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

Therapeutic cancer vaccine therapy for acute myeloid leukemia

Antitumor function of the immune system has been harnessed to eradicate tumor cells as cancer therapy. Therapeutic cancer vaccines aim to help immune cells recognize tumor cells, which are difficult to target owing to immune escape. Many attempts at vaccine designs have been conducted throughout the last decades. In addition, as the advanced understanding of immunosuppressive mechanisms mediated by tumor cells, combining cancer vaccines with other immune therapies seems to be more efficient for cancer treatment. Acute myeloid leukemia (AML) is the most common acute leukemia in adults with poor prognosis. Evidence has shown T-cell-mediated immune responses in AML, which encourages the utility of immune therapies in AML. This review discusses cancer vaccines in AML from vaccine design as well as recent progress in vaccination combination with other immune therapies.

WT1 peptide vaccine in Montanide in contrast to poly ICLC, is able to induce WT1-specific immune response with TCR clonal enrichment in myeloid leukemia

Background

The optimal strategy for vaccination to induce CD8⁺ T cell responses against WT1 is not known.

Methods

A pilot randomized study in HLA-A02⁺ patients to receive vaccination with WT1 in Montanide or in poly ICLC, a TLR3 agonist, to explore the novel immune adjuvant was conducted. Seven patients were randomized. Four patients received WT1 in Montanide, and three with WT1 in poly ICLC. Five patients were in morphologic remission and two had residual morphologic disease at the study entry.

Results

All patients finished the induction phase without any major toxicity except mild transient local injection reaction. One patient on the Montanide arm developed aseptic ulceration at two vaccine sites which healed without antibiotics. Three of 4 patients on the Montanide arm had a decreased expression of WT1 after WT1 vaccination, and two of them demonstrated generation of WT1-specific cytotoxic CD8⁺ T cell responses with biased TCR beta chain enrichment. In contrast, no obvious WT1-specific immune responses were detected in two patients on the poly ICLC arm, nor was there clonal enrichment by TCR alpha/beta sequencing; however, these patients did also have decreased WT1 expression and remained in remission several years after the initiation of treatment.

Conclusions

WT1 peptide vaccine with Montanide as an adjuvant induces detectable WT1-specific CD8⁺ T cell responses with clonal TCR enrichment, which may be capable of controlling leukemia recurrence in the setting of minimal residual disease. Poly ICLC may induce anti-leukemic activity in the absence of detectable WT1 specific CD8⁺ T cell responses.

Trial registration NCT01842139, 7/3/2012 retrospectively registered; https://clinicaltrials.gov/ct2/show/NCT01842139.

Vaccination with autologous myeloblasts admixed with GM-K562 cells in patients with advanced MDS or AML after allogeneic HSCT

We report a clinical trial testing vaccination of autologous myeloblasts admixed with granulocyte-macrophage colony-stimulating factor secreting K562 cells after allogeneic hematopoietic stem cell transplantation (HSCT). Patients with myelodysplastic syndrome (MDS) or acute myeloid leukemia (AML) with ≥5% marrow blasts underwent myeloblast collection before HSCT. At approximately day +30, 6 vaccines composed of irradiated autologous myeloblasts mixed with GM-K562 were administered. Tacrolimus-based graft-versus-host disease (GVHD) prophylaxis was not tapered until vaccine completion (∼day 100). Thirty-three patients with AML (25) and MDS (8) enrolled, 16 (48%) had ≥5% marrow blasts at transplantation. The most common vaccine toxicity was injection site reactions. One patient developed severe eosinophilia and died of eosinophilic myocarditis. With a median follow-up of 67 months, cumulative incidence of grade 2-4 acute and chronic GVHD were 24% and 33%, respectively. Relapse and nonrelapse mortality were 48% and 9%, respectively. Progression-free survival (PFS) and overall survival (OS) at 5 years were 39% and 39%. Vaccinated patients who were transplanted with active disease (≥5% marrow blasts) had similar OS and PFS at 5 years compared with vaccinated patients transplanted with <5% marrow blasts (OS, 44% vs 35%, respectively, P = .81; PFS, 44% vs 35%, respectively, P = .34). Postvaccination antibody responses to angiopoietin-2 was associated with superior OS (hazard ratio [HR], 0.43; P = .031) and PFS (HR, 0.5; P = .036). Patients transplanted with active disease had more frequent angiopoeitin-2 antibody responses (62.5% vs 20%, P = .029) than those transplanted in remission. GM-K562/leukemia cell vaccination induces biologic activity, even in patients transplanted with active MDS/AML. This study is registered at www.clinicaltrials.gov as #NCT 00809250.

Dendritic cell vaccine against leukemia: advances and perspectives

As with many other types of malignancies, sustainable eradication of leukemia has been a challenge. This is related to the inevitable failure of conventional chemotherapeutic agents and radiation therapy to target the relatively quiescent leukemia stem cells, which are believed to have multidrug resistance, antiapoptotic capacity and enhanced DNA repair mechanisms allowing them to evade the immune system. Considering other therapeutic options that are minimally toxic to normal cells and effectively target not only the majority and more differentiated cancer cells, but also the rare residual leukemia cells, is of paramount importance. A number of immunotherapeutic options have been proposed to counter this challenge. One of the remarkable achievements in the field of immunotherapy has been the successful use of antigen presenting cells as vehicles of tumor/pathogenic antigens to the T-cell compartments. This review will focus on advances and perspectives of this arm of immunotherapy against leukemia.

Vaccines and recommendations for their use in inflammatory bowel disease

The patient with inflammatory bowel disease will be predisposed to numerous infections due their immune status. It is therefore important to understand the immune and serologic status at diagnosis and to put the patient into an adapted vaccination program. This program would be applied differently according to two patient groups: the immunocompromised and the non-immunocompromised. In general, the first group would avoid the use of live-virus vaccines, and in all cases, inflammatory bowel disease treatment would take precedence over vaccine risk. It is important to individualize vaccination schedules according to the type of patient, the treatment used and the disease pattern.In addition, patient with inflammatory bowel disease should be considered for the following vaccines: varicella vaccine, human papilloma virus, influenza, pneumococcal polysaccharide vaccine and hepatitis B vaccine.

Dendritic Cells Loaded with Tumor Antigens and a Dual Immunostimulatory and Anti-Interleukin 10-Specific Small Interference RNA Prime T Lymphocytes against Leukemic Cells

Vaccines using dendritic cells (DCs) harboring leukemic antigens to stimulate T cells is a possible treatment of acute myeloid leukemia (AML). Limitations of breaking tolerance to leukemic cells and lack of specific activation of T cell-mediated cytotoxicity may explain the discouraging clinical results with this approach. To break self-tolerance against AML cells, we loaded DCs with AML antigens and a bifunctional small interference (si) RNA targeting interleukin (IL) 10 and simultaneously activating toll-like receptors (TLRs). In vitro, this active siRNA inhibited (P < .05) IL-10 production by silencing the IL-10 gene in DCs. The active siRNA stimulated production of tumor necrosis factor alpha, implying activation of TLRs. Vaccination in a nonimmunogenic rat model mimicking human AML with the loaded DCs induced a substantial and specific T-cell cytotoxicity. Leukemic rats treated with the active siRNA lived longer and had markedly less leukemic cell mass infiltrating their bone marrow compared with rats given inactive siRNA (P < .05). Furthermore, compared with inactive siRNA treatment, the active siRNA led to significantly less extramedullar leukemic dissemination, evidenced by reduced matrix metalloproteinase activity and smaller spleens. Our data demonstrate that this bifunctional siRNA may work as an immunomodulatory drug with antileukemic properties.

Relapse after allogeneic stem cell transplantation

Since allogeneic stem cell transplantation (SCT) represents an intensive curative treatment for high-risk malignancies, its failure to prevent relapse leaves few options for successful salvage treatment. While many patients have a high early mortality from relapse, some respond and have sustained remissions, and a minority has a second chance of cure with appropriate therapy. The prognosis for relapsed hematological malignancies after SCT depends on four factors: the time elapsed from SCT to relapse (with relapses occurring within 6 months having the worst prognosis), the disease type (with chronic leukemias and some lymphomas having a second possibility of cure with further treatment), the disease burden and site of relapse (with better treatment success if disease is treated early), and the conditions of the first transplant (with superior outcome for patients where there is an opportunity to increase either the alloimmune effect, the specificity of the antileukemia effect with targeted agents or the intensity of the conditioning in a second transplant). These features direct treatments toward either modified second transplants, chemotherapy, targeted antileukemia therapy, immunotherapy or palliative care.

Requisite considerations for successful adoptive immunotherapy with engineered T-lymphocytes using tumor antigen-specific T-cell receptor gene transfer

INTRODUCTION

Although engineered T-cell-based antitumor immunotherapy using tumor-antigen-specific T-cell receptor (TCR) gene transfer is undoubtedly a promising strategy, a number of studies have revealed that it has several drawbacks.

AREAS COVERED

This review covers selected articles detailing recent progress in this field, not only for solid tumors, but also for leukemias. In terms of achieving uniform therapeutic quality of TCR gene-modified T cells as an 'off-the-shelf' product, the authors abstract and discuss the requisite conditions for successful outcome, including: i) the optimal target choice reflecting the specificity of the introduced TCR, ii) the quality and quantity of expressed TCRs in gene-modified T cells, and additional genetic modification reflecting enhanced antitumor functionality, and iii) 'on-' and 'off-target' adverse events caused by the quality of the introduced TCRs and other adverse events related to genetic modification itself. Readers will be able to readily abstract recent advances in TCR gene-transferred T-cell therapy, centering notably on efforts to obtain uniformity in the therapeutic functionality of engineered T cells.

EXPERT OPINION

Harmonizing the functionality and target specificity of TCR will allow the establishment of clinically useful adoptive immunotherapy in the near future.

Allogeneic immunotherapy to optimize the graft-versus-tumor effect: concepts and controversies

This article focuses on the recent evolution of novel conditioning regimens in combination with adoptive cellular therapy in the allogeneic transplant setting for hematologic malignancies. Building on data from animal models, the field of allogeneic transplantation is undergoing a paradigm shift toward immunosuppressive regimens with less toxicity that allow donor hematopoietic engraftment in order to provide a graft-versus-tumor effect as the primary goal of transplantation, rather than chemoablation. In addition, the strategies described in this article, including the use of T-cell subsets as adoptive therapy, will apply to a much broader pool of patients than traditional transplant approaches, thereby allowing more patients with life-limiting illnesses, previously deemed ineligible, to pursue therapy with curative intent.

Do we have to kill the last CML cell?

Previous experience in the treatment of chronic myeloid leukaemia (CML) has shown that the achievement of clinical, morphological and cytogenetic remission does not indicate eradication of the disease. A complete molecular response (CMR; no detectable BCR-ABL mRNA) represents a deeper level of response, but even CMR is not a guarantee of elimination of the leukaemia, because the significance of CMR is determined by the detection limit of the assay that is used. Two studies of imatinib cessation in CMR are underway, cumulatively involving over 100 patients. The current estimated rate of stable CMR after stopping imatinib is approximately 40%, but the duration of follow-up is relatively short. The factors that determine relapse risk are yet to be identified. The intrinsic capacity of any residual leukaemia [corrected] cells to proliferate following the withdrawal of treatment may be important, but there may also be a role for immunological suppression of the leukaemia [corrected] clone. No currently available test can formally prove that the leukaemic clone is eradicated. Here we discuss the sensitive measurement of minimal residual disease, and speculate on the biology of BCR-ABL-positive cells that may persist after effective therapy of CML.

Immunosuppressive therapy for myelodysplastic syndromes: refining the indications

Myelodysplastic syndromes (MDS) are often associated with autoimmune processes that contribute to the cytopenias that characterize this disease group. Ten years ago, several investigators described improvement in the cytopenia of MDS following immunosuppressive treatments (IST) with antithymocyte globulin or cyclosporine. These findings have since been widely confirmed. The consensus is that about 30% of unselected transfusion-dependent patients with MDS given IST have sustained hematologic responses and can regain transfusion independence. Over the past decade, prognostic features have been defined that accurately identify the subset of patients most likely to benefit from IST. With increasing knowledge about the pathophysiology of myelosuppression in MDS, we are beginning to define the immunosuppressive agents and schedules with the greatest chance of causing hematologic improvement. Significantly, long-term follow-up indicates that IST responders have a better progression-free survival than comparable patients with MDS who do not receive IST.

Immunotherapy prospects for acute myeloid leukaemia

While chemotherapy is successful at inducing remission of acute myeloid leukaemia (AML), the disease has a high probability of relapse. Strategies to prevent relapse involve consolidation chemotherapy, stem cell transplantation and immunotherapy. Evidence for immunosurveillance of AML and susceptibility of leukaemia cells to both T cell and natural killer (NK) cell attack and justifies the application of immune strategies to control residual AML persisting after remission induction. Immune therapy for AML includes allogeneic stem cell transplantation, adoptive transfer of allogeneic or autologous T cells or NK cells, vaccination with leukaemia cells, dendritic cells, cell lysates, peptides and DNA vaccines and treatment with cytokines, antibodies and immunomodulatory agents. Here we describe what is known about the immunological features of AML at presentation and in remission, the current status of immunotherapy and strategies combining treatment approaches with a view to achieving leukaemia cure.

From bench to bedside: the growing use of translational research in cancer medicine

Cancer is responsible for one in eight deaths worldwide, with more than twelve million new cases diagnosed yearly. A large percentage of patients die after developing cancer despite aggressive treatment, indicating a need for new approaches to cancer therapy. The push for development of novel diagnostic and therapeutic agents has allowed translational cancer research to flourish. Genomic and proteomic technologies have generated an enormous amount of information critical to expanding our understanding of cancer biology. New research on the differences between normal and malignant cell biology has paved the way for the development of drugs targeted to specific biological molecules, potentially increasing antitumor efficacy while minimizing the toxicity to the patient that is seen with conventional therapeutics. Current targets in include regulators of cell cycle, angiogenesis, apoptosis, DNA repair, and growth factors and their receptors. Collaboration among researchers, clinicians, and pharmaceutical companies is vital to conducting clinical trials to translate laboratory findings into clinically applicable therapeutics. In this review, we discuss current therapeutic approaches and present an introduction to a wide range of topics undergoing investigation in an effort to highlight the importance of translational research in the development of clinically relevant therapeutic strategies.

Biologic activity of irradiated, autologous, GM-CSF-secreting leukemia cell vaccines early after allogeneic stem cell transplantation

Through an immune-mediated graft-versus-leukemia effect, allogeneic hematopoietic stem cell transplantation (HSCT) affords durable clinical benefits for many patients with hematologic malignancies. Nonetheless, subjects with high-risk acute myeloid leukemia or advanced myelodysplasia often relapse, underscoring the need to intensify tumor immunity within this cohort. In preclinical models, allogeneic HSCT followed by vaccination with irradiated tumor cells engineered to secrete GM-CSF generates a potent antitumor effect without exacerbating the toxicities of graft-versus-host disease (GVHD). To test whether this strategy might be similarly active in humans, we conducted a Phase I clinical trial in which high-risk acute myeloid leukemia or myelodysplasia patients were immunized with irradiated, autologous, GM-CSF-secreting tumor cells early after allogeneic, nonmyeloablative HSCT. Despite the administration of a calcineurin inhibitor as prophylaxis against GVHD, vaccination elicited local and systemic reactions that were qualitatively similar to those previously observed in nontransplanted, immunized solid-tumor patients. While the frequencies of acute and chronic GVHD were not increased, 9 of 10 subjects who completed vaccination achieved durable complete remissions, with a median follow-up of 26 months (range 12-43 months). Six long-term responders showed marked decreases in the levels of soluble NKG2D ligands, and 3 demonstrated normalization of cytotoxic lymphocyte NKG2D expression as a function of treatment. Together, these results establish the safety and immunogenicity of irradiated, autologous, GM-CSF-secreting leukemia cell vaccines early after allogeneic HSCT, and raise the possibility that this combinatorial immunotherapy might potentiate graft-versus-leukemia in patients.

WT1 peptide-specific T cells generated from peripheral blood of healthy donors: possible implications for adoptive immunotherapy after allogeneic stem cell transplantation

The Wilms tumor antigen, WT1, is expressed at high levels in various types of leukemia and solid tumors, including lung, breast, colon cancer and soft tissue sarcomas. The WT1 protein has been found to be highly immunogenic, and spontaneous humoral and cytotoxic T-cell responses have been detected in patients suffering from leukemia. Furthermore, major histocompatibility complexes class I- and II-restricted WT1 peptide epitopes have been shown to elicit immune responses in patients with WT1-expressing tumors. As a consequence, WT1 has become an attractive target for anticancer immunotherapy. In this study, we investigated the feasibility of generating WT1-specific T cells for adoptive immunotherapy after allogeneic stem cell transplantation. We analyzed the incidence of T cells specific for WT1 peptide epitopes in cancer patients and healthy volunteers. It is noted that we could generate WT1-specific responses in nine of ten healthy volunteer donors and established T-cell clones specific for two WT1-derived peptide epitopes. These in vitro expanded WT1-specific T cells effectively lysed WT1-expressing tumor cell lines, indicating the potential clinical impact of ex vivo expanded donor-derived WT1-specific T cells for adoptive immunotherapy after allogeneic stem cell transplantation.

Immunotherapy of acute myeloid leukemia: current approaches

Following standard therapy that consists of chemotherapy with or without stem cell transplantation, both relapsed and refractory disease shorten the survival of acute myeloid leukemia (AML) patients. Therefore, additional treatment options are urgently needed, especially to fight residual AML cells. The identification of leukemia-associated antigens and the observation that administration of allogeneic T cells can mediate a graft-versus-leukemia effect paved the way to the development of active and passive immunotherapy strategies, respectively. The aim of these strategies is the eradication of AML cells by the immune system. In this review, an overview is provided of both active and passive immunotherapy strategies that are under investigation or in use for the treatment of AML. For each strategy, a critical view on the state of the art is given and future perspectives are discussed.

Peptide vaccines for myeloid leukaemias

The development of cancer vaccines directed against myeloid leukaemias has been a research area of intense interest in the past decade. Both human studies in vitro and mouse models in vivo have demonstrated that leukaemia-associated antigens (LAAs), such as the fusion protein BCR-ABL, Wilms' tumour protein and proteinase 3, may serve as effective targets for cellular immunotherapy. Peptide-based vaccines are able to induce cytotoxic T-lymphocyte responses that kill leukaemia cells. Based on these results, pilot clinical trials have been initiated in chronic and acute myeloid leukaemia and other haematological malignancies, which include vaccination of patients with synthetic peptides derived from these LAAs. Results from these trials show that peptide vaccines are able to induce immune responses that are sometimes associated with clinical benefit. These early clinical results are promising and provide valuable information for future improvement of the vaccines. This chapter will focus mainly on discussing the preclinical studies of peptide vaccines in human systems, the results from clinical trials and the future prospects for vaccine therapy for myeloid leukaemia.

Dendritic cell vaccines in acute leukaemia

There is a need for novel treatment for acute leukaemia as relapse rates remain unacceptably high. Immunotherapy aims to stimulate the patient's immune responses to recognize and destroy leukaemia cells whilst activating immune memory. The qualities of the most potent professional antigen-presenting cell, the dendritic cell (DC), can be used to stimulate leukaemia-specific cytotoxic T cells. DCs can be loaded with leukaemia antigens, or leukaemia blasts can be modified to express DC-like properties for use in vaccine therapy. This chapter will review the rationale for DC vaccine therapy, the preclinical and clinical trials to date, the barriers to successful DC vaccine therapies and the role of immune adjuncts to improve outcomes.

Aurora-A kinase: a novel target of cellular immunotherapy for leukemia

Aurora-A kinase (Aur-A) is a member of the serine/threonine kinase family that regulates the cell division process, and has recently been implicated in tumorigenesis. In this study, we identified an antigenic 9-amino-acid epitope (Aur-A(207-215): YLILEYAPL) derived from Aur-A capable of generating leukemia-reactive cytotoxic T lymphocytes (CTLs) in the context of HLA-A*0201. The synthetic peptide of this epitope appeared to be capable of binding to HLA-A*2402 as well as HLA-A*0201 molecules. Leukemia cell lines and freshly isolated leukemia cells, particularly chronic myelogenous leukemia (CML) cells, appeared to express Aur-A abundantly. Aur-A-specific CTLs were able to lyse human leukemia cell lines and freshly isolated leukemia cells, but not normal cells, in an HLA-A*0201-restricted manner. Importantly, Aur-A-specific CTLs were able to lyse CD34+ CML progenitor cells but did not show any cytotoxicity against normal CD34+ hematopoietic stem cells. The tetramer assay revealed that the Aur-A(207-215) epitope-specific CTL precursors are present in peripheral blood of HLA-A*0201-positive and HLA-A*2402-positive patients with leukemia, but not in healthy individuals. Our results indicate that cellular immunotherapy targeting Aur-A is a promising strategy for treatment of leukemia.

Understanding and harnessing the graft-versus-leukaemia effect

The graft-versus-leukaemia (GVL) effect is a central component of the stem cell allograft's ability to cure haematological malignancies. The GVL effect is mediated by donor-derived natural killer cells and T lymphocytes, which have distinct mechanisms of recognizing and targeting the recipient's malignant cells. After transplantation the cytokine milieu is favourable to the early establishment of a GVL effect, but the need to prevent graft-versus-host disease limits the full potential of this process. Clinical studies have identified some critical components of the transplant preparation, donor selection, stem cell source (peripheral blood versus bone marrow) and post-transplant management that can be manipulated to optimize the GVL effect. However, further developments focusing on the selective depletion of unwanted alloreactivity with preservation of GVL effects, and the use of vaccines or the adoptive transfer of leukaemia-specific lymphocytes, will be required to enhance the GVL effect to reliably eradicate more resistant leukaemias.

Hematopoietic stem cells and progenitors of chronic myeloid leukemia express leukemia-associated antigens: implications for the graft-versus-leukemia effect and peptide vaccine-based immunotherapy

The cure of chronic myeloid leukemia (CML) patients following allogeneic stem cell transplantation (SCT) is attributed to graft-versus-leukemia (GVL) effects targeting alloantigens and/or leukemia-associated antigens (LAA) on leukemia cells. To assess the potential of LAA-peptide vaccines in eliminating leukemia in CML patients, we measured WT1, PR3, ELA2 and PRAME expression in CD34+ progenitor subpopulations in CML patients and compared them with minor histocompatibility antigens (mHAgs) HA1 and SMCY. All CD34+ subpopulations expressed similar levels of mHAgs irrespective of disease phase, suggesting that in the SCT setting, mHAgs are the best target for GVL. Furthermore, WT1 was consistently overexpressed in advanced phase (AdP) CML in all CD34+ subpopulations, and mature progenitors of chronic phase (CP) CML compared to healthy individuals. PRAME overexpression was limited to more mature AdP-CML progenitors only. Conversely, only CP-CML progenitors had PR3 overexpression, suggesting that PR1-peptide vaccines are only appropriate in CP-CML. Surface expression of WT1 protein in the most primitive hematopoietic stem cells in AdP-CML suggest that they could be targets for WT1 peptide-based vaccines, which in combination with PRAME, could additionally improve targeting differentiated progeny, and benefit patients responding suboptimally to tyrosine kinase inhibitors, or enhance GVL effects in SCT patients.

Allogeneic stem cell transplantation for myelodysplastic syndrome

Although it is only used to treat a minority of patients with myelodysplastic syndromes, stem cell transplantation (SCT) is the only proven curative treatment for this condition. Because MDS occurs in a population of older adults with significant comorbidities, reduced-intensity conditioning (RIC) regimens have been particularly important in extending safe SCT to the large MDS population over the age of 60 years. Extension of the unrelated donor pool together with the introduction of umbilical cord blood transplants in adults has extended the number of patients with suitable donors. Nevertheless overall mortality from SCT is greater than 50% because of relapse and non-relapse mortality (NRM). New developments to improve outcome include the tailoring of the transplant approach to the individual based on age and comorbidity, and the use of pretransplant chemotherapy to reduce disease bulk prior to transplant, as well as the introduction of post-transplant immunotherapy (pre-emptive donor lymphocyte infusions) and chemotherapy to prevent relapse. Further improvements in transplant outcome await better ways to reconstitute immunity and amplify the graft-versus-leukemia (GVL) effect without causing graft-versus-host disease (GVHD), as well as further extension of the donor pool and exploration of risk-adapted regimens for the population of MDS in their seventh to eighth decade.

Thymus repopulation after allogeneic reconstitution in hematological malignancies

OBJECTIVE

Active vaccination in the allogeneically reconstituted tumor-bearing host essentially requires donor T-cell tolerance. To create a basis for vaccination in the allogeneically reconstituted, lymphoma-bearing host, we elaborate a reconstitution protocol that supports thymus repopulation and tolerance induction.

METHODS

Myeloreductively conditioned, lymphoma-bearing mice were vaccinated after reconstitution with hematopoietic progenitor cells. Readout systems included recovery of donor-derived T cells, graft vs host disease (GVHD), anti-host and anti-lymphoma cytotoxicity, as well as tumor growth rate and tumor rejection.

RESULTS

In tumor-free mice, myeloreductive conditioning, together with natural killer cell depletion of the host and transfer of T cell-depleted bone marrow cells, allows reconstitution without severe GVHD. However, in hematological malignancies, donor-derived T-progenitor cells hardly immigrated into the thymus. As a consequence, the frequency of severe GVHD was significantly increased, which prohibited active vaccination. Thymus repopulation became improved by strengthening myeloreductive conditioning; by supporting thymocyte expansion via interleukin-7; and, most strongly, by a small dose of donor-derived CD4(+)CD8(+) thymocytes, which preferentially homed into the thymus. Active vaccination, in combination with this reconstitution protocol, did not strengthen GVHD, but significantly improved survival time and survival rate of lymphoma-bearing mice.

CONCLUSION

The negative impact of hematological malignancies on thymus repopulation and central tolerance induction can, at least in part, be corrected by application of a small number of donor-derived T-progenitor cells.