Multiple sclerosis (MS) is an autoimmune demyelinating disease of the central nervous system. The therapeutic landscape for MS has evolved significantly since the 1990s, with the development of more than 20 different disease-modifying therapies (DMTs). These therapies effectively manage relapses and inflammation, but most have failed to meaningfully prevent disease progression. While classically understood as a T cell-mediated condition, the most effective DMTs in slowing progression also target B cells. Novel classes of MS therapies in development, including anti-CD40L monoclonal antibodies, CD19 chimeric antigen receptor (CAR) T cells, and Bruton’s tyrosine kinase (BTK) inhibitors show greater capacity to target and eliminate B cells in the brain/CNS, as well as impacting T-cell and innate immune compartments. These approaches may help tackle the disease at its immunopathological core, addressing both peripheral and central immune responses that drive MS progression. Another emerging therapeutic strategy is to use bispecific antibodies, which have the potential for dual-targeting various disease aspects such as immune activation and neurodegeneration. As such, the next generation of MS therapies may be the first to reduce both inflammatory demyelination and disease progression in a clinically meaningful way. Their ability to target specific immune cell populations while minimizing broad immune suppression could also lead to better safety profiles. Here, we explore the biological rationale, advantages, limitations, and clinical progress of these emerging immunotherapies for relapsing–remitting and progressive forms of MS.

Peptidoglycans (PGNs) are structural polymers of the bacterial cell wall and a common microbial molecular pattern encountered by the immune system daily. Low levels of PGNs are constitutively present in the systemic circulation in humans and rise during inflammatory pathologies. Since all known PGN sensors are intracellular, PGN internalization is a prerequisite for the initiation of cellular immune responses. Here, we report the mechanisms controlling the recognition and uptake of polymeric PGNs by circulating human mononuclear phagocytes. We found that complement C3 and C4 opsonins govern PGN recognition and internalization, but no single opsonin is indispensable because of multiple uptake redundancies. We observed a bimodal internalization of polymeric PGNs with distinct requirements for complement C4. At low PGN concentrations, C3 mediated PGN recognition by surface receptors while the efficient internalization of PGN polymers critically required C4. Supraphysiologic PGN concentrations triggered a secondary uptake modality that was insensitive to C4 and mediated instead by C3 engagement of complement receptors 1 and 3. To our knowledge, this is the first description of nonoverlapping C3 and C4 opsonophagocytoses working in parallel. Controlling these uptake mechanisms has the potential to modulate PGN clearance or the dysregulated immune responses during bacterial infections.

Multiple sclerosis (MS) remains a leading cause of neurological disability, primarily due to the limited efficacy of current disease-modifying therapies in arresting progressive neurodegeneration. While peripheral lymphocyte depletion effectively manages relapsing activity, it fails to address the compartmentalized, smoldering inflammation driven by interactions between adaptive and innate immune systems within the central nervous system (CNS). The CD40–CD40L costimulatory pathway has emerged as a central regulator of these immune interactions, positioning it as a unique therapeutic target capable of addressing the full spectrum of MS pathology. This review examines the multimodal effects of CD40L blockade across peripheral and CNS-resident cell populations. Preclinical and genetic models demonstrate that inhibiting this axis suppresses pathogenic T-cell and B-cell responses while modulating innate immune activation, including macrophages, microglia, and astrocytes, and disrupting pro-inflammatory glial crosstalk. Early clinical data from second-generation, non-thromboembolic CD40L inhibitors, such as frexalimab, demonstrate reductions in markers of neuroaxonal injury and inflammatory disease activity. By simultaneously modulating systemic lymphocyte responses and CNS-resident innate immune processes, CD40L blockade represents a promising strategy to address both relapsing disease activity and progressive disability accumulation, thereby overcoming key therapeutic barriers in multiple sclerosis.

The transition from relapsing–remitting multiple sclerosis (RRMS) to secondary-progressive multiple sclerosis (SPMS) represents an ambiguous transition period characterized by diagnostic delays and a shifting therapeutic window. While inflammatory relapses are well-managed, the underlying neurodegeneration often remains undetected until substantial disability has accrued. This review evaluated the shift from traditional metrics, such as the Expanded Disability Status Scale (EDSS), toward more sensitive, multimodal monitoring strategies. We described characteristic MRI findings in SPMS and addressed the impact of comorbidities that frequently confound the diagnosis of disease transition. Furthermore, we evaluated the predictive potential of emerging fluid biomarkers and gut microbial signatures in identifying the early RRMS-to-SPMS transition. Finally, we described the current therapeutic landscape and emerging immunomodulatory interventions. Diagnosing SPMS remains a clinical challenge due to comorbidities and the lack of a singular definitive marker. Moving toward high-sensitivity imaging and molecular biomarkers is essential for the early initiation of treatments and improved patient outcomes.

Multiple sclerosis (MS) is a chronic autoimmune disease of the central nervous system that culminates in inflammation, neuronal degeneration and loss of nerve functioning. While there is no specific cause of MS, there are factors that can influence disease progression, in particular tobacco smoke exposure (smoking). Smoking has been shown to increase inflammation, disease activity, and disability progression – herein we aim to connect this to both early inflammation and late-stage neurodegeneration. We propose that smoking enhances immune cell aging (immunosenescence) and examine evidence showing that this induces immune cell phenotypes that mirror physiological aging, specifically the depletion of naïve T-cell pools and the expansion of terminally differentiated, senescent CD8+ populations. We also review literature that suggests potential mechanism(s), including oxidative stress, cholenergic signaling, and epigenetic remodeling. By integrating clinical and mechanistic studies, we provide a framework that suggests smoking-associated immune aging shifts the MS profile from acute relapses toward sustained, treatment-resistant disability – and that smoking cigarettes is an active driver of disease, not just an environmental risk factor.

The transition from relapsing-remitting multiple sclerosis (RRMS) to secondary-progressive multiple sclerosis (SPMS) represents an ambiguous transition period characterized by diagnostic delays and a shifting therapeutic window. While inflammatory relapses are well-managed, the underlying neurodegeneration often remains undetected until substantial disability has accrued. This review evaluated the shift from traditional metrics, such as the Expanded Disability Status Scale (EDSS), toward more sensitive, multimodal monitoring strategies. We described characteristic MRI findings in SPMS and addressed the impact of comorbidities that frequently confound the diagnosis of disease transition. Furthermore, we evaluated the predictive potential of emerging fluid biomarkers and gut microbial signatures in identifying the early RRMS-to-SPMS transition. Finally, we described the current therapeutic landscape and emerging immunomodulatory interventions. Diagnosing SPMS remains a clinical challenge due to comorbidities and the lack of a singular definitive marker. Moving toward high-sensitivity imaging and molecular biomarkers is essential for the early initiation of treatments and improved patient outcomes.