Esma S. Yolcu

Ex Vivo Expansion of CD4+CD25+FoxP3+ T Regulatory Cells Based on Synergy between IL-2 and 4-1BB Signaling

Naturally occurring CD4+CD25+FoxP3+ T regulatory (Treg) cells require three distinct signals transduced via TCR, CD28, and IL-2R for their development and maintenance. These requirements served as the basis for several recently developed ex vivo expansion protocols that relied on the use of solid support-bound Abs to CD3 and CD28 in the presence of high dose IL-2. We report in this study that Treg cells up-regulate the expression of inducible costimulatory receptor 4-1BB in response to IL-2, and stimulation using this receptor via a novel form of 4-1BB ligand (4-1BBL) fused to a modified form of core streptavidin (SA-4-1BBL) was effective in expanding these cells up to 110-fold within 3 wk. Expanded cells up-regulated CD25, 4-1BB, and membranous TGF-β, suppressed T cell proliferation, and prevented the rejection of allogeneic islets upon adoptive transfer into graft recipients. Importantly, SA-4-1BBL rendered CD4+CD25− T effector cells refractive to suppression by Treg cells. This dual function of signaling via 4-1BB, vis-à-vis Treg cell expansion and licensing T effector cells resistant to Treg cell suppression, as well as the up-regulation of 4-1BB by IL-2 may serve as important regulatory mechanisms for immune homeostasis following antigenic challenge. Stimulation using a soluble form of SA-4-1BBL represents a novel approach to expand Treg cells with potential therapeutic applications in autoimmunity and transplantation.

CD4+CD25+ T Regulatory Cells Dominate Multiple Immune Evasion Mechanisms in Early but Not Late Phases of Tumor Development in a B Cell Lymphoma Model

Tumors use a complex set of direct and indirect mechanisms to evade the immune system. Naturally arising CD4+CD25+FoxP3+ T regulatory (Treg) cells have been implicated recently in tumor immune escape mechanism, but the relative contribution of these cells to overall tumor progression compared with other immune evasion mechanisms remains to be elucidated. Using the A20 B cell lymphoma as a transplantable tumor model, we demonstrate that this tumor employs multiple direct (expression of immunoinhibitory molecule PD-L1, IDO, and IL-10, and lack of expression of CD80 costimulatory molecule) and indirect (down-regulation of APC function and induction of Treg cells) immune evasion mechanisms. Importantly, Treg cells served as the dominant immune escape mechanism early in tumor progression because the physical elimination of these cells before tumor challenge resulted in tumor-free survival in 70% of mice, whereas their depletion in animals with established tumors had no therapeutic effect. Therefore, our data suggest that Treg cells may serve as an important therapeutic target for patients with early stages of cancer and that more vigorous combinatorial approaches simultaneously targeting multiple immune evasion as well as immunosurveillance mechanisms for the generation of a productive immune response against tumor may be required for effective immunotherapy in patients with advanced disease.

Costimulation as a Platform for the Development of Vaccines: A Peptide-Based Vaccine Containing a Novel Form of 4-1BB Ligand Eradicates Established Tumors

Vaccines represent an attractive treatment modality for the management of cancer primarily because of their specificity and generation of immunologic memory important for controlling recurrences. However, the efficacy of therapeutic vaccines may require formulations that not only generate effective immune responses but also overcome immune evasion mechanisms employed by progressing tumor. Costimulatory molecules play critical roles in modulating innate, adaptive, and regulatory immunity and have potential to serve as effective immunomodulatory components of therapeutic vaccines. In this study, we tested the function of a novel soluble form of 4-1BB ligand (4-1BBL) costimulatory molecule in modulating innate, adaptive, and regulatory immunity and assessed its therapeutic efficacy in the HPV-16 E7-expressing TC-1 cervical cancer and survivin-expressing 3LL lung carcinoma mouse models. Vaccination with 4-1BBL activated dendritic cells and enhanced antigen uptake, generated CD8(+) T-cell effector/memory responses, and endowed T effector cells refractory to suppression by CD4(+)CD25(+)FoxP3(+) T regulatory cells. Immunization with 4-1BBL in combination with an E7 peptide or survivin protein resulted in eradication of TC-1 and 3LL tumors, respectively. 4-1BBL was more effective than TLR agonists LPS, MPL, and CpG and an agonistic 4-1BB antibody as a component of E7 peptide-based therapeutic vaccine for the generation of immune responses and eradication of TC-1 established tumors in the absence of detectable toxicity. Therapeutic efficacy was associated with reversal of tumor-mediated nonresponsiveness/anergy as well as establishment of long-term CD8(+) T-cell memory. Potent pleiotropic immunomodulatory activities combined with lack of toxicity highlight the potential of 4-1BBL molecule as an effective component of therapeutic cancer vaccines.

Immune reconstitution/immunocompetence in recipients of kidney plus hematopoietic stem/facilitating cell transplants.

Nineteen subjects have more than 18 months’ follow-up in a phase IIb tolerance protocol in HLA–mismatched recipients of living donor kidney plus facilitating cell enriched hematopoietic stem cell allografts (FCRx). Reduced intensity conditioning preceded a kidney allograft, followed the next day by FCRx. Twelve have achieved stable donor chimerism and have been successfully taken off immunosuppression (IS). We prospectively evaluated immune reconstitution and immunocompetence. Return of CD4+ and CD8+ T central and effector memory cell populations was rapid. T-cell receptor (TCR) Excision Circle analysis showed a significant proportion of chimeric cells produced were being produced de novo. The TCR repertoires posttransplant in chimeric subjects were nearly as diverse as pretransplant donors and recipients, and were comparable to subjects with transient chimerism who underwent autologous reconstitution. Subjects with persistent chimerism developed few serious infections when off IS. The majority of infectious complications occurred while subjects were still on conventional IS. BK viruria and viremia resolved after cessation of IS and no tissue-invasive cytomegalovirus infections occurred. Notably, although 2 of 4 transiently or nonchimeric subjects experienced recurrence of their underlying autoimmune disorders, none of the chimeric subjects have, suggesting that self-tolerance is induced in addition to tolerance to alloantigen. No persistently chimeric subject has developed donor-specific antibody, and renal function has remained within normal limits. Patients were successfully vaccinated per The American Society for Blood and Marrow Transplantation guidelines without loss of chimerism or rejection. Memory for hepatitis vaccination persisted after transplantation. Chimeric subjects generated immune responses to pneumococcal vaccine. These data suggest that immune reconstitution and immunocompetence are maintained in persistently chimeric subjects.

Fragmented Sleep Accelerates Tumor Growth and Progression through Recruitment of Tumor-Associated Macrophages and TLR4 Signaling

Sleep fragmentation (SF) is a highly prevalent condition and a hallmark of sleep apnea, a condition that has been associated with increased cancer incidence and mortality. In this study, we examined the hypothesis that sleep fragmentation promotes tumor growth and progression through proinflammatory TLR4 signaling. In the design, we compared mice that were exposed to sleep fragmentation one week before engraftment of syngeneic TC1 or LL3 tumor cells and tumor analysis four weeks later. We also compared host contributions through the use of mice genetically deficient in TLR4 or its effector molecules MYD88 or TRIF. We found that sleep fragmentation enhanced tumor size and weight compared with control mice. Increased invasiveness was apparent in sleep fragmentation tumors, which penetrated the tumor capsule into surrounding tissues, including adjacent muscle. Tumor-associated macrophages (TAM) were more numerous in sleep fragmentation tumors, where they were distributed in a relatively closer proximity to the tumor capsule compared with control mice. Although tumors were generally smaller in both MYD88(-/-) and TRIF(-/-) hosts, the more aggressive features produced by sleep fragmentation persisted. In contrast, these more aggressive features produced by sleep fragmentation were abolished completely in TLR4(-/-) mice. Our findings offer mechanistic insights into how sleep perturbations can accelerate tumor growth and invasiveness through TAM recruitment and TLR4 signaling pathways.

Apoptosis as a mechanism of T-regulatory cell homeostasis and suppression

Activation‐induced cell death is a general mechanism of immune homeostasis through negative regulation of clonal expansion of activated immune cells. This mechanism is involved in the maintenance of self‐ and transplant tolerance through polarization of the immune responses. The Fas/Fas‐ligand interaction is a major common executioner of apoptosis in lymphocytes, with a dual role in regulatory T cell (Treg) function: Treg cell homeostasis and Treg cell‐mediated suppression. Sensitivity to apoptosis and the patterns of Treg‐cell death are of outmost importance in immune homeostasis that affects the equilibrium between cytolytic and suppressor forces in activation and termination of immune activity. Naive innate (naturally occurring) Treg cells present variable sensitivities to apoptosis, related to their turnover rates in tissue under steady state conditions. Following activation, Treg cells are less sensitive to apoptosis than cytotoxic effector subsets. Their susceptibility to apoptosis is influenced by cytokines within the inflammatory environment (primarily interleukin‐2), the mode of antigenic stimulation and the proliferation rates. Here, we attempt to resolve some controversies surrounding the sensitivity of Treg cells to apoptosis under various experimental conditions, to delineate the function of cell death in regulation of immunity.

Pancreatic islets under attack : Cellular and molecular effectors

Abundant information is available on the involvement of various cellular and molecular mechanisms in beta cell apoptosis. The experimental evidence is controversial and difficult to reconcile, and the mechanisms of evasion of the autoreactive clones from immune surveillance are poorly understood. Multiple apoptotic pathways play a role in destructive insulitis, including perforin/granzyme, Fas/Fas-ligand (FasL), and other members of the necrosis factor superfamily. These pathways present redundant behaviors in both the initial and late stages of beta cell injury, and at the same time, each molecular mechanism is dispensable in the evolution of autoimmune diabetes. There may be a preferential use of perforin/granzyme in CD8(+) T cell-mediated lysis, which participates in onset of autoimmunity, and a predominance of FasL in CD4(+) T cell-mediated insulitis. Several cytokines released in the inflammatory infiltrate induce Fas expression in beta cells, priming them to FasL-mediated apoptosis. In this review, we focus on the possible participation of multiple cell subsets and molecular mechanisms in the pathogenesis of diabetes to the point where inflammation incites an irreversible vicious cycle that perpetuates beta cell death.

Stem cells as tools in regenerative therapy for retinal degeneration

OBJECTIVE To describe the use of stem cells (SCs) for regeneration of retinal degenerations. Regenerative medicine intends to provide therapies for severe injuries or chronic diseases where endogenous repair does not sufficiently restore the tissue. Pluripotent SCs, with their capacity to give rise to specialized cells, are the most promising candidates for clinical application. Despite encouraging results, a combination with up-to-date tissue engineering might be critical for ultimate success. DESIGN The focus is on the use of SCs for regeneration of retinal degenerations. Cell populations include embryonic, neural, and bone marrow-derived SCs, and engineered grafts will also be described. RESULTS Experimental approaches have successfully replaced damaged photoreceptors and retinal pigment epithelium using endogenous and exogenous SCs. CONCLUSIONS Stem cells have the potential to significantly impact retinal regeneration. A combination with bioengineering may bear even greater promise. However, ethical and scientific issues have yet to be solved.

4-1BB ligand as an effective multifunctional immunomodulator and antigen delivery vehicle for the development of therapeutic cancer vaccines

Therapeutic subunit vaccines based on tumor-associated antigens (TAA) represent an attractive approach for the treatment of cancer. However, poor immunogenicity of TAAs requires potent adjuvants for therapeutic efficacy. We recently proposed the tumor necrosis factor family costimulatory ligands as potential adjuvants for therapeutic vaccines and, hence, generated a soluble form of 4-1BBL chimeric with streptavidin (SA-4-1BBL) that has pleiotropic effects on cells of innate, adaptive, and regulatory immunity. We herein tested whether these effects can translate into effective cancer immunotherapy when SA-4-1BBL was also used as a vehicle to deliver TAAs in vivo to dendritic cells (DCs) constitutively expressing the 4-1BB receptor. SA-4-1BBL was internalized by DCs upon receptor binding and immunization with biotinylated antigens conjugated to SA-4-1BBL resulted in increased antigen uptake and cross-presentation by DCs, leading to the generation of effective T-cell immune responses. Conjugate vaccines containing human papillomavirus 16 E7 oncoprotein or survivin as a self-TAA had potent therapeutic efficacy against TC-1 cervical and 3LL lung carcinoma tumors, respectively. Therapeutic efficacy of the vaccines was associated with increased CD4(+) T and CD8(+) T-cell effector and memory responses and higher intratumoral CD8(+) T effector/CD4(+)CD25(+)Foxp3(+) T regulatory cell ratio. Thus, potent pleiotropic immune functions of SA-4-1BBL combined with its ability to serve as a vehicle to increase the delivery of antigens to DCs in vivo endow this molecule with the potential to serve as an effective immunomodulatory component of therapeutic vaccines against cancer and chronic infections.

Display of Fas Ligand Protein on Cardiac Vasculature as a Novel Means of Regulating Allograft Rejection

Background—Fas ligand (FasL) is a potent death-inducing molecule with important functions in immune homeostasis and tolerance to self-antigens. The complex biological activities of FasL and its inefficient expression using conventional gene transfer approaches limit its use for immunomodulation to prevent allograft rejection. We have recently generated a chimeric FasL with core streptavidin (SA-FasL) with potent apoptotic activity and designed a novel approach to display it on the surface of several cell types via biotinylation. We herein tested whether SA-FasL can also be displayed on vascular endothelial cells in the heart and examined its effect on graft survival after transplantation into syngeneic and allogeneic hosts. Methods and Results—SA-FasL was efficiently displayed on the vasculature of BALB/c hearts with a half-life of 9 days in vivo. Transplantation of hearts displaying SA-FasL into syngeneic hosts resulted in indefinite graft survival without detectable toxicity to the grafts and hosts. In contrast, transplantation of allogeneic C57BL/10 hearts displaying SA-FasL into BALB/c recipients resulted in graft rejection, but in a delayed fashion as compared with control hearts (mean survival time=17.4±5 versus 9.6±1 days). Allograft survival was further extended to 21±2.6 and 24±3 days (P <0.05) by intravenous treatment of graft recipients with 1 dose of SA-FasL–decorated donor splenocytes on days 2 and 6 after transplantation, respectively. Conclusions—This study shows for the first time that exogenous proteins can be displayed on the endothelium of solid organs for therapeutic purposes. This approach provides a convenient and rapid means of displaying exogenous proteins on the surface of cells, tissues, and solid organs, with broad research and therapeutic implications.