Immune Assessment Today: Optimizing and Standardizing Efforts to Monitor Immune Responses in Cancer and Beyond.

As part of a symposium, current and former directors of Immune Monitoring cores and investigative oncologists presented insights into the past, present and future of immune assessment. Dr. Gnjatic presented a classification of immune monitoring technologies ranging from universally applicable to experimental protocols, while emphasizing the need for assay harmonization. Dr. Obeng discussed physiologic differences among CD8 T cells that align with anti-tumor responses. Dr. Lyerly presented the Soldano Ferrone lecture, commemorating the passionate tumor immunologist who inspired many, and covered a timeline of monitoring technology development and its importance to immuno-oncology. Dr. Sonabend presented recent achievements in glioblastoma treatment, accentuating the range of monitoring techniques that allowed him to refine patient selection for clinical trials. Dr. Guevara-Patiño focused on hypoxia within the tumor environment and stressed that T cell viability is not to be confused with functionality. Dr. Butterfield accentuated monitoring of dendritic cell metabolic (dys)function as a determinant for tumor vaccine success. Lectures were interspersed with select abstract presentations. To summarize the concepts, Dr. Maecker from Stanford led an informative forum discussion, pointing towards the future of immune monitoring. Immune monitoring continues to be a guiding light towards effective immunotherapeutic strategies.

Bispecific CD33/CD123 targeted chimeric antigen receptor T cells for the treatment of acute myeloid leukemia.

CD33 and CD123 are expressed on the surface of human acute myeloid leukemia blasts and other noncancerous tissues such as hematopoietic stem cells. On-target off-tumor toxicities may limit chimeric antigen receptor T cell therapies that target both CD33 and CD123. To overcome this limitation, we developed bispecific human CD33/CD123 chimeric antigen receptor (CAR) T cells with an "AND" logic gate. We produced novel CD33 and CD123 scFvs from monoclonal antibodies that bound CD33 and CD123 and activated T cells. Screening of CD33 and CD123 CAR T cells for cytotoxicity, cytokine production, and proliferation was performed, and we selected scFvs for CD33/CD123 bispecific CARs. The bispecific CARs split 4-1BB co-stimulation on one scFv and CD3ζ on the other. In vitro testing of cytokine secretion and cytotoxicity resulted in selecting bispecific CAR 1 construct for in vivo analysis. The CD33/CD123 bispecific CAR T cells were able to control acute myeloid leukemia (AML) in a xenograft AML mouse model similar to monospecific CD33 and CD123 CAR T cells while showing no on-target off-tumor effects. Based on our findings, human CD33/CD123 bispecific CAR T cells are a promising cell-based approach to prevent AML and support clinical investigation.

Combination oncolytic virus, radiation therapy, and immune checkpoint inhibitor treatment in anti-PD-1-refractory cancer.

BACKGROUND: Immunotherapies are becoming front-line treatments for many advanced cancers, and combinations of two or more therapies are beginning to be investigated. Based on their individual antitumor capabilities, we sought to determine whether combination oncolytic virus (OV) and radiation therapy (RT) may improve cancer outcomes. METHODS: To investigate the activity of this combination therapy, we used in vitro mouse and human cancer cell lines as well as a mouse model of skin cancer. After initial results, we further included immune checkpoint blockade, whose addition constituted a triple combination immunotherapy. RESULTS: Our findings demonstrate that OV and RT reduce tumor growth via conversion of immunologically 'cold' tumors to 'hot', via a CD8+ T cell-dependent and IL-1α-dependent mechanism that is associated with increased PD-1/PD-L1 expression, and the triple combination of OV, RT, and PD-1 checkpoint inhibition impedes tumor growth and prolongs survival. Further, we describe the response of a PD-1-refractory patient with cutaneous squamous cell carcinoma who received the triple combination of OV, RT, and immune checkpoint inhibitor (ICI), and went on to experience unexpected, prolonged control and survival. He remains off-treatment and is without evidence of progression for >44 months since study entry. CONCLUSIONS: Effective systemic antitumor immune response is rarely elicited by a single therapy. In a skin cancer mouse model, we demonstrate improved outcomes with combination OV, RT, and ICI treatment, which is associated with mechanisms involving augmented CD8+ T cell infiltration and IL-1α expression. We report tumor reduction and prolonged survival of a patient with skin cancer treated with combination OV, RT, and ICI. Overall, our data provide strong rationale for combining OV, RT, and ICI for treatment of patients with ICI-refractory skin and potentially other cancers.

EGFR Inhibition by Cetuximab Modulates Hypoxia and IFN Response Genes in Head and Neck Squamous Cell Carcinoma.

Head and neck squamous cell carcinoma (HNSCC) has one of the most hypoxic and immunosuppressive tumor microenvironments (TME) among solid tumors. However, there is no proven therapeutic strategy to remodel the TME to be less hypoxic and proinflammatory. In this study, we classified tumors according to a Hypoxia-Immune signature, characterized the immune cells in each subgroup, and analyzed the signaling pathways to identify a potential therapeutic target that can remodel the TME. We confirmed that hypoxic tumors had significantly higher numbers of immunosuppressive cells, as evidenced by a lower ratio of CD8+ T cells to FOXP3+ regulatory T cells, compared with nonhypoxic tumors. Patients with hypoxic tumors had worse outcomes after treatment with pembrolizumab or nivolumab, anti-programmed cell death-1 inhibitors. Our expression analysis also indicated that hypoxic tumors predominantly increased the expression of the EGFR and TGFß pathway genes. Cetuximab, an anti-EGFR inhibitor, decreased the expression of hypoxia signature genes, suggesting that it may alleviate the effects of hypoxia and remodel the TME to become more proinflammatory. Our study provides a rationale for treatment strategies combining EGFR-targeted agents and immunotherapy in the management of hypoxic HNSCC. Significance: While the hypoxic and immunosuppressive TME of HNSCC has been well described, comprehensive evaluation of the immune cell components and signaling pathways contributing to immunotherapy resistance has been poorly characterized. We further identified additional molecular determinants and potential therapeutic targets of the hypoxic TME to fully leverage currently available targeted therapies that can be administered with immunotherapy.

Antibody-Drug Conjugates in the Treatment of Urothelial Cancer.

Antibody-drug conjugates (ADCs) have transformed the treatment landscape in oncology and become an essential therapeutic modality. In urothelial carcinoma (UC), the two ADCs that have been especially successful in clinical practice are enfortumab vedotin and sacituzumab govitecan. These drugs are currently approved as monotherapy for later lines of treatment in locally advanced or metastatic UC and have had a significant impact for patients with limited treatment options. Combinational trials, as well as additional ADCs, are currently being investigated in the treatment of UC for subsequent lines of therapy as overall survival rates remain dismal.

Emerging monoclonal antibody therapies in the treatment of metastatic urothelial carcinoma.

INTRODUCTION: The treatment landscape for advanced-stage, unresectable or metastatic urothelial carcinoma (mUC) has shifted dramatically over a short period of time, with new therapeutic agents available for clinical use. However, despite these recent advances in the field, mUC continues to be a disease with significant morbidity and mortality and remains generally incurable. While platinum-based therapy remains the backbone of therapy, many patients are ineligible for chemotherapy or have failed initial chemotherapy treatment. In post-platinum treated patients, immunotherapy and antibody drug conjugates have provided incremental advances, but agents with better therapeutic index guided by precision medicine are needed. AREAS COVERED: This article covers the available monoclonal antibody therapies in mUC excluding immunotherapy and antibody drug conjugates. Included are a review of data utilizing monoclonal antibodies targeting VEG-F, HER-2, FGFR, and KIR-2 in the setting of mUC. A literature search from 6/2022- 9/2022 was performed utilizing PubMed with key terms including urothelial carcinoma, monoclonal antibody, VEG-F, HER-2, FGFR. EXPERT OPINION: Often used in combination with immunotherapy or other therapeutic agents, monoclonal antibody therapies have exhibited efficacy in mUC in early trials. Upcoming clinical trials will further explore their full clinical utility in treating mUC patients.

NKG2D signaling shifts the balance of CD8 T cells from single cytokine- to polycytokine-producing effector cells.

CD8 T cells play a critical role in immunity against intracellular pathogens and cancer. A primary objective of T cell-based vaccine strategies is the induction of durable and effective immune responses. Achieving this goal involves more than simply boosting the numbers of responding T cells. Of particular interest is the induction of CD8 T cells with polycytokine capability, specifically with the ability of CD8 T cells to co-produce IFNγ, TNFα and IL-2. The presence of these polycytokine-producing CD8 T cells correlates strongly with protection against foreign pathogens and cancer. Therefore, approaches capable of inducing such polyfunctional responses are needed. NKG2D engagement on CD8 T cells has been shown to result in increased effector response. However, the manner in which NKG2D engagement results in improved CD8 T cell effector response is unclear. Here we demonstrate in vitro and in vivo that NKG2D engagement by its natural ligand, Rae-1ε, shifts the balance from single cytokine to polycytokine (IL-2, IFNγ, and TFNα) production. These data define a previously unrecognized process in which NKG2D costimulation on CD8 T cells results in improved effector responses.

Barriers and Opportunities for CAR T-Cell Targeting of Solid Tumors.

CAR T-cell therapy has transformed the treatment of hematological malignancies of the B cell lineage. However, the quest to fulfil the same promise for solid tumors is still in its infancy. This review summarizes some of the challenges that the field is trying to overcome for effective treatment of human carcinomas, including tumor heterogeneity, the paucity of truly tumor-specific targets, immunosuppression and metabolic restrictions at solid tumor beds, and defective T-cell trafficking. All these barriers are being currently investigated and, in some cases, targeted, by multiple independent groups. With clinical interventions against multiple human malignancies and different platforms under accelerated clinical development, the next few years will see an array of cellular therapies, including CAR T-cells, progressively becoming routine interventions to eliminate currently incurable diseases, as it happened with some hematological malignancies.

T cell repertoire in peripheral blood as a potential biomarker for predicting response to concurrent cetuximab and nivolumab in head and neck squamous cell carcinoma.

BACKGROUND: T cell receptor (TCR) signaling profile is a fundamental property that underpins both adaptive and innate immunity in the host. Despite its potential clinical relevance, the TCR repertoire in peripheral blood has not been thoroughly explored for its value as an immunotherapy efficacy biomarker in head and neck squamous cell carcinoma (HNSCC). The purpose of the present study is to characterize and compare the TCR repertoire in peripheral blood mononuclear cells (PBMC) from patients with HNSCC treated with the combination of cetuximab and nivolumab. METHODS: We used the immunoSEQ assay to sequence the TCR beta (TCR-B) chain repertoire from serially obtained PBMC at baseline and during the treatments from a total of 41 patients who received the combination (NCT03370276). Key TCR repertoire metrics, including diversity and clonality, were calculated and compared between patients with different therapy responses and clinical characteristics (eg, human papillomavirus (HPV) status and smoking history). Patient survival outcomes were compared according to patient groups stratified by the TCR-B clonotyping. To confirm the observed patterns in TCR spectrum, samples from patients who achieved complete response (CR) and partial response (PR) were further profiled with the immunoSEQ deep resolution assay. RESULTS: Our data indicated that the patients who achieved CR and PR had an increased TCR sequence diversity in their baseline samples, this tendency being more pronounced in HPV-negative patients or those with a smoking history. Notably, the CR/PR group had the lowest proportion of patients with oligoclonal TCR clones (2 out of 8 patients), followed by the stable disease group (9 out of 20 patients) and lastly the progressive disease group (7 out of 10 patients). An overall trend toward favorable patient survival was also observed in the polyclonal group. Finally, we reported the shared TCR clones across patients within the same response group, as well as the shared clones by aligning immunoSEQ reads with TCR data retrieved from The Cancer Genome Atlas- head and neck squamous cell carcinoma (TCGA-HNSC) cohort. CONCLUSIONS: Our data suggest that, despite the great clinical heterogeneity of HNSCC and the limited responders in the present cohort, the peripheral TCR repertoires from pretreatment PBMC may be developed as biomarkers for the benefit of immunotherapy in HNSCC.

Gut Microbial Shifts Indicate Melanoma Presence and Bacterial Interactions in a Murine Model.

Through a multitude of studies, the gut microbiota has been recognized as a significant influencer of both homeostasis and pathophysiology. Certain microbial taxa can even affect treatments such as cancer immunotherapies, including the immune checkpoint blockade. These taxa can impact such processes both individually as well as collectively through mechanisms from quorum sensing to metabolite production. Due to this overarching presence of the gut microbiota in many physiological processes distal to the GI tract, we hypothesized that mice bearing tumors at extraintestinal sites would display a distinct intestinal microbial signature from non-tumor-bearing mice, and that such a signature would involve taxa that collectively shift with tumor presence. Microbial OTUs were determined from 16S rRNA genes isolated from the fecal samples of C57BL/6 mice challenged with either B16-F10 melanoma cells or PBS control and analyzed using QIIME. Relative proportions of bacteria were determined for each mouse and, using machine-learning approaches, significantly altered taxa and co-occurrence patterns between tumor- and non-tumor-bearing mice were found. Mice with a tumor had elevated proportions of Ruminococcaceae, Peptococcaceae.g_rc4.4, and Christensenellaceae, as well as significant information gains and ReliefF weights for Bacteroidales.f__S24.7, Ruminococcaceae, Clostridiales, and Erysipelotrichaceae. Bacteroidales.f__S24.7, Ruminococcaceae, and Clostridiales were also implicated through shifting co-occurrences and PCA values. Using these seven taxa as a melanoma signature, a neural network reached an 80% tumor detection accuracy in a 10-fold stratified random sampling validation. These results indicated gut microbial proportions as a biosensor for tumor detection, and that shifting co-occurrences could be used to reveal relevant taxa.

HSP70iQ435A to subdue autoimmunity and support anti-tumor responses.

Developing immunosuppressive therapies for autoimmune diseases comes with a caveat that immunosuppression may promote the risk of developing other conditions or diseases. We have previously shown that biolistic delivery of an expression construct encoding inducible HSP70 (HSP70i) with one amino acid modification in the dendritic cell (DC) activating moiety 435-445 (HSP70iQ435A) to mouse skin resulted in significant immunosuppressive activity of autoimmune vitiligo, associated with fewer tissue infiltrating T cells. To prepare HSP70iQ435A as a potential therapeutic for autoimmune vitiligo, in this study we evaluated whether and how biolistic delivery of HSP70iQ435A in mice affects anti-tumor responses. We found that HSP70iQ435A in fact supports anti-tumor responses in melanoma-challenged C57BL/6 mice. Biolistic delivery of the HSP70iQ435A-encoding construct to mice elicited significant anti-HSP70 titers, and anti-HSP70 IgG and IgM antibodies recognize surface-expressed and cytoplasmic HSP70i in human and mouse melanoma cells. A peptide scan revealed that the anti-HSP70 antibodies recognize a specific C-terminal motif within the HSP70i protein. The antibodies elicited surface CD107A expression among mouse NK cells, representative of antibody-mediated cellular cytotoxicity (ADCC), supporting the concept, that HSP70iQ435A-encoding DNA elicits a humoral response to the stress protein expressed selectively on the surface of melanoma cells. Thus, besides limiting autoimmunity and inflammation, HSP70iQ435A elicits humoral responses that limit tumor growth and may be used in conjunction with immune checkpoint inhibitors to not only control tumor but to also limit adverse events following tumor immunotherapy.

The Role of the NKG2D in Vitiligo.

Vitiligo is an acquired multifactorial disease that affects melanocytes and results in skin depigmentation. In this review, we examine the role of cells stress and self-reactive T cells responses. Given the canonical and non-canonical functions of NKG2D, such as authenticating stressed target and enhance TCR signaling, we examine how melanocyte stress leads to the expression of ligands that are recognized by the activating receptor NKG2D, and how its signaling results in the turning of T cells against self (melanocyte suicide by proxy). We also discuss how this initiation phase is followed by T cell perpetuation, as NKG2D signaling results in self-sustained long-lasting T cells, with improved cytolytic properties.

NKG2D signaling certifies effector CD8 T cells for memory formation.

BACKGROUND: The development of memory responses is an evolutionary function of the adaptive immune system. We propose that for the immune system to populate the memory compartment with the best-suited CD8 T cells it utilizes a process of certification or molecular accreditation mediated through Natural Killer Group 2D (NKG2D). This process of certification assures that the memory compartment is filled with CD8 T cells that have demonstrated their ability to kill their cognate targets through a two-step process that utilizes T cell receptor (TCR) and NKG2D signaling. METHODS: One week after immunization with peptide-pulsed dendritic cells, NKG2D signaling was transiently blocked in vivo with a single injection of neutralizing antibodies. Under such conditions, we determined the importance of NKG2D signaling during the effector phase for memory formation without compromising NKG2D signaling at the memory phase. Both open (polyclonal) and closed (monoclonal) CD8 T cell repertoires were studied. RESULTS: We show that signaling through NKG2D mediated this certification. Temporary blockade of NKG2D signaling during the effector phase resulted in the formation of highly defective memory CD8 T cells characterized by altered expression of the ribosomal protein S6 and epigenetic modifiers, suggesting modifications in the T cell translational machinery and epigenetic programming. Finally, these uncertified memory cells were not protective against a B16 tumor challenge. CONCLUSION: Signaling through NKG2D during the effector phase (certification) favors the development of functional memory CD8 T cells, a previously undescribed role for NKG2D. Temporary blockade of NKG2D signaling during the effector phase results in the formation of highly defective memory CD8 T cells potentially by affecting the expression of the ribosomal protein S6 and epigenetic modifiers, suggesting alterations in T cell translational machinery and epigenetic programming.

HSP70iQ435A-Encoding DNA Repigments Vitiligo Lesions in Sinclair Swine.

Human HSP70iQ435A carries a single amino-acid modification within the dendritic cell activating region and tolerizes dendritic cells in vitro. The underlying DNA was used to prevent and treat disease in vitiligo mouse models through reduced dendritic cell activation and diminished skin T-cell infiltration, suggesting the same may be useful for patients. Physiologic differences between mouse and human skin then called for studies in large animals with human-like skin. We established the efficiency of DNA jet injection into swine skin before subcloning HSP70iQ435A into clinically suitable vector pUMVC3. Vitiligo lesions in Sinclair swine were treated with plasmid DNA to measure changes in depigmentation, T-cell infiltration, expression of HSP70i in skin, serum HSP70i, and anti-HSP70i serum titers. Remarkable repigmentation following HSP70iQ435A-encoding DNA treatment persisted throughout the 6-month follow-up period. Repigmentation was accompanied by an initial influx of T cells accompanied by increased CD4/CD8 ratios, waning by week 15. Melanocytes spanned the border of repigmenting skin, suggesting that melanocyte repopulation precedes skin melanization. Serum titer fluctuations were not treatment-associated. Importantly, treatment did not interfere with melanoma immunosurveillance. These data encourage clinical testing of HSP70iQ435A.

Functions of NKG2D in CD8+ T cells: an opportunity for immunotherapy.

Natural killer group 2 member D (NKG2D) is a type II transmembrane receptor. NKG2D is present on NK cells in both mice and humans, whereas it is constitutively expressed on CD8+ T cells in humans but only expressed upon T-cell activation in mice. NKG2D is a promiscuous receptor that recognizes stress-induced surface ligands. In NK cells, NKG2D signaling is sufficient to unleash the killing response; in CD8+ T cells, this requires concurrent activation of the T-cell receptor (TCR). In this case, the function of NKG2D is to authenticate the recognition of a stressed target and enhance TCR signaling. CD28 has been established as an archetype provider of costimulation during T-cell priming. It has become apparent, however, that signals from other costimulatory receptors, such as NKG2D, are required for optimal T-cell function outside the priming phase. This review will focus on the similarities and differences between NKG2D and CD28; less well-described characteristics of NKG2D, such as the potential role of NKG2D in CD8+ T-cell memory formation, cancer immunity and autoimmunity; and the opportunities for targeting NKG2D in immunotherapy.

Non-oncogenic Acute Viral Infections Disrupt Anti-cancer Responses and Lead to Accelerated Cancer-Specific Host Death.

In light of increased cancer prevalence and cancer-specific deaths in patients with infections, we investigated whether infections alter anti-tumor immune responses. We report that acute influenza infection of the lung promotes distal melanoma growth in the dermis and leads to accelerated cancer-specific host death. Furthermore, we show that during influenza infection, anti-melanoma CD8+ T cells are shunted from the tumor to the infection site, where they express high levels of the inhibitory receptor programmed cell death protein 1 (PD-1). Immunotherapy to block PD-1 reverses this loss of anti-tumor CD8+ T cells from the tumor and decreases infection-induced tumor growth. Our findings show that acute non-oncogenic infection can promote cancer growth, raising concerns regarding acute viral illness sequelae. They also suggest an unexpected role for PD-1 blockade in cancer immunotherapy and provide insight into the immune response when faced with concomitant challenges.

Enhanced responses to tumor immunization following total body irradiation are time-dependent.

The development of successful cancer vaccines is contingent on the ability to induce effective and persistent anti-tumor immunity against self-antigens that do not typically elicit immune responses. In this study, we examine the effects of a non-myeloablative dose of total body irradiation on the ability of tumor-naïve mice to respond to DNA vaccines against melanoma. We demonstrate that irradiation followed by lymphocyte infusion results in a dramatic increase in responsiveness to tumor vaccination, with augmentation of T cell responses to tumor antigens and tumor eradication. In irradiated mice, infused CD8(+) T cells expand in an environment that is relatively depleted in regulatory T cells, and this correlates with improved CD8(+) T cell functionality. We also observe an increase in the frequency of dendritic cells displaying an activated phenotype within lymphoid organs in the first 24 hours after irradiation. Intriguingly, both the relative decrease in regulatory T cells and increase in activated dendritic cells correspond with a brief window of augmented responsiveness to immunization. After this 24 hour window, the numbers of dendritic cells decline, as does the ability of mice to respond to immunizations. When immunizations are initiated within the period of augmented dendritic cell activation, mice develop anti-tumor responses that show increased durability as well as magnitude, and this approach leads to improved survival in experiments with mice bearing established tumors as well as in a spontaneous melanoma model. We conclude that irradiation can produce potent immune adjuvant effects independent of its ability to induce tumor ablation, and that the timing of immunization and lymphocyte infusion in the irradiated host are crucial for generating optimal anti-tumor immunity. Clinical strategies using these approaches must therefore optimize such parameters, as the correct timing of infusion and vaccination may mean the difference between an ineffective treatment and successful tumor eradication.

Mutant HSP70 reverses autoimmune depigmentation in vitiligo.

Vitiligo is an autoimmune disease characterized by destruction of melanocytes, leaving 0.5% of the population with progressive depigmentation. Current treatments offer limited efficacy. We report that modified inducible heat shock protein 70 (HSP70i) prevents T cell-mediated depigmentation. HSP70i is the molecular link between stress and the resultant immune response. We previously showed that HSP70i induces an inflammatory dendritic cell (DC) phenotype and is necessary for depigmentation in vitiligo mouse models. Here, we observed a similar DC inflammatory phenotype in vitiligo patients. In a mouse model of depigmentation, DNA vaccination with a melanocyte antigen and the carboxyl terminus of HSP70i was sufficient to drive autoimmunity. Mutational analysis of the HSP70i substrate-binding domain established the peptide QPGVLIQVYEG as invaluable for DC activation, and mutant HSP70i could not induce depigmentation. Moreover, mutant HSP70iQ435A bound human DCs and reduced their activation, as well as induced a shift from inflammatory to tolerogenic DCs in mice. HSP70iQ435A-encoding DNA applied months before spontaneous depigmentation prevented vitiligo in mice expressing a transgenic, melanocyte-reactive T cell receptor. Furthermore, use of HSP70iQ435A therapeutically in a different, rapidly depigmenting model after loss of differentiated melanocytes resulted in 76% recovery of pigmentation. Treatment also prevented relevant T cells from populating mouse skin. In addition, ex vivo treatment of human skin averted the disease-related shift from quiescent to effector T cell phenotype. Thus, HSP70iQ435A DNA delivery may offer potent treatment opportunities for vitiligo.

CD8(+) T cells sabotage their own memory potential through IFN-γ-dependent modification of the IL-12/IL-15 receptor α axis on dendritic cells.

CD8(+) T cell responses have been shown to be regulated by dendritic cells (DCs) and CD4(+) T cells, leading to the tenet that CD8(+) T cells play a passive role in their own differentiation. In contrast, by using a DNA vaccination model, to separate the events of vaccination from those of CD8(+) T cell priming, we demonstrate that CD8(+) T cells, themselves, actively limit their own memory potential through CD8(+) T cell-derived IFN-γ-dependent modification of the IL-12/IL-15Rα axis on DCs. Such CD8(+) T cell-driven cytokine alterations result in increased T-bet and decreased Bcl-2 expression, and thus decreased memory progenitor formation. These results identify an unrecognized role for CD8(+) T cells in the regulation of their own effector differentiation fate and a previously uncharacterized relationship between the balance of inflammation and memory formation.

NKG2D signaling on CD8⁺ T cells represses T-bet and rescues CD4-unhelped CD8⁺ T cell memory recall but not effector responses.

CD4-unhelped CD8(+) T cells are functionally defective T cells primed in the absence of CD4(+) T cell help. Given the co-stimulatory role of natural-killer group 2, member D protein (NKG2D) on CD8(+) T cells, we investigated its ability to rescue these immunologically impotent cells. We demonstrate that augmented co-stimulation through NKG2D during priming paradoxically rescues memory, but not effector, CD8(+) T cell responses. NKG2D-mediated rescue is characterized by reversal of elevated transcription factor T-box expressed in T cells (T-bet) expression and recovery of interleukin-2 and interferon-γ production and cytolytic responses. Rescue is abrogated in CD8(+) T cells lacking NKG2D. Augmented co-stimulation through NKG2D confers a high rate of survival to mice lacking CD4(+) T cells in a CD4-dependent influenza model and rescues HIV-specific CD8(+) T cell responses from CD4-deficient HIV-positive donors. These findings demonstrate that augmented co-stimulation through NKG2D is effective in rescuing CD4-unhelped CD8(+) T cells from their pathophysiological fate and may provide therapeutic benefits.