Doron Merkler

The local and systemic symptoms that follow vaccination, collectively referred to as reactogenicity, are common, yet the mechanisms underlying individual variability remain poorly understood. Through longitudinal immune profiling of vaccinated individuals and mechanistic studies in mice, we identified key immunological determinants of reactogenicity induced by mRNA vaccines. Systemic adverse events were associated with stronger interferon and pro-inflammatory responses after the second dose of a COVID-19 mRNA vaccine, which were also correlated with the magnitude of the antigen-specific adaptive responses. This heightened inflammation occurred within 24 hours of vaccination, originated primarily from the injection site, and was characterized by enhanced recruitment and activation of myeloid cells, particularly monocytes. Two mechanisms contributed to this response: early interferon production by muscle T cells generated after the first dose and Fcγ receptor–dependent chemokine induction by vaccine antigen–specific antibodies. Consistently, serum antibody levels before vaccination correlated positively with reactogenicity. In addition to this local amplification mechanism, variability in reactogenicity was influenced by the baseline immune state, given that individuals with a preexisting interferon-stimulated gene signature in monocytes, detectable at both transcriptomic and epigenetic levels, were more prone to systemic symptoms. Together, our findings revealed molecular and cellular mechanisms driving vaccine reactogenicity, providing a framework for the design of less reactogenic vaccines.

Glioblastoma (GBM) is characterized by a profoundly immunosuppressive tumor microenvironment (TME) that constrains the efficacy of chimeric antigen receptor (CAR)-T cell therapy. Here, we show that surgical resection in both male mice and human GBM ex vivo induces a rapid and sustained remodeling of the TME, marked by upregulation of TREM2 in myeloid cells followed by emergence of T cell exhaustion-like phenotypes. In male mice, targeting TREM2 reshapes the perioperative TME and potentiates tumor antigen-specific CAR-T cell responses, improving intratumoral persistence, proliferation, and effector differentiation, and resulting in enhanced survival. In parallel, we identify the timing of CAR-T cell administration as a critical determinant of therapeutic outcome, with neoadjuvant outperforming adjuvant treatment by preserving CAR-T cell effector function in mice. These findings establish perioperative myeloid cell remodeling and treatment timing as key determinants of CAR-T cell efficacy in GBM.

Circadian rhythms are intrinsic time-keeping mechanisms that play a critical role in tuning immunity. Here, we investigated the impact of circadian rhythms on the pathogenesis of experimental autoimmune encephalomyelitis (EAE), a mouse model for multiple sclerosis (MS). We demonstrate that circulating neutrophils in blood significantly increase early in EAE, prior to symptoms onset. Importantly, we found that these cells infiltrate the central nervous system (CNS) in a time-of-day (ToD)-dependent manner, with increased infiltration at the onset of the behavioral active phase of the mice (evening). Transcriptomic analysis of CNS-infiltrating neutrophils revealed distinct ToD-dependent gene expression profiles, which identified Formyl peptide receptor 2 (FPR2) as a potential therapeutic candidate, since pharmacological inhibition of FPR2 led to reduced EAE disease severity. Furthermore, combinatorial treatment with a drug that targets VLA-4 (used in clinical practice under the trade name Natalizumab to treat MS) led to additive effects, substantially reducing EAE symptoms. Together, these findings highlight the importance of circadian immune cell dynamics during EAE development and provide a characterization of the circadian immune landscape in an animal model of MS, identifying potential targets for MS therapies.

A key function of the germinal center (GC) reaction consists in the preferential expansion and enrichment of high-affinity B cell clones. Whether and how persistent viral infection thwarts this purpose remains ill-defined. Here, we transferred monoclonal lymphocytic choriomeningitis virus–specific B cells into persistently infected hosts. High-affinity B cells expanded vigorously, forming GCs and abundant antibody-secreting cells. When failing to clear viremia or to drive viral mutational escape, the expanded B cell population contracted, ending in its quasi-complete disappearance from the spleen, a process we termed “attrition.” In stark contrast, low-affinity B cells expanded and persisted irrespective of high viral loads. B cell attrition was associated with phenotypic and transcriptional alterations including a prominent Blimp-1 transcriptional signature in high-affinity GC B cells. Blimp-1-deficient B cells were resistant to attrition, suggesting a B cell–intrinsic process. Moreover, exogenously supplied antibody feedback prevented attrition, suggesting that the latter may have resulted from excessive antigenic stimulation. Our findings suggest that in chronic viral infection, the incessant exposure to overwhelming amounts of antigen perturbs B cell affinity hierarchies by preferentially dysregulating high-affinity B cells.

Single-cell studies have revealed substantial microglial diversity in development, homeostasis and disease. However, a framework enabling comparison and stratification of microglial states across contexts is needed. Here we generated an atlas of myeloid cell states by single-cell RNA sequencing more than one million central nervous system cells from more than 30 physiological and pathological conditions. This atlas enables us to establish a comprehensive taxonomy of myeloid cell states across brain disorders and related mouse models, comprising 27 superclusters and 192 clusters that are prevalent across diseases and largely conserved. We augment this taxonomic framework with spatial transcriptomics to map how immune cell states are organized within tissue and interact with their local cellular environment. Using in vivo perturbations, we also show that activation-associated microglial states are dependent on interferon and colony-stimulating factor 1 receptor signaling. Together, these findings provide a spatially aware taxonomic framework for central nervous system immune cells in health and disease.

Innate lymphoid cells type 2 (ILC2s) are key regulators of tissue homeostasis and inflammation. In cancer, ILC2s can exhibit pro-tumoral functions by increasing the myeloid derived suppressor cells (MDSC)/T-cell ratio. Nevertheless, the upstream ILC2 triggers remain poorly defined. Here, we identify nerve growth factor (NGF) as the driver of ILC2 pro-tumoral functions in patients with bladder cancer. We show that ILC2s express the NGF receptor TrkA and respond to NGF by secreting type-2 cytokines. In the tumor microenvironment, NGF-producing mast cells accumulate and activate ILC2s to induce regulatory T cells (Tregs), ultimately fostering tumor growth. In patients, NGF levels inversely correlate with survival in ILC2-rich tumors, underscoring the clinical significance of this axis. In vivo administration of a selective TrkA inhibitor improves survival in orthotopic tumor-bearing female mice and sensitizes them to immune checkpoint blockade (ICB). Overall, we identify NGF as an ILC2 activator that shapes pro-tumoral ILC2 functions. The blockade of TrkA ⁺ ILC2s might represent a targetable strategy to improve survival, particularly in ICB-resistant patients.

Foxp3-expressing regulatory T (T _reg ) cells protect against systemic autoimmunity. However, little is known about the significance of T _reg cells in inflammation-experienced tissues. Here, we use an experimental autoimmune encephalomyelitis model and show that T _reg cells accumulate and persist in the central nervous system (CNS) long after the resolution of the bulk of the inflammatory infiltrate. CNS-specific depletion of postinflammatory T _reg cells, but not systemic depletion of T _reg cells, results in autoimmune inflammatory flares in the CNS by residual local effector T cells. Expression of the NAD-consuming ectoenzyme CD38 is crucial for the functional adaptation of postinflammatory CNS T _reg cells to a stressful microenvironment, in which access to interleukin-2 (IL-2) is limited. CD38 counteracts ADP-ribosylation of the IL-2 receptor and thus maintains its high sensitivity to IL-2. This fully functional high-affinity IL-2 receptor prevents the loss of tissue-resident antigen-specific T _reg cells. These ‘stress-tolerant’ CNS T _reg cells impede the collapse of immune homeostasis in the CNS once acute inflammation is controlled.

Gray matter pathology, including the formation of cortical lesions, predicts progression in people with multiple sclerosis (PwMS). Here, we investigated whether positron emission tomography (PET) imaging using the synaptic vesicle protein 2A (SV2A)–targeting radioligand [ ¹⁸ F]UCB-H could help to detect and monitor synapse loss, an early feature of gray matter pathology in MS. First, we confirmed that SV2A is a suitable marker of synapse density in MS by analyzing SV2A mRNA and protein expression in cortical gray matter. We then used a mouse model of cortical MS pathology to demonstrate that SV2A-PET imaging can detect synapse loss in cortical lesions and that synapse densities measured by PET imaging correspond to the densities of genetically and immunohistochemically labeled synapses in the same lesions. Last, we performed SV2A-PET imaging in a total of 31 PwMS at different stages of the disease process, showing that PET imaging can detect synapse loss in cortical MS lesions in vivo. Moreover, we found that interhemispheric asymmetries in SV2A-PET tracer uptake can be leveraged to uncover further cortical alterations, the volume of which was more than 20-fold larger than the cortical lesion area detected by MRI. The extent of these PET-defined areas of cortical synapse pathology was larger in the progressive stage of the disease and correlated with the disability and cognitive performance of the same individuals. SV2A-PET imaging thus unmasked clinically relevant cortical pathology in MS thereby providing a promising tool to detect and monitor disease progression.