Bonny Gaby Lui

The therapeutic potential of interleukin-2 (IL-2) in cancer treatment is limited by toxicity challenges, partly due to an unfavorable pharmacokinetic profile and unintended activation of regulatory T (T _reg ) cells alongside the desired activation of CD8 ⁺ effector T cells. To selectively stimulate CD8 ⁺ T cells over T _reg cells, we engineered an IL-2 variant (IL-2var) with a dual-tuned affinity profile that features reduced binding to IL-2Rα (CD25) and enhanced binding to IL-2Rβ (CD122). To optimize its pharmacokinetics and facilitate tumor enrichment, the variant is fused to albumin and delivered as an mRNA encapsulated in a lipid nanoparticle (Alb–IL-2var RNA-LNP), enabling sustained systemic exposure from hepatic production upon intravenous administration. We show that Alb–IL-2var has a favorable pharmacokinetic profile and is tolerated at biologically active doses in immunocompetent mice and cynomolgus monkeys. Selective enhancement of CD8 ⁺ T cell responses over T _reg cells is demonstrated in vitro in human peripheral blood mononuclear cells and in vivo in mice and cynomolgus monkeys. When combined with an mRNA cancer vaccine in syngeneic subcutaneous mouse tumor models, Alb–IL-2var RNA-LNP stimulates the expansion of tumor-infiltrating and circulating tumor antigen–specific CD8 ⁺ T cells, but not T _reg cells. In advanced and cold syngeneic tumor models, it enhances the efficacy of radiotherapy, checkpoint inhibitors, and cancer vaccines. Combination with checkpoint inhibitors and vaccine induces profound proinflammatory conversion of cold tumors. These preclinical results validate a rational design approach to overcome the limitations of IL-2 therapy and support the clinical evaluation of Alb–IL-2var RNA-LNP for solid cancers.

The SARS-CoV-2 Omicron variant and its sublineages show pronounced viral escape from neutralizing antibodies elicited by vaccination or prior SARS-CoV-2 variant infection owing to over 30-amino acid alterations within the spike (S) glycoprotein. Breakthrough infection of vaccinated individuals with Omicron sublineages BA.1 and BA.2 is associated with distinct patterns of cross-neutralizing activity against SARS-CoV-2 variants of concern (VOCs). In continuation of our previous work, we characterized the effect of Omicron BA.4/BA.5 S glycoprotein exposure on the neutralizing antibody response upon breakthrough infection in vaccinated individuals and upon variant-adapted booster vaccination in mice. We found that immune sera from triple mRNA-vaccinated individuals with subsequent breakthrough infection during the Omicron BA.4/BA.5 wave showed cross-neutralizing activity against previous Omicron variants BA.1, BA.2, BA.2.12.1, and BA.4/BA.5 itself. Administration of a prototypic BA.4/BA.5-adapted mRNA booster vaccine to mice after SARS-CoV-2 wild-type strain-based primary immunization is associated with broader cross-neutralizing activity than a BA.1-adapted booster. Whereas the Omicron BA.1-adapted mRNA vaccine in a bivalent format (wild-type + BA.1) broadens cross-neutralizing activity relative to the BA.1 monovalent booster, cross-neutralization of BA.2 and descendants is more effective in mice boosted with a bivalent wild-type + BA.4/BA.5 vaccine. In naïve mice, primary immunization with the bivalent wild-type + Omicron BA.4/BA.5 vaccine induces strong cross-neutralizing activity against Omicron VOCs and previous variants. These findings suggest that, when administered as boosters, mono- and bivalent Omicron BA.4/BA.5-adapted vaccines enhance neutralization breadth and that the bivalent version also has the potential to confer protection to individuals with no preexisting immunity against SARS-CoV-2.

BNT162b2-vaccinated individuals after Omicron BA.1 breakthrough infection have strong serum-neutralizing activity against Omicron BA.1, BA.2, and previous SARS-CoV-2 variants of concern (VOCs) yet less against the highly contagious Omicron sublineages BA.4 and BA.5 that have displaced previous variants. Because the latter sublineages are derived from Omicron BA.2, we characterized serum-neutralizing activity of COVID-19 mRNA vaccine triple-immunized individuals who experienced BA.2 breakthrough infection. We demonstrate that sera of these individuals have broadly neutralizing activity against previous VOCs and all tested Omicron sublineages, including BA.2-derived variants BA.2.12.1 and BA.4/BA.5. Furthermore, applying antibody depletion, we showed that neutralization of BA.2 and BA.4/BA.5 sublineages by BA.2 convalescent sera is driven to a considerable extent by antibodies targeting the N-terminal domain (NTD) of the spike glycoprotein. However, neutralization by Omicron BA.1 convalescent sera depends exclusively on antibodies targeting the receptor binding domain (RBD). These findings suggest that exposure to Omicron BA.2, in contrast to BA.1 spike glycoprotein, triggers substantial NTD-specific recall responses in vaccinated individuals and thereby enhances the neutralization of BA.4/BA.5 sublineages. Given the current epidemiology with a predominance of BA.2-derived sublineages such as BA.4/BA.5 and rapidly ongoing evolution, these findings helped to inform development of our Omicron BA.4/BA.5-adapted vaccine.

Omicron is the evolutionarily most distinct severe acute respiratory syndrome coronavirus 2 (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 memory B (B _MEM ) cells against epitopes shared broadly among 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. Whereas 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.