Human cytotoxic T lymphocytes specific for Wilms' tumor antigen-1 inhibit engraftment of leukemia-initiating stem cells in non-obese diabetic-severe combined immunodeficient recipients

Allogeneic Tumor Antigen-Specific T Cells for Broadly Applicable Adoptive Cell Therapy of Cancer

T cells specific for major histocompatibility complex (MHC)-presented tumor antigens are capable of inducing durable remissions when adoptively transferred to patients with refractory cancers presenting such antigens. When such T cells are derived from healthy donors, they can be banked for off-the-shelf administration in appropriately tissue matched patients. Therefore, tumor antigen-specific, donor-derived T cells are expected to be a mainstay in the cancer immunotherapy armamentarium. In this chapter, we analyze clinical evidence that tumor antigen-specific donor-derived T cells can induce tumor regressions when administered to appropriately matched patients whose tumors are refractory to standard therapy. We also delineate the landscape of MHC-presented and unconventional tumor antigens recognized by T cells in healthy individuals that have been targeted for adoptive T cell therapy, as well as emerging antigens for which mounting evidence suggests their utility as targets for adoptive T cell therapy. We discuss the growing technological advancements that have facilitated sequence identification of such antigens and their cognate T cells, and applicability of such technologies in the pre-clinical and clinical settings.

Wilms tumor 1 peptide vaccination after hematopoietic stem cell transplant in leukemia patients

Although the prognosis of leukemia patients after allogeneic hematopoietic stem cell transplantation (HSCT) has greatly improved, relapse is still a major cause of death after HSCT. Cancer vaccines may have the potential to enhance the graft-versus-leukemia (GVL) effect. The post-allogeneic HSCT period provides a unique platform for vaccination, because (I) tumor burden is minimal, (II) lymphopenia allows for rapid expansion of cytotoxic T cells (CTLs), (III) donor-derived CTLs are not exhausted, (IV) inflammation is caused by alloreactions, and (V) the abundance of regulatory T cells is low due to their late recovery. Tumor cell lysates, dendritic cells (DCs), and peptides derived from leukemia-associated antigens (LAAs) have been used as vaccines. Clinical trials with several types of vaccines for post-HSCT patients revealed that the vaccination induced an immunological response and might benefit patients with minimal residual disease; however, the efficacy of this approach must be examined in randomized studies. In addition, it is important to consider the combination of cancer vaccine with checkpoint antibodies, recently shown to be useful in treating leukemia relapse after HSCT.

Patient-individualized CD8⁺ cytolytic T-cell therapy effectively combats minimal residual leukemia in immunodeficient mice

Adoptive transfer of donor-derived cytolytic T-lymphocytes (CTL) has evolved as a promising strategy to improve graft-versus-leukemia (GvL) effects in allogeneic hematopoietic stem-cell transplantation. However, durable clinical responses are often hampered by limited capability of transferred T cells to establish effective and sustained antitumor immunity in vivo. We therefore analyzed GvL responses of acute myeloid leukemia (AML)-reactive CD8(+) CTL with central and effector memory phenotype in a new allogeneic donor-patient specific humanized mouse model. CTL lines and clones obtained upon stimulation of naive CD45RA(+) donor CD8(+) T cells with either single HLA antigen-mismatched or HLA-matched primary AML blasts, respectively, elicited strong leukemia reactivity during cytokine-optimized short to intermediate (i.e., 2-8 weeks) culture periods. Single doses of CTL were intravenously infused into NOD/scidIL2Rcg(null) mice when engraftment with patient AML reached bone marrow infiltration of 1-5%, clinically defining minimal residual disease status. This treatment resulted in complete regression of HLA-mismatched and strong reduction of HLA-matched AML infiltration, respectively. Most importantly, mice receiving AML-reactive CTL showed significantly prolonged survival. Transferred CTL were detectable in murine bone marrow and spleen and demonstrated sustained AML-reactivity ex vivo. Moreover, injections with human IL-15 clearly promoted CTL persistence. In summary, we show that naive donor-derived CD8(+) CTL effectively combat patient AML blasts in immunodeficient mice. The donor-patient specific humanized mouse model appears suitable to evaluate therapeutic efficacy of AML-reactive CTL before adoptive transfer into patients. It may further help to identify powerful leukemia rejection antigens and T-cell receptors for redirecting immunity to leukemias even in a patient-individualized manner.

T-cell depleted allogeneic hematopoietic cell transplants as a platform for adoptive therapy with leukemia selective or virus-specific T-cells

Allogeneic hematopoietic cell transplants adequately depleted of T-cells can reduce or prevent acute and chronic GVHD in both HLA-matched and haplotype-disparate hosts, without post-transplant prophylaxis with immunosuppressive drugs. Recent trials indicate that high doses of CD34+ progenitors from G-CSF mobilized peripheral blood leukocytes isolated and T-cell depleted by immunoadsorption to paramagnetic beads, when administered after myeloablative conditioning with TBI and chemotherapy or chemotherapy alone can secure consistent engraftment and abrogate GVHD in patients with acute leukemia without incurring an increased risk of a recurrent leukemia. Early clinical trials also indicate that high doses of in vitro generated leukemia-reactive donor T-cells can be adoptively transferred and can induce remissions of leukemia relapse without GVHD. Similarly, virus-specific T-cells generated from the transplant donor or an HLA partially matched third party, have induced remissions of Rituxan-refractory EBV lymphomas and can clear CMV disease or viremia persisting despite antiviral therapy in a high proportion of cases. Analyses of treatment responses and failures illustrate both the advantages and limitations of donor or banked, third party-derived T-cells, but underscore the potential of adoptive T-cell therapy in the absence of ongoing immunosuppression.

Can immunotherapy specifically target acute myeloid leukemic stem cells?

Accumulating evidence supports the role of leukemic stem cells (LSCs) in the high relapse rate of acute myeloid leukemia (AML) patients. The clinical relevance of LSCs, which were originally characterized in xenograft models, has recently been confirmed by the finding that stem cell-like gene expression signatures can predict the clinical outcome of AML patients. The targeted elimination of LSCs might hence constitute an efficient therapeutic approach to AML. Here, we review immunotherapeutic strategies that target LSC-associated antigens, including T cell-mediated and monoclonal antibody-based regimens. Attention is given to the issue of antigen specificity because this is relevant to the therapeutic window and determines the superiority of LSC-targeting immunotherapy.

Wilms' Tumour 1 (WT1) peptide vaccination in patients with acute myeloid leukaemia induces short-lived WT1-specific immune responses

Wilms’ Tumour 1 (WT1) is a zinc finger transcription factor that is over-expressed in acute myeloid leukaemia (AML). Its restricted expression in normal tissues makes it a promising target for novel immunotherapies aiming to accentuate the cytotoxic T lymphocyte (CTL) response against AML. Here we report a phase I/II clinical trial of subcutaneous peptide vaccination with two separate HLA-A2-binding peptide epitopes derived from WT1, together with a pan-DR binding peptide epitope (PADRE), in Montanide adjuvant. Eight HLA-A2-positive patients with poor risk AML received five vaccination cycles at 3-weekly intervals. The three cohorts received 0·3, 0·6 and 1 mg of each peptide, respectively. In six patients, WT1-specific CTL responses were detected using enzyme-linked immunosorbent spot assays and pWT126/HLA-A*0201 tetramer staining, after ex vivo stimulation with the relevant WT1 peptides. However, re-stimulation of these WT1-specific T cells failed to elicit secondary expansion in all four patients tested, suggesting that the WT1-specific CD8⁺ T cells generated following vaccination may be functionally impaired. No correlation was observed between peptide dose, cellular immune response, reduction in WT1mRNA expression and clinical response. Larger studies are indicated to confirm these findings.

Role of T cell receptor affinity in the efficacy and specificity of adoptive T cell therapies

Over the last several years, there has been considerable progress in the treatment of cancer using gene modified adoptive T cell therapies. Two approaches have been used, one involving the introduction of a conventional αβ T cell receptor (TCR) against a pepMHC cancer antigen, and the second involving introduction of a chimeric antigen receptor (CAR) consisting of a single-chain antibody as an Fv fragment linked to transmembrane and signaling domains. In this review, we focus on one aspect of TCR-mediated adoptive T cell therapies, the impact of the affinity of the αβ TCR for the pepMHC cancer antigen on both efficacy and specificity. We discuss the advantages of higher-affinity TCRs in mediating potent activity of CD4 T cells. This is balanced with the potential disadvantage of higher-affinity TCRs in mediating greater self-reactivity against a wider range of structurally similar antigenic peptides, especially in synergy with the CD8 co-receptor. Both TCR affinity and target selection will influence potential safety issues. We suggest pre-clinical strategies that might be used to examine each TCR for possible on-target and off-target side effects due to self-reactivities, and to adjust TCR affinities accordingly.

Enhanced-affinity murine T-cell receptors for tumor/self-antigens can be safe in gene therapy despite surpassing the threshold for thymic selection

Many of the most promising tumor antigens for T-cell-based cancer immunotherapies are unmodified self-antigens. Unfortunately, the avidity of T cells specific for these antigens is limited by central tolerance during T-cell development in the thymus, resulting in decreased anti-tumor efficacy of these T cells. One approach to overcoming this obstacle is to mutate T-cell receptor (TCR) genes from naturally occurring T cells to enhance the affinity for the target antigen. These enhanced-affinity TCRs can then be developed for use in TCR gene therapy. Although TCRs with significantly enhanced affinity have been generated using this approach, it is not clear whether these TCRs, which bypass the affinity limits imposed by negative selection, remain unresponsive to the low levels of self-antigen generally expressed by some normal tissues. Here we show that 2 variants of a high-affinity WT1-specific TCR with enhanced affinity for WT1 are safe and do not mediate autoimmune tissue infiltration or damage when transduced into peripheral CD8 T cells and transferred in vivo. However, if expressed in developing T cells and subjected to thymic selection, the same enhanced-affinity TCRs signal tolerance mechanisms in the thymus, resulting in T cells with attenuated antigen sensitivity in the periphery.

Graft-versus-leukemia effect of HLA-haploidentical central-memory T-cells expanded with leukemic APCs and modified with a suicide gene

Allogeneic hematopoietic stem cell transplantation (HSCT) from a human leukocyte antigen (HLA)-haploidentical family donor (haplo-HSCT) is a readily available and potentially curative option for high-risk leukemia. In haplo-HSCT, alloreactivity plays a major role in the graft-versus-leukemia (GVL) effect, which, however, is frequently followed by relapse due to emerging leukemic cell variants that have lost the unshared HLA haplotype as a mechanism of immune escape. We report that stimulation of HLA-haploidentical donor T lymphocytes with leukemic antigen-presenting cells (L-APCs) expands a population of leukemia-reactive T cells, which, besides alloreactivity to unshared HLAs, contain leukemia-associated specificities restricted by shared HLAs. According to a preferential central-memory (T(CM)) phenotype and to high interleukin (IL)-7Rα expression, these T cells persist in vivo and sustain a major GVL effect in a clinically relevant xenograft model. Moreover, we demonstrate that modifying L-APC-expanded T cells to express the herpes simplex virus thymidine kinase (HSV-tk) suicide gene enables their elimination with the prodrug ganciclovir (GCV), therefore providing a safety switch in case of graft-versus-host disease (GVHD). These results warrant the clinical investigation of L-APC-expanded T cells modified with a suicide gene in the setting of haplo-HSCT.

Augmentation of anti-tumor immunity by adoptive T-cell transfer after allogeneic hematopoietic stem cell transplantation

Allogeneic hematopoietic stem cell transplantation (HCT) is currently the standard of care for most patients with high-risk acute leukemias and some other hematologic malignancies. Although HCT can be curative, many patients who undergo allogeneic HCT will later relapse. There is, therefore, a critical need for the development of novel post-HCT therapies for patients who are at high risk for disease recurrence following HCT. One potentially efficacious approach is adoptive T-cell immunotherapy, which is currently undergoing a renaissance that has been inspired by scientific insight into the key issues that impeded its previous clinical application. Translation of the next generation of adoptive T-cell therapies to the allogeneic HCT setting, using donor T cells of defined specificity and function, presents a unique set of challenges and opportunities. The challenges, progress and future of adoptive T-cell therapy following allogeneic HCT are discussed in this review.

Mapping of novel peptides of WT-1 and presenting HLA alleles that induce epitope-specific HLA-restricted T cells with cytotoxic activity against WT-1(+) leukemias

The Wilms tumor protein (WT-1) is widely recognized as a tumor antigen that is expressed differentially by several malignancies. However, WT-1 peptides known to induce tumoricidal T cells are few. In the present study, we evaluated T-cell responses of 56 healthy donors to in vitro sensitization with autologous APCs loaded with a pool of overlapping 15-mer peptides spanning the sequence of WT-1. Thereafter, we mapped the WT-1 peptides eliciting responses in each individual, defined the immunogenic peptides, and identified their presenting HLA alleles. We report 41 previously unreported epitopes of WT-1: 5 presented by class II and 36 by class I alleles, including 10 that could be presented by more than 1 class I allele. IFNγ(+) T cells responding to 98% of the class I and 60% of the class II epitopes exhibited HLA-restricted cytotoxicity against peptide-loaded targets. T cells specific for 36 WT-1 peptides were evaluable for leukemocidal activity, of which 27 (75%) lysed WT-1(+) leukemic targets sharing their restricting HLA allele. Each epitope identified induced T-cell responses in most donors sharing the epitopes' presenting allele; these responses often exceeded responses to flanking peptides predicted to be more immunogenic. This series of immunogenic epitopes of WT-1 should prove useful for immunotherapies targeting WT-1(+) malignancies.

Evaluation of current cancer immunotherapy: hemato-oncology

Hematologic malignancies were the first diseases in clinical oncology for which the potential of harnessing the immune system as targeted therapy was unequivocally demonstrated. Unfortunately, the use of this highly efficacious modality has been limited to only a subset of patients and diseases because of immune-mediated toxicities resulting from incomplete specificity, and disease-specific determinants of sensitivity versus resistance to immune effector mechanisms. Recent studies, however, have begun to elucidate the molecular basis of the observed clinical effects allowing the rational development of next generation of immunotherapeutic combinations. We discuss here cancer antigen targets in hematologic malignancies and the specific approaches to induce immunity being pursued, the importance of modulating the host immunoregulatory environment, and the special features of immunological monitoring in clinical investigation. The hematologic malignancies represent an ideal setting for the development of immunotherapy due to logistical, clinical monitoring, and disease biology factors and may represent an exemplar for immune-based treatment in other cancer types.

Vaccines as consolidation therapy for myeloid leukemia

Immunotherapy for myeloid leukemias remains a cornerstone in the management of this highly aggressive group of malignancies. Allogeneic (allo) stem cell transplantation (SCT), which can be curative in acute and chronic myeloid leukemias, exemplifies the success of immunotherapy for cancer management. However, because of its nonspecific immune response against normal tissue, allo-SCT is associated with high rates of morbidity and mortality, secondary to graft-versus-host disease, which can occur in up to 50% of allo-SCT recipients. Targeted immunotherapy using leukemia vaccines has been heavily investigated, as these vaccines elicit specific immune responses against leukemia cells while sparing normal tissue. Peptide and cellular vaccines have been developed against tumor-specific and leukemia-associated self-antigens. Although not yet considered the standard of care, leukemia vaccines continue to show promising results in the management of the myeloid leukemias.

Induction of complete and molecular remissions in acute myeloid leukemia by Wilms' tumor 1 antigen-targeted dendritic cell vaccination

Active immunization using tumor antigen-loaded dendritic cells holds promise for the adjuvant treatment of cancer to eradicate or control residual disease, but so far, most dendritic cell trials have been performed in end-stage cancer patients with high tumor loads. Here, in a phase I/II trial, we investigated the effect of autologous dendritic cell vaccination in 10 patients with acute myeloid leukemia (AML). The Wilms' tumor 1 protein (WT1), a nearly universal tumor antigen, was chosen as an immunotherapeutic target because of its established role in leukemogenesis and superior immunogenic characteristics. Two patients in partial remission after chemotherapy were brought into complete remission after intradermal administration of full-length WT1 mRNA-electroporated dendritic cells. In these two patients and three other patients who were in complete remission, the AML-associated tumor marker returned to normal after dendritic cell vaccination, compatible with the induction of molecular remission. Clinical responses were correlated with vaccine-associated increases in WT1-specific CD8+ T cell frequencies, as detected by peptide/HLA-A*0201 tetramer staining, and elevated levels of activated natural killer cells postvaccination. Furthermore, vaccinated patients showed increased levels of WT1-specific IFN-gamma-producing CD8+ T cells and features of general immune activation. These data support the further development of vaccination with WT1 mRNA-loaded dendritic cells as a postremission treatment to prevent full relapse in AML patients.

Adoptive transfer of unselected or leukemia-reactive T-cells in the treatment of relapse following allogeneic hematopoietic cell transplantation

Adoptive transfer of in vivo generated antigen-specific donor-derived T-cells is increasingly recognized as an effective approach for the treatment or prevention of EBV lymphomas and cytomegalovirus infections complicating allogeneic hematopoietic cell transplants. This review examines evidence from preclinical experiments and initial clinical trials to critically assess both the potential and current limitations of adoptive transfer of donor T-cells sensitized to selected minor alloantigens of the host or to peptide epitopes of proteins, differentially expressed by clonogenic leukemia cells, such as the Wilms tumor protein, WT-1, as a strategy to treat or prevent recurrence of leukemia in the post-transplant period.

The biological basis for immunotherapy in patients with chronic myelogenous leukemia

BACKGROUND

Chronic myelogenous leukemia (CML) has long been recognized as an entity responsive to immunotherapeutic interventions. Despite the success of the tyrosine kinase inhibitors (TKIs) in this disease, CML remains incurable. Only allogeneic bone marrow transplantation can provide long-term eradication of CML.

METHODS

This review summarizes the recent advances in the field of immunology in CML, specifically in tumor antigen discovery, that have been incorporated into the design of new clinical trials.

RESULTS

Multiple vaccine approaches are currently under clinical investigation. Recent laboratory and clinical data also point to a unique interaction of TKIs with the immune system.

CONCLUSIONS

A better understanding of these interactions combined with advances in the field of immunotherapy will likely lead to incorporation of TKIs in future therapeutic interventions to develop a cure for this disease.

Graft-versus-leukemia effects of transplantation and donor lymphocytes

Allogeneic transplantation of hematopoietic cells is an effective treatment of leukemia, even in advanced stages. Allogeneic lymphocytes produce a strong graft-versus-leukemia (GVL) effect, but the beneficial effect is limited by graft-versus-host disease (GVHD). Depletion of T cells abrogates GVHD and GVL effects. Delayed transfusion of donor lymphocytes into chimeras after T cell-depleted stem cell transplantation produces a GVL effect without necessarily producing GVHD. Chimerism and tolerance provide a platform for immunotherapy using donor lymphocytes. The allogeneic GVL effects vary from one disease to another, the stage of the disease, donor histocompatibility, the degree of chimerism, and additional treatment. Immunosuppressive therapy before donor lymphocyte transfusions may augment the effect as well as concomitant cytokine treatment. Possible target antigens are histocompatibility antigens and tumor-associated antigens. Immune escape of tumor cells and changes in the reactivity of T cells are to be considered. Durable responses may be the result of the elimination of leukemia stem cells or the establishment of a durable immune control on their progeny. Recently, we have learned from adoptive immunotherapy of viral diseases and HLA-haploidentical stem cell transplantation that T-cell memory may be essential for the effective treatment of leukemia and other malignancies.

PR1 vaccination in myeloid malignancies

The graft-versus-leukemia (GVL) effect following allogeneic stem cell transplantation is testament to the effectiveness of the immune system in recognizing and eliminating leukemia cells. The successful identification of a range of leukemia-associated antigens (LAAs) that drive the GVL response in recent years has stimulated research in the development of vaccines to treat hematological malignancies. Here, we review the current experience with the PR1 vaccine. PR1 is a nine amino acid, HLA-A(*)0201-restricted peptide, shared by two myeloid LAAs, proteinase (PR)3 and neutrophil elastase (NE). PR3 and NE are found in the primary (azurophil) granule proteins of normal granulocytes and are overexpressed in myeloid leukemia cells. PR1 induces powerful HLA-A(*)0201-restricted CD8+ T-cell responses that selectively kill myeloid leukemia cells in vitro. The detection of low frequencies of PR1-specific CD8+ T cells in patients with chronic myeloid leukemia and at higher frequencies in patients entering molecular remission after allogeneic stem cell transplantation supports the concept that there is natural immunity to PR1, which can be boosted further by vaccination to enhance immunity to leukemia. Preliminary reports indicate that PR1 peptide vaccination induces significant increases in PR1-specific CD8+ T cells, with rapid and durable remissions in some patients with myeloid leukemia. These promising early results point the way to optimizing the administration of peptide vaccines to improve the treatment of otherwise refractory myeloid leukemias.

WT1 protein expression in slowly proliferating myeloid leukemic cell lines is scarce throughout the cell cycle with a minimum in G0/G1 phase

Wilms' tumor gene 1 (WT1) is overexpressed in various hematological malignancies and has been proposed as a target for minimal residual disease (MRD) detection and for immunotherapy. Although WT1 is known as a key molecule for tumor cell proliferation, the expression pattern of WT1 in leukemic cells in dependency of proliferation has not yet been investigated. Furthermore, WT1 expression was mostly studied by reverse transcriptase PCR and the expression of WT1 protein has not been extensively studied. Here, we analyzed WT1 protein expression in the human myeloid leukemia cell lines K562 and HL-60 by indirect immunofluorescence and flow cytometry. Both cell lines exhibited varying nuclear WT1 immunoreactivity pointing to a cell cycle-dependent and/or proliferation-dependent WT1 expression. In rapidly proliferating cells high levels of WT1 protein were detected by flow cytometry. A reduced proliferation rate was associated with a low WT1 protein expression and an accumulation of cells in G(0)/G(1) phase. During G(0)/G(1) phase cells expressed WT1 at a lower level than in S or G(2)/M phase. Moreover, WT1 expression was diminished in all cell cycle phases in slowly proliferating cells. We conclude that WT1 protein expression is dependent on the cell cycle phase as well as on the proliferation rate. This finding might be relevant for MRD studies and immunotherapeutic strategies targeting WT1.

WT1 peptide vaccine for the treatment of cancer

Wilms' tumor gene WT1 is expressed in various kinds of cancers. Human WT1-specific cytotoxic T lymphocytes (CTLs) were generated, and mice immunized with WT1 peptide rejected challenges by WT1-expressing cancer cells without auto-aggression to normal organs. Furthermore, WT1 antibodies and WT1-specific CTLs were detected in cancer patients, indicating that WT1 protein was immunogenic. These findings provided us with the rationale for cancer immunotherapy targeting WT1. Clinical trials of WT1 peptide vaccination for cancer patients were started, and WT1 vaccination-related immunological responses and clinical responses, including reduction of leukemic cells, reduction of M-protein amount in myeloma, and shrinkage of solid cancer, were observed. Valuable information about immune responses against tumor antigens can be obtained by the analysis of samples from the vaccinated patients, which should lead to further improvement of cancer vaccine.

WT1-specific T cell receptor gene therapy: improving TCR function in transduced T cells

Adoptive transfer of antigen-specific T lymphocytes is an attractive form of immunotherapy for haematological malignancies and cancer. The difficulty of isolating antigen-specific T lymphocytes for individual patients limits the more widespread use of adoptive T cell therapy. The demonstration that cloned T cell receptor (TCR) genes can be used to produce T lymphocyte populations of desired specificity offers new opportunities for antigen-specific T cell therapy. The first trial in humans demonstrated that TCR gene-modified T cells persisted for an extended time period and reduced tumor burden in some patients. The WT1 protein is an attractive target for immunotherapy of leukemia and solid cancer since elevated expression has been demonstrated in AML, CML, MDS and in breast, colon and ovarian cancer. In the past, we have isolated high avidity CTL specific for a WT1-derived peptide presented by HLA-A2 and cloned the TCR alpha and beta genes of a WT1-specific CTL line. The genes were inserted into retroviral vectors for transduction of human peripheral blood T lymphocytes of leukemia patients and normal donors. The treatment of leukemia-bearing NOD/SCID mice with T cells transduced with the WT1-specific TCR eliminated leukemia cells in the bone marrow of most mice, while treatment with T cells transduced with a TCR of irrelevant specificity did not diminish the leukemia burden. In order to improve the safety and efficacy of TCR gene therapy, we have developed lentiviral TCR gene transfer. In addition, we employed strategies to enhance TCR expression while avoiding TCR mis-pairing. It may be possible to generate dominant TCR constructs that can suppress the expression of the endogenous TCR on the surface of transduced T cells. The development of new TCR gene constructs holds great promise for the safe and effective delivery of TCR gene therapy for the treatment of malignancies.

Review of current knowledge on HPV vaccination: an appendix to the European Guidelines for Quality Assurance in Cervical Cancer Screening

The recognition of a strong etiological relationship between infection with high-risk human papillomavirusses and cervical cancer has prompted research to develop and evaluate prophylactic and therapeutic vaccines. One prophylactic quadrivalent vaccine using L1 virus-like particles (VLP) of HPV 6, 11, 16 and 18 is available on the European market since the end of 2006 and it is expected that a second bivalent vaccine containing VLPs of HPV16 and HPV18 will become available in 2007. Each year, HPV16 and HPV18 cause approximately 43,000 cases of cervical cancer in the European continent. Results from the phase-IIb and III trials published thus far indicate that the L1 VLP HPV vaccine is safe and well-tolerated. It offers HPV-naive women a very high level of protection against HPV persistent infection and cervical intra-epithelial lesions associated with the types included in the vaccine. HPV vaccination should be offered to girls before onset of sexual activity. While prophylactic vaccination is likely to provide important future health gains, cervical screening will need to be continued for the whole generation of women that is already infected with the HPV types included in the vaccine. Phase IV studies are needed to demonstrate protection against cervical cancer and to verify duration of protection, occurrence of replacement by non-vaccine types and to define future policies for screening of vaccinated cohorts. The European Guidelines on Quality Assurance for Cervical Cancer Screening provides guidance for secondary prevention by detection and management of precursors lesions of the cervix. The purpose of the appendix on vaccination is to present current knowledge. Developing guidelines for future use of HPV vaccines in Europe, is the object of a new grant offered by the European Commission.

Improved human T-cell responses against synthetic HLA-0201 analog peptides derived from the WT1 oncoprotein

Wilms tumor protein 1 (WT1) is a transcription factor overexpressed in several types of leukemia and solid tumors. For this reason, WT1 is an attractive target for immunotherapy. Four peptide nonamers from WT1 have been identified by others to generate a WT1-specific cytotoxic response in the context of human leukocyte antigen (HLA)-A0201 and A2402. However, as WT1 is a self-antigen, breaking tolerance is a potential obstacle to vaccination. Here, we use a strategy to circumvent tolerance by designing synthetic immunogenic analog peptides that could crossreact to the native peptides (a heteroclitic response). A number of synthetic peptides derived from nonamer sequences of the WT1 protein were designed in which single amino-acid substitutions were introduced at HLA-A0201 major histocompatibility complex (MHC)-binding positions. Several of new peptides could stabilize MHC class I A0201 molecules better than native sequences. Some analogs were also able to elicit WT1-specific T-cell recognition and cytotoxic T-cell lymphocytes more effectively than native sequences. Importantly, T cells stimulated with the new analogs crossreacted with the native WT1 peptide sequence and were able to kill HLA-matched chronic myeloid leukemia cell lines. In conclusion, analog heteroclitic WT1 peptides with increased immunogenicity can be synthesized and are potential cancer vaccine candidates.

Cancer immunotherapy targeting Wilms' tumor gene WT1 product

The Wilms' tumor gene WT1 is expressed at high levels in leukemic blast cells in most acute myeloid and lymphoblastic leukemias. In myelodysplastic syndrome, WT1 mRNA expression levels increase along with disease progression; thus, WT1 mRNA is a tumor marker for leukemic blast cells. WT mRNA is also expressed at high levels in various types of solid cancers, including cancers of the lung, breast, colon and pancreas. Patients with WT1-expressing tumors produce antibodies and cytotoxic T-lymphocytes against WT1 protein, indicating that WT1 protein is highly immunogenic and a promising tumor antigen. Major histocompatibility complex class I-restricted cytotoxic T-lymphocyte and class II-restricted helper epitopes of WT1 protein were identified, and clinical studies of cancer immunotherapy using these cytotoxic T-lymphocyte epitope peptides were performed without significant adverse effect and with clinical results promising enough to encourage further clinical trials. The clinical efficacy of cancer immunotherapy targeting the WT1 protein should be clarified by a large-scale clinical study.

Autologous immune strategies to reduce the risk of leukemic relapse: Consideration for IL-15

The graft-versus-leukemia effect following allogeneic stem cell transplantation (SCT) reduces the incidence of leukemic relapse and establishes that effector cells can eliminate or at least contain resistant leukemic stem cells. Natural killer cells also appear to play a role in directly lowering the rate of relapse following allogeneic SCT in patients with acute myeloid leukemia. To date, however, effective prevention of leukemic relapse by autologous immune effector cells has not been demonstrated. This article examines some of the challenges that limit autologous antileukemia immunity as well as some possible immunotherapeutic approaches that may help control leukemic relapse following autologous SCT.

Generation of tumor-specific T-cell therapies

Antigen-specific tumor immunotherapy remains an attractive strategy for the treatment of malignancies. In this review we will discuss why, despite the identification of large numbers of T cell recognised tumor antigens, effective immunotherapy remains a formidable challenge. Effective strategies are needed to deal with the tolerogenic properties of many tumor antigens, and with the immunocompromised status of patients. We discuss different methods of generating tumor-specific T cells which are currently being evaluated in clinical practice, such as vaccination and adoptive transfer of tumor antigen-specific T cells. Finally, we shall discuss novel strategies in development, such as the adoptive transfer of T cell receptor (TCR) gene modified T cells to establish antigen-specific immunity in patients with leukemia and solid cancers. The transfer of validated high avidity TCRs, isolated from 'non-tolerant' repertoires or produced by in vitro affinity maturation, can serve to equip patient T cells with new anti-tumor specificities that are not naturally present in the autologous repertoire. TCR transfer into CD4(+) and CD8(+) T cells can serve to harness the function of both helper and cytotoxic T cells for tumor elimination and establishment of long-term tumor immunity.

Engineering T cells for cancer therapy

It is generally accepted that the immune system plays an important role in controlling tumour development. However, the interplay between tumour and immune system is complex, as demonstrated by the fact that tumours can successfully establish and develop despite the presence of T cells in tumour. An improved understanding of how tumours evade T-cell surveillance, coupled with technical developments allowing the culture and manipulation of T cells, has driven the exploration of therapeutic strategies based on the adoptive transfer of tumour-specific T cells. The isolation, expansion and re-infusion of large numbers of tumour-specific T cells generated from tumour biopsies has been shown to be feasible. Indeed, impressive clinical responses have been documented in melanoma patients treated with these T cells. These studies and others demonstrate the potential of T cells for the adoptive therapy of cancer. However, the significant technical issues relating to the production of natural tumour-specific T cells suggest that the application of this approach is likely to be limited at the moment. With the advent of retroviral gene transfer technology, it has become possible to efficiently endow T cells with antigen-specific receptors. Using this strategy, it is potentially possible to generate large numbers of tumour reactive T cells rapidly. This review summarises the current gene therapy approaches in relation to the development of adoptive T-cell-based cancer treatments, as these methods now head towards testing in the clinical trial setting.

Adult stem cells and cancer stem cells: tie in or tear apart?

Stem cell research is one of the new frontiers of medical science. Because of the unique self-renewable ability and powerful potential to differentiate, stem cells can be viewed as the mother of all cells in the body and have been investigated as a possible tool for reversing the degeneration and damage on organs. Recently, successful isolating cancerous stem cells from leukemia, breast and brain cancers provide a new target for eliminate cancer; however, it hints an increasing caution in using adult stem cells for organ repair. Cancerous stem cells share the same properties of self-renewal and differentiation with normal stem cells, with the addition of similar phenotype of adult stem cells isolated from the same tissue. Some believe that cancerous stem cells are derived from mutation of the normal stem cells, whereas others suspect it to be from different origins. Further investigation of the intrinsic factor underlying the behavior of adult stem cells and cancerous stem cells will shed light on both the fields of tissue engineering and cancer therapy. In this review, recent progresses in the studies of adult stem cells and cancerous stem cells are summarized to facilitate a better understanding and elicit much attention in this field.

Antigen-specific cellular immunotherapy of leukemia

Advances in cellular and molecular immunology have led to the characterization of leukemia-specific T-cell antigens and to the development of strategies for effective augmentation of T-cell immunity in leukemia patients. While several leukemia-related antigens have been identified, this review focuses on the Wilms' tumor 1 (WT1) antigen and the proteinase 3 (Pr3) antigen that are overexpressed in leukemic cells and are already being used in the clinical setting. Moreover, WT1 is also overexpressed in a vast number of nonhematological solid tumors, thereby expanding its use as a promising target for cancer vaccines. Examples of spontaneous immune responses against WT1 and Pr3 in leukemia patients are presented and the potential of WT1 and Pr3 for adoptive T-cell immunotherapy of leukemia is discussed. We also elaborate on the use of professional antigen-presenting cells loaded with mRNA encoding WT1 exploiting the advantage of broad HLA coverage for therapeutic vaccination purposes. Finally, the summarized data underscore the potential of WT1 for the manipulation of T-cell immunity in leukemia and in cancer in general, that will likely pave the way for the development of more effective and generic cancer vaccines.

Elimination of human leukemia cells in NOD/SCID mice by WT1-TCR gene-transduced human T cells

Cytotoxic T lymphocytes (CTLs) specific for an HLA-A2-presented peptide epitope of the Wilms tumor antigen-1 (WT1) can selectively kill immature human leukemia progenitor and stem cells in vitro. In this study we have used retroviral gene transfer to introduce a WT1-specific T-cell receptor (TCR) into T lymphocytes obtained from patients with leukemia and from healthy donors. TCR-transduced T cells kill leukemia cells in vitro and display WT1-specific cytokine production. Intravenous injection of TCR-transduced T cells into nonobese diabetic-severe combined immunodeficiency (NOD/SCID) mice harboring human leukemia cells resulted in leukemia elimination, whereas transfer of control T cells transduced with an irrelevant TCR was ineffective. The data suggest that adoptive immunotherapy with WT1-TCR gene-modified patient T cells should be considered for the treatment of leukemia.

Targeting the silent minority: emerging immunotherapeutic strategies for eradication of malignant stem cells in chronic myeloid leukaemia

Standard allogeneic stem cell transplantation (alloSCT) has provided a cure for chronic myeloid leukaemia (CML) over the last 25 years, but is only an option for a minority of patients. It was hoped that the introduction of imatinib mesylate (IM), a specific tyrosine kinase inhibitor that targets the Bcr-Abl oncogene product, would provide long-term remission or even cure for those patients without a donor, but studies have shown that IM does not eliminate leukaemic stem cells in CML patients. To overcome this problem of molecular persistence, research is underway to combine reduced intensity stem cell transplant or non-donor-dependent immunotherapies with IM with the aim of increasing cure rate, reducing toxicity and improving quality of life. The alternative approach is to combine IM or second-generation agents with other novel drugs that interrupt key signalling pathways activated by Bcr-Abl. This article will focus on the latest immunotherapy and molecularly targeted therapeutic options in CML and how they may be combined to improve the outcome for CML patients in the future.

In vitro Stimulation with WT1 Peptide-Loaded Epstein-Barr Virus-Positive B Cells Elicits High Frequencies of WT1 Peptide-Specific T Cells with In vitro and In vivo Tumoricidal Activity

The Wilms tumor protein (WT1) is overexpressed in most acute and chronic leukemias. To develop a practicable, clinically applicable approach for generation of WT1-specific T cells and to comparatively evaluate the immunogenicity of WT1 in normal individuals, we sensitized T cells from 13 HLA-A0201+ and 5 HLA-A2402+ donors with autologous EBV-transformed B cells or cytokine-activated monocytes, loaded with the HLA-A0201-binding WT1 peptides (126-134)RMFPNAPYL or (187-195)SLGEQQYSV or a newly identified HLA-A2402-binding WT1 peptide (301-310)RVPGVAPTL. WT1-specific T cells were regularly generated from each donor. T cells sensitized with peptide-loaded EBV-transformed B cells generated higher numbers of WT1-specific T cells than peptide-loaded cytokine-activated monocytes. Contrary to expectations, the frequencies of WT1 peptide-specific T cells were equivalent to those generated against individual highly immunogenic HLA-A0201-binding EBV peptides. Each of these T-cell lines specifically killed WT1+ leukemias and solid tumors in an HLA-restricted manner but did not lyse autologous or HLA-matched normal CD34+ hematopoietic progenitor cells or reduce their yield of colony-forming unit-granulocyte-macrophage (CFU-GM), burst-forming unit erythroid (BFU-E), or mixed colonies (CFU-mix). Furthermore, WT1 peptide-specific T cells after adoptive transfer into nonobese diabetic-severe combined immunodeficient mice bearing subcutaneous xenografts of WT1+ and WT1- HLA-A0201+ leukemias preferentially accumulated in and induced regressions of WT1+ leukemias that expressed the restricting HLA allele. Such cells are clinically applicable and may prove useful for adoptive cell therapy of WT1+ malignant diseases in humans.

Cellular immunotherapy after allogeneic stem cell transplantation in hematologic malignancies

PURPOSE OF REVIEW

The chimeric state after allogeneic stem cell transplantation provides an ideal platform for adoptive immunotherapy of hematologic malignancies using donor-derived cells. The present review aims to summarize recent results of the transfusion of donor-derived cells with regard to the diseases treated, the cells used for treatment, and the origin of these cells.

RECENT FINDINGS

The transfusion of donor lymphocytes has been studied widely, not only in patients with recurrent disease, persistent disease, and mixed chimerism but also in a variety of hematologic malignancies. Donors of lymphocytes and hematopoietic stem cells have been HLA-identical siblings, HLA-matched unrelated donors, and HLA-different haploidentical family members. A variety of cells have been used for adoptive immunotherapy, including plain lymphocytes, selected T cells, T cell lines, and T cell clones. The possible therapies have been expanded by natural killer cells and natural killer T cells as well as antibodies directing the effector cells toward the malignancy.

SUMMARY

Adoptive immunotherapy in chimeras has become not only a routine form of treatment of recurrent hematologic malignancy but also a prophylactic measure in high-risk leukemia and lymphoma.

Hematopoietic cell transplantation: five decades of progress

During the past 50 years, the role of allogeneic hematopoietic cell transplantation (HCT) has changed from a desperate therapeutic maneuver plagued by apparently insurmountable complications to a curative treatment modality for thousands of patients with hematologic diseases. Now, cure rates following human leukocyte antigen (HLA) allogeneic HCT with matched siblings exceed 85% for some otherwise lethal diseases, such as chronic myeloid leukemia, aplastic anemia, or thalassemia. In addition, the recent development of non-myeloablative conditioning and stem cell transplantation has opened the way to include elderly patients with a wide variety of hematologic malignancies. Further progress in adoptive transfer of T cell populations with relative tumor specificity would make the transplant procedure more effective and would extend the use of allogeneic HCT for treatment of non-hematopoietic malignancies.