Limited Infiltration of Exogenous Dendritic Cells and Naive T Cells Restricts Immune Responses in Peripheral Lymph Nodes

Generation of antigen-specific Foxp3+ regulatory T-cells in vivo following administration of diabetes-reversing tolerogenic microspheres does not require provision of antigen in the formulation

We have developed novel antisense oligonucleotide-formulated microspheres that can reverse hyperglycemia in newly-onset diabetic mice. Dendritic cells taking up the microspheres adopt a restrained co-stimulation ability and migrate to the pancreatic lymph nodes when injected into an abdominal region that is drained by those lymph nodes. Furthermore, we demonstrate that the absolute numbers of antigen-specific Foxp3+ T regulatory cells are increased only in the lymph nodes draining the site of administration and that these T-cells proliferate independently of antigen supply in the microspheres. Taken together, our data add to the emerging model where antigen supply may not be a requirement in "vaccines" for autoimmune disease, but the site of administration - subserved by lymph nodes draining the target organ - is in fact critical to foster the generation of antigen-specific regulatory cells. The implications of these observations on "vaccine" design for autoimmunity are discussed and summarized.

Efficiency of dendritic cell vaccination against B16 melanoma depends on the immunization route

Dendritic cells (DC) presenting tumor antigens are crucial to induce potent T cell-mediated anti-tumor immune responses. Therefore DC-based cancer vaccines have been established for therapy, however clinical outcomes are often poor and need improvement. Using a mouse model of B16 melanoma, we found that the route of preventive DC vaccination critically determined tumor control. While repeated DC vaccination did not show an impact of the route of DC application on the prevention of tumor growth, a single DC vaccination revealed that both the imprinting of skin homing receptors and an enhanced proliferation state of effector T cells was seen only upon intracutaneous but not intravenous or intraperitoneal immunization. Tumor growth was prevented only by intracutaneous DC vaccination. Our results indicate that under suboptimal conditions the route of DC vaccination crucially determines the efficiency of tumor defense. DC-based strategies for immunotherapy of cancer should take into account the immunization route in order to optimize tissue targeting of tumor antigen specific T cells.

Peripheral tissue homing receptors enable T cell entry into lymph nodes and affect the anatomical distribution of memory cells

Peripheral tissue homing receptors enable T cells to access inflamed nonlymphoid tissues. In this study, we show that two such molecules, E-selectin ligand and α4β1 integrin, enable activated and memory T cells to enter lymph nodes (LN) as well. This affects the quantitative and qualitative distribution of these cells among regional LN beds. CD8 memory T cells in LN that express these molecules were mostly CD62L(lo) and would normally be classified as effector memory cells. However, similar to central memory cells, they expanded upon Ag re-encounter. This led to differences in the magnitude of the recall response that depended on the route of immunization. These novel cells share properties of both central and effector memory cells and reside in LN based on previously undescribed mechanisms of entry.

Myeloma-specific multiple peptides able to generate cytotoxic T lymphocytes: a potential therapeutic application in multiple myeloma and other plasma cell disorders

PURPOSE

The efficacy of peptide vaccines may be enhanced by stimulating immune cells with multiple peptides derived from distinct tumor-associated antigens. We have evaluated the heteroclitic XBP1-US(184-192) (YISPWILAV), heteroclitic XBP1-SP(367-375) (YLFPQLISV), native CD138(260-268) (GLVGLIFAV), and native CS1(239-247) (SLFVLGLFL) peptides, which have strong HLA-A2 affinity and immunogenicity in combination, for their ability to elicit multiple myeloma antigen-specific responses.

EXPERIMENTAL DESIGN

Multipeptide-specific cytotoxic T lymphocytes (MP-CTL) were generated by the stimulation of CD3(+) T lymphocytes from HLA-A2(+) individuals with either autologous mature dendritic cells or T2 cells pulsed with a cocktail of these four peptides.

RESULTS

The peptide cocktail did not compromise tumor antigen-specific activity of CTLs. MP-CTLs displayed increased total, effector memory (CCR7(-)CD45RO(+)), and activated (CD69(+)) CD3(+)CD8(+) T lymphocytes. In addition, MP-CTL showed IFN-γ production, cell proliferation, and cytotoxicity against HLA-A2(+) multiple myeloma cells, including cells of HLA-A2(+) patients with multiple myeloma. Importantly, MP-CTLs showed specific responses in functional assays to each relevant peptide but not to an irrelevant HLA-A2-specific CMV pp65 (NLVPMVATV) peptide.

CONCLUSIONS

These results highlight the potential therapeutic application of vaccination with a cocktail of HLA-A2-specific peptides to induce CTLs with a broad spectrum of immune responses against multiple myeloma antigens.

The present and future of peptide vaccines for cancer: single or multiple, long or short, alone or in combination?

Peptide vaccines incorporate one or more short or long amino acid sequences as tumor antigens, combined with a vaccine adjuvant. Thus, they fall broadly into the category of defined antigen vaccines, along with vaccines using protein, protein subunits, DNA, or RNA. They remain one of the most immunogenic approaches, based on measures of T-cell response in the blood or in draining lymph nodes. However, existing peptide vaccines have had limited success at inducing clinical tumor regressions, despite reliable induction of T-cell responses. Several new developments offer promise for improving peptide vaccines, including use of long peptides, optimization of adjuvants including toll-like receptor agonists, and combination with systemic therapies that may reduce tumor-associated immune dysfunction, such as blockade of PD-1/PD-L1 interactions. To apply these new approaches optimally, it will be critical to study their effects in the context of defined antigens, for which peptide vaccines are optimal.

Chemokines: can effector cells be redirected to the site of the tumor?

Chemokines (ie, chemoattractant cytokines) are a family of small secreted molecules that mediate leukocyte migration. It is becoming increasingly more evident that chemokines play an integral role in the initiation of a specific immune response. With respect to cancer, chemokines are being studied for both their role in tumor biology and as promising immunotherapy candidates. We review several areas of chemokine importance in tumor immunity and discuss the experimental evidence that is leading to the clinical use of this cytokine family in new treatment approaches for patients with cancer.

Conditioning of the injection site with CpG enhances the migration of adoptively transferred dendritic cells and endogenous CD8+ T-cell responses

The efficiency of immunotherapy using tumor-antigen-loaded dendritic cells (DCs) is severely limited by the impaired migration of injected cells from the application site to the draining lymph nodes. As described earlier, pretreatment of the injection site with inflammatory cytokines enhances DC migration. We wanted to test whether toll-like receptor (TLR) ligands can improve migration of murine bone marrow-derived DC (BMDC) and the subsequent T-cell responses. For this purpose, we established an experimental setup closely resembling human vaccination protocols that served to investigate DC migration from the skin to the draining lymph nodes. We observed that BMDC, matured with a cytokine cocktail (tumor necrosis factor-alpha, interleukin-beta, interleukin-6, prostaglandin E2), strongly expressed CCR7. The migration efficiency of adoptively transferred mature BMDCs was determined by the number of cells injected and the application site. We decided to inject DC intradermally into the ear skin and investigated the effects of pretreatment of the injection site with various TLR ligands. Conditioning of the skin site with the TLR ligands CpG and Peptidoglycan increased the number of DCs arriving in the lymph node. Mechanical stress applied to the skin, such as tape stripping of the skin was equally effective. Importantly, only pretreatment with CpG enhanced responses of endogenous CD8 T cells. Thus, conditioning of the injection site with the TLR ligand CpG could be a new promising way to improve the outcome of DC immunotherapy.

CD8 T cells activated in distinct lymphoid organs differentially express adhesion proteins and coexpress multiple chemokine receptors

Previous work from this laboratory showed that generation of memory CD8 T cells by different immunization routes correlates with control of tumors growing in distinct sites. We hypothesized that effector CD8 T cell expression of adhesion proteins and chemokine receptors would be influenced by activation in different secondary lymphoid organs. In this report, CD8 T cells were activated by immunization with bone marrow-derived dendritic cells via i.p., i.v., or s.c. routes. Three distinct populations of activated CD8 T cells arise in mesenteric, axillary/brachial, and mediastinal lymph nodes and spleen based on differential expression of alpha4beta7 integrin, E-selectin ligand, and alpha4beta1 integrin, respectively. In contrast, three subsets of CD8 T cells defined by differential expression of P-selectin ligand and chemokine receptors were induced irrespective of activation site. The majority of activated CD8 T cells expressed CXCR3, with one subset additionally expressing P-selectin ligand, and another subset additionally expressing CCR3, CCR4, CCR5, CCR6, and CCR9. In the mesenteric lymph node, a fourth subset expressed CCR9 and CXCR3 in the absence of CCR5. Similar homing receptor profiles were induced in the same sites after localized vaccinia immunization. Homing receptor expression on CD8 T cells activated in vitro was distinct, revealing influences of both dendritic cells and the lymphoid microenvironment. Collectively, these results identify previously undescribed populations of activated CD8 T cells based on adhesion protein expression and coexpression of chemokine receptors that arise after activation in distinct secondary lymphoid organs.

Strategies and challenges in eliciting immunity to melanoma

The ability of CD8+ T cells to recognize melanoma tumors has led to the development of immunotherapeutic approaches that use the antigens CD8+ T cells recognize. However, clinical response rates have been disappointing. Here we summarize our work to understand the mechanisms of self-tolerance that limit responses to currently utilized antigens and our approach to identify new antigens directly tied to malignancy. We also explore several aspects of the anti-tumor immune response induced by peptide-pulsed dendritic cells (DCs). DCs differentially augment the avidity of recall T cells specific for self-antigens and overcome a process of aberrant CD8+ T-cell differentiation that occurs in tumor-draining lymph nodes. DC migration is constrained by injection route, resulting in immune responses in localized lymphoid tissue, and differential control of tumors depending on their location in the body. We demonstrate that CD8+ T-cell differentiation in different lymphoid compartments alters the expression of homing receptor molecules and leads to the presence of systemic central memory cells. Our studies highlight several issues that must be addressed to improve the efficacy of tumor immunotherapy.

Activated CD8 T cells redistribute to antigen-free lymph nodes and exhibit effector and memory characteristics

Exogenous dendritic cells display restricted trafficking when injected in vivo and stimulate CD8 T cell responses that are localized to a small number of lymphoid compartments. By examining these responses in the presence and absence of FTY720, a drug that causes sequestration of T cells in lymph nodes, we demonstrate that a significant fraction of divided CD8 T cells redistribute into Ag-free lymph nodes within 3 days of activation. Despite variation in the level of expression of CD62L, redistribution of these cells is CD62L-dependent. Redistributed CD8 T cells exhibit characteristics of differentiated effectors. However, when re-isolated from Ag-free lymph nodes 3 days after activation and transferred into naive mice, they persist for at least 3 wk and expand upon Ag challenge. Thus, CD8 T cells that redistribute to Ag-free lymph nodes 3 days after immunization contain memory precursors. We suggest that this redistribution process represents an important mechanism for establishment of lymph node resident central memory, and that redistribution to Ag-free nodes is an additional characteristic to be added to those that distinguish memory precursors from terminal effectors.

Immunologic and clinical outcomes of a randomized phase II trial of two multipeptide vaccines for melanoma in the adjuvant setting

PURPOSE

Human melanoma cells express shared antigens recognized by CD8(+) T lymphocytes, the most common of which are melanocytic differentiation proteins and cancer-testis antigens. However, peptide vaccines for melanoma usually target only one or two MHC class I-associated peptide antigens. Because melanomas commonly evade immune recognition by selective antigen loss, optimization of melanoma vaccines may require development of more complex multipeptide vaccines.

EXPERIMENTAL DESIGN

In a prospective randomized clinical trial, we have evaluated the safety and immunogenicity of a vaccine containing a mixture of 12 peptides from melanocytic differentiation proteins and cancer-testis antigens, designed for human leukocyte antigen types that represent 80% of the melanoma patient population. This was compared with a four-peptide vaccine with only melanocytic differentiation peptides. Immune responses were assessed in peripheral blood and in vaccine-draining lymph nodes.

RESULTS

These data show that (a) the 12-peptide mixture is immunogenic in all treated patients; (b) immunogenicity of individual peptides is maintained despite competition with additional peptides for binding to MHC molecules; (c) a broader and more robust immune response is induced by vaccination with the more complex 12-peptide mixture; and (d) clinical outcome in this peptide vaccine trial correlates with immune responses measured in the peripheral blood lymphocytes.

CONCLUSIONS

These data support continued investigation of complex multipeptide vaccines for melanoma.

Activation and route of administration both determine the ability of bone marrow-derived dendritic cells to accumulate in secondary lymphoid organs and prime CD8+ T cells against tumors

AIMS

To examine the effects of route of administration and activation status on the ability of dendritic cells (DC) to accumulate in secondary lymphoid organs, and induce expansion of CD8(+) T cells and anti-tumor activity.

METHODS

DC from bone marrow (BM) cultures were labeled with fluorochromes and injected s.c. or i.v. into naïve mice to monitor their survival and accumulation in vivo. Percentages of specific CD8(+) T cells in blood and delayed tumor growth were used as readouts of the immune response induced by DC immunization.

RESULTS

The route of DC administration was critical in determining the site of DC accumulation and time of DC persistence in vivo. DC injected s.c. accumulated in the draining lymph node, and DC injected i.v. in the spleen. DC appeared in the lymph node by 24 h after s.c. injection, their numbers peaked at 48 h and declined at 96 h. DC that had spontaneously matured in vitro were better able to migrate compared to immature DC. DC were found in the spleen at 3 h and 24 h after i.v. injection, but their numbers were low and declined by 48 h. Depending on the tumor cell line used, DC injected s.c. were as effective or more effective than DC injected i.v. at inducing anti-tumor responses. Pre-treatment with LPS increased DC accumulation in lymph nodes, but had no detectable effect on accumulation in the spleen. Pre-treatment with LPS also improved the ability of DC to induce CD8(+) T cell expansion and anti-tumor responses, regardless of the route of DC administration.

CONCLUSIONS

Injection route and activation by LPS independently determine the ability of DC to activate tumor-specific CD8(+) T cells in vivo.

Killer T cells regulate antigen presentation for early expansion of memory, but not naive, CD8+ T cell

Antigen presentation within the lymph node draining a site of infection is crucial for initiation of cytotoxic T cell responses. Precisely how this antigen presentation regulates T cell expansion in vivo is unclear. Here, we show that, in primary infection, antigen presentation peaks approximately 3 days postinfection and then slowly decays until day 12. This prolonged antigen presentation is required for optimal expansion of naive CD8(+) T cells, because early ablation of dendritic cells reduces the later CD8(+) T cell response. Antigen presentation during secondary infection was 10-fold lower in magnitude and largely terminated by day 4 postinfection. Expansion of memory, but not naive, antigen-specific T cells was tightly controlled by perforin-dependent cytolysis of antigen-presenting cells. The ability of the memory T cells to remove antigen-presenting cells provides a negative-feedback loop to directly limit the duration of antigen presentation in vivo.

Isoaspartyl post-translational modification triggers anti-tumor T and B lymphocyte immunity

A hallmark of the immune system is the ability to ignore self-antigens. In attempts to bypass normal immune tolerance, a post-translational protein modification was introduced into self-antigens to break T and B cell tolerance. We demonstrate that immune tolerance is bypassed by immunization with a post-translationally modified melanoma antigen. In particular, the conversion of an aspartic acid to an isoaspartic acid within the melanoma antigen tyrosinase-related protein (TRP)-2 peptide-(181-188) makes the otherwise immunologically ignored TRP-2 antigen immunogenic. Tetramer analysis of iso-Asp TRP-2 peptide-immunized mice demonstrated that CD8+ T cells not only recognized the isoaspartyl TRP-2 peptide but also the native TRP-2 peptide. These CD8+ T cells functioned as cytotoxic T lymphocytes, as they effectively lysed TRP-2 peptide-pulsed targets both in vitro and in vivo. Potentially, post-translational protein modification can be utilized to trigger strong immune responses to either tumor proteins or potentially weakly immunogenic pathogens.