CXCR5-engineered mesenchymal stromal cells home to spleen and mitigate post-sepsis syndrome by preventing secondary infection

Abstract

Background Sepsis survivors frequently develop compromised humoral immunity, manifesting as prolonged immunosuppression that increases susceptibility to secondary infections with high associated mortality. While mesenchymal stromal cells (MSCs) have demonstrated efficacy in mitigating initial inflammatory responses and improving early survival rates in murine cecal ligation and puncture (CLP) models, they show limited effectiveness against subsequent secondary infections. Given that lymphopenia represents a primary driver of this infection vulnerability, we sought to investigate whether spleen-targeted MSC therapy could prevent lymphocyte depletion and enhance protection against secondary infections. Methods In this study, we developed CXCR5-overexpressing MSCs (MSCCXCR5) to enhance their targeted migration toward splenic CXCL13. Using a CLP mouse model followed by secondary Staphylococcus aureus (S. aureus) infection, we systematically evaluated the therapeutic potential of MSCCXCR5 in combating post-sepsis immunosuppression. Results MSCCXCR5 demonstrated enhanced splenic migration, specifically homing to CXCL13-rich B-cell zones, and conferred significant protection against both S. aureus secondary infection and sepsis-induced lymphopenia. Mechanistic investigations revealed that MSCCXCR5 treatment preserved follicular and germinal center B-cell populations, maintaining splenic architecture and potentiating antigen-specific B-cell responses to CLP challenge. These effects collectively contributed to markedly improved survival outcomes in CLP mice following secondary infection. Conclusion Our findings demonstrate that MSCCXCR5 confers dual-phase protection in sepsis, improving survival during both the initial hyperinflammatory phase and subsequent immunosuppressive period. This comprehensive

1. Introduction

Sepsis mortality follows a biphasic pattern, with distinct peaks in patient fatalities. The initial peak occurs within days of onset, resulting from uncontrolled infection and hemodynamic collapse leading to cardiopulmonary failure [1]. The second mortality peak emerges weeks later, driven by persistent immunosuppression [2]. While advances in critical care have reduced early-phase mortality, most sepsis deaths now occur during this prolonged immunosuppressive phase, highlighting its crucial role in sepsis outcomes [3, 4]. Growing evidence confirms that immunosuppression represents the predominant contributor to sepsis mortality in modern clinical practice.

The immunological basis of this late-phase mortality was first demonstrated by Meakins et al., who identified impaired delayed-type hypersensitivity responses to recall antigens in fatal sepsis cases [5]. Subsequent work by Hotchkiss et al. revealed extensive apoptosis of both innate and adaptive immune cells as the pathological hallmark of terminal sepsis [6]. These findings suggest that preserving immune cell populations during the immunosuppressive phase could significantly improve survival outcomes.

Preclinical studies proved that acute-phase immunological activation induces splenomegaly initially [7, 8], mirroring the hyperinflammatory state in early sepsis. Subsequently, progressive lymphocyte apoptosis leads to splenic atrophy [9, 10], paralleling the immunosuppressive phase. This pathological lymphocyte loss severely compromises adaptive immunity, particularly impairing the survival and functional maintenance of B-cell subsets, which play a pivotal role in host defense through antibody production, establishing critical immunological memory against recurrent infections [11]. Their activation and maturation are orchestrated by CXCR5+ PD-1+ Bcl6+ follicular helper T (Tfh) cells, which recognize cognate antigens and secrete cytokines to initiate germinal center (GC) formation [12]. Within GCs, repeated antigen exposure drives affinity maturation and the generation of long-lived plasma cells and memory B cells, essential for sustained humoral immunity.