Active antitumor immunotherapy, with or without B7-mediated costimulation, increases tumor progression in an immunogenic murine T cell lymphoma model

Cancer, aging and immunotherapy: lessons learned from animal models

Aging of the immune system is associated with a dramatic reduction in responsiveness as well as functional dysregulation. This deterioration of immune function with advancing age is associated with an increased incidence of cancer. Although there is a plethora of reports evaluating the effect of immunotherapy in stimulating antitumor immune responses, the majority of these studies do not pay attention to the effect aging has on the immune system. Studies from our group and others indicate that immunotherapies could be effective in the young, are not necessarily effective in the old. To optimally stimulate an antitumor immune response in the old, it is necessary to (1) identify and understand the intrinsic defects of the old immune system and (2) use relevant models that closely reflect those of cancer patients, where self-tolerance and aging are present simultaneously. The present review summarizes some defects found in the old immune system affecting the activation of antitumor immune responses, the strategies used to activate stronger antitumor immune response in the old and the use of a tolerant animal tumor model to target a self-tumor antigen for the optimization of immunotherapeutic interventions in the old.

Peroxisome proliferator-activated receptor gamma (PPARgamma) ligands reverse CTL suppression by alternatively activated (M2) macrophages in cancer

Tumors may escape from immune control by the induction of CD11b(+)Gr-1(+) myeloid suppressor cells in the spleen. In this study, we demonstrate that this cell population can be subdivided into a CD11b(hi)Gr-1(int)SSC(lo)Ly6G(neg)M-CSFR(int) immature monocytic fraction and a CD11b(hi+)Gr-1(hi)SSC(hi)Ly6G(hi)M-CSFR(neg) granulocytic fraction. Upon in vitro culture, the monocytic CD11b(+)Gr-1(+) cell fraction is sufficient for cytotoxic T lymphocyte (CTL) suppression, which is linked to the gradual differentiation of these monocytic cells into mature F4/80(+) CD68(+) macrophages. These CTL-suppressive macrophages are alternatively activated (M2), as demonstrated by the expression of known and novel M2 signature genes. In search of M2-associated genes involved in the suppressive activity, it is shown that stimulation of peroxisome proliferator-activated receptor gamma (PPARgamma) and inhibition of phospholipase A(2) (PLA(2)) activity cooperate to alleviate CTL suppression. Of importance, purified tumor-associated macrophages display a similar M2 phenotype and are suppressive for antitumor CTLs, via a mechanism that can be almost completely reversed by PPARgamma ligands. Overall, our data identify PLA(2) and especially PPARgamma as new potential therapeutic targets to subvert macrophage-mediated CTL suppression in cancer.

B7/CD28 costimulation of T cells induces a distinct proteome pattern

Effective immune strategies for the eradication of human tumors require a detailed understanding of the interaction of tumor cells with the immune system, which might lead to an optimization of T cell responses. To understand the impact of B7-mediated costimulation on T cell activation comprehensive proteome analysis of B7-primed T cell populations were performed. Using this approach we identified different classes of proteins in T cells whose expression is either elevated or reduced upon B7-1- or B7-2-mediated CD28 costimulation. The altered proteins include regulators of the cell cycle and cell proliferation, signal transducers, components of the antigen processing machinery, transporters, cytoskeletal proteins, and metabolic enzymes. A number of differentially expressed proteins are further modified by phosphorylation. Our results provide novel insights into the complexity of the CD28 costimulatory pathway of T cells and will help to identify potential targets of therapeutic interventions for modulating anti-tumor T cell activation.

Aged mice develop protective antitumor immune responses with appropriate costimulation

There is a clear decrease in CD8(+) T cell effector function with aging, a loss once thought to be intrinsic to the CD8(+) T cells. Recent studies suggest, however, that this decline may be a consequence of altered stimulatory signals within the aged lymphoid microenvironment. In this study, we compared the immune responses of young and old mice against the BM-185 pre-B cell lymphoma expressing enhanced GFP (EGFP) as a surrogate tumor Ag. Young animals develop protective immune responses when immunized with BM-185-EGFP, but aged mice do not and ultimately succumb to the tumor. However, expression of CD80 (B7.1) on the BM-185-EGFP (BM-185-EGFP-CD80) results in rejection of the tumor by both young and old animals. Additionally, injection of BM-185-EGFP-CD80 cells in young mice promotes the development of long-lasting memory responses capable of rejecting BM-185 wild-type tumors. Aged animals similarly injected did not develop antitumor memory responses. Interestingly, old animals immunized with the BM-185-EGFP-CD80 cells plus injections of the agonist anti-OX40 mAb did develop long-lasting memory responses capable of rejecting the BM-185 wild-type tumors with the same vigor as the young animals. We show that old mice have the capacity to develop strong antitumor responses and protective memory responses as long as they are provided with efficient costimulation. These results have important implications for the development of vaccination strategies in the elderly, indicating that the aged T cell repertoire can be exploited for the induction of tumor immunity.

Nitric oxide-independent CTL suppression during tumor progression: association with arginase-producing (M2) myeloid cells

Most of the mice bearing a s.c. BW-Sp3 lymphoma tumor mount a CD8(+) T cell-mediated response resulting in tumor regression. Nonetheless, tumor progression occurs in some of the recipients and is associated with CTL inactivity. We demonstrated that T cell-activating APC were induced in regressors whereas T cell suppressive myeloid cells predominated in the spleen of progressors. Indeed, in vitro depletion of either the adherent or the CD11b(+) populations restored T cell cytotoxicity and proliferation in these mice. This CTL inhibition was cell-to-cell contact-dependent but not mediated by NO. However, the same progressor suppressive cells prevented the activity of in vitro-restimulated CTLs derived from regressors in a cell-to-cell contact and NO-dependent fashion. Thus, either the NO-dependent or -independent suppressive pathway prevailed, depending on the target CTL population. In addition, the suppressive population expressed a high arginase activity, suggesting an association of the suppressive phenotype with alternatively activated (M2) myeloid cells. However, the high arginase activity is not directly involved in the suppressive process. Our results provide new insights for myeloid cell-mediated CTL inhibition during cancer progression.

Antagonistic effect of NK cells on alternatively activated monocytes: a contribution of NK cells to CTL generation

Natural killer (NK) cells fulfill essential accessory functions for the priming of antigen-specific cytotoxic T lymphocytes (CTLs). On the basis of a NKG2D-ligand-positive tumor model, we obtained results implicating NK-mediated regulatory as well as NK-mediated cytolytic activities in the initiation and persistence of CTL activity. Indeed, CD8(+) T-cell-dependent tumor rejection requires NK cell function in vivo, because tumors will progress both on depletion of NK cells or in the absence of optimal NK activity. Here we provide evidence that the absence of NK cells during subcutaneous tumor growth will abrogate generation of antitumor CTL responses and that this process can be linked to the expansion of alternatively activated monocytes. Indeed, our in vitro studies demonstrate that in splenic cultures from NK-deficient tumor-bearing mice, lack of type 1-associated cytokines correlates with the presence of type 2 (alternatively activated) monocytes and the production of type 2 cytokines. Furthermore, these type 2 monocyte-containing splenic adherent populations potently suppress subsequent memory CTL restimulation. We evaluated the role of NK lytic effector functions in the efficient switch of the immune system toward classical (type 1) activation by including differentially activated monocytic populations as targets in cytotoxicity assays. The results indicate that the accessory function of NK cells depends partially on the ability of activated NK cells to preferentially engage type 2 antigen-presenting cells. Thus, when the immune system tends to be type 2 oriented, NK cells can drive an efficient type 2 --> type 1 switch in the population of antigen-presenting cells to provide signaling for the generation of CTLs.

Vaccination therapy for cutaneous T-cell lymphoma

Primary cutaneous T-cell lymphomas (CTCL) are defined as clonal proliferation of skin-infiltrating T lymphocytes. Despite their heterogeneity, CTCL are generally incurable, which has led to the development of various treatment strategies including vaccination. Here, the attempts to vaccinate against lymphoma will be reviewed with special emphasis on CTCL. Because an universal tumour antigen is not available so far, different targets - including whole tumour cells, idiotypes, cancer/testis antigens, proteins derived from tumour-associated mutations, and mimotopes - have been investigated for their applicability in CTCL vaccination. The antigenic information can be delivered in different ways. So far, tumour cells fused to dendritic cells, idiotypic proteins/peptides and DNA/RNA preparations have been applied in lymphoma. As most targets are weak immunogens, adjuvants and other helpers - including dendritic cells, immunogenic peptides and oligonucleotides, cytokines, and viral vectors - are required to enable proper presentation of the antigens and sufficient activation of the immune system. Although first data from CTCL patients prove the suitability of vaccination in CTCL therapy, the number of available antigens, carriers, adjuvants and application schemes creates a multitude of vaccine formulations; identification of the best-suited approach remains nearly impossible. Furthermore, the relationship between lymphoma and the host immune system is complex and incompletely understood. As a result, CTCL vaccination still requires a lot of research.

Negative effect of CTLA-4 on induction of T-cell immunity in vivo to B7-1+, but not B7-2+, murine myelogenous leukemia

B7 molecules provide important costimulatory signals to T cells, and B7 genes have been introduced into B7-negative tumor cells to enhance their immunogenicity. However, the role of B7 molecules in inducing tumor immunity is controversial because of conflicting results and reports of differential signaling through the B7 molecules and their ligands CD28 and CTLA-4. In this study, we compared the effect of B7-1 (CD80) and B7-2 (CD86) on the induction of T-cell immunity to C1498, a murine myelogenous leukemia. When cultured with exogenous cytokines in vitro, C1498/B7-1 and C1498/B7-2 induced syngeneic CD8+ T cells to kill parental C1498. In vivo, C1498/B7-1 grew progressively after subcutaneous injection, whereas C1498/B7-2 completely regressed after transient growth in naive mice. Spontaneous rejection of C1498/B7-2 resulted in immunity to challenge doses of C1498 and C1498/B7-1. Antibody-depletion studies in vivo showed that CD8+ T cells rejected C1498/B7-2, whereas only natural killer cells affected the growth of C1498/B7-1. Two approaches were used to determine whether preferential interaction of B7-1 with CTLA-4 contributed to the failure of C1498/B7-1 to activate CD8+ T cells in vivo. First, CTLA-4 specific monoclonal antibody was used to block B7-1-CTLA-4 interaction. Second, CTLA-4 deletional mutant (-/-) bone marrow chimeras were used as tumor hosts. In both systems, there was a significant increase in the rate of rejection of C1498/B7-1 tumors. Resistance to C1498/B7-1 in CTLA-4(minus sign/minus sign) hosts was mediated by CD8+ T cells. Blocking or deletion of CTLA-4 did not affect the growth of parental C1498, indicating that B7-1 was important for the induction of CD8+ T-cell immunity in the absence of CTLA-4.

Hybrid cell vaccination for cancer immune therapy: first clinical trial with metastatic melanoma

Hybrid cell vaccination is a new cancer immune therapy approach that aims at recruiting T cell help for the induction of tumour specific cytolytic immunity. The vaccines are generated by fusion of the patients' tumour cells with allogeneic MHC class II bearing cells to combine the tumour's antigenicity with the immunogenicity of allogeneic MHC molecules. Safety and anti-tumour activity of this treatment were assessed in a clinical trial that has yielded one complete and one partial remission, and 5 cases of stable disease among 16 patients with advanced stage metastatic melanoma. As evidenced by histology, the vaccination induced T cell relocation into tumour nodules. Stable disease could be maintained by repeated booster injections for more than 24 months in some patients. The side effects were minor. Occasional occurrences of vitiligo spots after vaccination were indicative of a restricted therapy induced auto-immune reactivity. The results suggest that hybrid cell vaccination is a safe cancer immune therapy potentially effective for induction of acute anti-tumour response as well as long-term maintenance.

Induction of effective antitumor immunity in a mouse brain tumor model using B7-1 (CD80) and intercellular adhesive molecule 1 (ICAM-1; CD54) transfection and recombinant interleukin 12

Although tumor-specific T lymphocytes recognize tumor-associated antigens (TAA) present on their cell surface via major histocompatibility complex (MHC) molecules, T cells require other activating signals. These are provided by costimulatory molecules, including B7-1 (CD80), B7-2 (CD86) and intercellular adhesive molecule 1 (ICAM-1; CD54). Transfecting mouse tumor cell lines with the B7 gene can lead to primary tumor rejection and the establishment of protective immunity. However, some studies have shown that the B7 effect upon T-cell-dependent tumor immunity is limited. Therefore, we examined the antitumor effects of recombinant interleukin 12 (IL-12) and genetically engineered glioma cells expressing B7-1 or both B7-1 and ICAM-1. Vaccination of mice with B7-1-expressing tumor cells substantially inhibited the growth of subcutaneously inoculated gliomas but not those located in the brain. Vaccination with B7-1-expressing tumor cells and systemic recombinant IL-12 (rIL-12) was more effective than either B7-1-expressing tumor cells or rIL-12 alone. Our murine brain tumor model also showed that vaccination with tumor cells expressing both B7-1 and ICAM-1 combined with rIL-12 prolonged survival. We have demonstrated the therapeutic potential of vaccination with rIL-12 and tumor cells expressing both B7-1 and ICAM-1 in the control of glioma growth.