Host MyD88 signaling protects against acute graft-versus-host disease after allogeneic bone marrow transplantation

The Confounding Role of Graft-Versus-Host Disease in Animal Models of Cancer Immunotherapy: A Systematic Review

BACKGROUND

Cancer immunotherapy has emerged as a transformative approach for treating various malignancies, including melanoma, lung cancer, breast cancer, and leukemia. Animal models have been instrumental in elucidating the mechanisms and potential of these therapies. However, graft-versus-host disease (GVHD) is an inherent challenge in these studies, primarily because the introduction of foreign immune cells or tissues often triggers immune responses.

METHODS

A detailed systematic search was conducted across various scientific databases, including PubMed, Scopus, Embase, and Web of Science. The search aimed to identify peer-reviewed articles published in English from January 2000 to September 2023. Keywords and phrases used in the search included "Graft-versus-Host Disease", "GVHD", "animal models", "cancer immunotherapy", and combinations thereof. Boolean operators (AND/OR) were employed to refine the search. Finally, 6 articles were included in this systematic review, which is registered on PROSPERO (ID number CRD42024488544).

RESULTS

Our systematic review identified several mechanisms employed in animal studies to mitigate the confounding effects of GVHD. These included genetically modified mouse models, immunosuppressive drugs, and humanized mice. Furthermore, the review highlights innovative approaches such as selective T-cell depletion and the use of specific cytokine inhibitors.

CONCLUSION

By systematically identifying and mitigating the confounding effects of GVHD, we can significantly improve the predictive validity of preclinical trials, obtain broadly applicable findings, improve the efficiency of drugs, enhance safety profiling, and develop better therapeutic strategies. This approach is crucial in ensuring that the immunotherapeutic strategies developed in the laboratory are reflective of the human physiological response, thereby bridging a critical translational gap in oncological research.

Toll-Like Receptor Signaling and Its Role in Cell-Mediated Immunity

Innate immunity is the first defense system against invading pathogens. Toll-like receptors (TLRs) are well-defined pattern recognition receptors responsible for pathogen recognition and induction of innate immune responses. Since their discovery, TLRs have revolutionized the field of immunology by filling the gap between the initial recognition of pathogens by innate immune cells and the activation of the adaptive immune response. TLRs critically link innate immunity to adaptive immunity by regulating the activation of antigen-presenting cells and key cytokines. Furthermore, recent studies also have shown that TLR signaling can directly regulate the T cell activation, growth, differentiation, development, and function under diverse physiological conditions. This review provides an overview of TLR signaling pathways and their regulators and discusses how TLR signaling, directly and indirectly, regulates cell-mediated immunity. In addition, we also discuss how TLR signaling is critically important in the host's defense against infectious diseases, autoimmune diseases, and cancer.

Toll-Like Receptor Signaling and Its Role in Cell-Mediated Immunity

Innate immunity is the first defense system against invading pathogens. Toll-like receptors (TLRs) are well-defined pattern recognition receptors responsible for pathogen recognition and induction of innate immune responses. Since their discovery, TLRs have revolutionized the field of immunology by filling the gap between the initial recognition of pathogens by innate immune cells and the activation of the adaptive immune response. TLRs critically link innate immunity to adaptive immunity by regulating the activation of antigen-presenting cells and key cytokines. Furthermore, recent studies also have shown that TLR signaling can directly regulate the T cell activation, growth, differentiation, development, and function under diverse physiological conditions. This review provides an overview of TLR signaling pathways and their regulators and discusses how TLR signaling, directly and indirectly, regulates cell-mediated immunity. In addition, we also discuss how TLR signaling is critically important in the host's defense against infectious diseases, autoimmune diseases, and cancer.

Toll-Like Receptors in Adaptive Immunity

The immune (innate and adaptive) system has evolved to protect the host from any danger present in the surrounding outer environment (microbes and associated MAMPs or PAMPs, xenobiotics, and allergens) and dangers originated within the host called danger or damage-associated molecular patterns (DAMPs) and recognizing and clearing the cells dying due to apoptosis. It also helps to lower the tissue damage during trauma and initiates the healing process. The pattern recognition receptors (PRRs) play a crucial role in recognizing different PAMPs or MAMPs and DAMPs to initiate the pro-inflammatory immune response to clear them. Toll-like receptors (TLRs) are first recognized PRRs and their discovery proved milestone in the field of immunology as it filled the gap between the first recognition of the pathogen by the immune system and the initiation of the appropriate immune response required to clear the infection by innate immune cells (macrophages, neutrophils, dendritic cells or DCs, and mast cells). However, in addition to their expression by innate immune cells and controlling their function, TLRs are also expressed by adaptive immune cells. We have identified 10 TLRs (TLR1-TLR10) in humans and 12 TLRs (TLR1-TLR13) in laboratory mice till date as TLR10 in mice is present only as a defective pseudogene. The present chapter starts with the introduction of innate immunity, timing of TLR evolution, and the evolution of adaptive immune system and its receptors (T cell receptors or TCRs and B cell receptors or BCRs). The next section describes the role of TLRs in the innate immune function and signaling involved in the generation of inflammation. The subsequent sections describe the expression and function of different TLRs in murine and human adaptive immune cells (B cells and different types of T cells, including CD4⁺T cells, CD8⁺T cells, CD4⁺CD25⁺T_regs, and CD8⁺CD25⁺T_regs, etc.). The modulation of TLRs expressed on T and B cells has a great potential to develop different vaccine candidates, adjuvants, immunotherapies to target various microbial infections, including current COVID-19 pandemic, cancers, and autoimmune and autoinflammatory diseases.

Graft-versus-host disease develops in mice transplanted with lymphocyte-depleted bone marrow cells from signal-transducing adaptor protein-2 transgenic mice

Graft-versus-host disease (GVHD) is the most frequent complication after allogeneic hematopoietic stem cell transplantation (HSCT), and is one of the major causes of non-relapse mortality. Transferred mature lymphocytes are thought to be responsible for GVHD based on the findings that mice transplanted with lymphocyte-depleted bone marrow (BM) cells from MHC-mismatched donors do not develop GVHD. However, we found that overexpression of signal-transducing adaptor protein (STAP)-2 in lymphoid cells could induce GVHD after lymphocyte-depleted BM transplantation. To examine the function of STAP-2, which has been shown to play an important role in development and function of lymphocytes, in GVHD, we transplanted BM cells from STAP-2 deficient, or Lck promoter/IgH enhancer-driven STAP-2 transgenic (Tg) mice into MHC-mismatched recipients. Unexpectedly, mice transplanted with lymphocyte-depleted BM cells from STAP-2 Tg mice developed severe acute GVHD with extensive colitis and atrophy of thymus, while no obvious GVHD developed in mice transplanted with the wild type or STAP-2 deficient graft. Furthermore, mice transplanted with lymphocyte-depleted BM cells from the syngeneic STAP-2 Tg mice developed modest GVHD with colitis and atrophy of thymus. These results suggest that STAP-2 overexpression may enhance survival of allo-, and even auto-, reactive lymphocytes derived from engrafted hematopoietic progenitor cells in lethally irradiated mice, and that clarification of the mechanism may help understanding induction of immune tolerance after HSCT.

NK cell predicts the severity of acute graft-versus-host disease in patients after allogeneic stem cell transplantation using antithymocyte globulin (ATG) in pretreatment scheme

Background

Graft-versus-host disease (GVHD) is one of the most complex complications after allogeneic stem cell transplantation. Current standard of grading system is based on clinical symptoms in skin, liver and intestinal. However, it’s difficult to differ GVHD and its extent just by clinical manifestation. Here we retrospectively analyzed cell immune function in patients implemented allogeneic stem cell transplantation in Ningbo first Hospital from Jan 2013 to Jan 2018.

Results

the data are collected from 51 patients (mean age was 42; 45.1% women). The average NK cell percentage was 39.31% in severe GVHD (Grade III-IV), was 16.98% in mild GVHD (GradeI-II), while was 21.15% in No GVHD group. The statistical analysis showed difference among each grade. Further analysis was performed in Antithymocyte globulin (ATG) treated group and control group. We showed NK Cell percentage was sharply different in ATG treated group: 47.34% in severe GVHD, 11.98% in mild GVHD group, while 18.3% in no GVHD group. However, in control group, the average percentage of NK cells was 23.27% in severe GVHD, was 23.22%in mild GVHD group, while was 21.13% in no GVHD group.

Conclusion

The data supports that ATG can prevent GVHD by increasing NK cell percentage. The percentage of NK cell seemed to be a useful probe to evaluate the severity of GVHD in allogeneic stem cell transplantation patients using ATG in pretreatment.