Peak transgene expression after intramuscular immunization of mice with adenovirus 26-based vector vaccines correlates with transgene-specific adaptive immune responses

Non-replicating adenovirus-based vectors have been broadly used for the development of prophylactic vaccines in humans and are licensed for COVID-19 and Ebola virus disease prevention. Adenovirus-based vectored vaccines encode for one or more disease specific transgenes with the aim to induce protective immunity against the target disease. The magnitude and duration of transgene expression of adenovirus 5- based vectors (human type C) in the host are key factors influencing antigen presentation and adaptive immune responses. Here we characterize the magnitude, duration, and organ biodistribution of transgene expression after single intramuscular administration of adenovirus 26-based vector vaccines in mice and evaluate the differences with adenovirus 5-based vector vaccine to understand if this is universally applicable across serotypes. We demonstrate a correlation between peak transgene expression early after adenovirus 26-based vaccination and transgene-specific cellular and humoral immune responses for a model antigen and SARS-CoV-2 spike protein, independent of innate immune activation. Notably, the memory immune response was similar in mice immunized with adenovirus 26-based vaccine and adenovirus 5-based vaccine, despite the latter inducing a higher peak of transgene expression early after immunization and a longer duration of transgene expression. Together these results provide further insights into the mode of action of adenovirus 26-based vector vaccines.

Phase 1/2a Safety and Immunogenicity of an Adenovirus 26 Vector Respiratory Syncytial Virus (RSV) Vaccine Encoding Prefusion F in Adults 18-50 Years and RSV-Seropositive Children 12-24 Months

BACKGROUND

Respiratory syncytial virus (RSV) remains a leading cause of pediatric morbidity, with no approved vaccine. We assessed the safety and immunogenicity of the Ad26.RSV.preF vaccine candidate in adults and children.

METHODS

In this randomized, double-blind, phase 1/2a, placebo-controlled study, 12 adults (18-50 years) and 36 RSV-seropositive children (12-24 months) were randomized 2:1 to Ad26.RSV.preF (1 × 1011 viral particles [vp] for adults, 5 × 1010 vp for children) or placebo, at day 1 and 29, with 6-month immunogenicity and 1-year safety follow-up. Respiratory syncytial virus infection was an exploratory outcome in children.

RESULTS

In adults, solicited adverse events (AEs) were generally mild to moderate, with no serious AEs. In children, no vaccination-related serious AEs were reported; fever was reported in 14 (58.3%) Ad26.RSV.preF recipients. Baseline pediatric geometric mean titers for RSV A2 neutralization increased from 121 (95% confidence interval [CI], 76-191) to 1608 (95% CI, 730-3544) at day 29, and 2235 (95% CI, 1586-3150) at day 57, remaining elevated over 7 months. Respiratory syncytial virus infection was confirmed in fewer children receiving Ad26.RSV.preF (1, 4.2%) than placebo (5, 41.7%).

CONCLUSIONS

Ad26.RSV.preF demonstrated immunogenicity in healthy adults and toddlers, with no safety concerns raised. Evaluations in RSV-seronegative children are underway.

Omicron BA.1 breakthrough infection drives cross-variant neutralization and memory B cell formation against conserved epitopes

Omicron is the evolutionarily most distinct SARS-CoV-2 variant of concern (VOC) to date. We report that Omicron BA.1 breakthrough infection in BNT162b2-vaccinated individuals resulted in strong neutralizing activity against Omicron BA.1, BA.2 and previous SARS-CoV-2 VOCs, but not against the Omicron sublineages BA.4 and BA.5. BA.1 breakthrough infection induced a robust recall response, primarily expanding B_MEM cells against epitopes shared broadly amongst variants, rather than inducing BA.1-specific B cells. The vaccination-imprinted B_MEM cell pool had sufficient plasticity to be remodeled by heterologous SARS-CoV-2 spike glycoprotein exposure. While selective amplification of B_MEM cells recognizing shared epitopes allows for effective neutralization of most variants that evade previously established immunity, susceptibility to escape by variants that acquire alterations at hitherto conserved sites may be heightened.

Transcription factor expression profiling to characterize differentiation of antigen-specific CD8 T cells induced by a live attenuated viral vaccine. (113.18)

Live attenuated SIV (SIVΔnef) is the most effective approach to induce protection to pathogenic SIV challenge in macaques. Protective immunity, in part mediated by CD8 T cell responses, correlates with phenotypic maturation of SIV-specific T cells, but remains incompletely understood. Expression profiling of T cell transcription factors (TF) offers a novel approach to characterize antigen-specific T cell differentiation. Highly parallel qRT-PCR was used to characterize the expression of 21 TF in naïve, central, transitional, and effector memory T cell subsets, and in SIV-specific CD8 T cells obtained at times associated with lesser protection (wk 5) and greater protection (wk 20) following SIVΔnef vaccination. Unsupervised clustering organized samples from CD4 and CD8 T cells into groups concordant with cell surface phenotype. TF expression in SIV-specific CD8+ T cells segregated by time, with wk 20 cells exhibiting increased expression of TF associated with both maintenance of quiescence (TCF7, BAZF) and promotion of effector function (Eomes, T-Bet). Different expression profiles were observed in T cells specific for different SIV epitopes, consistent with different epitope escape kinetics. TF expression profiling suggests T cell responses correlated with protection may include characteristics of both memory and effector cells. TF expression profiling can provide data complementary to the analysis of memory cell differentiation based on classical phenotypic markers.