Systemic immunostimulation induces glucocorticoid-mediated thymic involution succeeded by rebound hyperplasia which is impaired in aged recipients.

The thymus is the central organ involved with T-cell development and the production of naïve T cells. During normal aging, the thymus undergoes marked involution, reducing naïve T-cell output and resulting in a predominance of long-lived memory T cells in the periphery. Outside of aging, systemic stress responses that induce corticosteroids (CS), or other insults such as radiation exposure, induce thymocyte apoptosis, resulting in a transient acute thymic involution with subsequent recovery occurring after cessation of the stimulus.

Differential phenotypes of memory CD4 and CD8 T cells in the spleen and peripheral tissues following immunostimulatory therapy.

Background: Studies assessing immune parameters typically utilize human PBMCs or murine splenocytes to generate data that is interpreted as representative of immune status. Using splenocytes, we have shown memory CD4-T cells that expand following systemic immunostimulatory therapies undergo rapid IFNg-mediated activation induced cell death (AICD) resulting in a net loss of total CD4-T cells which correlates with elevated PD-1 expression. This is in contrast to CD8-T cells which expand with minimal PD-1 upregulation and apoptosis.

Repeated PD-1/PD-L1 monoclonal antibody administration induces fatal xenogeneic hypersensitivity reactions in a murine model of breast cancer.

Monoclonal antibodies (mAbs) targeting coinhibitory molecules such as PD-1, PD-L1 and CTLA-4 are increasingly used as targets of therapeutic intervention against cancer. While these targets have led to a critical paradigm shift in treatments for cancer, these approaches are also plagued with limitations owing to cancer immune evasion mechanisms and adverse toxicities associated with continuous treatment. It has been difficult to reproduce and develop interventions to these limitations preclinically due to poor reagent efficacy and reagent xenogenecity not seen in human trials.

Blocking Indolamine-2,3-Dioxygenase Rebound Immune Suppression Boosts Antitumor Effects of Radio-Immunotherapy in Murine Models and Spontaneous Canine Malignancies.

Purpose: Previous studies demonstrate that intratumoral CpG immunotherapy in combination with radiotherapy acts as an in-situ vaccine inducing antitumor immune responses capable of eradicating systemic disease. Unfortunately, most patients fail to respond. We hypothesized that immunotherapy can paradoxically upregulate immunosuppressive pathways, a phenomenon we term "rebound immune suppression," limiting clinical responses.

Late administration of murine CTLA-4 blockade prolongs CD8-mediated anti-tumor effects following stimulatory cancer immunotherapy.

We have demonstrated that immunostimulatory therapies such as interleukin-2 (IL-2) and anti-CD40 (αCD40) can be combined to deliver synergistic anti-tumor effects. While this strategy has shown success, efficacy varies depending on a number of factors including tumor type and severe toxicities can be seen. We sought to determine whether blockade of negative regulators such as cytotoxic T lymphocyte antigen-4 (CTLA-4) could simultaneously prolong CD8(+) T cell responses and augment T cell anti-tumor effects.

NK Cells Preferentially Target Tumor Cells with a Cancer Stem Cell Phenotype.

Increasing evidence supports the hypothesis that cancer stem cells (CSCs) are resistant to antiproliferative therapies, able to repopulate tumor bulk, and seed metastasis. NK cells are able to target stem cells as shown by their ability to reject allogeneic hematopoietic stem cells but not solid tissue grafts. Using multiple preclinical models, including NK coculture (autologous and allogeneic) with multiple human cancer cell lines and dissociated primary cancer specimens and NK transfer in NSG mice harboring orthotopic pancreatic cancer xenografts, we assessed CSC viability, CSC frequency, expression of death receptor ligands, and tumor burden.

Out-of-Sequence Signal 3 Paralyzes Primary CD4(+) T-Cell-Dependent Immunity.

Primary T cell activation involves the integration of three distinct signals delivered in sequence: (1) antigen recognition, (2) costimulation, and (3) cytokine-mediated differentiation and expansion. Strong immunostimulatory events such as immunotherapy or infection induce profound cytokine release causing "bystander" T cell activation, thereby increasing the potential for autoreactivity and need for control. We show that during strong stimulation, a profound suppression of primary CD4(+) T-cell-mediated immune responses ensued and was observed across preclinical models and patients undergoing high-dose interleukin-2 (IL-2) therapy.

Adiposity induces lethal cytokine storm after systemic administration of stimulatory immunotherapy regimens in aged mice.

Aging is a contributing factor in cancer occurrence. We recently demonstrated that systemic immunotherapy (IT) administration in aged, but not young, mice resulted in induction of rapid and lethal cytokine storm. We found that aging was accompanied by increases in visceral fat similar to that seen in young obese (ob/ob or diet-induced obese [DIO]) mice.

Bystander activation and anti-tumor effects of CD8+ T cells following Interleukin-2 based immunotherapy is independent of CD4+ T cell help.

We have previously demonstrated that immunotherapy combining agonistic anti-CD40 and IL-2 (IT) results in synergistic anti-tumor effects. IT induces expansion of highly cytolytic, antigen-independent "bystander-activated" (CD8(+)CD44high) T cells displaying a CD25(-)NKG2D(+) phenotype in a cytokine dependent manner, which were responsible for the anti-tumor effects. While much attention has focused on CD4(+) T cell help for antigen-specific CD8(+) T cell expansion, little is known regarding the role of CD4(+) T cells in antigen-nonspecific bystander-memory CD8(+) T cell expansion.

Aging predisposes to acute inflammatory induced pathology after tumor immunotherapy.

Cancer commonly occurs in the elderly and immunotherapy (IT) is being increasingly applied to this population. However, the majority of preclinical mouse tumor models assessing potential efficacy and toxicities of therapeutics use young mice. We assessed the impact of age on responses to systemic immune stimulation.

Influenza infection results in local expansion of memory CD8(+) T cells with antigen non-specific phenotype and function.

Primary viral infections induce activation of CD8(+) T cells responsible for effective resistance. We sought to characterize the nature of the CD8(+) T cell expansion observed after primary viral infection with influenza. Infection of naive mice with different strains of influenza resulted in the rapid expansion of memory CD8(+) T cells exhibiting a unique bystander phenotype with significant up-regulation of natural killer group 2D (NKG2D), but not CD25, on the CD44(high) CD8(+) T cells, suggesting an antigen non-specific phenotype.

Immunoediting and antigen loss: overcoming the achilles heel of immunotherapy with antigen non-specific therapies.

Cancer immunotherapy has emerged as a mainstream therapy option in the battle against cancer. Pre-clinical data demonstrates the ability of immunotherapy to harness the immune system to fight disseminated malignancy. Clinical translation has failed to recapitulate the promising results of pre-clinical studies although there have been some successes.

Specificity may be overrated in cancer immunotherapy: Getting to know the nonspecific side of memory T Cells.

For a long time, cancer immunotherapy has focused on the induction of tumor-specific T cell-mediated immune responses. Now, a mounting body of evidence indicates that efficient anticancer immune responses also rely on innate immunity. Tietze et al.

Mechanical disruption of tumors by iron particles and magnetic field application results in increased anti-tumor immune responses.

The primary tumor represents a potential source of antigens for priming immune responses for disseminated disease. Current means of debulking tumors involves the use of cytoreductive conditioning that impairs immune cells or removal by surgery. We hypothesized that activation of the immune system could occur through the localized release of tumor antigens and induction of tumor death due to physical disruption of tumor architecture and destruction of the primary tumor in situ.

The role of antigen-specific and non-specific immunotherapy in the treatment of cancer.

Immunotherapy in the treatment of cancer is increasing, particularly with the recent FDA approval of sipuleucel-T and ipilimumab. The efficacy of anti-tumor immunotherapies has been modest compared to their theoretical and pre-clinical promise. This review evaluates the promise and pitfalls of immunotherapy and highlight some of the obstacles to improving anti-tumor immunotherapy: the need for technical refinement of therapies, the need for an increased understanding of how best to combine therapies with traditional cytotoxic therapies, the inability of patients to mount an effective immune response either due to disease burden or tumor induced immune suppression, the significant toxicities associated with many immunotherapies, and the lack of strongly immunogenic antigens required by many therapies.

Delineation of antigen-specific and antigen-nonspecific CD8(+) memory T-cell responses after cytokine-based cancer immunotherapy.

Memory T cells exhibit tremendous antigen specificity within the immune system and accumulate with age. Our studies reveal an antigen-independent expansion of memory, but not naive, CD8(+) T cells after several immunotherapeutic regimens for cancer resulting in a distinctive phenotype. Signaling through T-cell receptors (TCRs) or CD3 in both mouse and human memory CD8(+) T cells markedly up-regulated programmed death-1 (PD-1) and CD25 (IL-2 receptor α chain), and led to antigen-specific tumor cell killing.

Antigen-specific versus antigen-nonspecific immunotherapeutic approaches for human melanoma: the need for integration for optimal efficacy?

Due to its immunogenecity and evidence of immune responses resulting in tumor regression, metastatic melanoma has been the target for numerous immunotherapeutic approaches. Unfortunately, based on the clinical outcomes, even the successful induction of tumor-specific responses does not correlate with efficacy. Immunotherapies can be divided into antigen-specific approaches, which seek to induce T cells specific to one or several known tumor associated antigens (TAA), or with antigen-nonspecific approaches, which generally activate T cells to become nonspecifically lytic effectors.