Defects in the acquisition of CD8 T cell effector function after priming with tumor or soluble antigen can be overcome by the addition of an OX40 agonist

Several members of the TNFR superfamily, including OX40 (CD134), 4-1BB (CD137), and CD27 provide critical costimulatory signals that promote T cell survival and differentiation in vivo. Although several studies have demonstrated that OX40 engagement can enhance CD4 T cell responses, the mechanisms by which OX40-mediated signals augment CD8 T cell responses are still unclear. Previously, we and others have shown that OX40 engagement on Ag-specific CD8 T cells led to increased CD8 T cell expansion, survival, and the generation of greater numbers of long-lived memory cells. Currently, we demonstrate that provision of an OX40 agonist during the activation of naive CD8 T cells primed in vivo with either soluble or tumor-associated Ag significantly augments granzyme B expression and CD8 T cell cytolytic function through an IL-2-dependent mechanism. Furthermore, augmented CTL function required direct engagement of OX40 on the responding CD8 T cells and was associated with increased antitumor activity against established prostate tumors and enhanced the survival of tumor-bearing hosts. Thus, in the absence of danger signals, as is often the case in a tumor-bearing host, provision of an OX40 agonist can overcome defective CD8 T cell priming and lead to a functional antitumor response in vivo.     

OX40 and Bcl-xL promote the persistence of CD8 T cells to recall tumor-associated antigen

The molecular signals that allow primed CD8 T cells to persist and be effective are particularly important during cancer growth. With response to tumor-expressed Ag following adoptive T cell transfer, we show that CD8 effector cells deficient in OX40, a TNFR family member, could not mediate short-term tumor suppression. OX40 was required at two critical stages. The first was during CD8 priming in vitro, in which APC-transmitted OX40 signals endowed the ability to survive when adoptively transferred in vivo before tumor Ag encounter. The second was during the in vivo recall response of primed CD8 T cells, the stage in which OX40 contributed to the further survival and accumulation of T cells at the tumor site. The lack of OX40 costimulation was associated with reduced levels of Bcl-x(L), and retroviral expression of Bcl-x(L) in tumor-reactive CD8 T cells conferred greatly enhanced tumor protection following adoptive transfer. These data demonstrate that OX40 and Bcl-x(L) can control survival of primed CD8 T cells and provide new insights into both regulation of CD8 immunity and control of tumors.     

OX40 costimulatory signals potentiate the memory commitment of effector CD8+ T cells

A T cell costimulatory molecule, OX40, contributes to T cell expansion, survival, and cytokine production. Although several roles for OX40 in CD8(+) T cell responses to tumors and viral infection have been shown, the precise function of these signals in the generation of memory CD8(+) T cells remains to be elucidated. To address this, we examined the generation and maintenance of memory CD8(+) T cells during infection with Listeria monocytogenes in the presence and absence of OX40 signaling. We used the expression of killer cell lectin-like receptor G1 (KLRG1), a recently reported marker, to distinguish between short-lived effector and memory precursor effector T cells (MPECs). Although OX40 was dispensable for the generation of effector T cells in general, the lack of OX40 signals significantly reduced the number and proportion of KLRG1(low) MPECs, and, subsequently, markedly impaired the generation of memory CD8(+) T cells. Moreover, memory T cells that were generated in the absence of OX40 signals in a host animal did not show self-renewal in a second host, suggesting that OX40 is important for the maintenance of memory T cells. Additional experiments making use of an inhibitory mAb against the OX40 ligand demonstrated that OX40 signals are essential during priming, not only for the survival of KLRG1(low) MPECs, but also for their self-renewing ability, both of which contribute to the homeostasis of memory CD8(+) T cells.     

Functional dichotomy between OX40 and 4-1BB in modulating effector CD8 T cell responses

Members of the TNFR family are thought to deliver costimulatory signals to T cells and modulate their function and survival. In this study, we compare the role of two closely related TNFR family molecules, OX40 and 4-1BB, in generating effector CD8 T cells to Ag delivered by adenovirus. OX40 and 4-1BB were both induced on responding naive CD8 T cells, but 4-1BB exhibited faster and more sustained kinetics than OX40. OX40-deficient CD8 T cells initially expanded normally; however, their accumulation and survival at late times in the primary response was significantly impaired. In contrast, 4-1BB-deficient CD8 T cells displayed hyperresponsiveness, expanding more than wild-type cells. The 4-1BB-deficient CD8 T cells also showed enhanced maturation attributes, whereas OX40-deficient CD8 T cells had multiple defects in the expression of effector cell surface markers, the synthesis of cytokines, and in cytotoxic activity. These results suggest that, in contrast to current ideas, OX40 and 4-1BB can have a clear functional dichotomy in modulating effector CD8 T cell responses. OX40 can positively regulate effector function and late accumulation/survival, whereas 4-1BB can initially operate in a negative manner to limit primary CD8 responses.     

OX40 ligation of CD4+ T cells enhances virus-specific CD8+ T cell memory responses independently of IL-2 and CD4+ T regulatory cell inhibition

We have previously shown that CD4(+) T cells are required to optimally expand viral-specific memory CD8(+) CTL responses using a human dendritic cell-T cell-based coculture system. OX40 (CD134), a 50-kDa transmembrane protein of the TNFR family, is expressed primarily on activated CD4(+) T cells. In murine models, the OX40/OX40L pathway has been shown to play a critical costimulatory role in dendritic cell/T cell interactions that may be important in promoting long-lived CD4(+) T cells, which subsequently can help CD8(+) T cell responses. The current study examined whether OX40 ligation on ex vivo CD4(+) T cells can enhance their ability to "help" virus-specific CTL responses in HIV-1-infected and -uninfected individuals. OX40 ligation of CD4(+) T cells by human OX40L-IgG1 enhanced the ex vivo expansion of HIV-1-specific and EBV-specific CTL from HIV-1-infected and -uninfected individuals, respectively. The mechanism whereby OX40 ligation enhanced help of CTL was independent of the induction of cytokines such as IL-2 or any inhibitory effect on CD4(+) T regulatory cells, but was associated with a direct effect on proliferation of CD4(+) T cells. Thus, OX40 ligation on CD4(+) T cells represents a potentially novel immunotherapeutic strategy that should be investigated to treat and prevent persistent virus infections, such as HIV-1 infection.     

OX40 signals during priming on dendritic cells inhibit CD4 T cell proliferation: IL-4 switches off OX40 signals enabling rapid proliferation of Th2 effectors

In this study we examined the role and regulation of OX40 signals during CD4 T cell priming on dendritic cells (DCs). Contrary to expectation, OX40-deficient cells proliferated more rapidly than their normal counterparts, particularly when stimulated with peptide in the absence of added cytokines. This proliferative advantage was not apparent for Th2-differentiated cells. When the reasons for this were investigated, we found that the cytokine IL-4 specifically down-regulated expression of OX40 ligand on T, B, and DCs, but not on the CD4(+)CD3(-) cells linked with selection of Th2 cells into the memory compartment. OX40 ligand expression was also down-regulated on rapidly proliferating Th1 effectors. These data are compatible with OX40 signals acting during priming as a check on naive T cell proliferation while T cells integrate additional DC signals. This would serve to limit inappropriate T cell responses. In contrast, OX40 signals from CD4(+)CD3(-) cells located in the outer T zone select proliferating Th2 effectors into the memory T cell pool.     

Evaluation of OX40 ligand as a costimulator of human antiviral memory CD8 T cell responses: comparison with B7.1 and 4-1BBL

CTL are important effectors of antiviral immunity. Designing adjuvants that can induce strong cytotoxic T cell responses in humans would greatly improve the effectiveness of an antiviral vaccination or therapeutic strategy. Recent evidence suggests that, in addition to its well-established role in costimulation of CD4 T cell responses, OX40L (CD134) can directly costimulate mouse CD8 T cells. In this study, we evaluated the role of OX40L in costimulation of human antiviral CD8 T cell responses and compared it with two other important costimulators, B7.1 (CD80) and 4-1BBL (CD137L). Delivery of OX40L to human monocytes using a recombinant replication-defective adenovirus led to greater expansion, up-regulation of perforin, enhanced cytolytic activity, and increased numbers of IFN-gamma- and TNF-alpha-producing antiviral memory CD8 T cells in cultures of total T cells. Synergistic or additive effects were observed when OX40L costimulation was combined with 4-1BBL (CD137L) or B7.1 (CD80) costimulation. In total T cell cultures, at low Ag dose, 4-1BBL provided the most potent costimulus for influenza-specific CD8 T cell expansion, followed by B7.1 (CD80) and then OX40L. For isolated CD8 T cells, 4-1BBL was also the most consistent costimulator, followed by B7.1. In contrast, OX40L showed efficacy in direct activation of memory CD8 T cells in only one of seven donors. Thus, OX40L costimulates human antiviral memory CD8 T cell responses largely through indirect effects and can enhance anti-influenza, anti-EBV, and anti-HIV responses, particularly in combination with 4-1BBL or B7.     

Listeria monocytogenes infection overcomes the requirement for CD40 ligand in exogenous antigen presentation to CD8(+) T cells.

In vivo priming of CD8(+) T lymphocytes against exogenously processed model Ags requires CD4(+) T cell help, specifically interactions between CD40 ligand (CD40L) expressed by activated CD4(+) T cells and CD40, which is present on professional APC such as dendritic cells (DCs). To address this issue in the context of bacterial infection, we examined CD40L-CD40 interactions in CD8(+) T cell priming against an exogenously processed, nonsecreted bacterial Ag. CD40L interactions were blocked by in vivo treatment with anti-CD40L mAb MR-1, which inhibited germinal center formation and CD8(+) T cell cross-priming against an exogenous model Ag, OVA. In contrast, MR-1 treatment did not interfere with CD8(+) T cell priming against a nonsecreted or secreted recombinant Ag expressed by Listeria monocytogenes. Memory and secondary responses of CD8(+) T cells against nonsecreted and secreted bacterial Ags were also largely unimpaired by transient MR-1 treatment. When MR-1-treated mice were concurrently immunized with L. monocytogenes and OVA-loaded splenocytes, cross-priming of OVA-specific naive CD8(+) T cells occurred. No significant decline in cross-priming against OVA was measured when either TNF or IFN-gamma was neutralized in L. monocytogenes-infected animals, demonstrating that multiple signals exist to overcome CD40L blockade of CD8(+) T cell cross-priming during bacterial infection. These data support a model in which DCs can be stimulated in vivo through signals other than CD40, becoming APC that can effectively stimulate CD8(+) T cell responses against exogenous Ags during infection.     

OX40 ligand-transduced tumor cell vaccine synergizes with GM-CSF and requires CD40-Apc signaling to boost the host T cell antitumor response

Efficient T cell priming by GM-CSF and CD40 ligand double-transduced C26 murine colon carcinoma is not sufficient to cure metastases in a therapeutic setting. To determine whether a cellular vaccine that interacts directly with both APC and T cells in vivo might be superior, we generated C26 carcinoma cells transduced with the T cell costimulatory molecule OX40 ligand (OX40L) either alone (C26/OX40L) or together with GM-CSF (C26/GM/OX40L), which is known to activate APC. Mice injected with C26/OX40L cells displayed only a delay in tumor growth, while the C26/GM/OX40L tumor regressed in 85% of mice. Tumor rejection required granulocytes, CD4+, CD8+ T cells, and APC-mediated CD40-CD40 ligand cosignaling, but not IFN-gamma or IL-12 as shown using subset-depleted and knockout (KO) mice. CD40KO mice primed with C26/GM/OX40L cells failed to mount a CTL response, and T cells infiltrating the C26/GM/OX40L tumor were OX40 negative, suggesting an impairment in APC-T cell cross-talk in CD40KO mice. Indeed, CD4+ T cell-depleted mice failed to mount any CTL activity against the C26 tumor, while treatment with agonistic mAb to CD40, which acts on APC, bypassed the requirement for CD4+ T cells and restored CTL activation. C26/GM/OX40L cells cured 83% of mice bearing lung metastases, whereas C26/OX40L or C26/GM vaccination cured only 28 and 16% of mice, respectively. These results indicate the synergistic activity of OX40L and GM-CSF in a therapeutic setting.     

Differential requirements for OX40 signals on generation of effector and central memory CD4+ T cells

Memory T cells can be divided into effector memory (T(EM)) and central memory (T(CM)) subsets based on their effector function and homing characteristics. Although previous studies have demonstrated that TCR and cytokine signals mediate the generation of the two memory subsets of CD8(+) T cells, the mechanisms for generation of the CD4(+) T(EM) and T(CM) cell subsets are unknown. We found that OX40-deficient mice showed a marked reduction in the number of CD4(+) T(EM) cells, whereas the number of CD4(+) T(CM) cells was normal. Adoptive transfer experiments using Ag-specific CD4(+) T cells revealed that OX40 signals during the priming phase were indispensable for the optimal generation of the CD4(+) T(EM), but not the CD4(+) T(CM) population. In a different transfer experiment with in vitro established CD4(+)CD44(high)CD62L(low) (T(EM) precursor) and CD4(+)CD44(high)CD62L(high) (T(CM) precursor) subpopulations, OX40-KO T(EM) precursor cells could not survive in the recipient mice, whereas wild-type T(EM) precursor cells differentiated into both T(EM) and T(CM) cells. In contrast, T(CM) precursor cells mainly produced T(CM) cells regardless of OX40 signals, implying the dispensability of OX40 for generation of T(CM) cells. Nevertheless, survival of OX40-KO T(EM) cells was partially rescued in lymphopenic mice. During in vitro recall responses, the OX40-KO T(EM) cells that were generated in lymphopenic recipient mice showed impaired cytokine production, suggesting an essential role for OX40 not only on generation but also on effector function of CD4(+) T(EM) cells. Collectively, the present results indicate differential requirements for OX40 signals on generation of CD4(+) T(EM) and T(CM) cells.     

A marked reduction in priming of cytotoxic CD8+ T cells mediated by stress-induced glucocorticoids involves multiple deficiencies in cross-presentation by dendritic cells

Protracted psychological stress elevates circulating glucocorticoids, which can suppress CD8(+) T cell-mediated immunity, but the mechanisms are incompletely understood. Dendritic cells (DCs), required for initiating CTL responses, are vulnerable to stress/corticosterone, which can contribute to diminished CTL responses. Cross-priming of CD8(+) T cells by DCs is required for initiating CTL responses against many intracellular pathogens that do not infect DCs. We examined the effects of stress/corticosterone on MHC class I (MHC I) cross-presentation and priming and show that stress/corticosterone-exposed DCs have a reduced ability to cross-present OVA and activate MHC I-OVA(257-264)-specific T cells. Using a murine model of psychological stress and OVA-loaded β(2)-microglobulin knockout "donor" cells that cannot present Ag, DCs from stressed mice induced markedly less Ag-specific CTL proliferation in a glucocorticoid receptor-dependent manner, and endogenous in vivo T cell cytolytic activity generated by cross-presented Ag was greatly diminished. These deficits in cross-presentation/priming were not due to altered Ag donation, Ag uptake (phagocytosis, receptor-mediated endocytosis, or fluid-phase uptake), or costimulatory molecule expression by DCs. However, proteasome activity in corticosterone-treated DCs or splenic DCs from stressed mice was partially suppressed, which limits formation of antigenic peptide-MHC I complexes. In addition, the lymphoid tissue-resident CD11b(-)CD24(+)CD8α(+) DC subset, which carries out cross-presentation/priming, was preferentially depleted in stressed mice. At the same time, CD11b(-)CD24(+)CD8α(-) DC precursors were increased, suggesting a block in development of CD8α(+) DCs. Therefore, glucocorticoid-induced changes in both the cellular composition of the immune system and intracellular protein degradation contribute to impaired CTL priming in stressed mice.     

During viral infection of the respiratory tract, CD27, 4-1BB, and OX40 collectively determine formation of CD8+ memory T cells and their capacity for secondary expansion

Independent studies have shown that CD27, 4-1BB, and OX40 can all promote survival of activated CD8+ T cells. We have therefore compared their impact on CD8+ memory T cell formation and responsiveness within one, physiologically relevant model system. Recombinant mice, selectively lacking input of one or two receptors, were challenged intranasally with influenza virus, and the immunodominant virus-specific CD8+ T cell response was quantified at priming and effector sites. Upon primary infection, CD27 and (to a lesser extent) 4-1BB made nonredundant contributions to accumulation of CD8+ virus-specific T cells in draining lymph nodes and lung, while OX40 had no effect. Interestingly though, in the memory response, accumulation of virus-specific CD8+ T cells in spleen and lung critically depended on all three receptor systems. This was explained by two observations: 1) CD27, 4-1BB, and OX40 were collectively responsible for generation of the same memory CD8+ T cell pool; 2) CD27, 4-1BB, and OX40 collectively determined the extent of secondary expansion, as shown by adoptive transfers with standardized numbers of memory cells. Surprisingly, wild-type CD8+ memory T cells expanded normally in primed OX40 ligand- or 4-1BB ligand-deficient mice. However, when wild-type memory cells were generated in OX40 ligand- or 4-1BB ligand-deficient mice, their secondary expansion was impaired. This provides the novel concept that stimulation of CD8+ T cells by OX40 and 4-1BB ligand during priming imprints into them the capacity for secondary expansion. Our data argue that ligand on dendritic cells and/or B cells may be critical for this.     

Paradoxical dampening of anti-islet self-reactivity but promotion of diabetes by OX40 ligand

Costimulatory signals received by diabetogenic T cells during priming by or upon secondary encounter with autoantigen are decisive in determining the outcome of autoimmune attack. The OX40-OX40 ligand (OX40L) costimulatory pathway is known to influence T cell responses, prompting us to examine its role in autoimmune diabetes. A null allele at OX40L completely prevented diabetes development in nonobese diabetic mice and strongly reduced its incidence in a TCR transgenic model (BDC2.5). However, somewhat paradoxically, the initial activation of T cells responsive to islet beta cell Ag was slightly faster and more efficient in the absence of OX40L, with an increased degree of cell proliferation and survival in the deficient hosts. Activated T cell migration into and retention within the islets was also slightly accelerated. When challenged in vitro, splenocytes from BDC2.5.OX40L(o/o) mice showed no altered reactivity to exogenously added peptide, no bias to the Th1 or Th2 phenotype, and no alteration in T cell survival. Thus, the OX40/OX40L axis has the paradoxical effect of dampening the early activation and migration of autoimmune T cells, but sustains the long-term progression to autoimmune destruction.     

Cutting edge: a critical role for CD70 in CD8 T cell priming by CD40-licensed APCs

The CD154/CD40 interaction is an important pathway of CD4 T cell help for CD8 T cell responses. In this study, we address the role of CD70, a member of the TNF superfamily and the ligand for the T cell costimulatory receptor CD27, in CD40-mediated priming of CD8 T cells. Using an agonistic anti-CD40 mAb to mimic the CD154/CD40 interaction we demonstrate that the priming of OT-I TCR transgenic or endogenous mouse OVA-specific CD8 T cells is critically dependent on CD70/CD27 interaction. CD70 blockade inhibited CD40-mediated clonal expansion of CD8 T cells and reduced the number of memory CD8 T cells generated. Furthermore, CD70 blockade during the initial priming of CD8 T cells inhibited the ability of memory CD8 T cells to expand in response to a second encounter with Ag. Our data indicate that CD70 expression on APCs plays a key role in CD40-dependent CD8 T cell responses.     

Critical, but conditional, role of OX40 in memory T cell-mediated rejection

Memory T cells can be a significant barrier to the induction of transplant tolerance. However, the molecular pathways that can regulate memory T cell-mediated rejection are poorly defined. In the present study we tested the hypothesis that the novel alternative costimulatory molecules (i.e., ICOS, 4-1BB, OX40, or CD30) may play a critical role in memory T cell activation and memory T cell-mediated rejection. We found that memory T cells, generated by either homeostatic proliferation or donor Ag priming, induced prompt skin allograft rejection regardless of CD28/CD154 blockade. Phenotypic analysis showed that, in contrast to naive T cells, such memory T cells expressed high levels of OX40, 4-1BB, and ICOS on the cell surface. In a skin transplant model in which rejection was mediated by memory T cells, blocking the OX40/OX40 ligand pathway alone did not prolong the skin allograft survival, but blocking OX40 costimulation in combination with CD28/CD154 blockade induced long-term skin allograft survival, and 40% of the recipients accepted their skin allograft for >100 days. In contrast, blocking the ICOS/ICOS ligand and the 4-1BB/4-1BBL pathways alone or combined with CD28/CD154 blockade had no effect in preventing skin allograft rejection. OX40 blockade did not affect the homeostatic proliferation of T cells in vivo, but markedly inhibited the effector functions of memory T cells. Our data demonstrate that memory T cells resisting to CD28/CD154 blockade in transplant rejection are sensitive to OX40 blockade and suggest that OX40 is a key therapeutic target in memory T cell-mediated rejection.     

Activation of NF-kappaB1 by OX40 contributes to antigen-driven T cell expansion and survival

The costimulatory molecule OX40 (CD134) is required in many instances for effective T cell-mediated immunity, controlling proliferation, and survival of T cells after encountering specific Ag. We previously found that the functional targets of OX40 are survivin and aurora B that regulate proliferation and Bcl-2 antiapoptotic family members that regulate survival. However, the intracellular pathways from OX40 that mediate these effects are unclear. In this study, we show that OX40 signaling can target the canonical NF-kappaB (NF-kappaB1) pathway in peripheral Ag-responding CD4 T cells. Phosphorylation of IkappaBalpha, nuclear translocation of NF-kappaB1/p50 and RelA, and NF-kappaB1 activity, are impaired in OX40-deficient T cells. Retroviral transduction of active IkappaB kinase that constitutively activates NF-kappaB1 rescues the poor expansion and survival of OX40-deficient T cells, directly correlating with increased expression and activity of survivin, aurora B, and Bcl-2 family members. Moreover, active IkappaB kinase expression alone is sufficient to restore the defective expansion and survival of OX40-deficient T cells in vivo when responding to Ag. Thus, OX40 signals regulate T cell number and viability through the NF-kappaB1 pathway that controls expression and activity of intracellular targets for proliferation and survival.     

Mice deficient in OX40 and CD30 signals lack memory antibody responses because of deficient CD4 T cell memory

Recently, we reported that a CD4(+)CD3(-)CD11c(-) accessory cell provided OX40-dependent survival signals to follicular T cells. These accessory cells express both OX40 ligand and CD30 ligand, and the receptors, OX40 and CD30, are both expressed on Th2-primed CD4 T cells. OX40 and CD30 signals share common signaling pathways, suggesting that CD30 signals might substantially compensate in OX40-deficient mice. In this report we have dissected the signaling roles of CD30 alone and in combination with OX40. CD30-deficient mice showed an impaired capacity to sustain follicular germinal center responses, and recall memory Ab responses were substantially reduced. Deficiencies in OX40 and CD30 signals were additive; secondary Ab responses were ablated in double-deficient mice. Although the initial proliferation of OX40/CD30 double-knockout OTII transgenic T cells was comparable to that of their normal counterparts, they failed to survive in vivo, and this was associated with reduced T cell numbers associated with CD4(+)CD3(-) cells in B follicles. Finally, we show that OX40/CD30 double-knockout OTII transgenic T cells fail to survive compared with normal T cells when cocultured with CD4(+)CD3(-) cells in vitro.     

OX40 costimulation synergizes with GM-CSF whole-cell vaccination to overcome established CD8+ T cell tolerance to an endogenous tumor antigen

T cell costimulation via OX40 is known to increase CD4+ T cell expansion and effector function and enhances the development of T cell memory. OX40 costimulation can also prevent, and even reverse, CD4+ T cell anergy. However, the role of OX40 in CD8+ T cell function is less well defined, particularly in the setting of immune tolerance. To determine the effects of OX40 costimulation on the induction of the host CD8+ T cell repertoire to an endogenous tumor Ag, we examined the fate of CD8+ T cells specific for the immunodominant rat HER-2/neu epitope, RNEU420-429, in FVB MMTV-neu (neu-N) mice, which express rat HER-2/neu protein in a predominantly mammary-restricted fashion. We show that the RNEU420-429-specific T cell repertoire in neu-N mice expands transiently after vaccination with a neu-targeted GM-CSF-secreting whole-cell vaccine, but quickly declines to an undetectable level. However, OX40 costimulation, when combined with GM-CSF-secreting tumor-targeted vaccination, can break established CD8+ T cell tolerance in vivo by enhancing the expansion, and prolonging the survival and effector function of CD8+ T cells specific for RNEU420-429. Moreover, we demonstrate that OX40 expression is up-regulated on both CD4+ and CD8+ T cells shortly after administration of a GM-CSF expressing vaccine. These studies highlight the increased efficacy of OX40 costimulation when combined with a GM-CSF-secreting vaccine, and define a new role for OX40 costimulation of CD8+ T cells in overcoming tolerance and boosting antitumor immunity.     

Caloric restriction maintains OX40 agonist-mediated tumor immunity and CD4 T cell priming during aging

Immune responses wane during aging, posing challenges to the potential effectiveness of cancer immunotherapies. We previously demonstrated that in the context of a promising immunotherapeutic, OX40 agonist (αOX40), older animals exhibited impaired anti-tumor immune responses and diminished CD4 T cell effector differentiation. In this study, we hypothesized that tumor immune responses could be maintained during aging through caloric restriction (CR) or dietary supplementation with resveratrol (RES), a CR mimetic. Mice were placed on either a calorically restricted diet or a RES-formulated diet starting between 4 and 6 months of age and continued until mice reached 12 months of age. Tumor immune responses were assessed after challenging with either sarcoma or breast tumor cells followed by αOX40 treatment. Our results show that CR, but not RES, maintained OX40-mediated anti-tumor immunity. In addition, CR fully sustained antigen-specific CD4 T cell priming in aged hosts (12 months old), whereas tumor-specific CD8 T cell priming was not fully maintained compared to young reference animals (2 months old). Thus, CR appears to maintain immunological fitness of the CD4 T cell priming environment during aging, which is critical for optimal OX40-mediated responses.