Haemopoietic stem-cell transplantation with antibody-based minimal-intensity conditioning: a phase 1/2 study.

BACKGROUND: Stem-cell transplantation can cure primary immunodeficiencies. However, in patients with pre-existing organ toxicity, patients younger than 1 year, and those with DNA or telomere repair disorders, chemotherapy-based conditioning is poorly tolerated and results in major morbidity and mortality. We tested a novel antibody-based minimal-intensity conditioning (MIC) regimen to assess whether this approach allowed curative donor stem-cell engraftment without non-haemopoietic toxicity. METHODS: 16 high-risk patients underwent stem-cell transplantation for primary immunodeficiencies with an MIC regimen consisting of two rat anti-CD45 monoclonal antibodies YTH 24.5 and YTH 54.12 for myelosuppression, and alemtuzumab (anti-CD52) and fludarabine, and low dose cyclophosphamide for immunosuppression. Donors were matched siblings (n=5), and matched (9) and mismatched (2) unrelated donors. FINDINGS: Antibody-based conditioning was well tolerated, with only two cases of grade 3 and no grade 4 toxicity. Rates of clinically significant acute (n=6, 36%) and chronic graft-versus-host disease (GVHD) (n=5, 31%) were acceptable. 15 of 16 patients (94%) engrafted, of whom 11 (69%) achieved full or high-level mixed chimerism in both lymphoid and myeloid lineages, and three achieved engraftment in the T-lymphoid lineage only. One patient needed retransplantation. At a median of 40 months post-transplant, 13 of 16 patients (81%) in this high-risk cohort were alive and cured from their underlying disease. INTERPRETATION: Monoclonal antibody-based conditioning seems well tolerated and can achieve curative engraftment even in patients with severe organ toxicity or DNA repair defects, or both. This novel approach represents a shift from the paradigm that intensive chemotherapy or radiotherapy, or both, is needed for donor stem-cell engraftment. This antibody-based conditioning regimen may reduce toxicity and late effects and enable SCT in virtually any primary immunodeficiency patient with a matched donor. FUNDING: None.

An inducible caspase 9 safety switch can halt cell therapy-induced autoimmune disease.

Transfer of either allogeneic or genetically modified T cells as a therapy for malignancies can be accompanied by T cell-mediated tissue destruction. The introduction of an efficient "safety switch" can potentially be used to control the survival of adoptively transferred cell populations and as such reduce the risk of severe graft-vs-host disease. In this study, we have tested the value of an inducible caspase 9-based safety switch to halt an ongoing immune attack in a murine model for cell therapy-induced type I diabetes. The data obtained in this model indicate that self-reactive T cells expressing this conditional safety switch show unimpaired lymphopenia- and vaccine-induced proliferation and effector function in vivo, but can be specifically and rapidly eliminated upon triggering. These data provide strong support for the evaluation of this conditional safety switch in clinical trials of adoptive cell therapy.

Complete responses of relapsed lymphoma following genetic modification of tumor-antigen presenting cells and T-lymphocyte transfer.

Epstein-Barr virus (EBV)-associated tumors developing in immunocompetent individuals present a challenge to immunotherapy, since they lack expression of immunodominant viral antigens. However, the tumors consistently express viral proteins including LMP2, which are immunologically "weak" but may nonetheless be targets for immune T cells. We previously showed that a majority of cytotoxic T lymphocytes (CTLs) reactivated using EBV-transformed B-lymphoblastoid cells lines (LCLs) contained minor populations of LMP2-specific T cells and homed to tumor sites. However, they did not produce remissions in patients with bulky disease. We have now used gene transfer into antigen-presenting cells (APCs) to augment the expression and immunogenicity of LMP2. These modified APCs increased the frequency of LMP2-specific CTLs by up to 100-fold compared with unmodified LCL-APCs. The LMP2-specific population expanded and persisted in vivo without adverse effects. Nine of 10 patients treated in remission of high-risk disease remain in remission, and 5 of 6 patients with active relapsed disease had a tumor response, which was complete in 4 and sustained for more than 9 months. It is therefore possible to generate immune responses to weak tumor antigens by ex vivo genetic modification of APCs and the CTLs so produced can have substantial antitumor activity. This study is registered at http://www.cancer.gov/clinicaltrials (protocol IDs: BCM-H-9936, NCT00062868, NCT00070226).

Characterization of latent membrane protein 2 specificity in CTL lines from patients with EBV-positive nasopharyngeal carcinoma and lymphoma.

Viral proteins expressed by EBV-associated tumors provide target Ags for immunotherapy. Adoptive T cell therapy has proven effective for posttransplant EBV-associated lymphoma in which all EBV latent Ags are expressed (type III latency). Application of immunotherapeutic strategies to tumors such as nasopharyngeal carcinoma and Hodgkin's lymphoma that have a restricted pattern of EBV Ag expression (type II latency) is under investigation. Potential EBV Ag targets for T cell therapy expressed by these tumors include latent membrane proteins (LMP) 1 and 2. A broad panel of epitopes must be identified from these target Ags to optimize vaccination strategies and facilitate monitoring of tumor-specific T cell populations after immunotherapeutic interventions. To date, LMP2 epitopes have been identified for only a limited number of HLA alleles. Using a peptide library spanning the entire LMP2 sequence, 25 CTL lines from patients with EBV-positive malignancies expressing type II latency were screened for the presence of LMP2-specific T cell populations. In 21 of 25 lines, T cell responses against one to five LMP2 epitopes were identified. These included responses to previously described epitopes as well as to newly identified HLA-A*0206-, A*0204/17-, A29-, A68-, B*1402-, B27-, B*3501-, B53-, and HLA-DR-restricted epitopes. Seven of the nine newly identified epitopes were antigenically conserved among virus isolates from nasopharyngeal carcinoma tumors. These new LMP2 epitopes broaden the diversity of HLA alleles with available epitopes, and, in particular, those epitopes conserved between EBV strains provide valuable tools for immunotherapy and immune monitoring.

A chimeric T cell antigen receptor that augments cytokine release and supports clonal expansion of primary human T cells.

The transduction of primary T cells to express chimeric T cell receptors (cTCR) for redirected targeting of tumor cells is an attractive strategy for generating tumor-specific T cells for adoptive therapy. However, tumor cells rarely provide costimulatory signals and hence cTCRs that transmit just a CD3zeta signal can only initiate target cell killing and interferon-gamma release and fail to induce full activation. Although incorporation of a CD28 component results in IL-2 release and limited proliferation, T cell activation remains incomplete. OX40 transmits a potent and prolonged T cell activation signal and is crucial for maintaining an immunological response. We hypothesize that the CD28-OX40-CD3zeta tripartite cytoplasmic domain will provide a full complement of activation, proliferation, and survival signals for enhanced anti-tumor activity.

An inducible caspase 9 safety switch for T-cell therapy.

The efficacy of adoptive T-cell therapy as treatment for malignancies may be enhanced by genetic modification of infused cells. However, oncogenic events due to vector/transgene integration, and toxicities due to the infused cells themselves, have tempered enthusiasm. A safe and efficient means of removing aberrant cells in vivo would ameliorate these concerns. We describe a "safety switch" that can be stably and efficiently expressed in human T cells without impairing phenotype, function, or antigen specificity. This reagent is based on a modified human caspase 9 fused to a human FK506 binding protein (FKBP) to allow conditional dimerization using a small molecule pharmaceutical. A single 10-nM dose of synthetic dimerizer drug induces apoptosis in 99% of transduced cells selected for high transgene expression in vitro and in vivo. This system has several advantages over currently available suicide genes. First, it consists of human gene products with low potential immunogenicity. Second, administration of dimerizer drug has no effects other than the selective elimination of transduced T cells. Third, inducible caspase 9 maintains function in T cells overexpressing antiapoptotic molecules. These characteristics favor incorporation of inducible caspase 9 as a safety feature in human T-cell therapies.

Human cytotoxic T lymphocytes with reduced sensitivity to Fas-induced apoptosis.

Effector-memory T cells expressing Fas (Apo-1/CD95) are switched to an apoptotic program by cross-linking with Fas-ligand (FasL). Consequently, tumors that express FasL can induce apoptosis of infiltrating Fas-positive T lymphocytes and subdue any antitumor host immune response. Since Epstein-Barr virus (EBV)-associated tumors such as Hodgkin lymphoma (HL) and nasopharyngeal carcinoma (NPC) express FasL, we determined whether EBV-specific cytotoxic T lymphocytes (EBV-CTLs) could be modified to resist this evasion strategy. We show that long-term down-modulation of Fas can be achieved in EBV-CTLs by transduction with small interfering RNA (siRNA) encoded in a retrovirus. Modified T cells resisted Fas/FasL-mediated apoptosis compared with control cells and showed minimal cleavage of the caspase3 substrate poly(ADP-ribose) polymerase (PARP) protein after Fas engagement. Prolonged Fas stimulation selected a uniformly Fas(low) and FasL resistant population. Removal of responsiveness to this single death signal had no other discernible effects on EBV-CTLs. In particular, it did not lead to their autonomous growth since the modified EBV-CTLs remained polyclonal, and their survival and proliferation retained dependence on antigen-specific stimulation and on the presence of other physiologic growth signals. EBV-CTLs with knocked down Fas should have a selective functional and survival advantage over unmodified EBV-CTLs in the presence of tumors expressing FasL and may be of value for adoptive cellular therapy.

Treatment of nasopharyngeal carcinoma with Epstein-Barr virus--specific T lymphocytes.

Conventional treatment for nasopharyngeal carcinoma (NPC) frequently fails and is accompanied by severe long-term side effects. Since virtually all undifferentiated NPCs are associated with Epstein-Barr virus (EBV), this tumor is an attractive candidate for cellular immunotherapy targeted against tumor-associated viral antigens. We now demonstrate that EBV-specific cytotoxic T-cell (CTL) lines can readily be generated from individuals with NPC, notwithstanding the patients' prior exposure to chemotherapy/radiation. A total of 10 patients diagnosed with advanced NPC were treated with autologous CTLs. All patients tolerated the CTLs, although one developed increased swelling at the site of pre-existing disease. At 19 to 27 months after infusion, 4 patients treated in remission from locally advanced disease remain disease free. Of 6 patients with refractory disease prior to treatment, 2 had complete responses, and remain in remission over 11 to 23 months after treatment; 1 had a partial remission that persisted for 12 months; 1 has had stable disease for more than 14 months; and 2 had no response. These results demonstrate that administration of EBV-specific CTLs to patients with advanced NPC is feasible, appears to be safe, and can be associated with significant antitumor activity.

Cytotoxic T lymphocyte therapy for Epstein-Barr virus+ Hodgkin's disease.

Epstein Barr virus (EBV)+ Hodgkin's disease (HD) expresses clearly identified tumor antigens derived from the virus and could, in principle, be a target for adoptive immunotherapy with viral antigen-specific T cells. However, like most tumor-associated antigens in immunocompetent hosts, these potential targets are only weakly immunogenic, consisting primarily of the latent membrane protein (LMP)1 and LMP2 antigens. Moreover, Hodgkin tumors possess a range of tumor evasion strategies. Therefore, the likely value of immunotherapy with EBV-specific cytotoxic effector cells has been questioned. We have now used a combination of gene marking, tetramer, and functional analyses to track the fate and assess the activity of EBV cytotoxic T lymphocyte (CTL) lines administered to 14 patients treated for relapsed EBV+ HD. Gene marking studies showed that infused effector cells could further expand by several logs in vivo, contribute to the memory pool (persisting up to 12 mo), and traffic to tumor sites. Tetramer and functional analyses showed that T cells reactive with the tumor-associated antigen LMP2 were present in the infused lines, expanded in peripheral blood after infusion, and also entered tumor. Viral load decreased, demonstrating the biologic activity of the infused CTLs. Clinically, EBV CTLs were well tolerated, could control type B symptoms (fever, night sweats, and weight loss), and had antitumor activity. After CTL infusion, five patients were in complete remission at up to 40 mo, two of whom had clearly measurable tumor at the time of treatment. One additional patient had a partial response, and five had stable disease. The performance and fate of these human tumor antigen-specific T cells in vivo suggests that they might be of value for the treatment of EBV+ Hodgkin lymphoma.

The generation and characterization of LMP2-specific CTLs for use as adoptive transfer from patients with relapsed EBV-positive Hodgkin disease.

Cellular adoptive immunotherapy for virus-associated malignant disease is an attractive strategy, since viral antigens provide targets for specific T lymphocytes. In Epstein-Barr virus (EBV)-positive Hodgkin disease (HD), a limited number of EBV-encoded antigens such as the latent membrane antigens (LMP) 1 and 2 are expressed on the malignant Reed-Sternberg cells. The authors aimed to generate cytotoxic T lymphocytes (CTLs) from patients with relapsed HD by specifically targeting LMP2A. Patients with relapsed HD have highly immunosuppressive tumors and have been heavily pretreated with cytotoxic agents. As a result, monocytes and lymphocytes are numerically reduced and functionally impaired. Approaches using dendritic cells (DCs) as the sole antigen-presenting cell to expand LMP2-specific CTL lines in vitro have proved impractical. The authors now show how small amounts of patient peripheral blood can be used to produce DCs expressing LMP2 after Ad5F35 transduction, and how an initial reactivation of LMP2-specific CTLs can be followed by stimulation with lymphoblastoid cell lines overexpressing LMP2 from the same vector. Large numbers of LMP2-specific cytotoxic lymphocytes are produced that contain both CD4+ and CD8+ T cells (favoring long-term persistence in vivo) and recognize multiple LMP2 epitopes (minimizing the risk of tumor antigen loss variants). This approach is being used in a current clinical trial.

Immunotherapy for Epstein-Barr virus-associated cancers in children.

Latent Epstein-Barr virus (EBV) infection is associated with several malignancies, including Burkitt's lymphoma, Hodgkin's disease, nasopharyngeal carcinoma, and post-transplant lymphoproliferative disease (LPD). The presence of EBV antigens in these tumors provides a target for immunotherapy approaches, and immunotherapy with EBV-specific cytotoxic T cells (CTLs) has proved effective in post-transplant LPDs, which are highly immunogenic tumors expressing type III latency. The malignant cells in Hodgkin's disease and nasopharyngeal carcinoma express type II latency and hence a more restricted pattern of EBV antigens. Trials with autologous EBV-specific CTL responses are under way in both of these diseases, and while some activity has been seen, no patient has yet been cured. This reduced CTL efficacy may reflect either downregulation of immunodominant EBV proteins, which are major CTL targets, or the ability of these tumors to evade the immune response by secreting inhibitory cytokines. Further improvement of EBV-specific CTL therapy for these type II latency tumors will require improved methods to activate and expand CTLs specific for the subdominant EBV genes expressed and to genetically modify the expanded CTLs to render them resistant to inhibitory cytokines. If these strategies to improve the therapeutic potential of immunotherapy for EBV-associated tumors prove successful, this type of treatment may be adapted to other tumors expressing known (viral) antigens.