Intratumoral STING agonist reverses immune evasion in PD-(L)1-refractory Merkel cell carcinoma: mechanistic insights from detailed biomarker analyses.

BACKGROUND: Antibodies blocking programmed death (PD)-1 or its ligand (PD-L1) have revolutionized cancer care, but many patients do not experience durable benefits. Novel treatments to stimulate antitumor immunity are needed in the PD-(L)1 refractory setting. The stimulator of interferon genes (STING) protein, an innate sensor of cytoplasmic DNA, is a promising target with several agonists in development. However, response rates in most recent clinical trials have been low and mechanisms of response remain unclear. We report detailed biomarker analyses in a patient with anti-PD-L1 refractory, Merkel cell polyomavirus (MCPyV)-positive, metastatic Merkel cell carcinoma (MCC) who was treated with an intratumoral (IT) STING agonist (ADU-S100) plus intravenous anti-PD-1 antibody (spartalizumab) and experienced a durable objective response with regression of both injected and non-injected lesions. METHODS: We analyzed pretreatment and post-treatment tumor and peripheral blood samples from our patient with single-cell RNA sequencing, 30-parameter flow cytometry, T cell receptor sequencing, and multiplexed immunohistochemistry. We analyzed cancer-specific CD8 T cells using human leukocyte antigen (HLA)-I tetramers loaded with MCPyV peptides. We also analyzed STING expression and signaling in the tumor microenvironment (TME) of 88 additional MCC tumor specimens and in MCC cell lines. RESULTS: We observed high levels of MCPyV-specific T cells (12% of T cells) in our patient's tumor at baseline. These cancer-specific CD8 T cells exhibited characteristics of exhaustion including high TOX and low TCF1 proteins. Following treatment with STING-agonist plus anti-PD-1, IT CD8 T cells expanded threefold. We also observed evidence of likely improved antigen presentation in the MCC TME (greater than fourfold increase of HLA-I-positive cancer cells). STING expression was not detected in any cancer cells within our patient's tumor or in 88 other MCC tumors, however high STING expression was observed in immune and stromal cells within all 89 MCC tumors. CONCLUSIONS: Our results suggest that STING agonists may be able to work indirectly in MCC via signaling through immune and stromal cells in the TME, and may not necessarily need STING expression in the cancer cells. This approach may be particularly effective in tumors that are already infiltrated by inflammatory cells in the TME but are evading immune detection via HLA-I downregulation.

Merkel cell carcinoma refractory to anti-PD(L)1: utility of adding ipilimumab for salvage therapy.

Merkel cell carcinoma (MCC) incidence has risen to approximately 3,000 cases annually in the USA. Although anti-programmed cell death (ligand) 1 (PD-(L)1) agents are now the first-line treatment for advanced MCC, approximately 50% of such patients do not persistently benefit. In PD-(L)1-refractory cases, ipilimumab (anti-cytotoxic T lymphocyte antigen-4) is often added; however, the extent of the clinical benefit of this combination is controversial. We identified one prospective study, three retrospective studies, and three case reports regarding this combination in refractory MCC. The aggregate response rate from retrospective studies was 32% (13 of 41 patients) with 4 complete responses (CR) and 9 partial responses (PR). In the prospective study, the response rate was very similar at 31% (8 of 26 patients; 4 CR, 4 PR). Response durability was highly variable (range 2 to >43 months), with patients achieving CR having greater durability. Immune-related adverse events (irAEs) were ≥grade III in 29% (retrospective cohort, N=41) and 36% (prospective cohort, N=50). While these aggregate data indicate adding ipilimumab should be considered in this setting, many patients with refractory MCC are ineligible due to comorbidities/irAEs, and approximately 70% will not benefit from this regimen. There is thus a significant unmet need in PD-(L)1-refractory MCC and clinical trials in this setting should be encouraged.

Postoperative Radiation Therapy Is Indicated for "Low-Risk" Pathologic Stage I Merkel Cell Carcinoma of the Head and Neck Region but Not for Other Locations.

Purpose: The role of postoperative radiation therapy (PORT) in early stage Merkel cell carcinoma (MCC) is controversial. We analyzed the role of PORT in preventing local recurrences (LR) among patients with low-risk, pathologic stage I MCC based on the location of the primary tumors: head/neck (HN) versus non-HN sites. Methods and Materials: One hundred forty-seven patients with MCC were identified that had "low risk" disease (pathologic T1 primary tumor, negative microscopic margins, negative pathologic node status, no immunosuppression or prior systemic therapy). LR was defined as tumor recurrence within 2 cm of the primary surgical bed, and its frequency was estimated with the cumulative incidence method. Results: Seventy-nine patients received PORT (30 HN, 49 non-HN) with a median dose of 50 Gy (range, 8-64 Gy) and 68 patients were treated with surgery alone (30 HN, 38 non-HN). Overall, PORT was associated with a decreased risk of LR (5-year rate: 0% vs 9.5%; P = .004) with 6 LRs observed in the surgery alone group. Although the addition of PORT significantly reduced LR rates among patients with HN MCC (0% vs. 21%; P = .034), no LRs were observed in patients with non-HN MCC managed with surgery alone. There was no significant difference in MCC-specific survival comparing HN versus non-HN groups, with or without PORT. Conclusions: For low-risk, pathologic stage I MCC of the extremities and trunk, excellent local control rates were achieved with surgery, and PORT is not indicated. However, PORT was associated with a significant reduction in LRs among low-risk MCC of the HN.

Increased risk of recurrence and disease-specific death following delayed postoperative radiation for Merkel cell carcinoma.

BACKGROUND: Merkel cell carcinoma (MCC) is often treated with surgery and postoperative radiation therapy (PORT). The optimal time to initiate PORT (Time-to-PORT [ttPORT]) is unknown. PURPOSE: We assessed if delays in ttPORT were associated with inferior outcomes. METHODS: Competing risk regression was used to evaluate associations between ttPORT and locoregional recurrence (LRR) for patients with stage I/II MCC in a prospective registry and adjust for covariates. Distant metastasis and death were competing risks. RESULTS: The cohort included 124 patients with median ttPORT of 41 days (range: 8-125 days). Median follow-up was 55 months. 17 (14%) patients experienced a LRR, 14 (82%) of which arose outside the radiation field. LRR at 5 years was increased for ttPORT >8 weeks vs ≤ 8 weeks, 28.0% vs 9.2%, P = .006. There was an increase in the cumulative incidence of MCC-specific death with increasing ttPORT (HR = 1.14 per 1-week increase, P = .016). LIMITATIONS: The relatively low number of LRRs limited the extent of our multivariable analyses. CONCLUSIONS: Delay of PORT was associated with increased LRR, usually beyond the radiation field. This is consistent with the tendency of MCC to spread quickly via lymphatics. Initiation of PORT within 8 weeks was associated with improved locoregional control and MCC-specific survival.

The Evolving Treatment Landscape of Merkel Cell Carcinoma.

OPINION STATEMENT: Merkel cell carcinoma (MCC) has a high risk of recurrence and requires unique treatment relative to other skin cancers. The patient population is generally older, with comorbidities. Multidisciplinary and personalized care is therefore paramount, based on patient preferences regarding risks and benefits. Positron emission tomography and computed tomography (PET-CT) is the most sensitive staging modality and reveals clinically occult disease in ~ 16% of patients. Discovery of occult disease spread markedly alters management. Newly diagnosed, localized disease is often managed with sentinel lymph node biopsy (SLNB), local excision, primary wound closure, and post-operative radiation therapy (PORT). In contrast, metastatic disease is usually treated systemically with an immune checkpoint inhibitor (ICI). However, one or more of these approaches may not be indicated. Criteria for such exceptions and alternative approaches will be discussed. Because MCC recurs in 40% of patients and early detection/treatment of advanced disease is advantageous, close surveillance is recommended. Given that over 90% of initial recurrences arise within 3 years, surveillance frequency can be rapidly decreased after this high-risk period. Patient-specific assessment of risk is important because recurrence risk varies widely (15 to > 80%: Merkelcell.org/recur) depending on baseline patient characteristics and time since treatment. Blood-based surveillance tests are now available (Merkel cell polyomavirus (MCPyV) antibodies and circulating tumor DNA (ctDNA)) with excellent sensitivity that can spare patients from contrast dye, radioactivity, and travel to a cancer imaging facility. If recurrent disease is locoregional, management with surgery and/or RT is typically indicated. ICIs are now the first line for systemic/advanced MCC, with objective response rates (ORRs) exceeding 50%. Cytotoxic chemotherapy is sometimes used for debulking disease or in patients who cannot tolerate ICI. ICI-refractory disease is the major problem faced by this field. Fortunately, numerous promising therapies are on the horizon to address this clinical need.

Neoadjuvant Therapy Induces a Potent Immune Response to Sarcoma, Dominated by Myeloid and B Cells.

PURPOSE: To characterize changes in the soft-tissue sarcoma (STS) tumor immune microenvironment induced by standard neoadjuvant therapy with the goal of informing neoadjuvant immunotherapy trial design. EXPERIMENTAL DESIGN: Paired pre- and postneoadjuvant therapy specimens were retrospectively identified for 32 patients with STSs and analyzed by three modalities: multiplexed IHC, NanoString, and RNA sequencing with ImmunoPrism analysis. RESULTS: All 32 patients, representing a variety of STS histologic subtypes, received neoadjuvant radiotherapy and 21 (66%) received chemotherapy prior to radiotherapy. The most prevalent immune cells in the tumor before neoadjuvant therapy were myeloid cells (45% of all immune cells) and B cells (37%), with T (13%) and natural killer (NK) cells (5%) also present. Neoadjuvant therapy significantly increased the total immune cells infiltrating the tumors across all histologic subtypes for patients receiving neoadjuvant radiotherapy with or without chemotherapy. An increase in the percentage of monocytes and macrophages, particularly M2 macrophages, B cells, and CD4+ T cells was observed postneoadjuvant therapy. Upregulation of genes and cytokines associated with antigen presentation was also observed, and a favorable pathologic response (≥90% necrosis postneoadjuvant therapy) was associated with an increase in monocytic infiltrate. Upregulation of the T-cell checkpoint TIM3 and downregulation of OX40 were observed posttreatment. CONCLUSIONS: Standard neoadjuvant therapy induces both immunostimulatory and immunosuppressive effects within a complex sarcoma microenvironment dominated by myeloid and B cells. This work informs ongoing efforts to incorporate immune checkpoint inhibitors and novel immunotherapies into the neoadjuvant setting for STSs.

Intersection of Two Checkpoints: Could Inhibiting the DNA Damage Response Checkpoint Rescue Immune Checkpoint-Refractory Cancer?

Metastatic cancers resistant to immunotherapy require novel management strategies. DNA damage response (DDR) proteins, including ATR (ataxia telangiectasia and Rad3-related), ATM (ataxia telangiectasia mutated) and DNA-PK (DNA-dependent protein kinase), have been promising therapeutic targets for decades. Specific, potent DDR inhibitors (DDRi) recently entered clinical trials. Surprisingly, preclinical studies have now indicated that DDRi may stimulate anti-tumor immunity to augment immunotherapy. The mechanisms governing how DDRi could promote anti-tumor immunity are not well understood; however, early evidence suggests that they can potentiate immunogenic cell death to recruit and activate antigen-presenting cells to prime an adaptive immune response. Merkel cell carcinoma (MCC) is well suited to test these concepts. It is inherently immunogenic as ~50% of patients with advanced MCC persistently benefit from immunotherapy, making MCC one of the most responsive solid tumors. As is typical of neuroendocrine cancers, dysfunction of p53 and Rb with upregulation of Myc leads to the very rapid growth of MCC. This suggests high replication stress and susceptibility to DDRi and DNA-damaging agents. Indeed, MCC tumors are particularly radiosensitive. Given its inherent immunogenicity, cell cycle checkpoint deficiencies and sensitivity to DNA damage, MCC may be ideal for testing whether targeting the intersection of the DDR checkpoint and the immune checkpoint could help patients with immunotherapy-refractory cancers.

Radiation and Modulation of the Tumor Immune Microenvironment in Non-Small Cell Lung Cancer.

Immune checkpoint inhibitors are approved for a variety of indications for locally advanced and metastatic non-small cell lung cancer (NSCLC), and trials are ongoing in the early-stage setting. There is an unmet need to understand which patients may derive benefit from immunotherapies and how to harness combined modality therapies to improve overall response rates and durability. Here, we review studies from the bench-to-bedside to examine the role of radiation therapy (RT) on the tumor immune microenvironment in NSCLC with an eye toward augmenting antitumor immunity. Together, these data provide a foundation for developing future clinical trials harnessing RT to augment antitumor immunity and highlight the need for correlative translational studies to directly characterize the impact of RT on the human NSCLC tumor immune microenvironment.

Combined Intranasal Nanoemulsion and RIG-I Activating RNA Adjuvants Enhance Mucosal, Humoral, and Cellular Immunity to Influenza Virus.

Current influenza virus vaccines are focused on humoral immunity and are limited by the short duration of protection, narrow cross-strain efficacy, and suboptimal immunogenicity. Here, we combined two chemically and biologically distinct adjuvants, an oil-in-water nanoemulsion (NE) and RNA-based agonists of RIG-I, to determine whether the diverse mechanisms of these adjuvants could lead to improved immunogenicity and breadth of protection against the influenza virus. NE activates TLRs, stimulates immunogenic apoptosis, and enhances cellular antigen uptake, leading to a balanced TH1/TH2/TH17 response when administered intranasally. RIG-I agonists included RNAs derived from Sendai and influenza viral defective interfering RNAs (IVT DI, 3php, respectively) and RIG-I/TLR3 agonist, poly(I:C) (pIC), which induce IFN-Is and TH1-polarized responses. NE/RNA combined adjuvants potentially allow for costimulation of multiple innate immune receptor pathways, more closely mimicking patterns of activation occurring during natural viral infection. Mice intranasally immunized with inactivated A/Puerto Rico/8/1934 (H1N1) (PR/8) adjuvanted with NE/IVT DI or NE/3php (but not NE/pIC) showed synergistic enhancement of systemic PR/8-specific IgG with significantly greater avidity and virus neutralization activity than the individual adjuvants. Notably, NE/IVT DI induced protective neutralizing titers after a single immunization. Hemagglutinin stem-specific antibodies were also improved, allowing recognition of heterologous and heterosubtypic hemagglutinins. All NE/RNAs elicited substantial PR/8-specific sIgA. Finally, a unique cellular response with enhanced TH1/TH17 immunity was induced with the NE/RNAs. These results demonstrate that the enhanced immunogenicity of the adjuvant combinations was synergistic and not simply additive, highlighting the potential value of a combined adjuvant approach for improving the efficacy of vaccination against the influenza virus.

Postoperative, Single-Fraction Radiation Therapy in Merkel Cell Carcinoma of the Head and Neck.

PURPOSE: Conventionally fractionated, postoperative radiation therapy (cPORT; 50 Gy in 25 fractions) is considered for patients with Merkel cell carcinoma (MCC) to improve locoregional control. However, cPORT is associated with acute toxicity, especially in the head and neck (H&N) region, and requires daily treatments over several weeks. We previously reported high rates of durable local control with minimal toxicity using 8-Gy single-fraction radiation therapy (SFRT) in the metastatic setting. We report early results on a cohort of patients with localized H&N MCC who received postoperative SFRT if a cPORT regimen was not feasible. METHODS AND MATERIALS: Twelve patients with localized MCC of the H&N (clinical/pathologic stages I-II) and no prior radiation therapy to the region were identified from an institutional review board-approved prospective registry who underwent surgical resection followed by postoperative SFRT. Time to event was calculated starting from the date of resection before SFRT. The cumulative incidence of in-field locoregional recurrences and out-of-field recurrences was estimated with death as a competing risk. RESULTS: Twelve patients with H&N MCC were identified with clinical/pathologic stages I-II H&N MCC. Median age at diagnosis was 81 years (range, 58-96 years); 25% had immunosuppression. At a median follow-up of 19 months (range, 8-34), there were no in-field locoregional recurrences. A single out-of-field regional recurrence was observed, which was successfully salvaged. There were no MCC-specific deaths. No radiation-associated toxicities greater than grade 1 (Common Terminology Criteria for Adverse Events v5) were observed. CONCLUSIONS: Preliminary data suggest that SFRT could offer a potential alternative to cPORT to treat the primary site for localized H&N MCC, particularly in elderly or frail patients, with promising in-field local control and minimal toxicity. Further data with validation in larger cohorts are needed to confirm the sustained safety and efficacy of postoperative SFRT.

Oncolytic Newcastle disease virus expressing a checkpoint inhibitor as a radioenhancing agent for murine melanoma.

BACKGROUND: Monoclonal antibodies (mAbs) targeting negative regulators, or checkpoint molecules (e.g. PD1/PD-L1 & CTLA4), of anti-tumoural T cells have demonstrated clinical efficacy in treating several neoplastic diseases. While many patients enjoy remarkable responses to checkpoint inhibitors, a majority show adverse effects. Understanding how checkpoint inhibitors may augment established chemotherapy or radiotherapy regimens or other immunotherapies like oncolytic viruses may lead to better clinical outcomes measured by improved efficacy with reduced toxicity. Here, we assess how Newcastle disease virus (NDV), an oncolytic virus in clinical testing, may interact with radiotherapy to enhance checkpoint inhibitor blockade. METHODS: An immunocompetent B16-F10 murine melanoma model, generally considered to be a poorly immunogenic or "cold" tumour, was utilised to query whether combining localised radiotherapy with NDV may be more effective than either therapy alone in controlling tumours in mice treated with anti-PD1 or anti-CTLA4 monoclonal antibodies. We also investigated whether localised administration of a checkpoint inhibitor through an intratumoural injection of NDV that expresses anti-CTLA4 single-chain variable fragment (scFv) is comparable to systemic administration of anti-CTLA4 when combined with radiation in mediating its anti-tumour efficacy. Response rates were characterised by measuring tumour size over time, observation of complete tumour regression, and overall survival. FINDINGS: Our results show that combining NDV plus radiotherapy with checkpoint inhibitors (PD1 or CTLA4 targeted mAbs) results in significantly better complete tumour regression rates with an abscopal effect in a murine model of melanoma than either single therapy combined with checkpoint inhibitors. Finally, we also show that localised administration of a recombinant NDV expressing anti-CTLA4 plus radiation is comparable to systemic anti-CTLA4 plus radiation in mediating its anti-tumour effect as assayed by survival benefit. INTERPRETATION: Our results show that oncolytic NDV plus radiotherapy work together with checkpoint inhibitors to enhance tumour clearance of murine melanoma. NDV is an effective radiotherapy dose-sparing and immunotherapeutic agent capable of transgenic, in vivo expression of an anti-CTLA4 targeted scFv antibody with the potential to spare systemic exposure. FUNDING: The National Institutes of Health grant HHSN272201400008C supported the work. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

2D kV orthogonal imaging with fiducial markers is more precise for daily image guided alignments than soft-tissue cone beam computed tomography for prostate radiation therapy.

PURPOSE: The hypothesis is that 2-dimensional kV orthogonal imaging with fiducial markers (kV-FM) and soft-tissue cone beam computed tomography (ST-CBCT) are equally reproducible for daily positional alignments for image guided (IG) intensity modulated radiation therapy (IMRT) for prostate cancer. METHODS AND MATERIALS: Ten patients undergoing definitive treatment for prostate cancer with IG-IMRT were imaged daily with kV-FM and ST-CBCT. For each acquired kV and CBCT image, offline alignments to the digitally reconstructed radiograph or planning CT, respectively, were made twice by the same physician to assess intraobserver test-retest reproducibility. The 256 kV and 142 CBCT images were analyzed, and the test-retest analysis was performed again on a subset of images by another physician to verify the results. RESULTS: The results demonstrated that kV-FM had better intraobserver test-retest reproducibility in the anterior-posterior (AP; 95% confidence interval [CI] Pearson correlation coefficient [r], 0.987-0.991), left-right (LR; 95% CI r, 0.955-0.969), and superior-inferior (SI; 95% CI r, 0.971-0.980) directions for daily IG alignments compared with ST-CBCT (AP: 95% CI r, 0.804-0.877; LR: 95% CI r, 0.877-0.924; SI: 95% CI r, 0.791-0.869). Errors associated with intraobserver test-retest reproducibility were submillimeter with kV-FM (AP: 0.4 ± 0.7 mm; RL: 0.4 ± 1.0 mm; SI: 0.5 ± 0.7 mm) compared with ST-CBCT (AP: 2.1 ± 2.2 mm; LR: 1.3 ± 1.4 mm; SI: 1.2 ± 1.8 mm). The mean shift differences between kV-FM and ST-CBCT were 0.3 ± 3.8 mm for AP, -1.1 ± 8.5 mm for LR, and -2.0 ± 3.7 mm for SI. Dose-volume histograms were generated and showed that test-retest variability associated with ST-CBCT IG-alignments resulted in significantly increased dose to normal structures and a reduced planning target volume dose in many patients. CONCLUSIONS: The kV-FM-based daily IG alignment for IMRT of prostate cancer is more precise than ST-CBCT, as assessed by a physician's ability to reproducibly align images. Given the magnitude of the error introduced by inconsistency in making ST-CBCT alignments, these data support a role for daily kV imaging of FM to enhance the precision of external beam dose delivery to the prostate.

Synthetic Toll-Like Receptor 4 (TLR4) and TLR7 Ligands Work Additively via MyD88 To Induce Protective Antiviral Immunity in Mice.

We previously demonstrated that the combination of synthetic small-molecule Toll-like receptor 4 (TLR4) and TLR7 ligands is a potent adjuvant for recombinant influenza virus hemagglutinin, inducing rapid and sustained immunity that is protective against influenza viruses in homologous, heterologous, and heterosubtypic murine challenge models. Combining the TLR4 and TLR7 ligands balances Th1 and Th2-type immune responses for long-lived cellular and neutralizing humoral immunity against the viral hemagglutinin. Here, we demonstrate that the protective response induced in mice by this combined adjuvant is dependent upon TLR4 and TLR7 signaling via myeloid differentiation primary response gene 88 (MyD88), indicating that the adjuvants function in vivo via their known receptors, with negligible off-target effects, to induce protective immunity. The combined adjuvant acts via MyD88 in both bone marrow-derived and non-bone marrow-derived radioresistant cells to induce hemagglutinin-specific antibodies and protect mice against influenza virus challenge. The protective efficacy generated by immunization with this adjuvant and recombinant hemagglutinin antigen is transferable with serum from immunized mice to recipient mice in a homologous, but not a heterologous, H1N1 viral challenge model. Depletion of CD4+ cells after an established humoral response in immunized mice does not impair protection from a homologous challenge; however, it does significantly impair recovery from a heterologous challenge virus, highlighting an important role for vaccine-induced CD4+ cells in cross-protective vaccine efficacy. The combination of the two TLR agonists allows for significant dose reductions of each component to achieve a level of protection equivalent to that afforded by either single agent at its full dose.IMPORTANCE Development of novel adjuvants is needed to enhance immunogenicity to provide better protection from seasonal influenza virus infection and improve pandemic preparedness. We show here that several dose combinations of synthetic TLR4 and TLR7 ligands are potent adjuvants for recombinant influenza virus hemagglutinin antigen induction of humoral and cellular immunity against viral challenges. The components of the combined adjuvant work additively to enable both antigen and adjuvant dose sparing while retaining efficacy. Understanding an adjuvant's mechanism of action is a critical component for preclinical safety evaluation, and we demonstrate here that a combined TLR4 and TLR7 adjuvant signals via the appropriate receptors and the MyD88 adaptor protein. This novel adjuvant combination contributes to a more broadly protective vaccine while demonstrating an attractive safety profile.

Synthetic Toll-like receptor 4 (TLR4) and TLR7 ligands as influenza virus vaccine adjuvants induce rapid, sustained, and broadly protective responses.

UNLABELLED: Current vaccines against influenza virus infection rely on the induction of neutralizing antibodies targeting the globular head of the viral hemagglutinin (HA). Protection against seasonal antigenic drift or sporadic pandemic outbreaks requires further vaccine development to induce cross-protective humoral responses, potentially to the more conserved HA stalk region. Here, we present a novel viral vaccine adjuvant comprised of two synthetic ligands for Toll-like receptor 4 (TLR4) and TLR7. 1Z105 is a substituted pyrimido[5,4-b]indole specific for the TLR4-MD2 complex, and 1V270 is a phospholipid-conjugated TLR7 agonist. Separately, 1Z105 induces rapid Th2-associated IgG1 responses, and 1V270 potently generates Th1 cellular immunity. 1Z105 and 1V270 in combination with recombinant HA from the A/Puerto Rico/8/1934 strain (rPR/8 HA) effectively induces rapid and sustained humoral immunity that is protective against lethal challenge with a homologous virus. More importantly, immunization with the combined adjuvant and rPR/8 HA, a commercially available split vaccine, or chimeric rHA antigens significantly improves protection against both heterologous and heterosubtypic challenge viruses. Heterosubtypic protection is associated with broadly reactive antibodies to HA stalk epitopes. Histological examination and cytokine profiling reveal that intramuscular (i.m.) administration of 1Z105 and 1V270 is less reactogenic than a squalene-based adjuvant, AddaVax. In summary, the combination of 1Z105 and 1V270 with a recombinant HA induces rapid, long-lasting, and balanced Th1- and Th2-type immunity; demonstrates efficacy in a variety of murine influenza virus vaccine models assaying homologous, heterologous, and heterosubtypic challenge viruses; and has an excellent safety profile. IMPORTANCE: Novel adjuvants are needed to enhance immunogenicity and increase the protective breadth of influenza virus vaccines to reduce the seasonal disease burden and ensure pandemic preparedness. We show here that the combination of synthetic Toll-like receptor 4 (TLR4) and TLR7 ligands is a potent adjuvant for recombinant influenza virus hemagglutinin, inducing rapid and sustained immunity that is protective against influenza viruses in homologous, heterologous, and heterosubtypic challenge models. Combining TLR4 and TLR7 ligands balances Th1- and Th2-type immune responses for long-lived cellular and neutralizing humoral immunity against the viral hemagglutinin. The combined adjuvant has an attractive safety profile and the potential to augment seasonal-vaccine breadth, contribute to a broadly neutralizing universal vaccine formulation, and improve response time in an emerging pandemic.

Guiding the immune response against influenza virus hemagglutinin toward the conserved stalk domain by hyperglycosylation of the globular head domain.

Influenza virus hemagglutinin consists of a highly variable and immunodominant head domain and a more conserved but immunosubdominant stalk domain. We introduced seven N-linked glycosylation sites in the hemagglutinin head domain to shield the immunodominant antigenic sites. The hyperglycosylated hemagglutinin enhanced stalk-directed seroreactivity while dampening the head response in immunized mice. Upon influenza virus challenge, mice vaccinated with the hyperglycosylated hemagglutinin were better protected against morbidity and mortality than mice receiving the wild-type hemagglutinin.

Adjuvants and immunization strategies to induce influenza virus hemagglutinin stalk antibodies.

The global population remains vulnerable in the face of the next pandemic influenza virus outbreak, and reformulated vaccinations are administered annually to manage seasonal epidemics. Therefore, development of a new generation of vaccines is needed to generate broad and persistent immunity to influenza viruses. Here, we describe three adjuvants that enhance the induction of stalk-directed antibodies against heterologous and heterosubtypic influenza viruses when administered with chimeric HA proteins. Addavax, an MF59-like nanoemulsion, poly(I:C), and an RNA hairpin derived from Sendai virus (SeV) Cantell were efficacious intramuscularly. The SeV RNA and poly(I:C) also proved to be effective respiratory mucosal adjuvants. Although the quantity and quality of antibodies induced by the adjuvants varied, immunized mice demonstrated comparable levels of protection against challenge with influenza A viruses on the basis of HA stalk reactivity. Finally, we present that intranasally, but not intramuscularly, administered chimeric HA proteins induce mucosal IgA antibodies directed at the HA stalk.

A small molecule multi-kinase inhibitor reduces influenza A virus replication by restricting viral RNA synthesis.

Currently available drugs against influenza virus target the viral neuraminidase or the M2 ion channel. The emergence of viral strains resistant to these drugs has been widely described; therefore, there is an urgent need for novel antiviral drugs. Targeting of host factors required for viral replication is an attractive option for circumventing the problem of drug resistance. Several RNAi screens have demonstrated that host kinases are required for the replication of influenza virus. To determine whether compounds that inhibit these kinases can impair viral replication, we tested several kinase inhibitors for activity against influenza A virus. We demonstrate that the multi-kinase inhibitor ON108110 reduces replication of influenza A virus in a dose-dependent manner by suppressing viral RNA synthesis. In addition, ON108110 also inhibits other viruses including vesicular stomatitis virus and Newcastle disease virus, suggesting that this compound may represent a novel class of antiviral agents.

Recombinant IgA is sufficient to prevent influenza virus transmission in guinea pigs.

A serum hemagglutination inhibition (HAI) titer of 40 or greater is thought to be associated with reduced influenza virus pathogenesis in humans and is often used as a correlate of protection in influenza vaccine studies. We have previously demonstrated that intramuscular vaccination of guinea pigs with inactivated influenza virus generates HAI titers greater than 300 but does not protect vaccinated animals from becoming infected with influenza virus by transmission from an infected cage mate. Only guinea pigs intranasally inoculated with a live influenza virus or a live attenuated virus vaccine, prior to challenge, were protected from transmission (A. C. Lowen et al., J. Virol. 83:2803-2818, 2009.). Because the serum HAI titer is mostly determined by IgG content, these results led us to speculate that prevention of viral transmission may require IgA antibodies or cellular immune responses. To evaluate this hypothesis, guinea pigs and ferrets were administered a potent, neutralizing mouse IgG monoclonal antibody, 30D1 (Ms 30D1 IgG), against the A/California/04/2009 (H1N1) virus hemagglutinin and exposed to respiratory droplets from animals infected with this virus. Even though HAI titers were greater than 160 1 day postadministration, Ms 30D1 IgG did not prevent airborne transmission to passively immunized recipient animals. In contrast, intramuscular administration of recombinant 30D1 IgA (Ms 30D1 IgA) prevented transmission to 88% of recipient guinea pigs, and Ms 30D1 IgA was detected in animal nasal washes. Ms 30D1 IgG administered intranasally also prevented transmission, suggesting the importance of mucosal immunity in preventing influenza virus transmission. Collectively, our data indicate that IgG antibodies may prevent pathogenesis associated with influenza virus infection but do not protect from virus infection by airborne transmission, while IgA antibodies are more important for preventing transmission of influenza viruses.