Nonmyeloablative stem cell transplantation for solid tumors: expanding the application of allogeneic immunotherapy

Immunotherapy options in metastatic renal cell cancer: where we are and where we are going

The treatment of renal cell carcinoma is rapidly changing as a result of recent evidence concerning the efficacy of biological drugs, antiangiogenetic agents and signal-transduction inhibitors. This paper will provide a critical overview of the use of immunotherapy in renal cell carcinoma and review the available data concerning the efficacy of interferons, interleukin-2 and other forms of immunological treatment, particularly allogenic transplantation and vaccines. Moreover, it will focus on the new mechanisms of regulation of the immune system with a better understanding of the interaction between host and tumor, the role of T regulatory cells, heat-shock proteins and vaccines. The mechanism of action and the results obtained in renal cell carcinoma using the new molecular targeted drugs will be examined, along with the possibility of using immunotherapy combined with the new biological agents. Future research will not only need to make every effort to optimize the use of the new molecules and to define their efficacy precisely, but also to consider how to integrate these drugs with the traditional immunotherapy.

A high antithymocyte globulin dose increases the risk of relapse after reduced intensity conditioning HSCT with unrelated donors

The study included 110 consecutive patients with hematological malignancies receiving fludarabine-based reduced intensity conditioning (RIC) and hematopoietic stem cell transplantation (HSCT) from matched unrelated donors. The median age was 55 yr (range 11-68) and all but 15 patients received peripheral blood stem cell grafts. Antithymocyte globulin (ATG) (Thymoglobulin, Genzyme) at a total dose of 6 mg/kg (n = 66) or 8 mg/kg (n = 44) was given to all patients according to protocol. The ATG dose did not affect time-to-neutrophil or platelet engraftment. The incidences of acute GVHD grades II-IV were 34% and 18% (p = 0.11) and of chronic GVHD were 40% and 26% (p = 0.46) in patients receiving 6 and 8 mg/kg of ATG, respectively. The five-yr relapse-free survival (RFS) was 61% and 36% (p = 0.14) in patients, given low and high ATG dose, respectively. In patients given low-dose ATG, the incidence of relapse was lower compared to those given high-dose ATG, 19% vs. 41% (p = 0.04). In multivariate analysis, age >50 yr (p < 0.001), absence of acute (p < 0.001) and chronic GVHD (p = 0.001) were correlated to relapse, and low-dose ATG was associated with improved RFS (p < 0.05). A high dose (8 mg/kg) of ATG in RIC HSCT with unrelated donors increased the risk for relapse and reduced the RFS.

Completely mismatched allogeneic CD3/CD28 cross-linked Th1 memory cells elicit anti-leukemia effects in unconditioned hosts without GVHD toxicity

Fully allogeneic CD3/CD28 cross-linked Th1 cells were found to elicit host-mediated anti-leukemia effects without GVHD toxicity. Mice inoculated with a lethal dose of BCL1 leukemia demonstrated significantly enhanced survival after allogeneic Th1 treatment. Cure rates of 12.5% with a single allogeneic cell infusion and 31.25% with multiple infusions were demonstrated. Cured mice were able to reject rechallenge with a lethal dose of tumor without further treatment. These results suggest that use of intentionally mis-matched, Th1 memory cells infused with cross-linked CD3/CD28 could represent a novel clinical approach to eliciting potent anti-tumor effects in patients without conditioning and without GVHD toxicity.

The anti-tumor effect of allogeneic bone marrow/stem cell transplant without graft vs. host disease toxicity and without a matched donor requirement?

The anti-tumor immune response that occurs in allogeneic bone marrow/stem cell transplant (BMT) settings is capable of eradicating tumors that are resistant to chemotherapy/radiation treatment. This anti-tumor immune response, known as the graft vs. tumor (GVT) effect, is the most effective immunotherapy treatment ever discovered. Unfortunately, the clinical application of GVT is severely limited due to the intimate association of GVT with the extremely toxic and often lethal side-effect known as graft vs. host disease (GVHD). It is a major research focus in the field of BMT to develop methods to separate the beneficial GVT effect from the detrimental GVHD toxicity. However, due to the intimate association of these effects, attempts to limit GVHD also have a tendency to limit the GVT effect. We propose a new concept for harnessing the power of the GVT effect without the toxicity of GVHD. Rather than trying to separate GVT from GVHD, we propose that these naturally coupled effects can 'mirrored' onto the host immune system and maintain their intimate association. The 'mirror' of GVHD is a host rejection of a graft (HVG). As rejection of an allograft would not be toxic, an HVG effect coupled to a host vs. tumor (HVT) effect, the 'mirror' of the GVT effect, would provide the anti-tumor effect of BMT without GVHD toxicity. In the 'mirror' setting, the HVT effect must occur against syngeneic tumors, while in the BMT setting the GVT effect occurs in the allogeneic setting. Previous attempts to elicit syngeneic anti-tumor immunity using therapeutic tumor vaccines have had disappointing results in the clinic due to the influence of tumor immunoavoidance mechanisms. We propose that the 'danger' signals that are released as a result of GVHD in the allogeneic BMT setting serve as an adjuvant to the GVT effect disabling tumor immunoavoidance. The chemotherapy/radiation conditioning prior to transplant is a required initiating event to the coupled GVT/GVHD effects. The conditioning releases 'danger' signals that mediate this adjuvant effect. To imitate this immunological event in immunocompetent, non-conditioned patients we propose that infusion of freshly activated, polyclonal CD4+ memory Th1 cells which express CD40L on the cell surface will stimulate a HVT/HVG 'mirror' effect, providing a non-toxic means to elicit the effective immune-mediated anti-tumor effect of BMT without the GVHD toxicity and without the requirement for a matched donor.

The role of purine analogues in low-intensity regimens with allogeneic hematopoietic stem cell transplantation

Host conditioning prior to allogeneic bone marrow transplantation (BMT) has traditionally involved the use of high-dose, myeloablative chemotherapy and irradiation, focusing on maximal tumor cytoreduction as well as adequate immunosuppression to allow engraftment of allogeneic stem cells. High-dose chemoradiation conditioning regimens have been associated with a significant incidence of organ toxicity and acute and chronic graft-versus-host disease (GVHD). Recent efforts to diminish the acute transplant-associated toxicities have focused on the development of relatively nontoxic, nonmyeloablative, or less myeloablative conditioning regimens, with the emphasis being predominantly on induction of immunosuppression to enable engraftment. Without ablative chemotherapy, disease control in these regimens is largely relegated to the graft-versus-leukemia/lymphoma (GVL) effect. While the evolution these regimens has resulted in successful engraftment of allogeneic stem cells with minimal toxicity, acute and chronic GVHD occurs in 20% to 50% of patients and remains a major cause of transplant-associated morbidity. Strategies to lower the incidence of acute GVHD have primarily focused on more precise molecular donor/recipient matching, alternative stem cell sources, and T-cell depletion of the graft. While successful in lowering the frequency and severity of GVHD, T-cell-depleted grafts have been associated with compromised the graft-versus-disease effect. Recent studies have suggested that, in addition to T-effector cells within the graft, donor and host dendritic cells may play a role in GVHD. Purine analogues have been evaluated as part of these regimens. While fludarabine and cladribine have been shown to be effective, these agents have been associated with an increased incidence of serious infection and severe acute GVHD. Pentostatin has a different mechanism of action and was also investigated as part of these preparative regimens. Regimens using pentostatin/extracorporeal photopheresis (ECP)/total body irradiation (TBI) have been shown to be well tolerated and associated with early full donor engraftment with a predominance of donor dendritic cell (DC)2 cells and a low incidence of acute GVHD. Further investigation evaluating this preparative regimen is warranted.

Nonmyeloablative conditioning does not prevent telomere shortening after allogeneic stem cell transplantation

BACKGROUND

Stem cell transplantation (SCT) may be associated with premature aging of the hematopoietic stem cells. Telomere length reflects the proliferative history of a cell. In most studies published so far on telomere dynamics after myeloablative allogeneic SCT, recipients had shorter telomeres than their respective donors, thus reflecting "accelerated aging" of hematopoietic cells. We evaluated telomere dynamics in patients who underwent transplantation with nonmyeloablative protocols, assuming that the decreased intensity of chemotherapy might prevent telomere attrition.

METHODS

Telomere length was measured using FISH-FACS method. Telomeres of recipients were compared to their respective donors. Twenty-three consecutive patients after nonmyeloablative SCT were evaluated. A control group consisted of 10 donor-recipient pairs after conventional myeloablative transplantation.

RESULTS

There was significant telomere shortening in both recipients of nonmyeloablative and myeloablative conditioning (0.487+/-0.65 kb, P=0.003; 0.361+/-0.50 kb, P=0.047 respectively). The extent of telomere shortening in the two groups was not different (P=0.64). There was no correlation between the degree of shortening and parameters such as time interval from transplant, age of donor or recipient, and the number of infused cells.

CONCLUSIONS

This is the first study on telomere dynamics after nonmyeloablative conditioning SCT. The study demonstrates significant shortening of telomeres in recipients in spite of decreased intensity conditioning. Results of this study suggest that the main mechanism following transplantation is the proliferative stress imposed upon the stem cells and not direct damage by cytotoxic drugs. The different kinetics of restoration of hematopoiesis and the probable ongoing process of graft-versus-leukemia in the bone marrow do not prevent the attrition of telomeric ends of chromosomes.

Hematologic aspects of myeloablative therapy and bone marrow transplantation

The transplantation of bone marrow cells or isolated hematopoietic stem cells from the bone marrow or peripheral blood is a widely utilized form of therapy for patients with incurable diseases of the hematopoietic and immune systems. Successful engraftment of the transplanted stem cells in an adequately prepared recipient normally leads to bone marrow reconstitution over a period of several weeks, accompanied by more gradual reconstitution of the immune system. Since the recipient is profoundly ill during the initial treatment period, laboratory data is critical for monitoring engraftment, detecting residual/recurrent disease, and identifying problems that may delay bone marrow reconstitution or lead to other medical complications. Accurate blood cell counts are imperative, and most bone marrow transplantation patients undergo periodic monitoring with bone marrow aspirates and biopsies with cytogenetic, molecular, and multiparametric flow cytometric studies. The potential complications of bone marrow transplantation include engraftment failure and delayed engraftment, infection, residual bone marrow disease, acute and chronic graft versus host disease, myelofibrosis, therapy-related acute leukemia, post-transplant lympho-proliferative disorders, and toxic myelopathy.

Allogeneic stem-cell transplantation for renalcellcancer

Metastatic renal-cell carcinoma (RCC) is resistant to chemotherapy, and patients with this disease have a poor outlook. Immunotherapy by use of cytokines and vaccines against tumour antigens has shown encouraging results in a small group of patients. Advances in the understanding of the graft-versus-tumour effect in haematological malignant disorders have led to the use of stem-cell transplantation for treatment of solid-organ malignant diseases such as RCC. Techniques of bone-marrow ablation have been superseded by safer conditioning regimens, with occasional complete remission and partial remission in some patients. Graft-versus-host disease, engraftment failure, and disease progression remain important obstacles to the widespread use of new techniques for metastatic RCC. Here, we summarise important issues surrounding immunotherapy for RCC, the problems encountered with use of immunotherapy, and the present use of non-myeloablative techniques for treatment of this disease.

Stem cell transplantation-harnessing of graft-versus-malignancy

PURPOSE OF REVIEW

Allogeneic transplantation can cure a number of hematologic malignancies; however, the cost in morbidity and mortality is high. Much of the toxicity is a direct consequence of the intensity of the conditioning regimen. It has gradually been recognized that the conditioning regimen is important but not critical for the success of transplantation, particularly in the less aggressive hematologic malignancies. The graft-versus-malignancy effect, that is, the recognition of residual cancer cells by the T cells of the donor, is a critical component of the transplantation process.

RECENT FINDINGS

This effect has been emphasized over high-dose therapy by using less intensive, and therefore less toxic conditioning regimens, thus allowing the graft-versus-malignancy effect to predominate. Reduced-intensity conditioning regimens have allowed the application of transplantation to older patients and to patients with underlying medical problems that preclude full-dose transplantation.

SUMMARY

Although the long-term results of this type of approach have not yet been defined, it appears to be effective in diseases such as chronic myelogenous leukemia, chronic lymphocytic leukemia, and low-grade lymphomas that are not intrinsically very aggressive. Although the therapy appears to be valuable, concerns about delayed immune reconstitution and graft-versus-host disease remain.

Nonmyeloablative allogeneic immunotherapy for solid tumors

Over the past decade, considerable advances have been made in the field of allogeneic hematopoietic stem cell transplantation. Recognition that transplanted donor immune cells can cure patients with leukemia has led to the development of nonmyeloablative or "low-intensity" conditioning regimens, which have expanded the application of allogeneic transplantation to a growing number of hematological malignancies. The improved safety and preliminary success of this transplant approach have justified applying allogeneic immunotherapy to patients with treatment-refractory solid tumors.

Cellular therapy services provided by blood centers and hospitals in the United States, 1999: an analysis from the Nationwide Blood Collection and Utilization Survey

BACKGROUND

The 2000 Nationwide Blood Collection and Utilization Survey was designed to assess cellular therapy product services in US blood centers and hospitals.

STUDY DESIGN AND METHODS

Questionnaires were returned by 2,040 institutions. Data were analyzed for 30 quantitative variables related to cellular therapy product activities.

RESULTS

269 institutions, including 231 (12.2%) of the hospitals, 37 (25.9%) of the blood centers, and one cryobank, performed HPC services. Collected PBSC (20,517) and cord blood products (12,628) far exceeded bone marrow (1,572), lymphocytes (578), and cultured cells (344). PBPC collections dropped 36.5 percent since the 1997 survey. Cord blood accounted for 35.4 percent of collections and 39.5 percent of products processed, but only 1.9 percent of infusions.

CONCLUSIONS

Most cellular therapy services in hospitals and blood centers were HPC-related. The dramatic drop in PBPC collections since 1997 reflects the decline in autologous PBPC transplantation for breast cancer. Cord blood's high collection-to-infusion ratio demonstrates a substantial resource expenditure for banking a product for future clinical needs. Lymphocytes and cultured cell products contributed minimally to activities in this survey, but will likely increase in the future. Data from additional academic and commercial manufacturers of cellular therapy products should be included in future surveys.

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.

Present results and perspectives of allogeneic non-myeloablative hematopoietic stem cell transplantation for treatment of human solid tumors

Several clinical observations have confirmed that a donor immune-mediated anti-malignancy effect, called graft-versus-leukemia or graft-versus-tumor, occurs following allogeneic hematopoietic stem cell transplantation. While the potential antitumor effect mediated by donor lymphocytes has been established in many hematological malignancies, its efficacy in inducing clinically meaningful responses in solid tumors has been largely unexplored despite evidence of its potential benefit in experimental animal models. Only in recent years has the investigational application of non-myeloablative stem cell transplantation in patients with refractory non-hematological cancers proved that a graft-versus-tumor effect can be generated in patients with metastatic renal cell cancer and possibly with other solid tumors. In the present article we review the biological basis, development and early clinical results of this novel immunotherapeutic approach for solid tumors.

Immunotherapy of cancer by active vaccination: does allogeneic bone marrow transplantation after non-myeloablative conditioning provide a new option?

The critical role of antigen-specific T cells in cancer immunotherapy has been amply demonstrated in many model systems. Though success of clinical trials still remains far behind expectation, the continuous improvement in our understanding of the biology of the immune response will provide the basis of optimized cancer vaccines and allow for new modalities of cancer treatment. This review focuses on the current status of active therapeutic vaccination and future prospects. The latter will mainly be concerned with allogeneic bone marrow cell transplantation after non-myeloablative conditioning, because it is my belief that this approach could provide a major breakthrough in cancer immunotherapy. Concerning active vaccination protocols the following aspects will be addressed: i) the targets of immunotherapeutic approaches; ii) the response elements needed for raising a therapeutically successful immune reaction; iii) ways to achieve an optimal confrontation of the immune system with the tumor and iv) supportive regimen of immunomodulation. Hazards which one is most frequently confronted with in trials to attack tumors with the inherent weapon of immune defense will only be briefly mentioned. Many question remain to be answered in the field of allogeneic bone marrow transplantation after non-myeloablative conditioning to optimize the therapeutic setting for this likely very powerful tool of cancer therapy. Current considerations to improve engraftment and to reduce graft versus host disease while strengthening graft versus tumor reactivity will be briefly reviewed. Finally, I will discuss whether tumor-reactive T cells can be "naturally" maintained during the process of T cell maturation in the allogeneic host. Provided this hypothesis can be substantiated, a T cell vaccine will meet a pool of virgin T cells in the allogeneically reconstituted host, which are tolerant towards the host, but not anergised towards tumor antigens presented by MHC molecules of the host.

New Developments in Allotransplant Immunology

After allogeneic stem cell transplantation, the establishment of the donor’s immune system in an antigenically distinct recipient confers a therapeutic graft-versus-malignancy effect, but also causes graft-versus-host disease (GVHD) and protracted immune dysfunction. In the last decade, a molecular-level description of alloimmune interactions and the process of immune recovery leading to tolerance has emerged. Here, new developments in understanding alloresponses, genetic factors that modify them, and strategies to control immune reconstitution are described.

In Section I, Dr. John Barrett and colleagues describe the cellular and molecular basis of the alloresponse and the mechanisms underlying the three major outcomes of engraftment, GVHD and the graft-versus-leukemia (GVL) effect. Increasing knowledge of leukemia-restricted antigens suggests ways to separate GVHD and GVL. Recent findings highlight a central role of hematopoietic-derived antigen-presenting cells in the initiation of GVHD and distinct properties of natural killer (NK) cell alloreactivity in engraftment and GVL that are of therapeutic importance. Finally, a detailed map of cellular immune recovery post-transplant is emerging which highlights the importance of post-thymic lymphocytes in determining outcome in the critical first few months following stem cell transplantation. Factors that modify immune reconstitution include immunosuppression, GVHD, the cytokine milieu and poorly-defined homeostatic mechanisms which encourage irregular T cell expansions driven by immunodominant T cell–antigen interactions.

In Section II, Prof. Anne Dickinson and colleagues describe genetic polymorphisms outside the human leukocyte antigen (HLA) system that determine the nature of immune reconstitution after allogeneic stem cell transplantation (SCT) and thereby affect transplant outcomethrough GVHD, GVL, and transplant-related mortality. Polymorphisms in cytokine gene promotors and other less characterized genes affect the cytokine milieu of the recipient and the immune reactivity of the donor. Some cytokine gene polymorphisms are significantly associated with transplant outcome. Other non-HLA genes strongly affecting alloresponses code for minor histocompatibility antigens (mHA). Differences between donor and recipient mHA cause GVHD or GVL reactions or graft rejection. Both cytokine gene polymorphisms (CGP) and mHA differences resulting on donor-recipient incompatibilities can be jointly assessed in the skin explant assay as a functional way to select the most suitable donor or the best transplant approach for the recipient.

In Section III, Dr. Nelson Chao describes non-pharmaceutical techniques to control immune reconstitution post-transplant. T cells stimulated by host alloantigens can be distinguished from resting T cells by the expression of a variety of activation markers (IL-2 receptor, FAS, CD69, CD71) and by an increased photosensitivity to rhodamine dyes. These differences form the basis for eliminating GVHD-reactive T cells in vitro while conserving GVL and anti-viral immunity. Other attempts to control immune reactions post-transplant include the insertion of suicide genes into the transplanted T cells for effective termination of GVHD reactions, the removal of CD62 ligand expressing cells, and the modulation of T cell reactivity by favoring Th2, Tc2 lymphocyte subset expansion. These technologies could eliminate GVHD while preserving T cell responses to leukemia and reactivating viruses.

Human colon adenocarcinoma in the SCID/CB6 radiation chimera is susceptible to adoptive transfer of allogeneic human peripheral blood mononuclear cells

The aim of this study was to develop a murine model of human colon carcinoma (hCC) and to ascertain the potential of cellular immunotherapy in this model. Fragments of hCC obtained at surgery from 6 patients were transplanted under the kidney capsule of lethally irradiated CB6 mice radioprotected with severe combined immunodeficient (SCID) mice bone marrow. Tumor xenografts conserved their malignant behavior in the new environment, invading the mouse kidney parenchyma and expanding into the peritoneal cavity and adjacent tissues. Their growth was typically exponential, and they expanded to dimensions that allowed their subsequent fragmentation and passage to further preconditioned mice. Human carcinoembryonic antigen (hCEA) was detected on the implanted tumor and at occasionally spontaneous lung metastases. Most significantly, high levels of this tumor marker were detected in the sera of tumor-bearing mice, providing a useful tool, which allowed long-term experiments, monitoring of tumor progression, and its response to some treatment modalities. For instance, complete resection of the transplanted tumors, by means of nephrectomy, resulted in the disappearance of hCEA from mice sera within 2 weeks. Similarly, adoptive transfer of allogeneic human peripheral blood mononuclear cells (PBMC) into the peritoneum of tumor-bearing mice, resulted in their rapid engraftment, infiltration of tumor mass, and a significant drop of hCEA levels in mice serum, accounting for inhibition of tumor growth. We suggest that this novel model of human colon carcinoma affords the opportunity for in vivo evaluation of different preclinical treatment modalities, particularly, those involving manipulation with immune effector cells.