tissues but a high capacity to eradicate tumor. In this chapter we describe approaches that generate cellular therapies using active immunization with cells, proteins, peptides, or nucleic acids, as well as efforts that use adoptive transfer of effector cells that directly target antigens on malignant cells. Many of these approaches are proving successful in hematologic malignancy and in melanoma. In this chapter we discuss the advantages and limitations of each and how over the next decade investigators will attempt to broaden their reach, increase their efficacy, and simplify their application.

Changing paradigms in the treatment of chronic lymphocytic leukemia

Progress in our understanding of chronic lymphocytic leukemia and its treatment has resulted in a more tailored approach to patient management, with different therapeutic regimens for different patient populations. The current standard of care has evolved from single-agent therapy with chlorambucil or cyclophosphamide, through the introduction of purine analogs to the more recent introduction of chemoimmunotherapy. Selection of appropriate initial therapy should be based primarily on patient characteristics such as age, performance status and the expected clinical course of the leukemia based on established risk factors. Achieving a complete and durable response is the major goal for fit patients; chemoimmunotherapy with fludarabine, cyclophosphamide and rituximab would be advantageous. Alternatively, in unfit patients, controlling symptoms is the essential treatment goal and a regimen with a more favorable toxicity profile should be applied. This manuscript reviews the data that has lead to current treatment choices, advises on tailored therapies and discusses emerging trends. Data for this review was identified by a search of electronic information including Medline and PubMed databases, conference proceedings and trial registers. Critical analysis of extracted data was undertaken with attention to trial phase, treatment schedules and end points, including response rates, follow-up times, progression-free survival and overall survival.

Selective depletion of a minor subpopulation of B-chronic lymphocytic leukemia cells is followed by a delayed but progressive loss of bulk tumor cells and disease regression

Cancer precursor/progenitor cells may initiate and sustain the growth of tumors, but evidence for their existence in human disease is indirect, relying on their in vitro properties and animal models. More directly, specific elimination of these rare cells from cancer patients should produce a delayed but progressive disappearance of differentiated malignant progeny. Here, we describe selective eradication of a putative precursor population in a patient with B-cell chronic lymphocytic leukemia, followed 6 months later by a progressive loss of mature tumor cells without further treatment. This outcome supports the presence of a rare population of precursor/progenitor cells in human malignancies, and suggests benefit from their removal.

Lymphoma immunotherapy: vaccines, adoptive cell transfer and immunotransplant

Therapy for non-Hodgkin lymphoma has benefited greatly from basic science and clinical research such that chemotherapy and monoclonal antibody therapy have changed some lymphoma subtypes from uniformly lethal to curable, but the majority of lymphoma patients remain incurable. Novel therapies with less toxicity and more specific targeting of tumor cells are needed and immunotherapy is among the most promising of these. Recently completed randomized trials of idiotype vaccines and earlier-phase trials of other vaccine types have shown the ability to induce antitumor T cells and some clinical responses. More recently, trials of adoptive transfer of antitumor T cells have demonstrated techniques to increase the persistence and antitumor effect of these cells. Herein, we discuss lymphoma immunotherapy clinical trial results and what lessons can be taken to improve their effect, including the combination of vaccination and adoptive transfer in an approach we have dubbed 'immunotransplant'.

The Janus faces of CD40 in cancer

CD40 is a TNF receptor family member that is widely recognized for its prominent role in immune regulation and homeostasis. Expression of CD40 is not restricted to normal lymphoid cells but is also evident in the majority of haemopoietic and epithelial malignancies where it has been implicated in oncogenic events. Accumulating evidence, however, suggests that the CD40 pathway can be exploited for cancer therapy by virtue of its ability to stimulate the host anti-tumor immune response, normalize the tumor microenvironment and directly suppress the growth of CD40-positive tumors. Here, we provide an overview of the multifaceted functions of the CD40 pathway in cancer and its emerging role in the treatment of malignancy.

Current and emerging treatments for chronic lymphocytic leukaemia

Chronic lymphocytic leukaemia (CLL) is the most common adult leukaemia in Europe and North America. The disease is characterized by proliferation and accumulation of small CD5+ B cells in blood, lymph nodes, spleen, liver and bone marrow. The natural clinical course of CLL is highly variable, and chemotherapy is usually not indicated in early and stable disease. However, patients with progressive and more advanced CLL require treatment. For many years, chlorambucil with or without corticosteroids was used in previously untreated patients with CLL. More recently, purine nucleoside analogues (PNAs) [fludarabine, cladribine and pentostatin] have been included in treatment approaches for this disease, and chlorambucil is no longer the leading standard everywhere. Currently, this drug is rather recommended for the treatment of older, unfit patients with co-morbidities, especially in European countries. Significantly higher overall response (OR) and complete response (CR) rates in patients treated initially with PNAs than in those treated with chlorambucil or cyclophosphamide-based combination regimens have been confirmed in randomized, prospective, multicentre trials. Moreover, PNAs administered in combination with cyclophosphamide produce higher response rates, including CR and molecular CR, compared with PNA as monotherapy. Recent reports suggest that the administration of monoclonal antibodies (mAbs) can significantly improve the course of CLL. At present, two mAbs have the most important clinical value in patients with CLL. The first is rituximab, a human mouse antibody that targets CD20 antigens, and the second is alemtuzumab, a humanized form of a rat antibody active against CD52. Several recent reports suggest that in patients with CLL, rituximab combined with a PNA can increase the OR and CR rates compared with PNA or rituximab alone, with acceptable toxicity. In randomized trials, the combination of rituximab with fludarabine and cyclophosphamide (FC-R regimen) demonstrated higher rates of OR, CR and progression-free survival in patients with previously untreated and relapsed or refractory CLL than fludarabine plus cyclophosphamide (FC regimen). Several reports have confirmed significant activity with alemtuzumab in relapsed or refractory CLL, as well as in previously untreated patients. Recently, several new agents have been investigated and have shown promise in treating patients with CLL. These treatments include new mAbs, agents targeting the antiapoptotic bcl-2 family of proteins and receptors involved in mediating survival signals from the microenvironment, antisense oligonucleotides and other agents. The most promising are new mAbs directed against the CD20 molecule, lumiliximab and anti-CD40 mAbs. Oblimersen, alvocidib (flavopiridol) and lenalidomide are also being evaluated both in preclinical studies and in early clinical trials. In recent years, a significant improvement in haematopoietic stem cell transplantation (HSCT) procedures in patients with high-risk CLL has been observed. However, the exact role of HSCT, autologous or allogeneic, in the standard management of CLL patients is still undefined.

Vaccine therapy and chronic lymphocytic leukaemia

B-cell chronic lymphocytic leukaemia (CLL) should be an ideal target for immune-mediated responses. CLL arises from B cells that can act as antigen-presenting cells (APCs), expresses unique tumour antigens, and has been shown to be a target of the allogeneic T cells which mediate a graft-versus-leukaemia effect. Despite these potential benefits, immune responses against CLL cells have been difficult to elicit. CLL induces immune defects in the host, the tumour cells are inefficient APCs, and therapies given to patients with CLL are themselves immunosuppressive. Successful vaccination approaches in this disease will require steps to overcome these difficulties, including identification of the targets of immune responses in this disease to enable monitoring of the immune response after vaccination, improved presentation of antigens, and steps to improve the immune defects that accompany this disease.

Development of a dendritic cell-based vaccine for chronic lymphocytic leukemia

Evidence for the existence of CLL-specific antigens recognized by the immune system can be gathered from the observation that many patients display monoclonal or oligoclonal expansions and skewed repertoire of T cells. In vitro functional studies have shown that tumor-specific T-cells are able to lyse the leukemic cells. Antileukemic cellular immunity may be boosted in vivo using dendritic cell-based immunotherapy. Our preclinical studies provide evidence that DC that had endocytosed apoptotic CLL cells (Apo-DC) were superior to fusion hybrids, tumor lysate or RNA in eliciting antileukemic T-cell responses in vitro. We have validated a method for enriching the small number of monocyte precursors present in the peripheral blood of CLL patients and utilize them for generating individualized, Apo-DC cellular vaccines. In most cases, a minimum of 50 x 10(6) Apo-DC could be generated, beginning with immunomagnetically enriched monocytes from a single leukapheresis product containing at least 1% CD14+ cells. Cryopreservation and thawing did not affect the phenotype or the T cell stimulatory function of Apo-DC. A phase I/II, open label clinical trial examining the feasibility, safety and immunogenicity of Apo-DC vaccination has been initiated. CLL patients receive 10(7) Apo-DC for at least five immunizations and monitored clinically and immunologically for 52 weeks. Three cohorts are accrued stepwise. Cohort I receives Apo-DC alone; Cohort II: Apo-DC+ repeated doses of low-dose GM-CSF; Cohort III: low-dose cyclophosphamide followed by Apo-DC + GM-CSF.

Cytotoxic T lymphocytes directed to the preferentially expressed antigen of melanoma (PRAME) target chronic myeloid leukemia

The cancer testis antigen (CTA) preferentially expressed antigen of melanoma (PRAME) is overexpressed in many hematologic malignancies, including chronic myeloid leukemia (CML). The sensitivity of CML to donor lymphocyte infusion after allogeneic stem cell transplantation suggests this tumor can be highly susceptible to cellular immunotherapy targeted to tumor associated antigens. We therefore tested whether functional PRAME-specific cytotoxic T lymphocytes (PRAME CTLs) could be generated and expanded from healthy donors and CML patients, or whether the limited immunogenicity of this CTA coupled with tumor-associated anergy would preclude this approach. Using optimized culture conditions and HLA-A*02-restricted PRAME-peptides, we have consistently generated PRAME CTLs from 8/9 healthy donors and 5/6 CML patients. These CTLs released IFNgamma in response to PRAME peptides (between 113 +/- 8 and 795 +/- 23 spot forming cells/10(5) T cells) and lysed PRAME peptide-loaded cells (45 +/- 19% at an effector:target [E:T] ratio of 20:1) in a MHC-restricted fashion. Importantly, these CTLs recognized and had cytotoxic activity against HLA-A*02(+)/PRAME(+) tumor cell lines, and could recognize and respond to primary CML cells. PRAME CTLs were generated almost exclusively from the naive T-cell compartment, and clonal analysis showed these cells could have high alphabetaTCR-peptide avidity. PRAME CTLs or vaccines may thus be of value for patients with CML.

Adoptive T-cell immunotherapy of chronic lymphocytic leukaemia

Immunotherapy for B-cell chronic lymphocytic leukaemia (B-CLL) and other haematological malignancies may consist of passive antibody, active immunization or adoptive T-cell transfer. This chapter will focus on T-lymphocyte immunotherapy; an approach supported by earlier observations that the beneficial effects of allogeneic stem cell transplantation depend, in part, on the graft-versus-leukaemia effects mediated by these cells. One promising strategy consists of the genetic manipulation of effector T lymphocytes to express tumour-specific T-cell receptors or chimeric antigen receptors directed against surface antigens on the B-CLL cells. This methodology is now being integrated with the concept that tumour recurrence may be due to the persistence of a reservoir of more primitive and chemoresistant tumour cells, dubbed 'cancer stem cells', with self-renewal capacity. Identification and characterization of these cancer stem cells in B-CLL is crucial for the development of new anti-tumour agents, and for the identification of target antigens for cellular immunotherapy. This chapter will describe how immunotherapy may be directed to a more primitive side population of B-CLL cells.