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.

E1A-induced apoptosis does not prevent replication of adenoviruses with deletion of E1b in majority of infected cancer cells

Apoptotic pathways are initiated as a cellular defense mechanism to eliminate adenovirus-infected cells. We have investigated how E1A-induced apoptosis interferes with viral replication in cancer cells. We found that E1B19K alone can efficiently suppress E1A-induced apoptosis in cancer cells. Viruses deleted for both E1B19K and E1B55K resulted in cellular DNA degradation. However, less than 20% of human lung cancer cells infected with a virus deleted for both E1B19K and E1B55 K had evidence of chromatin condensation and multiple-micronuclei formation (apoptotic hallmarks); these cells could not produce infectious viral particles. The majority of cancer cells infected with viruses deleted for the entire E1b gene did not undergo extended apoptosis and produced abundant viral progeny. Thus, only a fraction of cancer cells underwent apoptosis and did not allow E1b-deleted viruses to replicate, while the majority of cancer cells were resistant to E1A-induced apoptosis and could support virus-selective replication. The results of this study imply that, in addition to inhibiting E1A-induced apoptosis, E1B proteins may contribute other important roles in the viral life cycle. Our results also suggest that combining virus-induced apoptosis and selective viral replication into one vector will be a novel approach to destroy cancer cells.

A distinct "side population" of cells in human tumor cells: implications for tumor biology and therapy

Stem cells have an extensive capacity to proliferate, differentiate and self-renew. In many mammals, including humans, an adult stem cell subpopulation termed the "side population" (SP) has been identified. SP cells can rapidly efflux lipophilic fluorescent dyes to produce a characteristic profile based on fluorescence-activated flow cytometric analysis. Previous studies have demonstrated SP cells in bone marrow obtained from patients with acute myeloid leukemia, suggesting that these cells might be candidate leukemic stem cells, and recent studies have found a SP of tumor progenitor cells in human solid tumors. These new data indicate that the ability of malignant SP cells to expel anticancer drugs may directly improve their survival and sustain their clonogenicity during exposure to cytostatic drugs, allowing disease recurrence when therapy is withdrawn. Identification of a tumor progenitor population with intrinsic mechanisms for cytostatic drug resistance might also provide clues for improved therapeutic intervention.

Genetic modification of T lymphocytes for adoptive immunotherapy

Adoptive transfer of T lymphocytes is a promising therapy for malignancies-particularly of the hemopoietic system-and for otherwise intractable viral diseases. Efforts to broaden the approach have been limited by the physiology of the T cells themselves and by a range of immune evasion mechanisms developed by tumor cells. In this review we show how genetic modification of T cells is being used preclinically and in patients to overcome these limitations, by incorporation of novel receptors, resistance mechanisms, and control genes. We also discuss how the increasing safety and effectiveness of gene transfer technologies will lead to an increase in the use of gene-modified T cells for the treatment of a wider range of disorders.

Liposomal enhancement of the antitumor activity of conditionally replication-competent adenoviral plasmids

Many human tumors have a functional deficiency in p53. Numerous studies have taken advantage of this phenomenon to use a conditionally replication-competent adenovirus (Ad dl1520) that will grow in and lyse tumor cells while sparing normal tissues. However, success has been limited, in part due to difficulties in reaching a sufficiently high proportion of tumor cells. Preexisting or developing immune responses directed toward viral proteins further decrease the efficacy of the approach. We have developed a liposome-encapsulated conditionally replication-competent plasmid based on the dl1520 virus. Like the parent virus, this plasmid generates infectious particles following transfection of p53-defective, but not p53-wild-type tumor cells, but unlike the parent virus it is able to infect CAR-negative tumor cells. The antitumor efficacy of this infectious plasmid was demonstrated in mice with xenografted human tumors, in which it was active after both local and intravenous administration for subcutaneous tumors and following intravenous administration for disseminated malignancy. Activity was retained systemically, even in the presence of neutralizing antibody. Such liposomally encapsulated conditionally replication-competent plasmids may complement the use of conventional viral particles, particularly in settings in which liver uptake of adenoviral vector is undesirable or there are problematic inhibitory effects from humoral immune responses.

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.

Conserved CTL epitopes on the adenovirus hexon protein expand subgroup cross-reactive and subgroup-specific CD8+ T cells

Adenoviruses often cause lethal infections in immunocompromised individuals. Adoptive transfer of immune T cells offers a therapeutic option, but this strategy has been hindered by the paucity of information on molecular targets of cellular immunity and by the immunologic heterogeneity of the 51 human adenoviruses, which are grouped from A to F on the basis of genome size, composition, homology, and organization. Clonal analysis of the adenovirus-specific cytotoxic T lymphocyte (CTL) responses of seropositive individuals identified 5 novel CD8+ T-cell epitopes, all located in conserved regions of the capsid protein hexon. Reactive T cells were cross-reactive between 2 to 4 groups, while no T cells specific for a single subgroup were detected. Thus, by exploiting these peptide targets, it is possible to prepare a T-cell population capable of reacting with most adenoviruses that cause disease in immunocompromised patients.

A distinct "side population" of cells with high drug efflux capacity in human tumor cells

A subset of stem cells, termed the "side population" (SP), has been identified in several tissues in mammalian species. These cells maintain a high efflux capability for antimitotic drugs. We have investigated whether functionally equivalent stem cells also may be detected in human cancers. We initially examined primary tumor cells from 23 patients with neuroblastoma and cell lines derived from a range of other tumors. A distinct SP was found in neuroblastoma cells from 15 of 23 patients (65%). The SP was capable of sustained expansion ex vivo and showed evidence for asymmetric division, generating both SP and non-SP progeny. These cells also expressed high levels of ABCG2 and ABCA3 transporter genes and had a greater capacity to expel cytotoxic drugs, such as mitoxantrone, resulting in better survival. A SP also was detected in breast cancer, lung cancer, and glioblastoma cell lines, suggesting that this phenotype defines a class of cancer stem cells with inherently high resistance to chemotherapeutic agents that should be targeted during the treatment of malignant disease.

A strategy for treatment of Epstein-Barr virus-positive Hodgkin's disease by targeting interleukin 12 to the tumor environment using tumor antigen-specific T cells

Adoptive immunotherapy with Epstein-Barr virus (EBV)-specific cytotoxic T cells (CTL) is effective for the prophylaxis and treatment of EBV-induced lymphoma in hematopoietic stem cell recipients. However, in EBV-positive Hodgkin's disease (HD) the efficacy of adoptively transferred EBV-specific CTL may be limited by tumor-derived immunosuppressive factors, such as T-cell growth factor (TGF) beta, interleukin (IL)13 and the chemokine TARC. Local delivery of IL12 to tumor sites by tumor-specific CTL could provide direct antitumor effects and overcome the CTL-inhibitory effects of the Th2 tumor environment while avoiding the systemic toxicity of recombinant IL12. EBV-specific CTL transduced with a retrovirus vector expressing the p40 and p35 subunits of IL12 as a single molecule (Flexi-IL12), produced IL12 following antigenic stimulation. This resulted in an elevated production of Th1 cytokines, including interferon gamma and tumor necrosis factor alpha, and a reduction in the Th2 cytokines IL4 and IL5. Flexi-IL12-transduced CTL resisted the antiproliferative and anticytotoxic effects of exogenous TGFbeta, likely by antagonizing the TGFbeta-induced downregulation of the Th1 transcriptional factor T-bet. In addition, Flexi-IL12-transduced CTL demonstrated a proliferative advantage in the presence of inhibitory supernatants from HD-derived cell lines. Tumor-specific, Flexi-IL12-transduced EBV-specific CTL should have a functional advantage over unmodified CTL, particularly in the presence of the adverse Th2 cytokine environment produced by Hodgkin tumor cells.

Haematopoietic stem cell transplantation for autoimmune disease: limits and future potential

Stem cell transplantation (SCT) for autoimmune disease is handicapped by a lack of definitive clinical trials able to demonstrate an overall benefit. This deficiency will become more problematic as the impetus grows to introduce and evaluate additional technologies intended to improve the safety and efficacy of the procedure. The development of effective surrogate analyses to predict outcome by measuring resurgent autoimmune clones or by genomic- and proteomic-based technologies to detect early disease recurrence may be of value in assessing the benefits of these modifications without the need for full-scale, long-term, randomized trials. The introduction of safer allogeneic transplantation techniques may increase the effectiveness of the procedure, while work on marrow stem cell plasticity and/or fusion suggests that SCT may serve not simply to halt the autoimmune process, but also to contribute cells capable of healing or regenerating diseased organs. Finally, the introduction of therapeutic transgenes into transplanted cells may further increase the effectiveness of SCT, although the regulatory complexities of gene therapy trials will probably delay this process. All these innovations will ensure that the next decade will see major changes in the practice and purpose of SCT for autoimmune disease.

An in vivo propagated human acute myeloid leukemia expressing ABCA3

Analyzing the regenerative compartment in the blast cell population of patients with acute myeloid leukemia (AML) may yield important insights into the mechanisms of disease progression. Here we present findings with a human AML cell line (AML-SP1), initiated from leukemic precursor cells and consecutively propagated by serial xenotransplantation in vivo. AML-SP1 maintained the characteristics of a human AML, consistently exhibiting a small leukemic side population (SP) of blast cells with high Hoechst 33342 exclusion. In the AML-SP1 line, an increased expression of the ABC transporters MDR1, MRP, ABCG2 and ABCA3 was found in the SP cells. The detection of ABCA3 in leukemic progenitor cells merits further investigation with regard to intracellular drug transport in AML blast cells. In vivo propagation of leukemias, such as AML-SP1 is a model system of maintaining the populational heterogeneity of AML disease, especially the unique characteristics of leukemic SP cells.

Antigen-induced regulatory T cells

Regulatory T cells participate in immunologic homeostasis by active suppression of inappropriate immune responses. Regulatory T lymphocytes expressing CD4 and CD25 antigens and naturally present in the peripheral blood were the first to be phenotypically characterized. However, their small number and antigen nonspecific suppression has prompted efforts to identify and dissect antigen-specific regulatory T cells. In this review we discuss how antigen-specific regulatory T cells can be identified, the cellular and molecular mechanisms underlying their induction and activity, and the challenges facing their potential clinical application.

Expansion of EBV latent membrane protein 2a specific cytotoxic T cells for the adoptive immunotherapy of EBV latency type 2 malignancies: influence of recombinant IL12 and IL15

BACKGROUND

EBV-associated malignancies with a Type II latency gene expression pattern, such as EBV-positive HD, or nasopharyngeal carcinoma, frequently express the EBV latency Ag LMP2a. Hence, they provide a potential target for adoptive immunotherapy using in vitro-generated LMP2a-specific cytotoxic T lymphocytes (CTL). In this study, LMP2a-specific CTL were specifically amplified and the influence of rIL12 and rIL15 on the culture outcome was tested.

METHODS

PBMC from donors were stimulated twice with autologous DC transduced with an adenovirus vector expressing LMP2a. This led to a significant expansion of LMP2a-tetramer-specific CTL, which were subsequently further expanded with autologous EBV-transformed B-lymphoblastoid cells (LCL). The addition of rIL12 and rIL15 to the standard IL2-containing culture medium enhanced the proliferation of LMP2a-specific CTL.

RESULTS

While rIL15 did not change the pattern of cytokines secreted by LMP2a-CTL, rIL12 enhanced the production of Th1/Tc1 cytokines, such as IFN-n, while suppressing the production of the Th2/Tc2 cytokine IL5.

DISCUSSION

Stimulation of CTL cultures with rIL12 or rIL15 will generate CTL more rapidly, facilitating the application of this approach for patients with these EBV-associated disorders.

Evidence for the presentation of major histocompatibility complex class I-restricted Epstein-Barr virus nuclear antigen 1 peptides to CD8+ T lymphocytes

The Epstein-Barr virus (EBV)-encoded nuclear antigen 1 (EBNA1) is expressed in all EBV-associated tumors, making it an important target for immunotherapy. However, evidence for major histocompatibility complex (MHC) class I–restricted EBNA1 peptides endogenously presented by EBV-transformed B and tumor cells remains elusive. Here we describe for the first time the identification of an endogenously processed human histocompatibility leukocyte antigen (HLA)-B8–restricted EBNA1 peptide that is recognized by CD8⁺ T cells. T cell recognition could be inhibited by the treatment of target cells with proteasome inhibitors that block the MHC class I antigen processing pathway, but not by an inhibitor (chloroquine) of MHC class II antigen processing. We also demonstrate that new protein synthesis is required for the generation of the HLA-B8 epitope for T cell recognition, suggesting that defective ribosomal products (DRiPs) are the major source of T cell epitopes. Experiments with protease inhibitors indicate that some serine proteases may participate in the degradation of EBNA1 DRiPs before they are further processed by proteasomes. These findings not only provide the first evidence of the presentation of an MHC class I–restricted EBNA1 epitope to CD8⁺ T cells, but also offer new insight into the molecular mechanisms involved in the processing and presentation of EBNA1.

Prompt versus preemptive intervention for EBV lymphoproliferative disease

Posttransplantation lymphoproliferative disorders (PTLDs) caused by uncontrolled expansion of Epstein-Barr virus (EBV)-infected B cells after hematopoietic stem cell transplantation (HSCT) can be predicted by an increase in EBV DNA in peripheral blood mononuclear cells. We used real-time quantitative polymerase chain reaction (RQ-PCR) analysis to determine whether frequent monitoring of EBV DNA to allow preemptive treatment is truly of value in patients after HSCT. More than 1300 samples from 85 recipients were analyzed. No patient with consistently low EBV DNA levels developed PTLD. Nine patients had a single episode with a high EBV load (more than 4000 EBV copies/microg peripheral blood mononuclear cell [PBMC] DNA), and 16 patients had high EBV loads detected on 2 or more occasions. Only 8 of these developed symptoms consistent with PTLD, and all were promptly and successfully treated with EBV-specific cytotoxic T cells or CD20 monoclonal antibody. Hence, quantitative measurement of EBV DNA may best be used to enable the prompt rather than the preemptive treatment of PTLD.

Primitive adult hematopoietic stem cells can function as osteoblast precursors

Osteoblasts are continually recruited from stem cell pools to maintain bone. Although their immediate precursor is a plastic-adherent mesenchymal stem cell able to generate tissues other than bone, increasing evidence suggests the existence of a more primitive cell that can differentiate to both hematopoietic and mesenchymal cells. We show here that the "side population" (SP) of marrow stem cells, defined by their ability to rapidly expel a DNA-binding dye and to regenerate the hematopoietic compartment, can differentiate to osteoblasts through a mesenchymal intermediate. When transplanted into lethally irradiated mice, single gene-marked murine SP cells reconstituted depleted osteoprogenitor pools, such that a large proportion of the osteogenic cells in the epiphysis of long bone carried the donor SP cell marker. These findings suggest that the developmental capacity of SP cells is not restricted to the hematopoietic lineages but extends to osteogenic differentiation. This property not only elucidates a previously unrecognized step in osteoblast development, but also has intriguing implications for the use of SP cells in clinical orthopedics and stem cell-based disorders of bone.

Chimeric T-cell receptors for the targeting of cancer cells

Genetic engineering of human T lymphocytes to express tumor antigen-specific chimeric immune receptors is an attractive means for providing large numbers of effector cells for adoptive immunotherapy. Major mechanisms of tumor escape from immune recognition are efficiently bypassed. Although adoptive transfer of chimeric receptor-expressing peripheral blood-derived T lymphocytes has produced some anti-tumor activity in mice, the first clinical studies have revealed a disappointing lack of correlation between in vitro cytotoxicity and therapeutic efficacy. The most pertinent issue is that chimeric T cells fail to expand and rapidly lose their function in vivo. Potential strategies to enhance the therapeutic value of chimeric receptor-modified cells by preventing their functional inactivation in vivo are currently being investigated.

Overexpression of the Notch ligand, Jagged-1, induces alloantigen-specific human regulatory T cells

Graft-versus-host disease (GVHD) represents one of the major complications of allogeneic hematopoietic stem cell transplantation. Techniques to prevent GVHD have included ex vivo T-cell depletion of the graft or prolonged in vivo immunosuppression. Both reduce the frequency and severity of GVHD but also reduce T-cell-mediated graft-versus-malignancy effect, and increase the risk of infection. A major goal in transplantation is to prevent alloreactivity while preserving activity against tumors and infectious agents. We have used activation of the Notch pathway to try to generate T cells able to specifically regulate alloantigen responses. We used allogeneic Epstein-Barr virus lymphoblastoid B cells (EBV-LCLs) as stimulator cells. Such LCLs are excellent (allo) antigen-presenting cells and can be obtained in large numbers even from donors who have received extensive chemo/radiotherapy. We overexpressed a Notch ligand, Jagged-1, in these cells by adenoviral vector transduction. Stimulation of CD45RA+ naive T cells by Jagged-1 EBV-LCL reduces production of interferon-gamma, interleukin-2, and interleukin-5, but up-regulates transforming growth factor-beta 1 synthesis, consistent with induction of a regulatory T-cell phenotype. Transfer of these T cells to fresh lymphocyte cultures inhibits proliferative and cytotoxic immune responses to the priming alloantigens while sparing responses to third-party stimulator cells. Notch activation in the presence of alloantigen-presenting cells may therefore be a means of inducing specific regulatory T cells while preserving other T-cell functionality.

Induction of antigen-specific regulatory T cells following overexpression of a Notch ligand by human B lymphocytes

In mice, activation of the Notch pathway in T cells by antigen-presenting cells overexpressing Notch ligands favors differentiation of regulatory T lymphocytes responsible for antigen-specific tolerance. To determine whether this mechanism operates in human T cells, we used Epstein-Barr virus-positive lymphoblastoid cell lines (EBV-LCL) as our (viral) antigen-presenting cells and overexpressed the Notch ligand Jagged-1 (EBV-LCL J1) by adenoviral transduction. The EBV-LCL J1s were cocultured with autologous T cells, and the proliferative and cytotoxic responses to EBV antigens were measured. Transduction had no effect on EBV-LCL expression of major histocompatibility complex (MHC) antigens or of costimulatory molecules CD80, CD86, and CD40. However, we observed a 35% inhibition of proliferation and a >65% reduction in cytotoxic-T-cell activity, and interleukin 10 production was increased ninefold. These EBV-LCL J1-stimulated T lymphocytes act as antigen-specific regulatory cells, since their addition to fresh autologous T cells cultured with autologous nontransduced EBV-LCL cells significantly inhibited both proliferation and cytotoxic effector function. Within the inhibitory population, CD4(+)CD25(+) and CD8(+)CD25(-) T cells had the greatest activity. This inhibition appears to be antigen-specific, since responses to Candida and cytomegalovirus antigens were unaffected. Hence, transgenic expression of Jagged-1 by antigen-presenting cells can induce antigen-specific regulatory T cells in humans and modify immune responses to viral antigens.

Fiber-modified adenoviruses generate subgroup cross-reactive, adenovirus-specific cytotoxic T lymphocytes for therapeutic applications

Adenovirus (Ad) infections are responsible for considerable morbidity and mortality, particularly in pediatric hematopoietic stem cell transplant (HSCT) recipients. To date there is no therapy. The present study was motivated by the potential for using adoptive immunotherapy as either prophylaxis or treatment for Ad infections and associated diseases. The authors have developed a protocol to reactivate Ad-specific memory T cells from peripheral blood mononuclear cells (PBMCs) using a clinical-grade adenoviral vector. Such lines contain a specific CD4 and CD8 T-cell component and are capable of recognizing and lysing target cells infected with wild-type Ad serotypes from different Ad groups. Furthermore, the frequency of Ad-specific precursors can be determined in PBMCs ex vivo and used as a means to assess changes in Ad-specific T-cell memory responses after infusion. This is the first report of a simple and reproducible method to activate and expand Ad-specific cytotoxic T lymphocytes (CTLs), which should be protective against the range of different Ad subtypes that affect transplant recipients.

Selective depletion of donor alloreactive T cells without loss of antiviral or antileukemic responses

Poor immune reconstitution after haploidentical stem cell transplantation results in a high mortality from viral infections and relapse. One approach to overcome this problem is to selectively deplete the graft of alloreactive cells using an immunotoxin directed against the activation marker CD25. However, the degree of depletion of alloreactive cells is variable following stimulation with recipient peripheral blood mononuclear cells (PBMCs), and this can result in graft versus host disease (GVHD). We have refined this approach using recipient Epstein-Barr virus (EBV)-transformed lymphoblastoid cell lines (LCLs) as stimulators to activate donor alloreactive T cells. Our studies demonstrate that allodepletion with an anti-CD25 immunotoxin following stimulation with HLA-mismatched host LCLs more consistently depleted in vitro alloreactivity than stimulation with host PBMCs, as assessed in primary mixed lymphocyte reactions (MLRs). Allodepletion using this approach specifically abrogates cytotoxic T-cell responses against host LCLs. In interferon-gamma (IFN-gamma) enzyme-linked immunospot (ELISPOT) assays, antiviral responses to adenovirus and cytomegalovirus (CMV) were preserved following allodepletion. Likewise, using HLA-A2-pp65 tetramers, we have shown that the frequency of CMV-specific T cells is unaffected by allodepletion. Moreover, the donor anti-EBV response is partially retained by recognition of EBV antigens through the nonshared haplotype. Finally, we studied whether allodepletion affects the response to candidate tumor antigens in myeloid malignancies. Using HLA-A2-PR1 tetramer analysis, we found that the frequency of T cells recognizing the PR1 epitope of proteinase 3 was not significantly different in allodepleted and unmanipulated PBMCs from patients with chronic myeloid leukemia (CML) undergoing transplantation. Based on these data, we have embarked on a phase 1 clinical trial of addback of allo-LCL-depleted donor T cells in the haplo-identical setting.

Selection of chronic lymphocytic leukemia binding peptides

To provide cell-binding ligands for ex vivo gene therapy and chronic lymphocytic leukemia (CLL)-targeting ligands for in vivo drug and gene therapy, we selected 44 20-mer peptides from peptide-presenting phage libraries by panning against primary patient CLL cancer cells. Twenty-nine of the selected peptides were assayed for cell binding. Eight of the selected peptides bound CLL cells, B cells, T cells, and monocyte cells, 12 bound only CLL cells and B cells, and 1 peptide bound only B cells. However, eight of the selected peptides were CLL specific. When two of the peptides were tested out of the context of phage, the synthetic peptides were able to bind cells and functionally retarget adenovirus to increase ex vivo gene delivery to primary CLL cells. These data demonstrate the ability to identify lead cancer-targeting peptides by selection of phage libraries against primary human cancers cells.

Expression of a fusogenic membrane glycoprotein by an oncolytic herpes simplex virus potentiates the viral antitumor effect

Oncolytic viruses have shown considerable promise in the treatment of solid tumors, but their potency must be improved if their full clinical potential is to be realized. We inserted the gene encoding a truncated form of the gibbon ape leukemia virus envelope fusogenic membrane glycoprotein (GALV.fus) into an oncolytic herpes simplex virus, using an enforced ligation procedure. Subsequent in vitro and in vivo studies showed that expression of GALV.fus in the context of an oncolytic virus significantly enhances the antitumor effect of the virus. Furthermore, by controlling GALV.fus expression through a strict late viral promoter, whose activity depends on the initiation of viral DNA replication, we were able to express this glycoprotein in tumor cells but not in normal nondividing cells. It will be of interest to confirm whether functional expression of a strong fusogenic gene by an oncolytic herpes simplex virus enhances viral antitumor activity without increasing its toxicity.