Liposomes with incorporated MHC class II/peptide complexes as antigen presenting vesicles for specific T cell activation

Liposomes and polymersomes: a comparative review towards cell mimicking

Minimal cells: we compare and contrast liposomes and polymersomes for a bettera priorichoice and design of vesicles and try to understand the advantages and shortcomings associated with using one or the other in many different aspects (properties, synthesis, self-assembly, applications).

Killer artificial antigen-presenting cells: the synthetic embodiment of a 'guided missile'

At present, the treatment of T-cell-dependent autoimmune diseases relies exclusively on strategies leading to nonspecific suppression of the immune systems causing a substantial reduced ability to control concomitant infections or malignancies. Furthermore, long-term treatment with most drugs is accompanied by several serious adverse effects and does not consequently result in cure of the primary immunological malfunction. By contrast, antigen-specific immunotherapy offers the potential to achieve the highest therapeutic efficiency in accordance with minimal adverse effects. Therefore, several studies have been performed utilizing antigen-presenting cells specifically engineered to deplete allo- or antigen-specific T cells ('guided missiles'). Many of these strategies take advantage of the Fas/Fas ligand signaling pathway to efficiently induce antigen-presenting cell-mediated apoptosis in targeted T cells. In this article, we discuss the advantages and shortcomings of a novel non-cell-based 'killer artificial antigen-presenting cell' strategy, developed to overcome obstacles related to current cell-based approaches for the treatment of T-cell-mediated autoimmunity.

Adoptive transfer of pTRP2-specific CTLs expanding by bead-based artificial antigen-presenting cells mediates anti-melanoma response

Cytotoxic CD8(+) T cells are key effectors in the immunotherapy of malignant and viral diseases. However, the lack of efficient methods for their in vitro priming and expansion has become a bottleneck to the development of vaccines and adoptive transfer strategies. Synthetic artificial antigen-presenting cells (aAPCs) are now emerging as an attractive tool for eliciting and expanding CTL responses. This study reported a novel approach for targeting malignant melanoma with pTRP2-specific cytotoxic T lymphocytes (CTLs) expanded from the C57BL/6 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 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 CTLs specific for malignant melanoma expanding by the aAPCs can mediate effective anti-melanoma response. These results suggested the bead-based aAPCs coated with an MHC-Ig/peptide complex, anti-CD28 antibody, 4-1BBL and CD83 could provide a useful tool for the reproducible expansion of specific CTLs for adoptive immunotherapy.

Synthetic CD4+ T cell-targeted antigen-presenting cells elicit protective antitumor responses

CD4(+) helper T cells are critical for protective immune responses and yet suboptimally primed in response to tumors. Cell-based vaccination strategies are under evaluation in clinical trials but limited by the need to derive antigen-presenting cells (APC) from patients or compatible healthy donors. To overcome these limitations, we developed CD4(+) T cell-targeted synthetic microbead-based artificial APC (aAPC) and used them to activate CD4(+) T lymphocytes specific for a tumor-associated model antigen (Ag) directly from the naive repertoire. In vitro, aAPC specifically primed Ag-specific CD4(+) T cells that were activated to express high levels of CD44, produced mainly interleukin 2, and could differentiate into Th1-like or Th2-like cells in combination with polarizing cytokines. I.v. administration of aAPC led to Ag-specific CD4(+) T-cell activation and proliferation in secondary lymphoid organs, conferred partial protection against subcutaneous tumors, and prevented the establishment of lung metastasis. Taken together, our data support the use of cell-free, synthetic aAPC as a specific and versatile alternative to expand peptide-specific CD4(+) T cells in adoptive and active immunotherapy.

A comprehensive platform for ex vivo T-cell expansion based on biodegradable polymeric artificial antigen-presenting cells

Efficient T-cell stimulation and proliferation in response to specific antigens is a goal of immunotherapy against infectious disease and cancer. Manipulation of this response can be accomplished by adoptive immunotherapy involving the infusion of antigen-specific T-cell populations expanded ex vivo with antigen presenting cells. We mimicked physiological antigen presentation on a biodegradable microparticle constructed from poly(lactide-co-glycolide) (PLGA), a polymer system whose safety has been established for use in humans. These particles present a high density of adaptor elements for attaching both recognition ligands and co-stimulatory ligands to a biodegradable core encapsulating the cytokine interleukin-2 (IL-2). We demonstrate the utility of this system in efficient polyclonal and antigen-specific T-cell stimulation and expansion, showing that sustained release of IL-2 in the vicinity of T-cell contacts dramatically improves the stimulatory capacity of these acellular systems, as compared to the effect of exogenous addition of cytokine. This results in a 45-fold enhancement in T-cell expansion. In addition, this mode of antigen presentation skews the expansion toward the CD8(+) T-cell phenotype. This comprehensive acellular platform, capable of delivering recognition, co-stimulatory, and cytokine signals, represents a promising new technology for artificial antigen presentation.

HLA Tetramer Based Artificial Antigen-Presenting Cells Efficiently Stimulate CTLs Specific for Malignant Glioma

PURPOSE

The interleukin-13 receptor alpha 2 (IL-13R alpha 2) is a glioma-restricted cell-surface epitope not otherwise detected within the central nervous system. Here, we report a novel approach for targeting malignant glioma with IL-13R alpha 2-specific CTLs.

EXPERIMENTAL DESIGN

Artificial antigen-presenting cells (aAPC) were made by coating human leukocyte antigen (HLA)-A2/pIL-13R alpha 2(345-354) tetrameric complexes, anti-CD28 antibody, and CD83 molecules to cell-sized latex beads, and used to stimulate IL-13R alpha 2-specific CTLs from the peripheral blood mononuclear cells of HLA-A2+ healthy donors. After multiple stimulations, the induced CTLs were analyzed for tetramer staining, IFN-gamma production, and CTL reactivity.

RESULTS

Tetramer staining assay showed that the induced CTLs specifically bound HLA-A2/pIL-13R alpha 2(345-354) tetramers. The CTLs specifically produced IFN-gamma in response to the HLA-A2/pIL-13R alpha 2(345-354)-aAPCs and exhibited specific lysis against T2 cells pulsed with the peptide pIL-13R alpha 2(345-354) and HLA-A2+ glioma cells expressing IL-13R alpha 2(345-354), whereas HLA-A2(-) glioma cell lines that express IL-13R alpha 2(345-354) could not be recognized by the CTLs. The peptide-specific activity was inhibited by anti-HLA class I monoclonal antibody.

CONCLUSION

The induced CTLs specific for IL-13R alpha 2(345-354) peptide could be a potential target of specific immunotherapy for HLA-A2+ patients with malignant glioma.

Induction of cytotoxic T-lymphocytes specific for malignant glioma by HLA dimer-based artificial antigen-presenting cells

AIM

The aim of this study was to investigate the novel approach for targeting malignant glioma.

METHODS

Interleukin-13 receptor alpha2 (IL-13Ralpha2)-specific cytotoxic T-cells (CTLs) were induced from the peripheral blood lymphocytes (PBLs) of human leukocyte antigen (HLA)-A2 positive healthy donors by multiple stimulations with artificial antigen-presenting cells (aAPCs) made by coating HLA-A2-Ig/pIL-13Ralpha2(345-354) dimeric complexes, anti-CD28 antibody, and CD83 molecules to cell-sized latex beads.

RESULTS

The induced CTLs exhibited a specific lysis against T2 cells pulsed with the peptide pIL-13Ralpha2(345-354) and HLA-A2(+) glioma cells expressing IL-13Ralpha2(345-354), while HLA-A2(-) glioma cell lines that express IL-13Ralpha2(345-354) could not be recognized by the CTLs. The peptide-specific activity was inhibited by the anti-HLA class I monoclonal antibody.

CONCLUSIONS

The induced CTLs specific for the IL-13Ralpha2(345-354) peptide could be a potential target of specific immunotherapy for HLA-A2(+) patients with malignant glioma.

Induction of the Epstein-Barr virus latent membrane protein 2 antigen-specific cytotoxic T lymphocytes using human leukocyte antigen tetramer-based artificial antigen-presenting cells

Cytotoxic T lymphocytes (CTLs) specific for the Epstein-Barr virus (EBV) latent membrane protein 2 (LMP2) antigen are important reagents for the treatment of some EBV-associated malignancies, such as EBV-positive Hodgkin's disease and nasopharyngeal carcinoma. However, the therapeutic amount of CTLs is often hampered by the limited supply of antigen-presenting cells. To address this issue, an artificial antigen-presenting cell (aAPC) was made by coating a human leukocyte antigen (HLA)-pLMP2 tetrameric complex, anti-CD28 antibody and CD54 molecule to a cell-sized latex bead, which provided the dual signals required for T cell activation. By co-culture of the HLA-A2-LMP2 bearing aAPC and peripheral blood mononuclear cells from HLA-A2 positive healthy donors, LMP2 antigen-specific CTLs were induced and expanded in vitro. The specificity of the aAPC-induced CTLs was demonstrated by both HLA-A2-LMP2 tetramer staining and cytotoxicity against HLA-A2-LMP2 bearing T2 cell, the cytotoxicity was inhibited by the anti-HLA class I antibody (W6/32). These results showed that LMP2 antigen-specific CTLs could be induced and expanded in vitro by the HLA-A2-LMP2-bearing aAPC. Thus, aAPCs coated with an HLA-pLMP2 complex, anti-CD28 and CD54 might be promising tools for the enrichment of LMP2-specific CTLs for adoptive immunotherapy.

Artificial antigen-presenting constructs efficiently stimulate minor histocompatibility antigen–specific cytotoxic T lymphocytes

Cytotoxic T lymphocytes (CTLs) specific for hematopoietic-restricted minor histocompatibility antigens (mHags) are important reagents for adoptive immunotherapy of relapsed leukemia after allogeneic stem cell transplantation. However, expansion of these CTLs to therapeutic numbers is often hampered by the limited supply of antigen-presenting cells (APCs). Therefore, we evaluated whether cell-sized latex beads coated with HLA/mHag complexes HLA-A2/HA-1 or HLA-A2/HA-2 and recombinant CD80 and CD54 molecules can replace professional APCs. The artificial antigen-presenting constructs (aAPCs) effectively stimulated HA-1– and HA-2–specific CTL clones as shown by ligand-specific expansion, cytokine production, and maintenance of cytotoxic activity, without alteration of CTL phenotype. Furthermore, HA-1–specific polyclonal CTL lines were enriched as efficiently by aAPCs as by autologous HA-1 peptide-pulsed dendritic cells. Thus, aAPCs coated with HLA/mHag complexes, CD80, and CD54 may serve as tools for in vitro enrichment of immunotherapeutic mHag-specific CTL lines.

Artificial antigen-presenting cells as a tool to exploit the immune 'synapse'

Recent progress in molecular medicine has provided important tools to identify antigen-specific T cells. In most cases, the approach is based on oligomeric combinations of recombinant major histocompatibility complex-peptide complexes fixed to various rigid supports available for binding by the T-cell receptor. These tools have greatly increased our insight into mechanisms of immune responses mediated by CD8+ T cells. Examples of the diverse fields of application for this technology include immunization, viral infections and oral tolerance induction.

Endogenous carriers and ligands in non-immunogenic site-specific drug delivery

Targeted drug delivery has gained recognition in modern therapeutics and attempts are being made to explore the potentials and possibilities of cell biology related bioevents in the development of specific, programmed and target oriented systems. The components which have been recognized to be tools include receptors and ligands, where the receptors act as molecular targets or portals, and ligands, with receptor specificity and selectivity, are trafficked en route to the target site. Although ligands of exogenous or synthetic origin contribute to the selectivity component of carrier constructs, they may impose immunological manifestations of different magnitudes. The latter may entail a continual quest for bio-compatible, non-immunogenic and target orientated delivery. Endogenous serum, cellular and extracellular bio-ligands interact with the colloidal carrier constructs and influence their bio-fate. However, these endogenous bio-ligands can themselves serve as targeting modules either in their native form or engineered as carrier cargo. Bio-regulatory, nutrient and immune ligands are sensitive, specific and effective site directing handles which add to targeted drug delivery. The present review provides an exhaustive account of the identified bio-ligands, which are not only non-immunogenic in nature but also site-specific. The cell-related bioevents which are instrumental in negotiating the uptake of bio-ligands are discussed. Further, a brief account of ligand-receptor interactions and the set of biological events which ensures ligand-driven trafficking of the ligand-receptor complex to the cellular interior is also presented. Since ligand-receptor interaction is a critical pre-requisite for negotiating cellular uptake of endogenous ligands and anchored carrier cargo, an attempt has been made to identify differential expression of receptors and bio-ligands under normal and etiological conditions. Studies which judiciously utilized bio-ligands or their analogs in negotiating site-specific drug delivery have been reviewed and presented. Targeted delivery of bioactives using endogenous bio-ligands offers enormous options and opportunities through carrier construct engineering and could become a future reality in clinical practice.

Induction of T cell anergy by liposomes with incorporated major histocompatibility complex (MHC) II/peptide complexes

PURPOSE

The aim of this study was to use small unilamellar liposomes with incorporated MHC II/peptide complexes as a carrier system for multivalent antigen presentation to CD4 + T cells.

METHODS

Purified peptide pre-loaded MHC II molecules were incorporated into small unilamellar liposomes and tested for their ability to activate A2b T cells. The outcome of T cell activation by such liposomes in the absence of accessory cells was tested via flow cytometry and a T cell anergy assay.

RESULTS

Provided the presence of external co-stimulation, MHC II/ peptide liposomes were able to induce proliferation of the A2b T cell clone. More importantly incubation of these T cells with MHC II/ peptide liposomes in the absence of co-stimulation did not induce proliferation, however, a MHC/peptide ligand-density dependent down-regulation of the TCR was observed. Interestingly, when T cells after incubation with the MHC II/peptide liposomes were restimulated with their specific antigen in the presence of professional APC, these cells were anergic.

CONCLUSIONS

We propose MHC II/peptide liposomes as a novel means to induce T cell anergy. The possibility to prepare 'tailor-made' liposomal formulations may provide liposomes with an important advantage for applications in immunotherapy.

Liposomes in autoimmune diseases: selected applications in immunotherapy and inflammation detection

In this contribution three examples are discussed of ongoing research where liposomes are used as carrier systems for immunotherapy and inflammation detection in autoimmune diseases. Liposomes can be used as carrier systems of antigenic peptides to peripheral blood mononuclear cells. The second example deals with their use as carrier systems for MHC-peptide complexes for multivalent Ag-presentation to autoreactive T lymphocytes to specifically modulate the activity of these T lymphocytes. The third example relates to our work on long circulating liposomes which are currently being tested in man for their potential to image inflammation sites.