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Triple negative breast cancer (TNBC) is a heterogenous disease that disproportionately affects Black women. TNBC outcomes among Black women are dismal secondary to multiple factors, such as poor healthcare accessibility resulting in delays in diagnosis, and aggressive disease biology in addition to a pro-tumor immune microenvironment (TME). Black women with breast cancer exhibit elevated levels of serum pro-inflammatory cytokines, and a pro-tumorigenic TME with higher immunosuppressive regulatory T cells (Tregs), M2 macrophages and exhausted CD8+ T cells. We have shown that the combined use of toll-like receptor 3 (TLR3) ligands with interferon-α (chemokine modulation: CKM) is able to enrich the tumor with CD8+ T cells, while not increasing immunosuppressive cells. Recent clinical trials have revealed the efficacy of immune checkpoint inhibitors (ICI) in rejuvenizing exhausted CD8+ T cells. We hypothesize that strategies to modulate the TME by enriching chemokines that attract CD8+T cells followed by reversal of CD8+ T cell exhaustion (ICI), when added to standard treatment, could potentially improve clinical outcomes, and mitigate the racial disparities in TNBC outcomes between Black and White Women. [ABSTRACT FROM AUTHOR]

Intratumoral immunotherapies are those that are administered directly into a tumor to remodel the local tumor microenvironment and stimulate systemic anti‐tumor immunity. Small molecule toll‐like receptor (TLR) agonists are undergoing development as intratumoral immunotherapies, and here the TLR3 agonist poly(I:C) is considered. Because small molecule therapeutics often suffer rapid washout effects and ineffective immune cell uptake, poly(I:C) is encapsulated into nanoparticles derived from cowpea chlorotic mottle virus (CCMV). The particles (but not the separate components) stimulate the activity of macrophages in vitro and are able to reduce tumor growth and prolong survival in mouse models of colon cancer and melanoma. CCMV‐poly(I:C) is also combined with oxaliplatin and found the combination therapy to be even more potent, strongly inhibiting tumor growth and increasing survival. The analysis of immune markers reveals that CCMV‐poly(I:C) VLPs with oxaliplatin promoted the infiltration and activation of CD4+ and CD8+ cells and the production of IL‐4 and IFN‐γ, indicating a synergistic immunogenic effect. The combined treatment also enhances the rate of apoptosis and immunogenic cell death (ICD). The data support the development of combination therapies involving immunomodulatory plant virus nanoparticles and antineoplastic drugs to attack tumors directly and via the activation of innate and adaptive immune responses. [ABSTRACT FROM AUTHOR]

Triple negative breast cancer (TNBC) is a heterogenous disease that disproportionately affects Black women. TNBC outcomes among Black women are dismal secondary to multiple factors, such as poor healthcare accessibility resulting in delays in diagnosis, and aggressive disease biology in addition to a pro-tumor immune microenvironment (TME). Black women with breast cancer exhibit elevated levels of serum pro-inflammatory cytokines, and a pro-tumorigenic TME with higher immunosuppressive regulatory T cells (Tregs), M2 macrophages and exhausted CD8+ T cells. We have shown that the combined use of toll-like receptor 3 (TLR3) ligands with interferon-α (chemokine modulation: CKM) is able to enrich the tumor with CD8+ T cells, while not increasing immunosuppressive cells. Recent clinical trials have revealed the efficacy of immune checkpoint inhibitors (ICI) in rejuvenizing exhausted CD8+ T cells. We hypothesize that strategies to modulate the TME by enriching chemokines that attract CD8+T cells followed by reversal of CD8+ T cell exhaustion (ICI), when added to standard treatment, could potentially improve clinical outcomes, and mitigate the racial disparities in TNBC outcomes between Black and White Women.

Simple Summary: Nexavant, a newly reported TLR3 agonist, has advantages over Poly(I:C) in terms of quality control and pre-clinical efficacy. Here, we further investigated the physicochemical properties, downstream signaling pathways, anti-cancer efficacy, and mechanism of action of Nexavant. The Nexavant was homogenous in solution and less sensitive to RNase A, and showed thermostability compared with Poly(I:C). Unlike Poly(I:C), which activates TLR3, RIG-I, and MDA5, Nexavant only activated TLR3 and RIG-I, not MDA5. The administration of Nexavant via either the intratumoral route or the intranasal route suppressed tumor growth in various cancer models. Combination therapy with anti-PD-1 antibodies resulted in better, synergistic tumor growth inhibition compared to the respective monotherapies. This study demonstrated that Nexavant could be more suitable for clinical use than Poly(I:C) and applied as an anti-cancer agent in the presence or absence of anti-PD-1 antibodies. Nexavant was reported as an alternative to the TLR3 agonist of Poly(I:C) and its derivatives. The physicochemical properties, signaling pathways, anti-cancer effects, and mechanisms of Nexavant were investigated. The distinctive characteristics of Nexavant compared to that of Poly(I:C) were demonstrated by precise quantification, enhanced thermostability, and increased resistance to RNase A. Unlike Poly(I:C), which activates TLR3, RIG-I, and MDA5, Nexavant stimulates signaling through TLR3 and RIG-I but not through MDA5. Compared to Poly(I:C), an intratumoral Nexavant treatment led to a unique immune response, immune cell infiltration, and suppression of tumor growth in various animal cancer models. Nexavant therapy outperformed anti-PD-1 antibody treatment in all the tested models and showed a synergistic effect in combinational therapy, especially in well-defined cold tumor models. The effect was similar to that of nivolumab in a humanized mouse model. Intranasal instillation of Nexavant led to the recruitment of immune cells (NK, CD4+ T, and CD8+ T) to the lungs, suppressing lung metastasis and improving animal survival. Our study highlighted Nexavant's defined nature for clinical use and unique signaling pathways and its potential as a standalone anti-cancer agent or in combination with anti-PD-1 antibodies. [ABSTRACT FROM AUTHOR]

• Implanted tumors regress slightly with radiation therapy (RT), and the non-inflammatory dendritic cell-targeting adjuvant ARNAX enhances RT-mediated tumor regression. • In both C57BL/6 and BALB/c mice, the Th1-inducing adjuvant enhances RT-mediated tumor shrinkage in EG7 and 4T1 tumors, respectively. • PD-L1 antibody in combination with RT induces 4T1 regression and show an additive shrinkage with ARNAX. • The combination of RT and ARNAX reduced the number of lung metastases compared to RT alone. Radiation therapy (RT) rarely induces tumor regression at untreated metastatic sites, the so-called abscopal effect. A syngeneic tumor (EG7) transplanted into a Th1-dominant mouse strain (C57BL/6) regressed significantly on the treated side and less on the contralateral side after RT. Additional subcutaneous administration of ARNAX, a non-inflammatory adjuvant, further accelerated tumor regression on the untreated side. This suggests that ARNAX after RT significantly enhances the tumor regression effect on the irrelevant tumor. Based on this setting, we next observed similar tumor shrinkage after RT and ARNAX by transplanting syngeneic breast cancer tumors (4T1) into a Th2-dominant mouse strain (BALB/c). The results were as follows: 1. ARNAX enhanced RT-mediated tumor shrinkage comparable to polyI:C; 2. In the Th2 mouse strain, little tumor regression occurred on the untreated side compared to tumor regression on the treated side after RT alone; 3. RT+ARNAX treatment caused additive regression on the treated side and induced slight tumor regression on the untreated side; 4. PD-L1 antibody + RT combination therapy caused tumor regression and further induced additive regression with ARNAX; 5. The combination of RT and ARNAX reduced the number and volume of lung metastases compared to RT alone. However, tumor regression was not always accompanied by a significant prolongation of survival in the mice receiving our regimen and protocol (one 10Gy radiation and a single ARNAX treatment). In conclusion, RT therapy promoted abscopal tumor regression in both Th2 and Th1 models with the addition of the non-inflammatory adjuvant ARNAX. [ABSTRACT FROM AUTHOR]

Synthetic double-stranded RNA analogs recognized by Toll-like receptor 3 (TLR3) are an attractive adjuvant candidate for vaccines, especially against intracellular pathogens or tumors, because of their ability to enhance T cell and antibody responses. Although poly(I:C) is a representative dsRNA with potent adjuvanticity, its clinical application has been limited due to heterogeneous molecular size, inconsistent activity, poor stability, and toxicity. To overcome these limitations, we developed a novel dsRNA-based TLR3 agonist named NexaVant (NVT) by using PCR-coupled bidirectional in vitro transcription. Agarose gel electrophoresis and reverse phase-HPLC analysis demonstrated that NVT is a single 275-kDa homogeneous molecule. NVT appears to be stable since its appearance, concentration, and molecular size were unaffected under 6 months of accelerated storage conditions. Moreover, preclinical evaluation of toxicity under good laboratory practices showed that NVT is a safe substance without any signs of serious toxicity. NVT stimulated TLR3 and increased the expression of viral nucleic acid sensors TLR3, MDA-5, and RIG-1. When intramuscularly injected into C57BL/6 mice, ovalbumin (OVA) plus NVT highly increased the migration of dendritic cells (DCs), macrophages, and neutrophils into inguinal lymph node (iLN) compared with OVA alone. In addition, NVT substantially induced the phenotypic markers of DC maturation and activation including MHC-II, CD40, CD80, and CD86 together with IFN-β production. Furthermore, NVT exhibited an appropriate adjuvanticity because it elevated OVA-specific IgG, in particular, higher levels of IgG2c (Th1- type) but lower IgG1 (Th2-type). Concomitantly, NVT increased the levels of Th1- type T cells such as IFN-γ+ CD4+ and IFN-γ+ CD8+ cells in response to OVA stimulation. Collectively, we suggest that NVT with appropriate safety and effectiveness is a novel and promising adjuvant for vaccines, especially those requiring T cell mediated immunity such as viral and cancer vaccines. [ABSTRACT FROM AUTHOR]

Toll-like receptor 3 (TLR3) is a prominent member of the Toll-like receptor (TLR) family and has the ability to recognize and bind intracellular double-stranded RNA (dsRNA). Once triggered by a viral infection or other pathological condition, TLR3 activates immune cells and induces the production of interferons and other immune response molecules. Additionally, TLR3 is considered an important immune modulator, as it can regulate cell apoptosis and promote anticancer immunity. The investigation and application of TLR3 agonists in digestive system tumors have attracted widespread attention and are regarded as a promising cancer treatment strategy with potential clinical applications. TLR3 expression levels are generally elevated in most digestive system tumors, and higher TLR3 expression is associated with a better prognosis. Therefore, TLR3 has emerged as a novel therapeutic target for digestive system tumors. It has been used in combination with chemotherapy, radiotherapy, and targeted therapy and demonstrated excellent efficacy and tolerability. This has provided new ideas and hopes for the treatment of digestive system tumors. This review discusses the mechanisms of TLR3 and its frontier research in digestive system tumors.

Malaria is a major public health concern, as a highly effective human vaccine remains elusive. The efficacy of a subunit vaccine targeting the most abundant protein of the sporozoite surface, the circumsporozoite protein (CSP) has been hindered by difficulties in generating an effective humoral response in both quantity and quality. Using the rodent Plasmodium yoelii model we report here that immunization with CSP adjuvanted with 5'ppp-dsRNA, a RIG-I agonist, confers early and long-lasting sterile protection in mice against stringent sporozoite and mosquito bite challenges. The immunization induced high levels of antibodies, which were functional in targeting and killing the sporozoites and were sustained over time through the accumulation of long-lived plasma cells in the bone marrow. Moreover, 5'ppp-dsRNA-adjuvanted immunization with the CSP of P. falciparum was also significantly protective against challenges using a transgenic Pf CSP-expressing P. yoelii parasite. Conversely, using the TLR3 agonist poly(A:U) as adjuvant resulted in a formulation that despite inducing high antibody levels was unable to generate equally functional antibodies and was, consequently, less protective. In conclusion, we demonstrate that using 5'ppp-dsRNA as an adjuvant to vaccines targeting CSP induces effective anti- Plasmodium humoral immunity. [ABSTRACT FROM AUTHOR]

Toll-like receptor (TLR) agonists are emerging as promising vaccine adjuvants and immunomodulators in poultry against many diseases. Infectious bursa disease (IBD) still remains as a major threat to poultry industry. Improving the vaccine mediated immune response would help in better protection against IBD virus infection. Adjuvant potential of TLR3 agonist, Polinosinic polycytidylic acid (Poly I:C) with different IBD vaccines has been analyzed in chicken in the present study. Intermediate, intermediate plus IBD vaccine, bursaplex vaccine and their respective poly I:C combinations were used for immunization of chicken. IBD specific antibody titers, bursa to body weight ratio, body weight gain and bursal lesion scores were evaluated at weekly interval in different immunization groups. Fold changes in cytokines IL-1β and IFN-γ mRNA expression levels in spleen were also analyzed in different groups. Intermediate plus IBD vaccine induced significantly (P ≤ 0.05) higher IBD specific antibody response at 35 days of age than other groups with comparatively lower body weight gain and moderate bursal lesion score. Poly I:C co-administration with intermediate IBD vaccine and bursaplex vaccine improved the IBD specific antibody titers, better body weight gain and moderately less bursal lesion score. However, Poly I:C combination with intermediate plus IBD vaccine did not improve the specific immune response. IL-1β levels were up-regulated in intermediate plus and bursaplex group, whereas IFN-γ m RNA expression levels were upregulated in intermediate IBD with Poly I:C group. In conclusion, poly I:C co-administration with intermediate IBD and bursaplex vaccine was beneficial and improved the specific immune response with least immunosuppression and bursal damage. [ABSTRACT FROM AUTHOR]

Toll-like receptor (TLR) agonists have received considerable attention as therapeutic targets for cancer immunotherapy owing to their ability to convert immunosuppressive tumor microenvironments towards a more T-cell inflamed phenotype. However, TLRs differ in their cell expression profiles and intracellular signaling pathways, raising the possibility that distinct TLRs differentially influence the tumor immune microenvironment. Using single-cell RNA-sequencing, we address this by comparing the tumor immune composition of B16F10 melanoma following treatment with agonists of TLR3, TLR7, and TLR9. Marked differences are observed between treatments, including decreased tumor-associated macrophages upon TLR7 agonist treatment. A biased type-1 interferon signature is elicited upon TLR3 agonist treatment as opposed to a type-2 interferon signature with TLR9 agonists. TLR3 stimulation was associated with increased macrophage antigen presentation gene expression and decreased expression of PD-L1 and the inhibitory receptors Pirb and Pilra on infiltrating monocytes. Furthermore, in contrast to TLR7 and TLR9 agonists, TLR3 stimulation ablated FoxP3 positive CD4 T cells and elicited a distinct CD8 T cell activation phenotype highlighting the potential for distinct synergies between TLR agonists and combination therapy agents.

Toll-like receptor (TLR) agonists have received considerable attention as therapeutic targets for cancer immunotherapy owing to their ability to convert immunosuppressive tumor microenvironments towards a more T-cell inflamed phenotype. However, TLRs differ in their cell expression profiles and intracellular signaling pathways, raising the possibility that distinct TLRs differentially influence the tumor immune microenvironment. Using single-cell RNA-sequencing, we address this by comparing the tumor immune composition of B16F10 melanoma following treatment with agonists of TLR3, TLR7, and TLR9. Marked differences are observed between treatments, including decreased tumor-associated macrophages upon TLR7 agonist treatment. A biased type-1 interferon signature is elicited upon TLR3 agonist treatment as opposed to a type-2 interferon signature with TLR9 agonists. TLR3 stimulation was associated with increased macrophage antigen presentation gene expression and decreased expression of PD-L1 and the inhibitory receptors Pirb and Pilra on infiltrating monocytes. Furthermore, in contrast to TLR7 and TLR9 agonists, TLR3 stimulation ablated FoxP3 positive CD4 T cells and elicited a distinct CD8 T cell activation phenotype highlighting the potential for distinct synergies between TLR agonists and combination therapy agents. [ABSTRACT FROM AUTHOR]

A comprehensive SAR study of a putative TLR 3/8/9 agonist was conducted. Despite the excitement surrounding the potential of the first small molecule TLR3 agonist with a compound that additionally displayed agonist activity for TLR8 and TLR9, compound 1 displayed disappointing activity in our hands, failing to match the potency (EC50) reported and displaying only a low efficacy for the extent of stimulated NF-κB activation and release. The evaluation of >75 analogs of 1, many of which constitute minor modifications in the structure, failed to identify any that displayed significant activity and none that exceeded the modest activity found for 1. [ABSTRACT FROM AUTHOR]

Abstract Adjuvant stimulates pattern-recognition receptors (PRRs) expressed by dendritic cells, which causes immune-enhancing of T lymphocytes. Adjuvant also induces innate immune response in whole-body cells via PRRs to evoke cytokinemia. A cytokine-mediated immune response is important for the systemic protection of a host from microbial infections. Using an influenza subcomponent vaccine in a mouse model, we intranasally administered a TLR3-specific adjuvant ARNAX + HA split vaccine to mice. ARNAX efficiently induced mucosal IgA and systemic IgG production by nasal drop. Moreover, ARNAX + HA simultaneously induced CD8 and CD4 T cell activation. We have previously shown that ARNAX does not induce harmful systemic cytokine production. Thus, our findings indicate that the ARNAX + HA vaccine is a harmless prophylactic vaccine for flu that induces HA-specific T cell activation and IgA/IgG production. These results suggested that ARNAX + antigen enhanced the immune response without inducing inflammatory toxicity for vaccination against infectious diseases. [ABSTRACT FROM AUTHOR]

We have previously shown that antibody-dependent cellular cytotoxicity (ADCC) cooperates with immunotoxin (IT)-mediated killing of human leukaemia cells in an severe combined immunodeficient (SCID) mouse model of human T-cell acute lymphoblastic leukaemia (SCID-HSB-2 mice), but not in an equivalent non-obese diabetic (NOD)/SCID mouse model. In these earlier studies, we reasoned that diminished ADCC due to the functional deficit in natural killer (NK) cell activity in NOD/SCID mice resulted in a failure of effective perforin/granzyme-mediated cytotoxicity necessary for the delivery of the augmentative effect. Poly-inosinic-cytidylic acid [poly (I:C)] is a synthetic dsRNA toll-like receptor 3 (TLR3) agonist that possesses a number of biological properties that includes the in vivo activation of NK cells. We show here that intravenous (i.v.) injection of SCID mice with [poly (I:C)] results in characteristic time-related changes in serum interleukin 2 (IL-2), IL-12, and interferon γ (INFγ) cytokine levels that are consistent with TLR3 driven activation of SCID mouse NK cells. Concomitantly, there are changes in the expression levels of CD2, CD16/32 (FcγRII/RIII), CD161 (NK1.1), and F4/80 in the bulk splenocyte population. These observed changes correlate with an increase in the in vitro lytic capabilities of putative NK cells from within the splenocyte population of [poly (I:C)] treated SCID mice. We demonstrate that the in vivo activation of NK cells with [poly (I:C)] in SCID mice bearing disseminated human T-cell leukaemia xenografts resulted in a significant improvement in the therapeutic activity exerted by an intact murine monoclonal antibody against human CD7. This was also seen for a saporin-based immunotoxin constructed with the same intact antibody (HB2-SAPORIN), but not with an F(ab’)2 derivative of the same antibody or of an IT constructed with the same F(ab’)2 HB2 antibody derivative. This study further demonstrates the previously reported reinforcing role of ADCC for the therapeutic activity of IT in an SCID mouse model of human T-ALL and the potential to significantly boost this further with [poly (I:C)]. Our study provides the rationale to justify the exploration of the clinical utility of IT based therapeutics in combination with TLR3 agonists, such as [poly (I:C)], for the treatment of haematological, and possibly other, malignancies.

Chronic fatigue syndrome/ Myalgic encephalomyelitis (CFS/ME) is a poorly understood seriously debilitating disorder in which disabling fatigue is an universal symptom in combination with a variety of variable symptoms. The only drug in advanced clinical development is rintatolimod, a mismatched double stranded polymer of RNA (dsRNA). Rintatolimod is a restricted Toll-Like Receptor 3 (TLR3) agonist lacking activation of other primary cellular inducers of innate immunity (e.g.- cytosolic helicases). Rintatolimod also activates interferon induced proteins that require dsRNA for activity (e.g.- 2ʹ-5ʹ adenylate synthetase, protein kinase R). Rintatolimod has achieved statistically significant improvements in primary endpoints in Phase II and Phase III double-blind, randomized, placebo-controlled clinical trials with a generally well tolerated safety profile and supported by open-label trials in the United States and Europe. The chemistry, mechanism of action, clinical trial data, and current regulatory status of rintatolimod for CFS/ME including current evidence for etiology of the syndrome are reviewed. [ABSTRACT FROM PUBLISHER]

Immunotherapies including immune checkpoint blockade (ICB) have become integral to treatments for immunogenic tumors by reinvigorating host immune functions to attack tumor cells. However, the clinical applications of ICB are limited by relatively low response rates as well as inherent and acquired resistance in many types of cancer. A potential solution is to selectively deliver immune modulators to tumors to activate the tumor microenvironment (TME) and enhance the therapeutic effect of ICB. Here we report the design of polyinosinic: polycytidylic acid (pIC) nanoscale coordination polymer (NCP), pIC@NCP, and its ability to activate tumor-specific immune responses and synergize with ICB for potent antitumor effects. With prolonged blood circulation, facile cell uptake, and triggered release of pIC in acidic TMEs, pIC@NCP shows robust tumor growth inhibition via activation of the endosomal toll-like receptor 3 signaling pathway. The synergistic combination of pIC@NCP and ICB further controls tumor growth in syngeneic mouse models of colorectal cancer and a spontaneous mouse model of prostate cancer. This study highlights the potential of NCP delivery of nucleic acid therapeutics for immune activation and cancer therapy. [ABSTRACT FROM AUTHOR]

Although cancer vaccine-based immunotherapy holds great potential for cancer treatment, tumor-induced dendritic cell (DC) dysfunction remains to be the major obstacle for developing effective vaccines. Compared with normal DCs, tumor-associated DCs (TADCs) are less matured with poor responsiveness to Toll-like receptor (TLR) stimulation, which has been related with STAT3 hyperactivity. In the present study, Poly I:C (PIC, a TLR3 agonist), STAT3 siRNA and OVA antigen were co-encapsulated by poly (ethylene glycol)-b-poly ( l -lysine)-b-poly ( l -leucine) (PEG-PLL-PLLeu) polypeptide micelles to generate PMP/OVA/siRNA nanovaccine, which was aimed to effectively overcome DC dysfunction in vivo by deleting STAT3 gene in situ. The results showed that PMP/OVA/siRNA simultaneously facilitated the cellular uptake of OVA antigen and siRNA about 3–200 folds, and decreased STAT3 expression in TADCs over 50% both in vitro and in vivo . PMP/OVA/siRNA also elevated CD86 and CD40 expression as well as IL-12 production by TADCs more effectively than PMP/OVA did, indicating its strong potency of inducing TADC maturation and activation. Moreover, the immunization of PMP/OVA/siRNA rather than PMP/OVA effectively abrogated immunosuppression in the tumor microenvironment by increasing mature DCs and decreasing immunosuppressive cells in tumor-draining lymph nodes, which thereby led to potent anti-tumor immune responses and dramatic tumor regression with prolonged survival. Hence, in vivo co-delivery of immunopotentiator (PIC) and immunosuppressive gene silencer (STAT3 siRNA) by nanovaccines are expected to be a promising strategy to improve the therapeutic efficacy of cancer vaccines by modulating TADCs and overcoming tumor immunosupression. [ABSTRACT FROM AUTHOR]

Abstract: We have recently reported that the toll-like receptor 3 (TLR3) agonist poly(I:C) induces adjuvant effects to post vaccination CD8+ T cells responses through rapid induction of innate mediators, including NK cells, macrophages, dendritic cells (DCs), and inflammatory cytokines. However, whether this TLR3 agonist directly targets CD8+ T cells needs to be carefully investigated. In this study, we found that optimal post vaccination CD8+ T cell responses to ex vivo DC-based vaccination requires triggering of TLR3 signaling pathway in DCs in vitro as well as in the recipient host, indicating a role for other cell types. Real-time PCR analysis revealed that TLRs (TLR1–TLR13) are expressed in purified (>99% pure) CD4+ and CD8+ T cells from C57BL/6 and BALB/c mice, where the magnitude of the expression was strain and cell type dependent. In vitro, treatment of these purified T cells with poly(I:C) modulated the expression of TLRs including TLR3. Furthermore, non-specific and antigen-specific stimulation of CD8+ T cells by phorbol myristate acetate and MHC class I peptide-pulsed splenocytes, respectively, modulated TLR expression in purified CD4+ and CD8+ T cells. Importantly, brief conditioning of purified naïve TCR transgenic OT-1 (CD8+) T cells in vitro with poly(I:C) induced activation of these cells in absence of antigen stimulation. Interestingly, when these in vitro poly(I:C)-conditioned OT-1 cells were adoptively transferred into naïve recipient followed by peptide vaccination, they showed superior expansion and activation to their naïve counterparts. These results suggest that CD8+ T cells can be activated by triggering their TLR3. Furthermore, the data support the notion of direct involvement of TLRs in adaptive immune responses. [Copyright &y& Elsevier]

Mesenchymal stem cells (MSCs) help fight infection by promoting direct bacterial killing or indirectly by modulating the acute phase response, thereby decreasing tissue injury. Recent evidence suggests that extracellular vesicles (EVs) released from MSCs retain antimicrobial characteristics that may be enhanced by pretreatment of parent MSCs with the toll-like receptor 3 (TLR3) agonist poly(I:C). Our aim was to determine whether poly(I:C) priming can modify EV content of miRNAs and/or proteins to gain insight into the molecular mechanisms of their enhanced antimicrobial function. Human bone marrow-derived MSCs were cultured with or without 1 μg/ml poly(I:C) for 1 h and then conditioned media was collected after 64 h of culture in EV-depleted media. Mass spectrometry and small RNA next-generation sequencing were performed to compare proteomic and miRNA profiles. Poly(I:C) priming resulted in 49 upregulated EV proteins, with 21 known to be important in host defense and innate immunity. In contrast, EV miRNA content was not significantly altered. Functional annotation clustering analysis revealed enrichment in biological processes and pathways including negative regulation of endopeptidase activity, acute phase, complement and coagulation cascades, innate immunity, immune response, and Staphylococcus aureus infection. Several antimicrobial peptides identified in EVs remained unaltered by poly(I:C) priming, including dermcidin, lactoferrin, lipocalin 1, lysozyme C, neutrophil defensin 1, S100A7 (psoriasin), S100A8/A9 (calprotectin), and histone H4. Although TLR3 activation of MSCs improves the proteomic profile of EVs, further investigation is needed to determine the relative importance of particular functional EV proteins and their activated signaling pathways following EV interaction with immune cells., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Pierce and Kurata.)

We have previously shown that antibody-dependent cellular cytotoxicity (ADCC) cooperates with immunotoxin (IT)-mediated killing of human leukaemia cells in an severe combined immunodeficient (SCID) mouse model of human T-cell acute lymphoblastic leukaemia (SCID-HSB-2 mice), but not in an equivalent non-obese diabetic (NOD)/SCID mouse model. In these earlier studies, we reasoned that diminished ADCC due to the functional deficit in natural killer (NK) cell activity in NOD/SCID mice resulted in a failure of effective perforin/granzyme-mediated cytotoxicity necessary for the delivery of the augmentative effect. Poly-inosinic-cytidylic acid [poly (I:C)] is a synthetic dsRNA toll-like receptor 3 (TLR3) agonist that possesses a number of biological properties that includes the in vivo activation of NK cells. We show here that intravenous (i.v.) injection of SCID mice with [poly (I:C)] results in characteristic time-related changes in serum interleukin 2 (IL-2), IL-12, and interferon γ (INFγ) cytokine levels that are consistent with TLR3 driven activation of SCID mouse NK cells. Concomitantly, there are changes in the expression levels of CD2, CD16/32 (FcγRII/RIII), CD161 (NK1.1), and F4/80 in the bulk splenocyte population. These observed changes correlate with an increase in the in vitro lytic capabilities of putative NK cells from within the splenocyte population of [poly (I:C)] treated SCID mice. We demonstrate that the in vivo activation of NK cells with [poly (I:C)] in SCID mice bearing disseminated human T-cell leukaemia xenografts resulted in a significant improvement in the therapeutic activity exerted by an intact murine monoclonal antibody against human CD7. This was also seen for a saporin-based immunotoxin constructed with the same intact antibody (HB2-SAPORIN), but not with an F(ab')2 derivative of the same antibody or of an IT constructed with the same F(ab')2 HB2 antibody derivative. This study further demonstrates the previously reported reinforcing role of ADCC for the therapeutic activity of IT in an SCID mouse model of human T-ALL and the potential to significantly boost this further with [poly (I:C)]. Our study provides the rationale to justify the exploration of the clinical utility of IT based therapeutics in combination with TLR3 agonists, such as [poly (I:C)], for the treatment of haematological, and possibly other, malignancies. [ABSTRACT FROM AUTHOR]