Development of Vaccines against Visceral Leishmaniasis

Leishmaniasis is a neglected disease resulting in a global morbidity of 2,090 thousand Disability-Adjusted Life Years and a mortality rate of approximately 60,000 per year. Among the three clinical forms of leishmaniasis (cutaneous, mucosal, and visceral), visceral leishmaniasis (VL) accounts for the majority of mortality, as if left untreated VL is almost always fatal. Caused by infection with Leishmania donovani or L. infantum, VL represents a serious public health problem in endemic regions and is rapidly emerging as an opportunistic infection in HIV patients. To date, no vaccine exists for VL or any other form of leishmaniasis. In endemic areas, the majority of those infected do not develop clinical symptoms and past infection leads to robust immunity against reinfection. Thus the development of vaccine for Leishmania is a realistic public health goal, and this paper summarizes advances in vaccination strategies against VL

Following acute encephalitis, Semliki Forest virus is undetectable in the brain by infectivity assays but functional virus RNA capable of generating infectious virus persists for life

Alphaviruses are mosquito-transmitted RNA viruses which generally cause acute disease including mild febrile illness, rash, arthralgia, myalgia and more severely, encephalitis. In the mouse, peripheral infection with Semliki Forest virus (SFV) results in encephalitis. With non-virulent strains, infectious virus is detectable in the brain, by standard infectivity assays, for around ten days. As we have shown previously, in severe combined immunodeficient (SCID) mice, infectious virus is detectable for months in the brain. Here we show that in MHC-II-/- mice, with no functional CD4 T-cells, infectious virus is also detectable in the brain for long periods. In contrast, in the brains of CD8-/- mice, virus RNA persists but infectious virus is not detectable. In SCID mice infected with SFV, repeated intraperitoneal administration of anti-SFV immune serum rapidly reduced the titer of infectious virus in the brain to undetectable, however virus RNA persisted. Repeated intraperitoneal passive transfer of immune serum resulted in maintenance of brain virus RNA, with no detectable infectious virus, for several weeks. When passive antibody transfer was stopped, antibody levels declined and infectious virus was again detectable in the brain. In aged immunocompetent mice, previously infected with SFV, immunosuppression of antibody responses many months after initial infection also resulted in renewed ability to detect infectious virus in the brain. In summary, antiviral antibodies control and determine whether infectious virus is detectable in the brain but immune responses cannot clear this infection from the brain. Functional virus RNA capable of generating infectious virus persists and if antibody levels decline, infectious virus is again detectable

Flavivirus Receptors: Diversity, Identity, and Cell Entry

Flaviviruses are emerging and re-emerging arthropod-borne pathogens responsible for significant mortality and morbidity worldwide. The genus comprises more than seventy small, positive-sense, single-stranded RNA viruses, which are responsible for a spectrum of human and animal diseases ranging in symptoms from mild, influenza-like infection to fatal encephalitis and haemorrhagic fever. Despite genomic and structural similarities across the genus, infections by different flaviviruses result in disparate clinical presentations. This review focusses on two haemorrhagic flaviviruses, dengue virus and yellow fever virus, and two neurotropic flaviviruses, Japanese encephalitis virus and Zika virus. We review current knowledge on host-pathogen interactions, virus entry strategies and tropism

Induction of Protective CD4+ T Cell-Mediated Immunity by a Leishmania Peptide Delivered in Recombinant Influenza Viruses

The available evidence suggests that protective immunity to Leishmania is achieved by priming the CD4+ Th1 response. Therefore, we utilised a reverse genetics strategy to generate influenza A viruses to deliver an immunogenic Leishmania peptide. The single, immunodominant Leishmania-specific LACK158–173 CD4+ peptide was engineered into the neuraminidase stalk of H1N1 and H3N2 influenza A viruses. These recombinant viruses were used to vaccinate susceptible BALB/c mice to determine whether the resultant LACK158–173-specific CD4+ T cell responses protected against live L. major infection. We show that vaccination with influenza-LACK158–173 triggers LACK158–173-specific Th1-biased CD4+ T cell responses within an appropriate cytokine milieu (IFN-γ, IL-12), essential for the magnitude and quality of the Th1 response. A single intraperitoneal exposure (non-replicative route of immunisation) to recombinant influenza delivers immunogenic peptides, leading to a marked reduction (2–4 log) in parasite burden, albeit without reduction in lesion size. This correlated with increased numbers of IFN-γ-producing CD4+ T cells in vaccinated mice compared to controls. Importantly, the subsequent prime-boost approach with a serologically distinct strain of influenza (H1N1->H3N2) expressing LACK158–173 led to a marked reduction in both lesion size and parasite burdens in vaccination trials. This protection correlated with high levels of IFN-γ producing cells in the spleen, which were maintained for 6 weeks post-challenge indicating the longevity of this protective effector response. Thus, these experiments show that Leishmania-derived peptides delivered in the context of recombinant influenza viruses are immunogenic in vivo, and warrant investigation of similar vaccine strategies to generate parasite-specific immunity

Robust and prototypical immune responses towards COVID-19 BNT162b2 vaccines in Indigenous people

SARS-CoV-2 has led to >270 million infections and >5 million deaths globally. Indigenous people are disproportionately affected by infectious diseases, therefore also more susceptible to the COVID-19 pandemic. There are an estimated 476 million indigenous people globally, including an estimated 798,365 Aboriginal and Torres Strait Islander in Australia. With the high vulnerability to COVID-19, this knowledge is urgently needed to better protect indigenous populations. We evaluated a breadth of immune responses in indigenous (n=57) and non-indigenous (n=49) individuals after COVID-19 vaccination. We tested RBD antibodies, spike/RBD-probe-specific B cells, peptide stimulations with activation-induced marker (AIM) assay and intracellular cytokine staining. We found 22% and 34% seroconversion rates after 1st dose of BNT162b2 vaccine for Indigenous and non-indigenous individuals, respectively, which increased to 100% at 1-mth after 2nd dose for both groups. RBD-specific IgG levels in indigenous individuals at 1-mth after 2nd dose positively correlated with their body mass index. At 1-mth after the 2nd COVID-19 vaccination, CD4+ and CD8+ T cell responses via AIM expression and IFN-γ+TNF+ production was comparable between indigenous and non-indigenous individuals. We are also going to assess the longevity of antibodies and T cells. Therefore, COVID-19 vaccination induced similar immune responses in indigenous and non-indigenous individuals

A point-of-care lateral flow assay for neutralising antibodies against SARS-CoV-2

Background: As vaccines against SARS-CoV-2 are now being rolled out, a better understanding of immunity to the virus, whether from infection, or passive or active immunisation, and the durability of this protection is required. This will benefit from the ability to measure antibody-based protection to SARS-CoV-2, ideally with rapid turnaround and without the need for laboratory-based testing. Methods: We have developed a lateral flow POC test that can measure levels of RBD-ACE2 neutralising antibody (NAb) from whole blood, with a result that can be determined by eye or quantitatively on a small instrument. We compared our lateral flow test with the gold-standard microneutralisation assay, using samples from convalescent and vaccinated donors, as well as immunised macaques. Findings: We show a high correlation between our lateral flow test with conventional neutralisation and that this test is applicable with animal samples. We also show that this assay is readily adaptable to test for protection to newly emerging SARS-CoV-2 variants, including the beta variant which revealed a marked reduction in NAb activity. Lastly, using a cohort of vaccinated humans, we demonstrate that our whole-blood test correlates closely with microneutralisation assay data (specificity 100% and sensitivity 96% at a microneutralisation cutoff of 1:40) and that fingerprick whole blood samples are sufficient for this test. Interpretation: Taken together, the COVID-19 NAb-testTM device described here provides a rapid readout of NAb based protection to SARS-CoV-2 at the point of care

The SPRY domain–containing SOCS box protein SPSB2 targets iNOS for proteasomal degradation

Macrophages lacking SPSB2 have increased NO production and enhanced pathogen-killing capabilities due to decreased ubiquitin-mediated destruction of iNOS

Broad spectrum SARS‐CoV ‐2‐specific immunity in hospitalized First Nations peoples recovering from COVID ‐19

Indigenous peoples globally are at increased risk of COVID‐19‐associated morbidity and mortality. However, data that describe immune responses to SARS‐CoV‐2 infection in Indigenous populations are lacking. We evaluated immune responses in Australian First Nations peoples hospitalized with COVID‐19. Our work comprehensively mapped out inflammatory, humoral and adaptive immune responses following SARS‐CoV‐2 infection. Patients were recruited early following the lifting of strict public health measures in the Northern Territory, Australia, between November 2021 and May 2022. Australian First Nations peoples recovering from COVID‐19 showed increased levels of MCP‐1 and IL‐8 cytokines, IgG‐antibodies against Delta‐RBD and memory SARS‐CoV‐2‐specific T cell responses prior to hospital discharge in comparison with hospital admission, with resolution of hyperactivated HLA‐DR+CD38+ T cells. SARS‐CoV‐2 infection elicited coordinated ASC, Tfh and CD8+ T cell responses in concert with CD4+ T cell responses. Delta and Omicron RBD‐IgG, as well as Ancestral N‐IgG antibodies, strongly correlated with Ancestral RBD‐IgG antibodies and Spike‐specific memory B cells. We provide evidence of broad and robust immune responses following SARS‐CoV‐2 infection in Indigenous peoples, resembling those of non‐Indigenous COVID‐19 hospitalized patients

SARS-CoV-2-specific T cell memory with common TCRαβ motifs is established in unvaccinated children who seroconvert after infection

As establishment of SARS-CoV-2-specific T cell memory in children remains largely unexplored, we recruited convalescent COVID-19 children and adults to define their circulating memory SARS-CoV-2-specific CD4+ and CD8+ T cells prior to vaccination. We analysed epitope-specific T cells directly ex vivo using seven HLA class-I and class-II tetramers presenting SARS-CoV-2 epitopes, together with Spike-specific B cells. Unvaccinated children who seroconverted had comparable spike-specific, but lower ORF1a- and N-specific memory T cell responses compared to adults. This agreed with our TCR sequencing data showing reduced clonal expansion in children. A strong stem cell memory phenotype and common T cell receptor motifs were detected within tetramer-specific T cells in seroconverted children. Conversely, children who did not seroconvert had tetramer-specific T cells of predominantly naïve phenotypes and diverse TCRαβ repertoires. Our study demonstrates generation of SARS-CoV-2-specific T cell memory with common TCRαβ motifs in unvaccinated seroconverted children after their first virus encounter

CD8+ T cells specific for an immunodominant SARS-CoV-2 nucleocapsid epitope display high naive precursor frequency and TCR promiscuity

To better understand primary and recall T cell responses during coronavirus disease 2019 (COVID-19), it is important to examine unmanipulated severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-specific T cells. By using peptide-human leukocyte antigen (HLA) tetramers for direct ex vivo analysis, we characterized CD8+ T cells specific for SARS-CoV-2 epitopes in COVID-19 patients and unexposed individuals. Unlike CD8+ T cells directed toward subdominant epitopes (B7/N257, A2/S269, and A24/S1,208) CD8+ T cells specific for the immunodominant B7/N105 epitope were detected at high frequencies in pre-pandemic samples and at increased frequencies during acute COVID-19 and convalescence. SARS-CoV-2-specific CD8+ T cells in pre-pandemic samples from children, adults, and elderly individuals predominantly displayed a naive phenotype, indicating a lack of previous cross-reactive exposures. T cell receptor (TCR) analyses revealed diverse TCRαβ repertoires and promiscuous αβ-TCR pairing within B7/N105+CD8+ T cells. Our study demonstrates high naive precursor frequency and TCRαβ diversity within immunodominant B7/N105-specific CD8+ T cells and provides insight into SARS-CoV-2-specific T cell origins and subsequent responses