Robust CD8 Research Articles

Abstract A031: Unhelpful CD4 help: Removal of conventional CD4+ T cells promotes priming of tumor antigen-specific CD8 T cells in the context of CD4-depletion therapy

Abstract Preclinical and clinical studies have used antibodies to deplete CD4-expressing cells to promote anti-tumor immunity. Specifically, a monoclonal anti-CD4 antibody (anti-CD4) has been employed to remove FOXP3+ CD4+ regulatory T cells (Tregs), which are known to impede anti-tumor immunity. Our previous studies demonstrated that administering anti-CD4 during B16 melanoma tumor growth in mice leads to the generation of tumor Ag-specific CD8 T cells that disseminate and form memory following surgical tumor excision. However, the importance of co-depleting other CD4-expressing cell compartments for anti-CD4 treatment efficacy are unknown. We utilized flow cytometry and single-cell RNA sequencing (scRNAseq) to evaluate the primary response of tumor Ag-specific CD8 T cells (pmel) in B16 melanoma tumor bearing mice treated with anti-CD4. Responses were compared to those induced by anti-PD1 and anti-CTLA4 dual immune checkpoint blockade (ICB). To determine the importance of homeostatic space in priming, homeostatic expansion and priming were decoupled, and neutralizing antibodies were administered. Treg-depleted (Foxp3-DTR) mice were used for comparison, and Batf3-/- mice and IL-2R blocking antibodies were used to determine requirements for CD8 T cell priming. Finally, scRNAseq was conducted on CD4 T cells from human melanoma tumors previously treated with ICB to characterize transcriptional properties of intratumoral CD4 T cells. Compared to ICB, anti-CD4 treatment elicited a more robust, disseminated, and persistent primary tumor Ag-specific CD8 T cell response. ScRNAseq revealed that anti-CD4 treatment induced more stem-like (TCF1+) memory precursor cells, whereas ICB induced more differentiated effector (Gzmb+) cells. Removal of homeostatic space or blockade of IL-7R and IL-15 during priming did not diminish pmel responses in anti-CD4 treated mice, indicating that homeostatic space was not required. Importantly, pmel cells were shown to produce their own IL-2, and pmel priming was significantly lower after IL-2 receptor blockade, suggesting dependence on autocrine IL-2 signals. Using DT-treated FOXP3-DTR mice, we found that targeted Treg depletion was insufficient for the pmel priming that disseminated and formed memory, indicating that total CD4 T cell depletion was required for this systemic response. Depletion of total CD4 T cells uniquely increased cDC1 proportions in tumor-draining LNs as well as their expression of CD86. However, treatment of tumor-bearing RAG-/- mice with anti-CD4 confirmed that depletion of CD4-expressing APC compartments does not contribute to anti-CD4 treatment efficacy. ScRNAseq of CD4 T cells from human melanoma tumors showed dominance of Tr1-like cells and other subsets without transcriptional evidence of helper differentiation, despite prior ICB. In mice, combination of anti-CD4 with dual ICB restored the systemic response of tumor-specific CD8 T cells. This study underscores the importance of eliminating conventional CD4 T cells in tumor-bearing hosts to elicit systemic primary and memory CD8 T cell responses. Citation Format: Christo P. C. Dragnev, Delaney E. Ramirez, Tyler G. Searles, Nathaniel Spicer, TIffany Chen, J. Louise Lines, Aaron R. Hawkes, Wilson L. Davis III, Asmaa Mohamed, Keisuke Shirai, Joesph D. Phillips, Pamela C. Rosato, Yina H. Huang, Mary Jo Turk. Unhelpful CD4 help: Removal of conventional CD4+ T cells promotes priming of tumor antigen-specific CD8 T cells in the context of CD4-depletion therapy [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor Immunology and Immunotherapy; 2024 Oct 18-21; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2024;12(10 Suppl):Abstract nr A031.

Lipopolyplex-formulated mRNA cancer vaccine elicits strong neoantigen-specific T cell responses and antitumor activity.

mRNA neoantigen cancer vaccine inducing neoantigen-specific T cell responses holds great promise for cancer immunotherapy; however, its clinical translation remains challenging because of suboptimal neoantigen prediction accuracy and low delivery efficiency, which compromise the in vivo therapeutic efficacy. We present a lipopolyplex (LPP)-formulated mRNA cancer vaccine encoding tandem neoantigens as a cancer therapeutic regimen. The LPP-formulated mRNA vaccines elicited robust neoantigen-specific CD8+ T cell responses in three syngeneic murine tumor models (CT26, MC38, and B16F10) to suppress tumor growth. Prophylactic cancer vaccine treatment completely prevented tumor development, and long-lasting memory T cells protected mice from tumor cell rechallenge. Combining the vaccine with immune checkpoint inhibitor further boosted the antitumor activity. Of note, LPP-based personalized cancer vaccine was administered in two cancer patients and induced meaningful neoantigen-specific T cell and clinical responses. In conclusion, we demonstrated that the LPP-based mRNA vaccine can elicit strong antitumor immune responses, and the results support further clinical evaluation of the therapeutic mRNA cancer vaccine.

Precise identification and tracking of HMGCR-reactive CD4+ T cells in the target tissue of patients with anti-HMGCR immune-mediated necrotising myopathy

BackgroundAnti-3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGCR)-positive immune-mediated necrotising myopathy (IMNM) is characterised by the presence of IgG autoantibodies against HMGCR and a strong association with specific HLA-DR alleles. Although these findings...

Potent neutralization of SARS-CoV-2 variants by RBD nanoparticle and prefusion-stabilized spike immunogens

We previously described a two-component protein nanoparticle vaccine platform that displays 60 copies of the SARS-CoV-2 spike protein RBD (RBD-NP). The vaccine, when adjuvanted with AS03, was shown to elicit robust neutralizing antibody and CD4 T cell responses in Phase I/II clinical trials, met its primary co-endpoints in a Phase III trial, and has been licensed by multiple regulatory authorities under the brand name SKYCovioneTM. Here we characterize the biophysical properties, stability, antigenicity, and immunogenicity of RBD-NP immunogens incorporating mutations from the B.1.351 (β) and P.1 (γ) variants of concern (VOCs) that emerged in 2020. We also show that the RBD-NP platform can be adapted to the Omicron strains BA.5 and XBB.1.5. We compare β and γ variant and E484K point mutant nanoparticle immunogens to the nanoparticle displaying the Wu-1 RBD, as well as to soluble prefusion-stabilized (HexaPro) spike trimers harboring VOC-derived mutations. We find the properties of immunogens based on different SARS-CoV-2 variants can differ substantially, which could affect the viability of variant vaccine development. Introducing stabilizing mutations in the linoleic acid binding site of the RBD-NPs resulted in increased physical stability compared to versions lacking the stabilizing mutations without deleteriously affecting immunogenicity. The RBD-NP immunogens and HexaPro trimers, as well as combinations of VOC-based immunogens, elicited comparable levels of neutralizing antibodies against distinct VOCs. Our results demonstrate that RBD-NP-based vaccines can elicit neutralizing antibody responses against SARS-CoV-2 variants and can be rapidly designed and stabilized, demonstrating the potential of two-component RBD-NPs as a platform for the development of broadly protective coronavirus vaccines.

Non-pathogenic E. coli displaying decoy-resistant IL18 mutein boosts anti-tumor and CAR NK cell responses.

The tumor microenvironment can inhibit the efficacy of cancer therapies through mechanisms such as poor trafficking and exhaustion of immune cells. Here, to address this challenge, we exploited the safety, tumor tropism and ease of genetic manipulation of non-pathogenic Escherichia coli (E. coli) to deliver key immune-activating cytokines to tumors via surface display on the outer membrane of E. coli K-12 DH5α. Non-pathogenic E. coli expressing murine decoy-resistant IL18 mutein (DR18) induced robust CD8+ T and natural killer (NK) cell-dependent immune responses and suppressed tumor progression in immune-competent colorectal carcinoma and melanoma mouse models. E. coli K-12 DH5α engineered to display human DR18 potently activated mesothelin-targeting chimeric antigen receptor (CAR) NK cells and enhance their trafficking into tumors, which extended survival in an NK cell treatment-resistant mesothelioma xenograft model by enhancing TNF signaling and upregulating NK activation markers. Our live bacteria-based immunotherapeutic system safely and effectively induces potent anti-tumor responses in treatment-resistant solid tumors, motivating further evaluation of this approach in the clinic.

Humoral and cellular immune responses in vaccinatedandunvaccinated children following SARS-CoV-2 Omicron infection.

The immune response in children elicited by SARS-CoV-2 Omicron infection alone or in combination with COVID-19 vaccination (hybrid immunity) is poorly understood. We examined the humoral and cellular immune response following SARS-CoV-2 Omicron infection in unvaccinated children and children who were previously vaccinated with COVID-19 mRNA vaccine. Participants were recruited as part of a household cohort study conducted during the Omicron predominant wave (Jan to July 2022) in Victoria, Australia. Blood samples were collected at 1, 3, 6 and 12 months following COVID-19 diagnosis. Humoral immune responses to SARS-CoV-2 Spike proteins from Wuhan, Omicron BA.1, BA.4/5 and JN.1, as well as cellular immune responses to Wuhan and BA.1 were assessed. A total of 43 children and 113 samples were included in the analysis. Following Omicron infection, unvaccinated children generated low antibody responses but elicited Spike-specific CD4 and CD8 T-cell responses. In contrast, vaccinated children infected with the Omicron variant mounted robust humoral and cellular immune responses to both ancestral strain and Omicron subvariants. Hybrid immunity persisted for at least 6 months post infection, with cellular immune memory characterised by the generation of Spike-specific polyfunctional CD8 T-cell responses. SARS-CoV-2 hybrid immunity in children is characterised by persisting SARS-CoV-2 antibodies and robust CD4 and CD8 T-cell activation and polyfunctional responses. Our findings contribute to understanding hybrid immunity in children and may have implications regarding COVID-19 vaccination and SARS-CoV-2 re-infections.

Co-regulation of innate and adaptive immune responses induced by ID93+GLA-SE vaccination in humans.

Development of an effective vaccine against tuberculosis is a critical step towards reducing the global burden of disease. A therapeutic vaccine might also reduce the high rate of TB recurrence and help address the challenges of drug-resistant strains. ID93+GLA-SE is a candidate subunit vaccine that will soon be evaluated in a phase 2b efficacy trial for prevention of recurrent TB among patients undergoing TB treatment. ID93+GLA-SE vaccination was shown to elicit robust CD4+ T cell and IgG antibody responses among recently treated TB patients in the TBVPX-203 Phase 2a study (NCT02465216), but the mechanisms underlying these responses are not well understood. In this study we used specimens from TBVPX-203 participants to describe the changes in peripheral blood gene expression that occur after ID93+GLA-SE vaccination. Analyses revealed several distinct modules of co-varying genes that were either up- or down-regulated after vaccination, including genes associated with innate immune pathways at 3 days post-vaccination and genes associated with lymphocyte expansion and B cell activation at 7 days post-vaccination. Notably, the regulation of these gene modules was affected by the dose schedule and by participant sex, and early innate gene signatures were correlated with the ID93-specific CD4+ T cell response. The results provide insight into the complex interplay of the innate and adaptive arms of the immune system in developing responses to vaccination with ID93+GLA-SE and demonstrate how dosing and schedule can affect vaccine responses.

Sequential immunization with chimeric hemagglutinin ΔNS1 attenuated influenza vaccines induces broad humoral and cellular immunity

Influenza viruses pose a threat to public health as evidenced by severe morbidity and mortality in humans on a yearly basis. Given the constant changes in the viral glycoproteins owing to antigenic drift, seasonal influenza vaccines need to be updated periodically and effectiveness often drops due to mismatches between vaccine and circulating strains. In addition, seasonal influenza vaccines are not protective against antigenically shifted influenza viruses with pandemic potential. Here, we have developed a highly immunogenic vaccination regimen based on live-attenuated influenza vaccines (LAIVs) comprised of an attenuated virus backbone lacking non-structural protein 1 (ΔNS1), the primary host interferon antagonist of influenza viruses, with chimeric hemagglutinins (cHA) composed of exotic avian head domains with a highly conserved stalk domain, to redirect the humoral response towards the HA stalk. In this study, we showed that cHA-LAIV vaccines induce robust serum and mucosal responses against group 1 stalk and confer antibody-dependent cell cytotoxicity activity. Mice that intranasally received cH8/1-ΔNS1 followed by a cH11/1-ΔNS1 heterologous booster had robust humoral responses for influenza A virus group 1 HAs and were protected from seasonal H1N1 influenza virus and heterologous highly pathogenic avian H5N1 lethal challenges. When compared with mice immunized with the standard of care or cold-adapted cHA-LAIV, cHA-ΔNS1 immunized mice had robust antigen-specific CD8+ T-cell responses which also correlated with markedly reduced lung pathology post-challenge. These observations support the development of a trivalent universal influenza vaccine for the protection against group 1 and group 2 influenza A viruses and influenza B viruses.

Enhancing the effectiveness of anti-respiratory virus vaccines by bolsteringmucosal immunityand cellular defenses.

A schematic diagram of intratracheal (IT) boosting, which leads to enhanced mucosal immunity and protective efficacy. IT boosting leads to significant expansion of mucosal neutralizing antibodies, along with robust CD8+and CD4+T-cell responses. Notably, IT boosting results in substantial and sustained activation of cytokine, natural killer, T, and B-cell pathways in the lung, contributing to enhanced mucosal immunity and overall protective efficacy.

CD4+ T cells exhibit distinct transcriptional phenotypes in the lymph nodes and blood following mRNA vaccination in humans.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and mRNA vaccination induce robust CD4+ T cell responses. Using single-cell transcriptomics, here, we evaluated CD4+ T cells specific for the SARS-CoV-2 spike protein in the blood and draining lymph nodes (dLNs) of individuals 3 months and 6 months after vaccination with the BNT162b2 mRNA vaccine. We analyzed 1,277 spike-specific CD4+ T cells, including 238 defined using Trex, a deep learning-based reverse epitope mapping method to predict antigen specificity. Human dLN spike-specific CD4+ follicular helper T (TFH) cells exhibited heterogeneous phenotypes, including germinal center CD4+ TFH cells and CD4+IL-10+ TFH cells. Analysis of an independent cohort of SARS-CoV-2-infected individuals 3 months and 6 months after infection found spike-specific CD4+ T cell profiles in blood that were distinct from those detected in blood 3 months and 6 months after BNT162b2 vaccination. Our findings provide an atlas of human spike-specific CD4+ T cell transcriptional phenotypes in the dLNs and blood following SARS-CoV-2 vaccination or infection.

Integration of Bioinformatics and Machine Learning to Identify CD8+ T Cell-Related Prognostic Signature to Predict Clinical Outcomes and Treatment Response in Breast Cancer Patients.

We assessed the abundance of CD8+ T cells in the TCGA and METABRIC datasets and obtained CTRGs through WGCNA. Subsequently, a prognostic signature (CTR score) was constructed from CTRGs screened by seven machine learning algorithms, and the relationship between the CTR score and TME, immunotherapy, and drug sensitivity was analyzed. Additionally, CTRGs' expression in different cells within TME was identified through single-cell analysis and spatial transcriptomics. Finally, the expression of CTRGs in clinical tissues was verified via RT-PCR. The CD8+ T cell-related prognostic signature consists of two CTRGs. In the TCGA and METABRIC datasets, the CTR score appeared to be negatively linked to the abundance of CD8+ T cells, and BC patients with higher risk score show a worse prognosis. The low CTR score group exhibits higher immune infiltration levels, closely associated with inhibiting the tumor microenvironment. Compared with the high CTR score group, the low CTR score group shows better responses to chemotherapy and immune checkpoint therapy. Single-cell analysis and spatial transcriptomics reveal the heterogeneity of two CTRGs in different cells. Compared with the adjacent tissues, CD163L1 and KLRB1 mRNA are downregulated in tumor tissues. This study establishes a robust CD8+ T cell-related prognostic signature, providing new insights for predicting the clinical outcomes and treatment responses of breast cancer patients.

A genetically engineered therapeutic lectin inhibits human influenza A virus infection and sustains robust virus-specific CD8 T cell expansion.

Native banana lectin (BanLec) is antiviral but highly mitogenic, which limits its therapeutic value. In contrast, the genetically engineered H84T BanLec (H84T) is not mitogenic but remains effective against influenza A virus (IAV) infection in mouse models. However, the potency and effect of H84T on human immune cells and IAV-specific immune responses is undetermined. We found that H84T efficiently inhibited IAV replication in human dendritic cells (DCs) from blood and tonsils, which preserved DC viability and allowed acquisition and presentation of viral antigen. Consequently, H84T-treated DCs initiated effective expansion of IAV-specific CD8 T cells. Furthermore, H84T preserved the capacity of IAV-exposed DCs to present a second non-IAV antigen and induce robust CD8 T cell expansion. This supports H84T as a potent antiviral in humans as it effectively inhibits IAV infection without disrupting DC function, and preserves induction of antigen-specific adaptive immune responses against diverse antigens, which likely is clinically beneficial.

Uniform Polymeric Nanovaccine Platform for Improving the Availability and Efficacy of Neoantigen Peptides.

Personalized cancer vaccines targeting specific neoantigens have been envisioned as one of the most promising approaches in cancer immunotherapy. However, the physicochemical variability of the identified neoantigens limits their efficacy as well as vaccine manufacturing in a uniform format. Herein, we developed a uniform nanovaccine platform based on poly(2-oxazoline)s (POx) to chemically conjugate neoantigen peptides, regardless of their physicochemical properties. This vaccine system could self-assemble into nanoparticles with uniform size (around 50 nm) and improve antigen accumulation as well as infiltration in the lymph node to increase antigen presentation. In vivo vaccination using this system conjugated with three predicted peptide neoantigen peptides from the MC38 tumor cell line induced 100% robust CD8+ T cell responses and superior tumor clearance compared to free peptides. This POx-based vaccine carrier represents a generalizable approach to increase the availability and efficacy of screened neoantigen peptides for a personalized cancer vaccine.

Heterologous mRNA/MVA delivering trimeric-RBD as effective vaccination regimen against SARS-CoV-2: COVARNA Consortium

ABSTRACT Despite the high efficiency of current SARS-CoV-2 mRNA vaccines in reducing COVID-19 morbidity and mortality, waning immunity and the emergence of resistant variants underscore the need for novel vaccination strategies. This study explores a heterologous mRNA/Modified Vaccinia virus Ankara (MVA) prime/boost regimen employing a trimeric form of the receptor binding domain (RBD) of the SARS-CoV-2 spike (S) protein compared to a homologous MVA/MVA regimen. In C57BL/6 mice, the RBD was delivered during priming via an mRNA vector encapsulated in nanoemulsions (NE) or lipid nanoparticles (LNP), followed by a booster with a replication-deficient MVA-based recombinant virus (MVA-RBD). This heterologous mRNA/MVA regimen elicited strong anti-RBD binding and neutralizing antibodies (BAbs and NAbs) against both the ancestral SARS-CoV-2 strain and different variants of concern (VoCs). Additionally, this protocol induced robust and polyfunctional RBD-specific CD4 and CD8 T cell responses, particularly in animals primed with mLNP-RBD. In K18-hACE2 transgenic mice, the LNP-RBD/MVA combination provided complete protection from morbidity and mortality following a live SARS-CoV-2 challenge compared with the partial protection observed with mNE-RBD/MVA or MVA/MVA regimens. Although the mNE-RBD/MVA regimen only protects half of the animals, it was able to induce antibodies with Fc-mediated effector functions besides NAbs. Moreover, viral replication and viral load in the respiratory tract were markedly reduced and decreased pro-inflammatory cytokine levels were observed. These results support the efficacy of heterologous mRNA/MVA vaccine combinations over homologous MVA/MVA regimen, using alternative nanocarriers that circumvent intellectual property restrictions of current mRNA vaccine formulations.

Dual‐Targeted Engineered Bacterial Outer Membrane Vesicles for Hepatocellular Carcinoma Immunotherapy

AbstractCluster of differentiation 47 (CD47) is an important innate immune checkpoint that empowers tumors to send “don't eat me” signals, leading to immune escape. CD47 monoclonal antibodies have achieved remarkable therapeutic success in hematological malignancies. However, their efficacy in solid tumors is limited, mainly because of immunosuppression in the tumor microenvironment. In addition, hematotoxicity severely hinders the clinical translation of CD47 antibodies. Here, a novel genetically programmed nanovesicle, OMV‐CD47/GPC3, is generated for hepatocellular carcinoma (HCC) immunotherapy by fusing anti‐CD47 nanobodies and anti‐GPC3 scFv onto bacterial outer membrane vesicles (OMVs). Following intravenous administration, dual‐targeted OMV‐CD47/GPC3 specifically recognized tumor cells expressing both CD47 and GPC3, thereby actively targeting and accumulating at the orthotopic HCC tumor site without hematotoxicity. OMV‐CD47/GPC3 potently blocked tumor CD47 and promoted macrophage phagocytosis. More importantly, immunogenic OMV‐CD47/GPC3 can effectively remodel the tumor immune microenvironment of orthotopic HCC, especially reprogram tumor‐associated macrophages (TAMs) to the M1‐phenotype and promote dendritic cell maturation, synergistically inducing a robust CD8+ T cell‐mediated anti‐tumor immune response. With the two‐pronged approach of immune checkpoint inhibition and immune activation, engineered OMV‐CD47/GPC3 significantly suppressed orthotopic HCC growth and prevented tumor recurrence and metastasis, thus providing a promising strategy for HCC immunotherapy.

Immature dendritic cell-targeting mRNA vaccine expressing PfCSP enhances protective immune responses against Plasmodium liver infection.

Resurgence in malaria has been noted in 2022 with 249 million clinical cases resulting in 608,000 deaths, mostly in children under five. Two vaccines, RTS, S, and more recently R21, targeting the circumsporozoite protein (CSP) are recommended by the WHO but are not yet widely available. Strong humoral responses to neutralize sporozoites before they can infect the hepatocytes are important for vaccine-mediated protection. Suboptimal protection conferred by these first-generation vaccines highlight the need for approaches to improve vaccine-induced immune responses. With the recent success of mRNA-LNP vaccines against COVID-19, there is growing interest in leveraging this approach to enhance malaria vaccines. Here, we present the development of a novel chemokine fusion mRNA vaccine aimed at boosting immune responses to PfCSP by targeting the immunogen to immature dendritic cells (iDC). Vaccination of mice with mRNA encoding full-length CSP fused to macrophage inflammatory protein 3 alpha (MIP3α) encapsulated within lipid nanoparticles (LNP) elicited robust CD4 + T cell responses and enhanced antibody titers against NANP repeat epitopes compared to a conventional CSP mRNA-LNP vaccine. Importantly, the CSP-MIP3α fusion vaccine provided significantly greater protection against liver infection upon challenge with P. berghei PfCSP transgenic sporozoites. This enhanced protection was associated with multifunctional CD4 + T cells levels and anti-NANP repeat titers. This study highlights the potential to augment immune responses to PfCSP through iDC targeting and bolster protection against malaria liver infection.

Arenavirus-Based Vectors Generate Robust SIV Immunity in Non-Human Primates.

Arenavirus-based vectors are being investigated as therapeutic vaccine candidates with the potential to elicit robust CD8 T-cell responses. We compared the immunogenicity of replicating (artPICV and artLCMV) and non-replicating (rPICV and rLCMV) arenavirus-based vectors expressing simian immunodeficiency virus (SIV) Gag and Envelope (Env) immunogens in treatment-naïve non-human primates. Heterologous regimens with non-replicating and replicating vectors elicited more robust SIV IFN-γ responses than a homologous regimen, and replicating vectors elicited significantly higher cellular immunogenicity than non-replicating vectors. The heterologous regimen elicited high anti-Env antibody titers when administered intravenously, with replicating vectors inducing significantly higher titers than non-replicating vectors. Intramuscular immunization resulted in more durable antibody responses than intravenous immunization for both vector platforms, with no difference between the replicating and non-replicating vectors. Overall, both replicating and non-replicating arenavirus vectors generated robust T- and B-cell-mediated immunity to SIV antigens in treatment-naïve non-human primates, supporting further evaluation of these vectors in a clinical setting for HIV therapy.

Stimuli-Responsive mRNA Vaccines to Induce Robust CD8+ T Cell Response via ROS-Mediated Innate Immunity Boosting.

The messenger RNA (mRNA) vaccines hold great significance in contagion prevention and cancer immunotherapy. However, safely and effectively harnessing innate immunity to stimulate robust and durable adaptive immune protection is crucial, yet challenging. In this study, we synthesized a library of stimuli-responsive bivalent ionizable lipids (srBiv iLPs) with smart molecular blocks responsive to esterase, H2O2, cytochrome P450, alkaline phosphatase, nitroreductase, or glutathione (GSH), aiming to leverage physiological cues to trigger fast lipid degradation, promote mRNA translation, and induce robust antitumor immunity via reactive oxygen species (ROS)-mediated boosting. After subcutaneous immunization, esterase-responsive vaccine (eBiv-mVac) was rapidly internalized and transported into the draining lymph nodes. It then underwent fast decaging and self-immolative degradation in esterase-rich antigen-presenting cells, releasing sufficient mRNA for antigen translation and massive reactive quinone methides to elevate ROS levels. This resulted in broad activation of innate immunity to boost T cell response, prompting a large number of primed antigen-specific CD8+ T cells to circulate and infiltrate into tumors (>1000-fold versus unvaccinated control), thereby orchestrating innate and adaptive immunity to control tumor growth. Moreover, by further combining our vaccination strategy with immune checkpoint blockade, we demonstrated a synergism that significantly amplified the magnitude and function of antigen-specific CD8+ T cells. This, in turn, caused potent systemic antitumor efficacy and prolonged survival with high complete response rate in xenograft and metastasis models. Overall, our generalized stimuli-responsive mRNA delivery platform promises a paradigm shift in the design of potent vaccines for cancer immunotherapy, as well as effective and precise carriers for gene editing, protein replacement, and cell engineering.

Regulatory T cells restrict immunity and pathology in distal tissue sites following a localized infection

Regulatory T cells (Tregs) are well-known to mediate peripheral tolerance at homeostasis, and there is a growing appreciation for their role in modulating infectious disease immunity. Following acute and chronic infections, Tregs can restrict pathogen-specific T cell responses to limit immunopathology. However, it is unclear if Tregs mediate control of pathology and immunity in distal tissue sites during localized infections. We investigated the role of Tregs in immunity and disease in various tissue compartments in the context of “mild” vaginal Zika virus infection. We found that Tregs are critical to generating robust virus-specific CD8 T cell responses in the initial infection site. Further, Tregs limit inflammatory cytokines and immunopathology during localized infection; a dysregulated immune response in Treg-depleted mice leads to increased T cell infiltrates and immunopathology in both the vagina and the central nervous system (CNS). Importantly, these CNS infiltrates are not present at the same magnitude during infection of Treg-sufficient mice, in which there is no CNS immunopathology. Our data suggest that Tregs are necessary to generate a robust virus-specific response at the mucosal site of infection, while Treg-mediated restriction of bystander inflammation limits immunopathology both at the site of infection as well as distal tissue sites.

DIPG-32. NEOANTIGEN HEAT SHOCK PROTEIN VACCINE, RHSC-DIPGVAX, IS ASSOCIATED WITH INCREASED VACCINE-INDUCED B CELLS AND BCR/TCR REPERTOIRE DIVERSITY IN PEDIATRIC PATIENTS WITH DIFFUSE MIDLINE GLIOMAS

Abstract BACKGROUND Diffuse midline gliomas (DMG/DIPG) remain a devastating class of tumors with limited treatment options. Cancer vaccines educate the immune system to tumor neoantigens to facilitate immune-mediated tumor destruction. DMGs have high-frequency, co-occurring neoantigens and are therefore a relevant target for activation of anti-tumor immunity via vaccine. To this end, we have initiated a clinical trial (NCT04943848) to determine if a neoantigen peptide-based vaccine with recombinant human heat-shock constitutive protein 70 and QS-21 adjuvant can promote anti-tumor immunity against DMG/DIPG. NCT04943848 is ongoing and now enrolling subsequent arms with rHSC-DIPGVax plus checkpoint blockade. METHODS Whole blood was collected before the first vaccine cycle (C1D1). Vaccine doses were administered every 2 weeks and blood was collected prior to the third or fifth vaccine cycle (C3D1 & C5D1). Peripheral blood mononuclear cells (PBMCs) were isolated and stored at -160°C. PBMCs from each patient, pre- and post-vaccine, were stained with human T-cell, myeloid, and B-cell antibody panels before spectral flow cytometry, single-cell RNA sequencing, and genomic DNA isolation for T- and B-cell receptor (TCR/BCR) sequencing. Spectral flow cytometry data was analyzed via FlowJo v10. TCR/BCR sequencing was processed via MiXCR and Immunarch. RESULTS Following vaccination, there were higher percentages of two mature CD20+CD19+IgM+ B cell populations, including a 4-1BBL+CD86+ population previously shown to induce robust CD8+ T-cell activation in adults with glioblastoma. Interestingly, given the recent discovery of TIM3’s importance in DIPG, we also identified TIM3-expressing CD4+ and CD8+ T cell populations. Finally, TCR/BCR sequencing demonstrated increased receptor repertoire diversity after vaccination, which is indicative of the vaccine shaping adaptive immunity. CONCLUSIONS Peripheral immune populations and TCR/BCR sequences change during vaccination with rHSC-DIPGVax. Ongoing analyses will determine the specificity of the patient immune response to vaccine antigens and correlate changes in immune populations to clinical course.