Agonistic anti-CD40 antibody profoundly suppresses the immune response to infection with lymphocytic choriomeningitis virus

Virus-specific CD4+ T cells contribute to clearance of human metapneumovirus despite exhibiting an impaired phenotype

Human metapneumovirus (HMPV) is a leading cause of respiratory tract infection in pediatric, elderly, and immunocompromised populations. Clearance of HMPV relies primarily on the destruction of infected cells by cytotoxic CD8+ T cells. However, signals provided by CD4+ helper T cells significantly impact the magnitude and effectiveness of CD8+ T cells. The role of CD4+ helper T cells in the immune response to HMPV is largely unknown. Antibody-mediated depletion of CD4+ T cells in a mouse model of acute infection led to delayed viral clearance and enhanced PD-1 expression on virus-specific CD8+ T cells. In accord with CD4 depletion experiments, blocking of CD40L reduced viral control and CD8+ T cell responses while stimulation of this pathway with an agonist antibody decreased the duration of infection. We identified a dominant CD4+ T cell epitope in the viral nucleoprotein and constructed the first MHC-II tetramer for HMPV. Analysis of pulmonary T cells revealed that virus-specific cells peak on day 10 post-infection and were TH1-skewed. Additionally, virus-specific CD4+ T cells displayed phenotypic and functional markers of impairment, including inhibitory receptor co-expression and prolonged PD-1 upregulation. However, genetic ablation of PD-1 signaling did not improve virus-specific CD4+ T cell functionality. Further characterization of virus-specific CD4+ helper T cells, their regulation by PD-1, and their role in CD8+ T cell impairment will provide new insights that aid in the design of effective vaccines for HMPV.

CD40 stimulation activates CD8+ T cells and controls HBV in CD4-depleted mice

Background & Aims

HBV treatment is challenging due to the persistence of the covalently closed circular DNA replication pool, which remains unaffected by antiviral intervention. In this study, we determined whether targeting antigen-presenting cells via CD40 stimulation represents an appropriate therapeutic approach for achieving sustained HBV control in a mouse model of HBV replication.

Methods

Mice were transduced with an adeno-associated virus encoding the HBV genome (AAV-HBV) to initiate HBV replication and were administered agonistic CD40 antibody. CD4-depleting antibody was administered in addition to the CD40 antibody. Viral antigens in the blood were measured over time to determine HBV control. HBV-specific CD8+ T cells were quantified in the spleen and liver at the experimental endpoint.

Results

CD40 stimulation in CD4-depleted AAV-HBV mice resulted in the clearance of HBsAg and HBeAg, along with a reduction in liver HBV mRNA, contrasting with CD4-competent counterparts. CD8+ T cells were indispensable for CD40-mediated HBV control, determined by HBV persistence following their depletion. In CD4-replete mice, CD40 stimulation initially facilitated the expansion of HBV-specific CD8+ T cells, which subsequently could not control HBV. Finally, α-CD4/CD40 treatment reduced antigenemia and liver HBV mRNA levels in chronic AAV-HBV mice, with further enhancement through synergy with immunization by VSV-MHBs (vesicular stomatitis virus expressing middle HBsAg).

Conclusions

Our findings underscore the potential of CD40 stimulation as a targeted therapeutic strategy for achieving sustained HBV control and reveal a CD4+ T cell-dependent limitation on CD40-mediated antiviral efficacy.

Impact and implications

Immunotherapy has the potential to overcome immune dysfunction in chronic HBV infection. Using a mouse model of HBV replication, this study shows that CD40 stimulation can induce sustained HBV control, which is dependent on CD8+ T cells and further enhanced by co-immunization. Unexpectedly, CD40-mediated HBV reduction was improved by the depletion of CD4+ cells. These findings suggest potential strategies for reversing HBV persistence in infected individuals.

Time-dependent enhancement of mRNA vaccines by 4-1BB costimulation

mRNA vaccines have demonstrated efficacy against COVID-19. However, concerns regarding waning immunity and breakthrough infections have motivated the development of next-generation vaccines with enhanced efficacy. In this study, we investigated the impact of 4-1BB costimulation on immune responses elicited by mRNA vaccines in mice. We first vaccinated mice with an mRNA vaccine encoding the SARS-CoV-2 spike antigen like the Moderna and Pfizer-BioNTech vaccines, followed by administration of 4-1BB costimulatory antibodies at various times post-vaccination. Administering 4-1BB costimulatory antibodies during the priming phase did not enhance immune responses. However, administering 4-1BB costimulatory antibodies after 96 hours elicited a significant improvement in CD8 T cell responses, leading to enhanced protection against breakthrough infections. A similar improvement in immune responses was observed with multiple mRNA vaccines, including vaccines against common cold coronavirus, human immunodeficiency virus (HIV), and arenavirus. These findings demonstrate a time-dependent effect by 4-1BB costimulation and provide insights for developing improved mRNA vaccines.

Adenovirus based virus-like-vaccines targeting endogenous retroviruses can eliminate growing colorectal cancers in mice

Endogenous retroviruses (ERVs) that make up 8% of the human genome have been associated with the development and progression of cancer. The murine model system of the melanoma associated retrovirus (MelARV), which is expressed in different murine cancer cell lines, can be used to study mechanisms and therapeutic approaches against ERVs in cancer. We designed a vaccine strategy (Ad5-MelARV) of adenoviruses encoding the MelARV proteins Gag and Env that assemble in vivo into virus-like particles displaying the cancer-associated MelARV Env to the immune system. The novel vaccine was designed to induce both humoral as well as cellular immune responses in order to attack ERV expressing tumor cells. Despite a lack of antibody induction, we found that T cell responses were strong enough to prevent colorectal CT26 tumor growth and progression in BALB/c mice after a single vaccination before or after tumor challenge. A combination with the checkpoint inhibitor anti-PD-1 further increased the efficacy of the vaccination leading to complete tumor regression. Furthermore, immune responses in vaccinated mice were not restricted to only one cancer cell line but vaccinated animals were also protected from a rechallenge with the distinct breast cancer cell line 4T1. Thus, the developed vaccine strategy could represent a novel tool to successfully target diverse ERV-bearing tumors in cancer patients.

Features of Effective T Cell-Inducing Vaccines against Chronic Viral Infections

For many years, the focus of prophylactic vaccines was to elicit neutralizing antibodies, but it has become increasingly evident that T cell-mediated immunity plays a central role in controlling persistent viral infections such as with human immunodeficiency virus, cytomegalovirus, and hepatitis C virus. Currently, various promising prophylactic vaccines, capable of inducing substantial vaccine-specific T cell responses, are investigated in preclinical and clinical studies. There is compelling evidence that protection by T cells is related to the magnitude and breadth of the T cell response, the type and homing properties of the memory T cell subsets, and their cytokine polyfunctionality and metabolic fitness. In this review, we evaluated these key factors that determine the qualitative and quantitative properties of CD4+ and CD8+ T cell responses in the context of chronic viral disease and prophylactic vaccine development. Elucidation of the mechanisms underlying T cell-mediated protection against chronic viral pathogens will facilitate the development of more potent, durable and safe prophylactic T cell-based vaccines.

Emerging nanotechnologies for cancer immunotherapy

Founded on the growing insight into the complex cancer-immune system interactions, adjuvant immunotherapies are rapidly emerging and being adapted for the treatment of various human malignancies. Immune checkpoint inhibitors, for example, have already shown clinical success. Nevertheless, many approaches are not optimized, require frequent administration, are associated with systemic toxicities and only show modest efficacy as monotherapies. Nanotechnology can potentially enhance the efficacy of such immunotherapies by improving the delivery, retention and release of immunostimulatory agents and biologicals in targeted cell populations and tissues. This review presents the current status and emerging trends in such nanotechnology-based cancer immunotherapies including the role of nanoparticles as carriers of immunomodulators, nanoparticles-based cancer vaccines, and depots for sustained immunostimulation. Also highlighted are key translational challenges and opportunities in this rapidly growing field.

Role of CD154 in cancer pathogenesis and immunotherapy

Many factors and molecules have been investigated as potential players in the pathogenesis or immunosurveillance of cancer. Among these, CD154 has been recognized as a co-stimulatory molecule with high potential for treating cancer, in addition to its contribution in the development of the disease. CD154 was initially described for its pivotal role in T cell-dependent humoral responses via an interaction with its classical receptor, CD40. Subsequent studies showed that CD154 is also implicated in cell-mediated immunity and inflammation via an interaction with CD40 alone or in combination with newly identified receptors, members of the integrin family, leading to the development of chronic inflammatory and autoimmune diseases. In the current article, we present an overview of the role of CD154 as a potential etiological factor in tumors inducing proliferation of malignant cells, their rescue from apoptosis and their invasiveness. In addition, this review describes the immuno-regulatory functions of CD154 against cancer reflected by its stimulation of antigen-presenting cells and the subsequent activation of effector cells, its enhancement of malignant cells' immunogenicity, its modulation of immune settings around tumors, and its initiation of proliferation inhibiting effects in malignant cells. In vitro as well as in vivo studies are outlined and a particular attention is given to clinical studies and progress reached at this point. Findings reviewed herein will improve our knowledge of the role of the CD154 system in cancers from causative to immunotherapeutic functions, paving the way for the identification of new targets for prevention and/or treatment of malignant disorders.

CD4⁺ and CD8⁺ T cell-dependent antiviral immunity requires STIM1 and STIM2

Calcium signaling is critical for lymphocyte function, and intracellular Ca2+ concentrations are regulated by store-operated Ca2+ entry (SOCE) through Ca2+ release-activated Ca2+ (CRAC) channels. In patients, loss-of-function mutations in CRAC channel components ORAI1 and STIM1 abolish SOCE and are associated with recurrent and chronic viral infections. Here, using mice with conditional deletion of Stim1 and its homolog Stim2 in T cells, we determined that both components are required for the maintenance of virus-specific memory CD8+ T cells and recall responses following secondary infection. In the absence of STIM1 and STIM2, acute viral infections became chronic. Early during infection, STIM1 and STIM2 were required for the differentiation of naive CD8+ T cells into fully functional cytolytic effector cells and mediated the production of cytokines and prevented cellular exhaustion in viral-specific CD8+ effector T cells. Importantly, memory and recall responses by CD8+ T cells required expression of STIM1 and STIM2 in CD4+ T cells. CD4+ T cells lacking STIM1 and STIM2 were unable to provide "help" to CD8+ T cells due to aberrant regulation of CD40L expression. Together, our data indicate that STIM1, STIM2, and CRAC channel function play distinct but synergistic roles in CD4+ and CD8+ T cells during antiviral immunity.

CD40 signaling to the rescue: A CD8 exhaustion perspective in chronic infectious diseases

Chronic infectious diseases such as HIV, HBV, and HCV, among others, cause severe morbidity and mortality globally. Progressive decline in CD8 functionality, survival, and proliferative potential-a phenomenon referred to as CD8 exhaustion-is believed to be responsible for poor pathogen control in chronic infectious diseases. While the role of negative inhibitory receptors such as PD-1 in augmenting CD8 exhaustion has been extensively studied, the role of positive costimulatory receptors remains poorly understood. In this review, we discuss how one such costimulatory pathway, CD40-CD40L, regulates CD8 dysfunction and rescue. While the significance of this pathway has been extensively investigated in models of autoimmunity, acute infectious diseases, and tumor models, the role played by CD40-CD40L in regulating CD8 exhaustion in chronic infectious diseases is just beginning to be understood. Considering that monotherapy with blocking antibodies targeting inhibitory PD-1-PD-L1 pathway is only partially effective at ameliorating CD8 exhaustion and that humanized CD40 agonist antibodies are currently available, a better understanding of the role of the CD40-CD40L pathway in chronic infectious diseases will pave the way for the development of more robust immunotherapeutic and prophylactic vaccination strategies.

Influenza-induced, helper-independent CD8+ T cell responses use CD40 costimulation at the late phase of the primary response

The helper-dependent pathway of priming CD8(+) T cells involves "licensing" of DCs by CD40L on CD4(+) T cells. The helper-independent ("helpless") pathways elicited by many viruses, including influenza, are less widely understood. We have postulated that CD40L can be up-regulated on DCs by such viruses, and this promotes priming of CD8(+) T cells via CD40. Most studies on costimulation have been performed in the presence of CD4(+) T cells, and so the role of CD40L costimulation under helpless circumstances has not been fully elucidated. Here, we investigated such a role for CD40L using CD40L KO mice. Although the number of influenza-specific CD8(+) T cells was unaffected by the absence of CD4(+) T cells, it was markedly decreased in the absence of CD40L. Proliferation (the number of CD44(+)BrdU(+) influenza-specific CD8(+) T cells) in the primary response was diminished in CD40L KO mice at Day 8 but not at Day 5 after infection. MLR studies indicated that CD40L expression on DCs was critical for CD8(+) T cell activation. Adoptive transfer of CD40 KO CD8(+) T cells compared with WT cells confirmed that CD40 on such cells was critical for the generation of primary anti-influenza CD8(+) T cell responses. The late effect also corresponded with the late expression of CD40 by influenza-specific CD8(+) T cells. We suggest that costimulation via CD40L on DCs and CD40 on CD8(+) T cells is important in optimizing primary CD8(+) T cell responses during influenza infection.

Agonistic antibodies directed at cell surface receptors and cardiovascular disease

Antibodies directed at receptors can block or stimulate them. Hallmark example of the latter action is Graves' disease where antibodies directed at the thyroid-stimulating hormone receptor exert an agonistic action. Recently, compelling evidence has been presented regarding agonistic antibodies directed against the alpha-adrenergic receptor, the beta-adrenergic receptors, the angiotensin II AT1 receptor, and the platelet-derived growth factor-alpha receptor. The antibodies could play a pathogenic role in various cardiovascular diseases, including hypertension, cardiomyopathy, pre-eclampsia, acute humoral rejection, and connective tissue disease. The mechanisms that result in the production of these antibodies are unclear, automated assays to determine their presence are beset with technical difficulties, and the therapeutic implications are uncertain. Nevertheless, the signaling phenomena resulting from these antibodies are well established and mechanistic studies are being intensively pursued. The discovery of agonistic antibodies may provide additional therapeutic avenues.

Synergistic CD40 signaling on APCs and CD8 T cells drives efficient CD8 response and memory differentiation

The role of CD4 help during CD8 response and memory differentiation has been clearly demonstrated in different experimental models. However, the exact mechanisms of CD4 help remain largely unknown and preclude replacement therapy to develop. Interestingly, studies have shown that administration of an agonist aCD40ab can substitute CD4 help in vitro and in vivo, whereas the targets of this antibody remain elusive. In this study, we address the exact role of CD40 expression on APCs and CD8 T cells using aCD40ab treatment in mice. We demonstrate that aCD40 antibodies have synergetic effects on APCs and CD8 T cells. Full efficiency of aCD40 treatment requires CD40 expression on both populations: if one of these cell populations is CD40-deficient, the CD8 T cell response is impaired. Most importantly, direct CD40 signaling on APCs and CD8 T cells affects CD8 T cell differentiation differently. In our model, CD40 expression on APCs plays an important but dispensable role on CD8 T cell expansion and effector functions during the early phase of the immune response. Conversely, CD40 on CD8 T cells is crucial and nonredundant for their progressive differentiation into memory cells. Altogether, these results highlight that CD40-CD40L-dependent and independent effects of CD4 help to drive a complete CD8 T cell differentiation.

Induction of potent anti-tumor responses while eliminating systemic side effects via liposome-anchored combinatorial immunotherapy

Immunostimulatory therapies that activate immune response pathways are of great interest for overcoming the immunosuppression present in advanced tumors. Agonistic anti-CD40 antibodies and CpG oligonucleotides have previously demonstrated potent, synergistic anti-tumor effects, but their clinical use even as monotherapies is hampered by dose-limiting inflammatory toxicity provoked upon systemic exposure. We hypothesized that by anchoring immuno-agonist compounds to lipid nanoparticles we could retain the bioactivity of therapeutics in the local tumor tissue and tumor-draining lymph node, but limit systemic exposure to these potent molecules. We prepared PEGylated liposomes bearing surface-conjugated anti-CD40 and CpG and assessed their therapeutic efficacy and systemic toxicity compared to soluble versions of the same immuno-agonists, injected intratumorally in the B16F10 murine model of melanoma. Anti-CD40/CpG-liposomes significantly inhibited tumor growth and induced a survival benefit similar to locally injected soluble anti-CD40 + CpG. Biodistribution analyses following local delivery showed that the liposomal carriers successfully sequestered anti-CD40 and CpG in vivo, reducing leakage into systemic circulation while allowing draining to the tumor-proximal lymph node. Contrary to locally-administered soluble immunotherapy, anti-CD40/CpG-liposomes did not elicit significant increases in serum levels of ALT enzyme, systemic inflammatory cytokines, or overall weight loss, confirming that off-target inflammatory effects had been minimized. The development of a delivery strategy capable of inducing robust anti-tumor responses concurrent with minimal systemic side effects is crucial for the continued progress of potent immunotherapies toward widespread clinical translation.

mTOR kinase inhibitor AZD8055 enhances the immunotherapeutic activity of an agonist CD40 antibody in cancer treatment

mTOR is a central mediator of cancer cell growth, but it also directs immune cell differentiation and function. On this basis, we had explored the hypothesis that mTOR inhibition can enhance cancer immunotherapy. Here, we report that a combination of αCD40 agonistic antibody and the ATP-competitive mTOR kinase inhibitory drug AZD8055 elicited synergistic antitumor responses in a model of metastatic renal cell carcinoma. In contrast to the well-established mTOR inhibitor rapamycin, AZD8055 increased the infiltration, activation, and proliferation of CD8(+) T cells and natural killer cells in liver metastatic foci when combined with the CD40 agonist. AZD8055/αCD40-treated mice also display an increased incidence of matured macrophages and dendritic cells compared with that achieved in mice by αCD40 or AZD8055 treatment alone. We found that the combination treatment also increased macrophage production of TNFα, which played an indispensable role in activation of the observed antitumor immune response. Levels of Th1 cytokines, including interleukin 12, IFN-γ, TNFα, and the Th1-associated chemokines RANTES, MIG, and IP-10 were each elevated significantly in the livers of mice treated with the combinatorial therapy versus individual treatments. Notably, the AZD8055/αCD40-induced antitumor response was abolished in IFN-γ(-/-) and CD40(-/-) mice, establishing the reliance of the combination therapy on host IFN-γ and CD40 expression. Our findings offer a preclinical proof of concept that, unlike rapamycin, the ATP-competitive mTOR kinase inhibitor AZD8055 can contribute with αCD40 treatment to trigger a restructuring of the tumor immune microenvironment to trigger regressions of an established metastatic cancer.

Parenchymal expression of CD40 exacerbates adenovirus-induced hepatitis in mice

The healthy adult human liver expresses low levels of major histocompatibility complex class II (MHC II) and undetectable levels of immune costimulatory molecules. However, high levels of MHC II, CD40, and B7 family molecules are expressed in the activated Kupffer cells and hepatocytes of patients with viral hepatitis. The precise role of these molecules in viral clearance and immune-mediated liver injury is not well understood. We hypothesized that parenchymal CD40 expression enhances T cell recruitment and effector functions, which may facilitate viral clearance and alleviate liver injury. To test this hypothesis, we generated novel liver-specific, conditional CD40 transgenic mice, and we challenged them intravenously with a recombinant replication-deficient adenovirus carrying Cre recombinase (AdCre). Wild-type mice infected with AdCre developed a relatively mild course of viral hepatitis and recovered spontaneously. CD40 expression in the livers of transgenic animals, however, resulted in CD80 and CD86 expression. The dysregulation of population dynamics and effector functions of intrahepatic lymphocytes (IHLs) resulted in severe lymphocytic infiltration, apoptosis, necroinflammation, and serum alanine aminotransferase elevations in a dose-dependent fashion. To our surprise, an early expansion and subsequent contraction of IHLs (especially CD8(+) and natural killer cells), accompanied by increased granzyme B and interferon-γ production, did not lead to faster viral clearance in CD40 transgenic mice.

CONCLUSION

Our results demonstrate that hepatic CD40 expression does not accelerate adenoviral clearance but rather exacerbates liver injury. This study unveils a previously unknown deleterious effect of hepatic CD40 on adenovirus-induced liver inflammation.

Immune modulation with weekly dosing of an agonist CD40 antibody in a phase I study of patients with advanced solid tumors

BACKGROUND

Single-dose infusion of the agonistic anti-CD40 monoclonal antibody (mAb) CP-870,893 accomplishes immune activation and clinical responses in patients with advanced cancers, but repeat dosing of this agent has not been reported.

RESULTS

Twenty-seven patients were enrolled. The most common adverse event was transient, infusion-related cytokine release syndrome (CRS). Dose-limiting toxicities included grade 3 CRS and grade 3 urticaria; the maximum tolerated dose (MTD) was estimated to be 0.2 mg/kg. Seven patients (26%) had stable disease as the best clinical response; no partial or complete responses were observed. At the MTD, patient B lymphocytes exhibited persistently increased expression of costimulatory and adhesion molecules without resetting to baseline between doses. In 4 of 8 patients (50%) evaluated at the MTD, there were marked declines in total CD3(+) T lymphocytes, as well as CD4(+) and CD8(+) subsets.

PATIENTS AND METHODS

Patients with advanced solid tumor malignancies received weekly intravenous infusions of CP-870,893 in four dose level cohorts. Safety and immune pharmacodynamics were assessed.

CONCLUSIONS

Weekly infusions of the agonist CD40 antibody CP-870,893 were well-tolerated, but there was little clinical activity in advanced cancer patients. Correlative studies demonstrate chronic B cell activation and in some patients, T cell depletion. Longer dosing intervals may be desirable for optimal immune pharmacodynamics.

Immunotherapy of viral infections

Among the microorganisms that cause diseases of medical or veterinary importance, the only group that is entirely dependent on the host, and hence not easily amenable to therapy via pharmaceuticals, is the viruses. Since viruses are obligate intracellular pathogens, and therefore depend a great deal on cellular processes, direct therapy of viral infections is difficult. Thus, modifying or targeting nonspecific or specific immune responses is an important aspect of intervention of ongoing viral infections. However, as a result of the unavailability of effective vaccines and the extended duration of manifestation, chronic viral infections are the most suitable for immunotherapies. We present an overview of various immunological strategies that have been applied for treating viral infections after exposure to the infectious agent.

Activation of tolerogenic dendritic cells in the tumor draining lymph nodes by CD8+ T cells engineered to express CD40 ligand

Tolerogenic dendritic cells in the tumor microenvironment can inhibit the generation and maintenance of robust antitumor T cell responses. In this study, we investigated the effects of local delivery of CD40L by tumor-reactive CD8(+) T cells on dendritic cell activation and antitumor T cell responses in the TRAMP model. To increase the immunostimulatory signal, CD40L was engineered, by deleting the majority of the cytoplasmic domain, to increase its levels of expression and duration on the surface of CD8(+) T cells. Tumor-reactive CD8(+) T cells expressing the truncated form of CD40L stimulated maturation of dendritic cells in vitro and in the prostate draining lymph nodes in vivo. Following dendritic cell maturation, a significantly higher fraction of adoptively transferred, tumor-reactive (reporter) CD8(+) T cells was stimulated to express IFN-gamma and infiltrate the prostate tissue. The antitumor CD8(+) T cell response was further enhanced if TRAMP mice were also immunized with a tumor-specific Ag. These findings demonstrate that augmented T cell responses can be achieved by engineering tumor-reactive T cells to deliver stimulatory signals to dendritic cells in the tumor microenvironment.

Principles of memory CD8 T-cells generation in relation to protective immunity

Memory T-cell responses are of vital importance in understanding the host's response against pathogens and cancer cells and to begin establishing the correlation of protection against disease. In this review, we discuss our own data in the general context of current knowledge to sketch tentative working principles for the induction of protective T-cell responses by vaccination. We draw attention to quantitative and qualitative aspects of the initial contact with antigen, as well as to the kinetics of events leading to the generation of memory T cells thereafter. Our arguments are based on the current distinction of memory T cells into two lineages: effector memory T cells (T(EM)) and central memory T cells (T(CM)). Our provisional conclusion is that protective T-cell responses correlate positively with the T cells of the central memory phenotype. In proposing a set of working principles to enable protective memory T cells by vaccination we address vaccination both in the context of the immunologically-inexperienced and immunologically-experienced individual, respectively. Finally, we draw attention to the interplay between systemic and local immunity as important factors in determining the success of memory T-cell responses in protecting the individual. We believe that considerations on the immunodynamics of memory induction and maintenance, memory lineage differentiation and their relation to protection may help design strategies to control disease caused by pathogens and cancer.

Recall responses by helpless memory CD8+ T cells are restricted by the up-regulation of PD-1

CD4 help is crucial for memory CD8(+) T cell development, yet the mechanisms of CD4 help and why (CD4) helpless memory CD8(+) T cells elicit poor recall responses are currently not well understood. In this study we investigated these questions using an in vivo acute virus infection model. We show herein that CD4 help during priming is required for memory CD8(+) T cell differentiation, and that stimulation of CD40 during priming rescues the helpless defects in the absence of CD4(+) T cells. The defective recall response by helpless memory cells did not correlate with the amount of cell death and was independent of TRAIL. However, helpless memory cells excessively up-regulated the inhibitory receptor PD-1 (programmed cell death-1), and PD-1 blockade enhanced the recall response of helpless memory cells. Furthermore, providing IL-2 signaling in vivo during the recall response reduced PD-1 expression and rescued the recall response of helpless memory cells. Our study identifies molecular pathways involved in CD4 help for memory CD8(+) T cell generation that are independent of TRAIL, and it provides therapeutic implications that helpless memory cell function can be restored at multiple stages through various immunological interventions.

TCR down-regulation controls virus-specific CD8+ T cell responses

The CD3gamma di-leucine-based motif plays a central role in TCR down-regulation. However, little is understood about the role of the CD3gamma di-leucine-based motif in physiological T cell responses. In this study, we show that the expansion in numbers of virus-specific CD8(+) T cells is impaired in mice with a mutated CD3gamma di-leucine-based motif. The CD3gamma mutation did not impair early TCR signaling, nor did it compromise recruitment or proliferation of virus-specific T cells, but it increased the apoptosis rate of the activated T cells by increasing down-regulation of the antiapoptotic molecule Bcl-2. This resulted in a 2-fold reduction in the clonal expansion of virus-specific CD8(+) T cells during the acute phase of vesicular stomatitis virus and lymphocytic choriomeningitis virus infections. These results identify an important role of CD3gamma-mediated TCR down-regulation in virus-specific CD8(+) T cell responses.

Breaking of CD8+ T cell tolerance through in vivo ligation of CD40 results in inhibition of chronic graft-versus-host disease and complete donor cell engraftment

In the DBA/2 --> unirradiated (C57BL/6 x DBA/2)F(1) model of chronic graft-vs-host disease (cGVHD), donor CD4(+) T cells play a critical role in breaking host B cell tolerance, while donor CD8(+) T cells are rapidly removed and the remaining cells fall into anergy. Previously we have demonstrated that in vivo ligation of GITR (glucocorticoid-induced TNF receptor-related gene) can activate donor CD8(+) T cells, subsequently converting the disease pattern from cGVHD to an acute form. In this study, we investigated the effect of an agonistic mAb against CD40 on cGVHD. Treatment of anti-CD40 mAb inhibited the production of anti-DNA IgG1 autoantibody and the development of glomerulonephritis. The inhibition of cGVHD occurred because anti-CD40 mAb prevented donor CD8(+) T cell anergy such that subsequently activated donor CD8(+) T cells deleted host CD4(+) T cells and host B cells involved in autoantibody production. Additionally, functionally activated donor CD8(+) T cells induced full engraftment of donor hematopoietic cells and exhibited an increased graft-vs-leukemia effect. However, induction of acute GVHD by donor CD8(+) T cells seemed to be not so apparent. Further CTL analysis indicated that there were lower levels of donor CTL activity against host cells in mice that received anti-CD40 mAb, compared with mice that received anti-GITR mAb. Taken together, our results suggest that a different intensity of donor CTL activity is required for removal of host hematopoietic cells, including leukemia vs induction of acute GVHD.

Regulatory and conventional CD4+ T cells show differential effects correlating with PD-1 and B7-H1 expression after immunotherapy

Recently, our laboratory reported that secondary CD8+ T cell-mediated antitumor responses were impaired following successful initial antitumor responses using various immunotherapeutic approaches. Although immunotherapy stimulated significant increases in CD8+ T cell numbers, the number of CD4+ T cells remained unchanged. The current investigation revealed a marked differential expansion of CD4+ T cell subsets. Successful immunotherapy surprisingly resulted in an expansion of CD4+Foxp3+ regulatory T (Treg) cells concurrent with a reduction of conventional CD4+ T (Tconv) cells, despite the marked antitumor responses. Following immunotherapy, we observed differential up-regulation of PD-1 on the surface of CD4+Foxp3+ Treg cells and CD4+Foxp3- Tconv cells. Interestingly, it was the ligand for PD-1, B7-H1 (PDL-1), that correlated with Tconv cell loss after treatment. Furthermore, IFN-gamma knockout (IFN-gamma-/-) and IFN-gamma receptor knockout (IFN-gammaR-/-) animals lost up-regulation of surface B7-H1 even though PD-1 expression of Tconv cells was not changed, and this correlated with CD4+ Tconv cell increases. These results suggest that subset-specific expansion may contribute to marked shifts in the composition of the T cell compartment, potentially influencing the effectiveness of some immunotherapeutic approaches that rely on IFN-gamma.

Enhanced efficacy and reduced toxicity of multifactorial adjuvants compared with unitary adjuvants as cancer vaccines

Identification of Toll-like receptors (TLRs) and their ligands, and tumor necrosis factor-tumor necrosis factor receptor (TNF-TNFR) pairs have provided the first logical, hypothesis-based strategies to molecularly concoct adjuvants to elicit potent cell-mediated immunity via activation of innate and adaptive immunity. However, isolated activation of one immune pathway in the absence of others can be toxic, ineffective, and detrimental to long-term, protective immunity. Effective engineered vaccines must include agents that trigger multiple immunologic pathways. Here, we report that combinatorial use of CD40 and TLR agonists as a cancer vaccine, compared with monotherapy, elicits high frequencies of self-reactive CD8(+) T cells, potent tumor-specific CD8(+) memory, CD8(+) T cells that efficiently infiltrate the tumor-burdened target organ; therapeutic efficacy; heightened ratios of CD8(+) T cells to FoxP3(+) cells at the tumor site; and reduced hepatotoxicity. These findings provide intelligent strategies for the formulation of multifactorial vaccines to achieve maximal efficacy in cancer vaccine trials in humans.