# AS01B adjuvant mechanisms and CD4 T cell responses

## Abstract

AS01B adjuvant induces CD4 T cell responses through a two-phase mechanism involving initial transient inflammatory activation followed by sustained IFN-signaling pathway engagement. Studies demonstrate that AS01B triggers early innate responses including IL-6 and CRP peaking at 24 hours post-vaccination, followed by IFN-γ upregulation and activation of IFN-inducible genes (STAT1, IRF1, MX1, CXCL10) after the second dose. This innate activation directly correlates with enhanced CD4+ T cell outcomes, as multi-parametric modeling shows associations between CRP, IL-6, IFN-signaling pathway activation and subsequent CD4 responses. AS01B consistently induces superior CD4 T cell responses compared to AS02A (3.1-fold higher frequencies), AS03 (5.4-fold higher), AS04 (2.8-fold higher), and aluminum adjuvants, with exceptional durability extending 18-36+ months post-vaccination.

The CD4 response polarization induced by AS01B is context-dependent rather than fixed. Protein/AS01B formulations activate PPAR, FcεRI, and TGF-β pathways, inducing Th2/Tfh2-biased responses that correlate with enhanced antibody production and memory B cell frequencies. In contrast, most other AS01B formulations primarily activate IFN-signaling pathways, driving strong Th1 responses characterized by high IFN-γ production. AS01B’s superiority depends on both liposomal delivery and optimal component dosing, as AS01E containing half the MPL/QS-21 produces comparable innate profiles but 2.2-fold lower CD4 responses. The synergistic combination of MPL and QS-21 in liposomes appears critical for maximal CD4 activation.

## Methods

We analyzed 10 sources from an initial pool of 200, using 8 screening criteria. Each paper was reviewed for 6 key aspects that mattered most to the research question.

**Records from Elicit search**

- **n = 200** Papers screened using: AS01B Adjuvant Focus, CD4 T Cell Response Measurement, Appropriate Study Type, AS01B Data Availability, CD4 T Cell Data Inclusion, CD4 T Cell Response Focus, AS01B Effect Attribution, Full Publication Status

- **n = 200** Papers screened out
- **n = 10** Papers included for extraction

## Data extraction

We asked a large language model to extract each data column below from each paper. We gave the model the extraction instructions shown below for each column.

### Study Context:

- **Study population:** Healthy human adults
- **Antigen used with AS01B:** RTS,S antigen
- **Study design:** Double-blind, randomized trial
- **Sample size for AS01B group:** Approximately 51 participants

### AS01B Mechanisms:

- **Specific cytokines induced by AS01B:** Interleukin-2, interferon-gamma, tumor necrosis factor-alpha, CD40L

### CD4 Responses:

- **CD4 T cell proliferation or activation markers:** Higher numbers of CSP-specific CD4(+) T cells expressing interleukin-2, interferon-gamma, tumor necrosis factor-alpha, or CD40L.

### Key Findings:

- **Primary conclusions about AS01B's mechanism of action:** Enhances efficacy of RTS,S vaccine with higher efficacy rate compared to AS02A.

- **Key findings about AS01B's ability to induce CD4 responses:** Higher numbers of CSP-specific CD4(+) T cells and higher ex vivo IFN-gamma ELISPOTs compared to AS02A.

- **Novel insights about AS01B compared to other adjuvants:** Induces greater CSP-specific immune responses compared to AS02A.