Unlocking cancer vaccine potential: What are the key factors?

Cancer is a global health challenge, with changing demographics and lifestyle factors producing an increasing burden worldwide. Screening advancements are enabling earlier diagnoses, but current cancer immunotherapies only induce remission in a small proportion of patients and come at a high cost. Cancer vaccines may offer a solution to these challenges, but they have been mired by poor results in past decades. Greater understanding of tumor biology, coupled with the success of vaccine technologies during the COVID-19 pandemic, has reinvigorated cancer vaccine development. With the first signs of efficacy being reported, cancer vaccines may be beginning to fulfill their potential. Solid tumors, however, present different hurdles than infectious diseases. Combining insights from previous cancer vaccine clinical development and contemporary knowledge of tumor immunology, we ask: who are the 'right' patients, what are the 'right' targets, and which are the 'right' modalities to maximize the chances of cancer vaccine success?

HBV001: Phase I study evaluating the safety and immunogenicity of the therapeutic vaccine ChAdOx1-HBV

Background & Aims

Millions of people worldwide are infected chronically with HBV, which results in significant morbidity and mortality. Therapeutic vaccination is a strategy that aims to induce functional cure by restoring cellular immunity to HBV. Previously we have shown the candidate HBV immunotherapeutic vaccine ChAdOx1-HBV, encoding all major HBV antigens and a genetic adjuvant (shark invariant chain), is highly immunogenic in mice.

Methods

Here we report the results of HBV001, a first-in-human, phase I, non-randomised, dose-escalation trial of ChAdOx1-HBV assessed in healthy volunteers and patients with chronic HBV (CHB).

Results

Vaccination with a single dose of ChAdOx1-HBV was safe and well tolerated in both healthy and CHB cohorts. Vaccination induced high magnitude HBV-specific T cell responses against all major HBV antigens (core, polymerase, and surface) in healthy volunteers. Responses were detected but lower in patients with CHB. T cells generated by vaccination were cross-reactive between HBV C and D genotypes.

Conclusions

ChAdOx1-HBV is safe and immunogenic in healthy volunteers and patients with CHB. In further studies, ChAdOx1-HBV will be used in combination with other therapeutic strategies with an aim to overcome the attenuated immunogenicity in patients with CHB.

Impact and implications

Therapeutic vaccine ChAdOx1-HBV, a novel treatment for chronic hepatitis B infection (CHB), has been shown to be immunogenic in preclinical studies. In HBV001, a first-in-human phase I study, we show vaccination with ChAdOx1-HBV is safe and generates high magnitude T cell responses in healthy volunteers and lower levels of responses in patients with CHB. This is an important first step in the development of ChAdOx1-HBV as part of a wider therapeutic strategy to induce hepatitis B functional cure, and is of great interest to patients CHB and clinicians treating the condition.

Clinical Trials Registration

This study is registered at ClinicalTrials.gov (NCT04297917).

A pan-genotype hepatitis C virus viral vector vaccine generates T cells and neutralizing antibodies in mice

BACKGROUND AND AIMS

A prophylactic vaccine targeting multiple HCV genotypes (gt) is urgently required to meet World Health Organization elimination targets. Neutralizing antibodies (nAbs) and CD4⁺ and CD8⁺ T cells are associated with spontaneous clearance of HCV, and each may contribute to protective immunity. However, current vaccine candidates generate either nAbs or T cells targeting genetically variable epitopes and have failed to show efficacy in human trials. We have previously shown that a simian adenovirus vector (ChAdOx1) encoding conserved sequences across gt1-6 (ChAd-Gt1-6), and separately gt-1a E2 protein with variable regions deleted (E2Δ123_HMW ), generates pan-genotypic T cells and nAbs, respectively. We now aim to develop a vaccine to generate both viral-specific B- and T-cell responses concurrently.

APPROACH AND RESULTS

We show that vaccinating with ChAd-Gt1-6 and E2Δ123_HMW sequentially in mice generates T-cell and antibody (Ab) responses comparable to either vaccine given alone. We encoded E2Δ123 in ChAdOx1 (ChAd-E2Δ123) and show that this, given with an E2Δ123_HMW protein boost, induces greater CD81-E2 inhibitory and HCV-pseudoparticle nAb titers compared to the E2Δ123_HMW prime boost. We developed bivalent viral vector vaccines (ChAdOx1 and modified vaccinia Ankara [MVA]) encoding both Gt1-6 and E2Δ123 immunogens (Gt1-6-E2Δ123) generating polyfunctional CD4⁺ and CD8⁺ T cells and nAb titers in prime/boost strategies. This approach generated nAb responses comparable to monovalent E2Δ123 ChAd/MVA vaccines and superior to three doses of recombinant E2Δ123_HMW protein, while also generating high-magnitude T-cell responses.

CONCLUSIONS

These data are an important step forward for the development of a pan-genotype HCV vaccine to elicit T cells and nAbs for future assessment in humans.

Adenovirus vectors activate Vδ2+ γδT cells in a type I interferon-, TNF-, and IL-18-dependent manner

Vδ2+ γδT cells are unconventional T cells that can be activated by cytokines without TCR signaling. Adenovirus vaccine vectors activated Vδ2+ γδT cells in an interleukin 18-, TNF-, and type I interferon-dependent manner. This stimulatory capacity was associated with adenovirus vectors of non-species C origin, including the ChAdOx1 vaccine platform.

T cell assays differentiate clinical and subclinical SARS-CoV-2 infections from cross-reactive antiviral responses

Identification of protective T cell responses against SARS-CoV-2 requires distinguishing people infected with SARS-CoV-2 from those with cross-reactive immunity to other coronaviruses. Here we show a range of T cell assays that differentially capture immune function to characterise SARS-CoV-2 responses. Strong ex vivo ELISpot and proliferation responses to multiple antigens (including M, NP and ORF3) are found in 168 PCR-confirmed SARS-CoV-2 infected volunteers, but are rare in 119 uninfected volunteers. Highly exposed seronegative healthcare workers with recent COVID-19-compatible illness show T cell response patterns characteristic of infection. By contrast, >90% of convalescent or unexposed people show proliferation and cellular lactate responses to spike subunits S1/S2, indicating pre-existing cross-reactive T cell populations. The detection of T cell responses to SARS-CoV-2 is therefore critically dependent on assay and antigen selection. Memory responses to specific non-spike proteins provide a method to distinguish recent infection from pre-existing immunity in exposed populations.

MAIT cell activation augments adenovirus vector vaccine immunogenicity

Mucosal-associated invariant T (MAIT) cells are innate sensors of viruses and can augment early immune responses and contribute to protection. We hypothesized that MAIT cells may have inherent adjuvant activity in vaccine platforms that use replication-incompetent adenovirus vectors. In mice and humans, ChAdOx1 (chimpanzee adenovirus Ox1) immunization robustly activated MAIT cells. Activation required plasmacytoid dendritic cell (pDC)-derived interferon (IFN)-α and monocyte-derived interleukin-18. IFN-α-induced, monocyte-derived tumor necrosis factor was also identified as a key secondary signal. All three cytokines were required in vitro and in vivo. Activation of MAIT cells positively correlated with vaccine-induced T cell responses in human volunteers and MAIT cell-deficient mice displayed impaired CD8+ T cell responses to multiple vaccine-encoded antigens. Thus, MAIT cells contribute to the immunogenicity of adenovirus vectors, with implications for vaccine design.

Detection of neutralising antibodies to SARS-CoV-2 to determine population exposure in Scottish blood donors between March and May 2020

BackgroundThe progression and geographical distribution of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in the United Kingdom (UK) and elsewhere is unknown because typically only symptomatic individuals are diagnosed. We performed a serological study of blood donors in Scotland in the spring of 2020 to detect neutralising antibodies to SARS-CoV-2 as a marker of past infection and epidemic progression.AimOur objective was to determine if sera from blood bank donors can be used to track the emergence and progression of the SARS-CoV-2 epidemic.MethodsA pseudotyped SARS-CoV-2 virus microneutralisation assay was used to detect neutralising antibodies to SARS-CoV-2. The study comprised samples from 3,500 blood donors collected in Scotland between 17 March and 18 May 2020. Controls were collected from 100 donors in Scotland during 2019.ResultsAll samples collected on 17 March 2020 (n = 500) were negative in the pseudotyped SARS-CoV-2 virus microneutralisation assay. Neutralising antibodies were detected in six of 500 donors from 23 to 26 March. The number of samples containing neutralising antibodies did not significantly rise after 5-6 April until the end of the study on 18 May. We found that infections were concentrated in certain postcodes, indicating that outbreaks of infection were extremely localised. In contrast, other areas remained comparatively untouched by the epidemic.ConclusionAlthough blood donors are not representative of the overall population, we demonstrated that serosurveys of blood banks can serve as a useful tool for tracking the emergence and progression of an epidemic such as the SARS-CoV-2 outbreak.

Viral vectored hepatitis C virus vaccines generate pan-genotypic T cell responses to conserved subdominant epitopes

BACKGROUND

Viral genetic variability presents a major challenge to the development of a prophylactic hepatitis C virus (HCV) vaccine. A promising HCV vaccine using chimpanzee adenoviral vectors (ChAd) encoding a genotype (gt) 1b non-structural protein (ChAd-Gt1b-NS) generated high magnitude T cell responses. However, these T cells showed reduced cross-recognition of dominant epitope variants and the vaccine has recently been shown to be ineffective at preventing chronic HCV. To address the challenge of viral diversity, we developed ChAd vaccines encoding HCV genomic sequences that are conserved between all major HCV genotypes and adjuvanted by truncated shark invariant chain (sIi_tr).

METHODS

Age-matched female mice were immunised intramuscularly with ChAd (10⁸ infectious units) encoding gt-1 and -3 (ChAd-Gt1/3) or gt-1 to -6 (ChAd-Gt1-6) conserved segments spanning the HCV proteome, or gt-1b (ChAd-Gt1b-NS control), with immunogenicity assessed 14-days post-vaccination.

RESULTS

Conserved segment vaccines, ChAd-Gt1/3 and ChAd-Gt1-6, generated high-magnitude, broad, and functional CD4⁺ and CD8⁺ T cell responses. Compared to the ChAd-Gt1b-NS vaccine, these vaccines generated significantly greater responses against conserved non-gt-1 antigens, including conserved subdominant epitopes that were not targeted by ChAd-Gt1b-NS. Epitopes targeted by the conserved segment HCV vaccine induced T cells, displayed 96.6% mean sequence homology between all HCV subtypes (100% sequence homology for the majority of genotype-1, -2, -4 sequences and 94% sequence homology for gt-3, -6, -7, and -8) in contrast to 85.1% mean sequence homology for epitopes targeted by ChAd-Gt1b-NS induced T cells. The addition of truncated shark invariant chain (sIi_tr) increased the magnitude, breadth, and cross-reactivity of the T cell response.

CONCLUSIONS

We have demonstrated that genetically adjuvanted ChAd vectored HCV T cell vaccines encoding genetic sequences conserved between genotypes are immunogenic, activating T cells that target subdominant conserved HCV epitopes. These pre-clinical studies support the use of conserved segment HCV T cell vaccines in human clinical trials.

Novel minigene vaccine stimulates CD8+ memory inflation to control growth of murine colorectal tumor

Fundamental science

Memory “inflation” describes the sustained accumulation of expanded pools of antigen-specific CD8+ T-cells, which occurs in certain persistent viral infections e.g. cytomegalovirus, and after vaccination with replication deficient adenoviral vectors. Inflating T cells are sustained at high frequencies, possess an effector memory phenotype and home to non-lymphoid tissues – characteristics which are desirable in anti-tumor responses. Use of minigene (epitope only) vaccines allows targeting of responses and reliable generation of strong memory inflation. To explore this, adenoviral vectors were designed to stimulate an anti-tumor response against the dominant antigen in CT26 tumors, AH1, either as a full length or peptide immunogen. Groups of mice were immunized with the minigene AH1 vector. Tumor growth and immune responses were monitored using prophylactic or therapeutic regimens.

Results

Our lab has previously demonstrated that minigene vaccines generate strong inflationary responses compared to a full-length vector. Compared to the controls, tumors from minigene-immunized mice grew at a significantly slower rate, and the intra-tumoral environment was enriched for functional effector cells. The presence of AH1-specific CD8+ T cell populations in peripheral blood correlated overall with the anti-tumor effect.

Conclusions

Inflationary CD8+ T cells can be targeted against tumor antigens using our adenovirus minigene approach. Such responses show anti-tumor activity in prophylactic and therapeutic settings. Further studies to assess the impact of increasing the breadth of targeting and the impact of checkpoint inhibition are ongoing.

Use of an Outbred Rat Hepacivirus Challenge Model for Design and Evaluation of Efficacy of Different Immunization Strategies for Hepatitis C Virus

BACKGROUND AND AIMS

The lack of immunocompetent small animal models for hepatitis C virus (HCV) has greatly hindered the development of effective vaccines. Using rodent hepacivirus (RHV), a homolog of HCV that shares many characteristics of HCV infection, we report the development and application of an RHV outbred rat model for HCV vaccine development.

APPROACH AND RESULTS

Simian adenovirus (ChAdOx1) encoding a genetic immune enhancer (truncated shark class II invariant chain) fused to the nonstructural (NS) proteins NS3-NS5B from RHV (ChAd-NS) was used to vaccinate Sprague-Dawley rats, resulting in high levels of cluster of differentiation 8-positive (CD8⁺ ) T-cell responses. Following RHV challenge (using 10 or 100 times the minimum infectious dose), 42% of vaccinated rats cleared infection within 6-8 weeks, while all mock vaccinated controls became infected with high-level viremia postchallenge. A single, 7-fold higher dose of ChAd-NS increased efficacy to 67%. Boosting with ChAd-NS or with a plasmid encoding the same NS3-NS5B antigens increased efficacy to 100% and 83%, respectively. A ChAdOx1 vector encoding structural antigens (ChAd-S) was also constructed. ChAd-S alone showed no efficacy. Strikingly, when combined with ChAd-NS, ChAD-S produced 83% efficacy. Protection was associated with a strong CD8⁺ interferon gamma-positive recall response against NS4. Next-generation sequencing of a putative RHV escape mutant in a vaccinated rat identified mutations in both identified immunodominant CD8⁺ T-cell epitopes.

CONCLUSIONS

A simian adenovirus vector vaccine strategy is effective at inducing complete protective immunity in the rat RHV model. The RHV Sprague-Dawley rat challenge model enables comparative testing of vaccine platforms and antigens and identification of correlates of protection and thereby provides a small animal experimental framework to guide the development of an effective vaccine for HCV in humans.

Divergent memory responses driven by adenoviral vectors are impacted by epitope competition

Adenoviral vectors induce robust epitope-specific CD8+ T cell responses. Within the repertoire of responses generated both conventional memory evolution and the phenomenon of memory inflation are seen. The rules governing which epitopes inflate are not fully known, but may include a role for both antigen processing and competition. To investigate this, we looked at memory generated from vectors targeting the Gp33-41 (KAVYNFATC/K9C) epitope from the gp of lymphocytic choriomeningitis virus (LCMV) in mice. This well-described epitope has both the Gp33-41 and Gp34-41 epitopes embedded within it. Vaccination with a full-length gp or a minigene Ad-Gp33/K9C vector-induced conventional memory responses against the immunodominant Gp33/K9C epitope but a strong inflationary response against the Gp34/A8C epitope. These responses showed sustained in vivo function, with complete protection against LCMV infectious challenge. Given the unexpected competition between epitopes seen in the minigene model, we further tested epitope competition using the full-length Ad-LacZ (β-galactosidase) model. Generation of an Ad-LacZ vector with a single amino acid disruption of the inflationary β-gal96-103 /D8V epitope transformed the β-gal497-504 /I8V epitope from conventional to inflationary memory. This work collectively demonstrates the importance of epitope competition within adenoviral vector inserts and is of relevance to future studies using adenoviral vectored immunogens.

The generation of a simian adenoviral vectored HCV vaccine encoding genetically conserved gene segments to target multiple HCV genotypes

BACKGROUND

Hepatitis C virus (HCV) genomic variability is a major challenge to the generation of a prophylactic vaccine. We have previously shown that HCV specific T-cell responses induced by a potent T-cell vaccine encoding a single strain subtype-1b immunogen target epitopes dominant in natural infection. However, corresponding viral regions are highly variable at a population level, with a reduction in T-cell reactivity to these variants. We therefore designed and manufactured second generation simian adenovirus vaccines encoding genomic segments, conserved between viral genotypes and assessed these for immunogenicity.

METHODS

We developed a computer algorithm to identify HCV genomic regions that were conserved between viral subtypes. Conserved segments below a pre-defined diversity threshold spanning the entire HCV genome were combined to create novel immunogens (1000-1500 amino-acids), covering variation in HCV subtypes 1a and 1b, genotypes 1 and 3, and genotypes 1-6 inclusive. Simian adenoviral vaccine vectors (ChAdOx) encoding HCV conserved immunogens were constructed. Immunogenicity was evaluated in C57BL6 mice using panels of genotype-specific peptide pools in ex-vivo IFN-ϒ ELISpot and intracellular cytokine assays.

RESULTS

ChAdOx1 conserved segment HCV vaccines primed high-magnitude, broad, cross-reactive T-cell responses; the mean magnitude of total HCV specific T-cell responses was 1174 SFU/10⁶ splenocytes for ChAdOx1-GT1-6 in C57BL6 mice targeting multiple genomic regions, with mean responses of 935, 1474 and 1112 SFU/10⁶ against genotype 1a, 1b and 3a peptide panels, respectively. Functional assays demonstrated IFNg and TNFa production by vaccine-induced CD4 and CD8 T-cells. In silico analysis shows that conserved immunogens contain multiple epitopes, with many described in natural HCV infection, predicting immunogenicity in humans.

CONCLUSIONS

Simian adenoviral vectored vaccines encoding genetic segments that are conserved between all major HCV genotypes contain multiple T-cell epitopes and are highly immunogenic in pre-clinical models. These studies pave the way for the assessment of multi-genotypic HCV T-cell vaccines in humans.

Novel Bivalent Viral-Vectored Vaccines Induce Potent Humoral and Cellular Immune Responses Conferring Protection against Stringent Influenza A Virus Challenge

Seasonal influenza viruses are a common cause of acute respiratory illness worldwide and generate a significant socioeconomic burden. Influenza viruses mutate rapidly, necessitating annual vaccine reformulation because traditional vaccines do not typically induce broad-spectrum immunity. In addition to seasonal infections, emerging pandemic influenza viruses present a continued threat to global public health. Pandemic influenza viruses have consistently higher attack rates and are typically associated with greater mortality compared with seasonal strains. Ongoing strategies to improve vaccine efficacy typically focus on providing broad-spectrum immunity; although B and T cells can mediate heterosubtypic responses, typical vaccine development will augment either humoral or cellular immunity. However, multipronged approaches that target several Ags may limit the generation of viral escape mutants. There are few vaccine platforms that can deliver multiple Ags and generate robust cellular and humoral immunity. In this article, we describe a novel vaccination strategy, tested preclinically in mice, for the delivery of novel bivalent viral-vectored vaccines. We show this strategy elicits potent T cell responses toward highly conserved internal Ags while simultaneously inducing high levels of Abs toward hemagglutinin. Importantly, these humoral responses generate long-lived plasma cells and generate Abs capable of neutralizing variant hemagglutinin-expressing pseudotyped lentiviruses. Significantly, these novel viral-vectored vaccines induce strong immune responses capable of conferring protection in a stringent influenza A virus challenge. Thus, this vaccination regimen induces lasting efficacy toward influenza. Importantly, the simultaneous delivery of dual Ags may alleviate the selective pressure that is thought to potentiate antigenic diversity in avian influenza viruses.