Allo-Major Histocompatibility Complex–Restricted Cytotoxic T Lymphocytes Engraft in Bone Marrow Transplant Recipients Without Causing Graft-Versus-Host Disease

Immunotherapy for neuroblastoma by hematopoietic cell transplantation and post-transplant immunomodulation

Neuroblastoma represents a relatively common childhood tumor that imposes therapeutic difficulties. High risk neuroblastoma patients have poor prognosis, display limited response to radiochemotherapy and may be treated by hematopoietic cell transplantation. Allogeneic and haploidentical transplants have the distinct advantage of reinstitution of immune surveillance, reinforced by antigenic barriers. The key factors favorable to ignition of potent anti-tumor reactions are transition to adaptive immunity, recovery from lymphopenia and removal of inhibitory signals that inactivate immune cells at the local and systemic levels. Post-transplant immunomodulation may further foster anti-tumor reactivity, with positive but transient impact of infusions of lymphocytes and natural killer cells both from the donor, the recipient or third party. The most promising approaches include introduction of antigen-presenting cells in early post-transplant stages and neutralization of inhibitory signals. Further studies will likely shed light on the nature and actions of suppressor factors within tumor stroma and at the systemic level.

Genetically engineered donor T cells to optimize graft-versus-tumor effects across MHC barriers

Hematopoietic stem cell transplantation has been used for more than 50 years to combat hematologic malignancies. In addition to being the first stem cell therapy, transplantation has provided evidence for the potent anti-tumor effects of T cells. Facilitating T-cell-based immunity against malignancies requires a careful balancing act between generating a robust response and avoiding off-target killing of healthy tissues, which is difficult to accomplish using bulk donor T cells. To address these issues, several approaches have been developed, drawing on basic T-cell biology, to potentiate graft-versus-tumor activity while avoiding graft-versus-host disease. Current strategies for anti-tumor cell therapies include: (i) selecting optimal T cells for transfer; (ii) engineering T cells to possess enhanced effector functions; and (iii) generating T-cell precursors that complete development after adoptive transfer. In this review, we assess the current state of the art in T-lineage cell therapy to treat malignancies in the context of allogeneic hematopoietic stem cell transplantation.

Tumor rejection effects of allorestricted tumor peptide-specific CD4(+) T cells on human cervical cancer cell xenograft in nude mice

Generation of tumor specific alloreactive CD4(+) T cells is important to circumvent tumor tolerance. Here, we generate allorestricted peptide-specific CD4(+) T cells by coculture of lymphocytes and autologous monocytes bearing allogeneic HLA-DR15 molecule associated with its restricted peptide. Binding of a dimeric HLA-DR15/IgG1-Fc fusion protein (the dimer) to HLA-DR15 negative (HLA-DR15-ve) monocytes made the monocytes coated with the allogeneic epitope. An increased proliferation of CD4(+) T cells and induction of Th1 cells appeared after coculturing of HLA-DR15-ve lymphocytes and the autologous monocytes loaded with the dimer. The cocultural bulks showed an increased frequency of the specific dimer-stained CD4(+) T cells and the expanded CD4(+) T cells exhibited an elevated IFN-γ production in response to specific TCR ligand. Tumor rejection effects of the allorestricted E7-specific CD4(+) T cells raised by the coculture were observed in nude mice challenged with human cervical cancer cell SiHa expressing both HLA-DR15 and E7 antigens, as the tumor avoidance and life span of the mice were improved after adoptive transfer of the CD4(+) T cells. This study may help to develop strategies to separate graft-versus-leukemia or graft-versus-tumor reaction from graft-versus-host disease, and add to the pool of human high-avidity TCRs specific for tumor or virus antigens.

The cyclins: a family of widely expressed tumor antigens?

Continuous cell division is a hallmark of cancer and cell-cycle regulators therefore represent relevant target molecules for tumor therapy. Among these targets the cyclins are of particular interest as they are overexpressed in various tumor entities with little expression in normal tissue. Here we review evidence that these molecules are recognized by the immune system, summarize why cyclins A, B and D in particular appear to be interesting targets for active and passive immunotherapy, and discuss whether the entire family could be an interesting novel class of tumor antigens for cancer treatment and prevention.

Overcoming self-tolerance to tumour cells

Over the past decade, immunotherapy has emerged as a promising alternative form of cancer treatment with the potential to eradicate tumour metastasis. However, its curative potential is in general limited by peripheral tolerance mechanisms and the elimination of self-reactive T cells via thymic negative selection. Unlike infectious challenges, tumour cells arise endogenously, and therefore the majority of tumour antigens are recognized as self. Under appropriate conditions, however, tumour reacting T cells can be activated through a mechanism of molecular mimicry, which involves the recognition of cross reactive foreign antigens mimicking tumour antigens. Moreover, dendritic cells can be reprogrammed by RNA interference to present self-antigens and activate anti-tumour T cells. This review highlights some of the strategies used to break self-tolerance against solid and blood tumour cells. Also, the possibility of reprogramming DC and/or lymphocyte functions using small interfering RNAi (siRNA) is discussed.

Recent advances in hematopoietic stem cell transplantation and perspectives of RNAi applications

In adults, the bone marrow compartment contains hematopoietic stem cells (HSCs) which can differentiate into progenitors with more restricted lineage potential and generate all cellular elements of the blood. HSCs for stem cell transplantation can be obtained by bone marrow collection, mobilization into peripheral blood followed by apheresis, or use of stem cells from cord blood. Currently, hematopoietic stem cell transplantation (SCT) is used to treat patients with various hematological diseases. Although substantial progress has been made, a number of challenges can limit the efficacy of HSC transplantation, including the occurrence of graft-versus-host disease (GvHD) in allogeneic stem cell transplantation (ASCT), the susceptibility of patients to opportunistic infections and relapse of malignancies after SCT. Recent studies indicate that small interfering RNAs (siRNAs) can specifically and efficiently interfere with the expression of oncogenic genes. Therefore, the possibility of interfering with the expression of these proteins in hematopoietic cells may offer a new option to correct cell differentiation and function. In addition to the generation of T cells restricted by nonself MHC as reviewed by Stauss and colleagues in 1999, the modulation of NK cell receptor expression and T-cell activation is a new strategy that could limit GvHD. This chapter reviews the recent advances in ASCT and discusses the potential application of RNAi in hematopoietic cells.

Does our current understanding of immune tolerance, autoimmunity, and immunosuppressive mechanisms facilitate the design of efficient cancer vaccines?

The therapeutic use of the immune system to attack cancer cells has been a longstanding vision among tumour immunologists. However, most human tumours are poorly immunogenic and are able to invade the host immune system. Although these obstacles are clearly critical to cancer vaccine development, the induction of a strong anti-tumour immune response may rely on the activation of high affinity T cells through a molecular mimicry mechanism which involves cross-reactive recognition of foreign antigens mimicking the structure of tumour proteins. Taking into account the disparity in HLA molecules needed to present shared antigens; in late 1990s Stauss et al. described the possibility of generating allorestricted high affinity cytotoxic T cells against synthetic self-peptides bound to non-self-MHC molecules. In addition to the strategies indicated above, the inhibition of the immunosuppressive mechanisms associated with tumour invasion of the immune system using RNA interference also offers a new approach to vaccine design. This review highlights the problem of immune tolerance, the induction of autoreactive T cells, and describes strategies to enhance tumour immunity.

In vivo anti-melanoma efficacy of allo-restricted CTLs specific for melanoma expanded by artificial antigen-presenting cells

Cytotoxic CD8(+) T cells are key effectors in the immunotherapy of malignant and viral diseases. However, autologous T cell responses to tumor antigens presented by self-MHC are usually weak and ineffective. Allo-restricted T cells represent a potent source of tumor-specific T cells for adoptive immunotherapy. This study reports in vivo anti-melanoma efficacy of the pTRP2-specific allo-restricted CTLs expanded from the BALB/c splenocytes by multiple stimulations with aAPCs made by coating H-2K(b)-Ig/pTRP2 dimeric complexes, anti-CD28 antibody, 4-1BBL molecules and CD83 molecules to cell-sized latex beads. The induced allo-restricted CTLs exhibited specific lysis against RMA-S cells pulsed with the peptide pTRP2 and H-2K(b+) melanoma cells expressing TRP2, while a murine Lewis lung carcinoma cell line 3LL could not be recognized by the CTLs. The peptide-specific activity was inhibited by anti-H-2K(b) monoclonal antibody Y3. Adoptive transfer of the allo-restricted CTLs specific for malignant melanoma expanded by the aAPCs can mediate effective anti-melanoma response in vivo. These results suggested that the specific allo-restricted CTLs expanded by aAPCs coated with an MHC-Ig/peptide complex, anti-CD28 antibody, 4-1BBL and CD83 could be a potential option of specific immunotherapy for patients with malignant melanoma.

CD8alpha/alpha homodimers fail to function as co-receptor for a CD8-dependent TCR

In this study, we have started to dissect the molecular basis of CD8 dependence of a high and low avidity CTL clone specific for the same peptide epitope. Using anti-CD8alpha and anti-CD8beta antibodies, we found that cytotoxicity and IFN-gamma production by high but not by low avidity CTL was strongly CD8 dependent. We isolated the TCR genes of both types of CTL clones and used retroviral gene transfer to analyse the function of these TCR in primary T cells of wild-type and CD8beta-deficient mice. Both TCR triggered antigen-specific killing in wild-type T cells, and blocking experiments showed that CD8 dependence/independence co-transferred with the TCR into primary T cells, indicating that it was dictated by the TCR itself. Gene transfer experiments into CD8beta-deficient T cells revealed that only the TCR derived from the CD8-independent CTL clone elicited antigen-specific cytotoxicity, while the CD8-dependent TCR was non-functional in the absence of the CD8beta-chain. These data indicate a striking difference between CD8alpha/beta heterodimers and CD8alpha/alpha homodimers as only the former were able to provide co-receptor function for the CD8-dependent TCR.

Depletion of alloreactive T cells via CD69: implications on antiviral, antileukemic and immunoregulatory T lymphocytes

Selective depletion of alloreactive T cells from stem-cell allografts should abrogate graft-versus-host disease while preserving beneficial T cell specificities to facilitate engraftment and immune reconstitution. We therefore explored a refined immunomagnetic separation strategy to effectively deplete alloreactive donor lymphocytes expressing the activation antigen CD69 upon stimulation, and examined the retainment of antiviral, antileukemic, and immunoregulatory T cells. In addition to the CD69high T cell fraction, our studies retrieved two T cell subsets based on residual CD69 expression. Whereas, truly CD69(neg) cells were devoid of detectable alloresponses to original stimulators, CD69-low (CD69low)-expressing T cells elicited significant residual alloreactivity upon restimulation. In interferon-gamma enzyme linked immunospot assays, anti-cytomegalovirus and anti-Epstein-Barr virus responses were preserved at significant numbers among CD69neg T lymphocytes. Accordingly, T cells recognizing the leukemia-associated Wilm's tumor-1 antigen were still detectable in the CD69neg subset. However, antiviral and antileukemic specificities were also consistently found within CD69low T cells, suggesting that memory-type donor T cells were partially captured due to residual CD69 expression. Finally, CD4+CD25+ Foxp3+ immunoregulatory T cells did not upregulate CD69 upon allogeneic stimulation. Our data suggest that CD69-mediated removal of alloreactivity can result in efficient allodepletion, but may partially affect the persistence of antiviral and antileukemic donor memory specificities captured among CD69low-expressing lymphocytes.

Exploiting T cell receptor genes for cancer immunotherapy

Adoptive antigen-specific immunotherapy is an attractive concept for the treatment of cancer because it does not require immunocompetence of patients, and the specificity of transferred lymphocytes can be targeted against tumour-associated antigens that are poorly immunogenic and thus fail to effectively trigger autologous T cell responses. As the isolation and in vitro expansion of antigen-specific lymphocytes is difficult, 'conventional' adoptive T cell therapy can only be carried out in specialized centres in small numbers of patients. However, T cell receptor (TCR) genes isolated from antigen-specific T cells can be exploited as generic therapeutic molecules for 'unconventional' antigen-specific immunotherapy. Retroviral TCR gene transfer into patient T cells can readily produce populations of antigen-specific lymphocytes after a single round of polyclonal T cell stimulation. TCR gene modified lymphocytes are functionally competent in vitro, and can have therapeutic efficacy in murine models in vivo. TCR gene expression is stable and modified lymphocytes can develop into memory T cells. Introduction of TCR genes into CD8(+) and CD4(+) lymphocytes provides an opportunity to use the same TCR specificity to produce antigen-specific killer and helper T lymphocytes. Thus, TCR gene therapy provides an attractive strategy to develop antigen-specific immunotherapy with autologous lymphocytes as a generic treatment option.

Treatment of advanced Ewing tumors by combined radiochemotherapy and engineered cellular transplants

This review will focus primarily on own recent work on the treatment of advanced Ewing tumors (AETs) and will attempt, in addition, to give a comprehensive overview of novel developments. The field under review has been shaped by investigators from both Europe and the United States of America in a scientific debate evolving over more than a decade at the meetings of the International Society of Pediatric Oncology and other scientific meetings. In the light of this debate, most oncologists will agree that patients with AETs are facing the worst prognosis of all patients with this disease and include both: (i) patients with primary metastatic disease with the worst prognosis as well as (ii) patients with relapse with the worst prognosis. The contributions of various investigators have lead to the identification of specific risk stratification criteria to overcome the heterogeneity of patients within the conventionally defined clinical stages of localized metastatic and relapsed disease. This review will address the following issues of treatment of AETs: (i) a definition of AET; (ii) risks and benefits of allogeneic vs. autologous stem cell transplantation; (iii) the role of total body irradiation; (iv) the number of involved bones as a risk factor in multifocal bone disease in AET; (v) the development of immunogene therapy in AET; (vi) the matching of radiochemo- and immunotherapy in AET; (vii) the future perspective of functional genomics and targeted therapy.

Tolerance and cancer: mechanisms of tumor evasion and strategies for breaking tolerance

The development of malignant disease might be seen as a failure of immune surveillance. However, not all tumors are naturally immunogenic, and even among those that are immunogenic, the uncontrolled rapid growth of a tumor may sometimes out-run a robust immune response. Nevertheless, recent evidence suggests that mechanisms of tolerance that normally exist to prevent autoimmune disease may also preclude the development of an adequate antitumor response and that tumors themselves have the ability to thwart the development of effective immune responses against their antigens. A major challenge has been to develop approaches to breaking this tolerance in tumor-bearing hosts, and recent advances in our understanding of antigen presentation and tolerance have led to some promising strategies. An alternative approach is to use T cells from nontumor-bearing, allogeneic hosts in the form of lymphocyte infusions, with or without hematopoietic cell transplantation. Immunotherapy may occur in this setting via the response of nontolerant, tumor antigen-specific T cells from nontumor-bearing hosts or via the powerful destructive effect of an alloresponse directed against antigens shared by malignant cells in the recipient. Approaches to exploiting this beneficial effect without the deleterious consequence of graft-versus-host disease in allogeneic hematopoietic cell recipients are discussed.

Graft-versus-leukemia reactions in allogeneic chimeras

There is a strong graft-versus-leukemia (GVL) effect of allogeneic stem cell transplantation (SCT) due to elimination of tumor cells by alloimmune effector lymphocytes. When leukemia relapses after allogeneic SCT, donor lymphocyte transfusions (DLTs) can induce sustained remissions in some patients. This review summarizes the current status on clinical use of DLT, the basis of GVL reactions, problems associated with this therapy, and new strategies to improve DLT. Several multicenter surveys demonstrated that the GVL effect of DLT is most effective in chronic myelogenous leukemia (CML), whereas it is less pronounced in acute leukemia and myeloma. Cytokine stimulation to induce differentiation of myeloid progenitor cells or to up-regulate costimulatory molecules on tumor cells may improve the efficacy of DLT. Infections and graft-versus-host disease (GVHD) are major complications of DLT. Control of GVHD may be improved using suicide gene-modified T cells for DLT, allowing T-cell elimination if severe GVHD develops. Hopefully, in the future, GVL effect can be separated from GVHD through adoptive transfer of selected T cells that recognize leukemia-specific antigens or minor histocompatibility antigens, which are expressed predominantly on hematopoietic cells, thereby precluding attack of normal tissues. In patients with leukemia and lymphomas with fast progression, tumor growth may outpace development of effector T cells. Here it may be preferable to select stem cell transplant donors with HLA-mismatches that allow alloreactive natural killer cells, which appear early after transplantation, to retain their cytolytic function. New approaches for adoptive immune therapy of leukemia, which promise a better prognosis for these patients, are being developed.

Identification of new MHC-restriction elements for presentation of the p210(BCR-ABL) fusion region to human cytotoxic T lymphocytes

Chronic myelogenous leukemia (CML) is characterized by a t(9;22) translocation resulting in expression of BCR-ABL fusion oncoproteins which are unique to the leukemic cells, necessary for oncogenesis, and potentially immunogenic. We have previously shown that human dendritic cells transduced with an adeno-associated virus vector encoding the fusion region of the b3a2 splice variant (p210(b3a2)) of the BCR-ABL oncoprotein elicit specific T-cell responses in vitro. Two cytotoxic T lymphocyte (CTL) clones generated in this fashion displayed restriction with previously unreported HLA alleles. The first, T1/B9, was CD4(+) and restricted by DRB5*0101 (autologous) or DRB1*1101 (allogeneic). The minimum cytotoxic epitope (MCE) binding to DRB5*0101 for this clone was identified as FKQSSKALQ, overlapping the p210(b3a2) fusion point (boldface). The MCE of DRB1*1101 for this clone differed from DRB5*0101, but also included the fusion point. The clonality of CTL T1/B9 was verified by analyses of TCRalpha/beta chain usage and DNA sequence analyses. To our knowledge, this is the first description of a single clone recognizing both DRB5*0101 and DRB1*1101. The other CTL clone, T1/33, was CD8+ and recognized HLA-B*3501 or B*3503 complexed with an MCE, RPVASDFEP, derived from the c-abl sequence in proximity to the p210(b3a2) fusion point. K562 cells transfected with plasmids encoding HLA-DRA + B5*0101, B*3501, or B*3503 but not controls expressing DRA + DRB1*1501 were lysed by cognate CTL clones, confirming that DRB5*0101 and B*3501/3 could present p210(b3a2) joining region epitopes via endogenous processing. The identification of three additional HLA alleles (DRB5*0101, B*3501, and B*3503) presenting the p210(b3a2) fusion-region antigen will broaden the application of vaccine strategies for targeting CML cells. The findings of single CTL clones cross-recognizing autologous (DRB5*0101 or B*3501) and allogeneic (DRB1*1101 or B*3503) HLA alleles presenting BCR-ABL fusion-region epitopes implies the potential separation of graft-versus-leukemia from graft-versus-host effects.

Murine acute graft-versus-host disease can be prevented by depletion of alloreactive T lymphocytes using activation-induced cell death

Depletion of T lymphocytes from allogeneic bone marrow transplants successfully prevents the development of graft-versus-host disease (GvHD) but is associated with impaired engraftment, immunosuppression, and abrogation of the graft-versus-leukemia effect. We therefore explored the possibility of selectively eliminating alloreactive T cells by CD95/CD95L-mediated activation-induced cell death (AICD) in a major histocompatibility complex allogeneic murine model system. Activation of resting or preactivated T lymphocytes from C3H/HeJ (H-2(k)) mice was induced with irradiated BALB/cJ (H-2(d)) mouse-derived stimulators. Substantial decrease (> or = 80%) of proliferative and lytic responses by activated alloreactive T cells was subsequently achieved by incubating the mixed lymphocyte culture with an agonistic monoclonal antibody to CD95, and residual T cells recovered did not elicit alloreactivity upon challenge to H-2(d). Depletion of alloreactive T lymphocytes by AICD was specific because reactivity to an I-A(d)-restricted ovalbumin (OVA) peptide by OVA-specific CD4(+) T cells mixed into the allogeneic T-cell pool and subjected to induction of AICD in the absence of OVA peptide could be preserved. Adoptive transfer of donor-derived allogeneic T lymphocytes, depleted from alloreactive T cells by AICD in vitro, in the parent (C3H/He) to F(1) (C3H/He x BALB/c) GvHD model prevented lethal GvHD. The results presented suggest that alloreactive T cells can effectively be depleted from allogeneic T cells by induction of AICD to prevent GvHD and might introduce a new strategy for the separation of GvH-reactive T cells and T cells mediating antiviral and possibly graft-versus-leukemia effects.

Hematopoietic cellular therapy: implications for the flow cytometry laboratory

Advances in hematopoietic stem cell transplantation, gene therapy, and immunotherapy have necessitated a host of novel monitoring procedures. Cell sorting is also coming of age as a clinical procedure designed to organize hematopoietic grafts for specificity of cellular components designed for individual patients or diseases. This article has focused on these novel developments in their historical context. The next generation of transplantation flow cytometry promises to be an exciting one.

Allogeneic MHC class I ligands and their role in positive and negative regulation of human cytotoxic effector cells

The allogeneic mixed lymphocyte culture (MLC) has served as an important experimental system for elucidating the cellular and molecular basis of human lymphocyte responses. Complex mixtures of lymphocytes are stimulated by disparate alloantigens, inducing cellular activation and generating a cytokine milieu that is an excellent breeding ground for the proliferation and differentiation of many distinct lymphocyte subsets. Cloning of individual lymphocytes following alloactivation has allowed various cytotoxic lymphocytes to be isolated and characterized with respect to phenotype and specificity. These analyses have revealed that all types of cytotoxic effector cells are regulated by interactions with MHC-peptide ligands, however, the consequences of these interactions can result in opposite functional outcomes. In this review we summarize how allogeneic MHC class I-peptide ligands positively or negatively regulate the activities of four distinct groups of cytotoxic lymphocytes and how this information might be transferred into clinical use.

Cutting edge: characterization of allorestricted and peptide-selective alloreactive T cells using HLA-tetramer selection

The vast majority of alloreactive T cells recognize foreign MHC molecules in a peptide-dependent manner. A subpopulation of these peptide-dependent alloreactive T cells is peptide-specific and contains T cells that are of interest for tumor immunotherapy. Allorestricted T cells (i.e., peptide-specific and alloreactive) specific for tumor-associated Ags can be raised in vitro. However, it is technically difficult to distinguish between peptide-specific and peptide-nonspecific alloreactive T cells by functional assays in vitro. Here we show for the first time that allorestricted T cells specifically bind HLA-peptide tetrameric complexes, as nominal Ag-specific T cells would do. In consequence, fluorescent HLA-peptide tetrameric complexes can be used for sorting and cloning of allorestricted CTLs specific for a peptide of interest. We also show by the mean of HLA-peptide tetramers the existence of peptide-selective alloreactive T cells that recognize a conformation on the foreign-MHC brought about by some but not all peptides bound.