Regulatory T Cells as a Therapeutic Tool To Induce Solid-Organ Transplant Tolerance: Current Clinical Experiences

New insights in immunomodulation for intestinal transplantation

Tolerance is the Holy Grail of solid organ transplantation (SOT) and remains its primary challenge since its inception. In this topic, the seminal contributions of Thomas Starzl at Pittsburgh University outlined foundational principles of graft acceptance and tolerance, with chimerism emerging as a pivotal factor. Immunologically, intestinal transplantation (ITx) poses a unique hurdle due to the inherent characteristics and functions of the small bowel, resulting in increased immunogenicity. This necessitates heavy immunosuppression (IS) while IS drugs side effects cause significant morbidity. In addition, current IS therapies fall short of inducing clinical tolerance and their discontinuation has been proven unattainable in most cases. This underscores the unfulfilled need for immunological modulation to safely reduce IS-related burdens. To address this challenge, the Leuven Immunomodulatory Protocol (LIP), introduced in 2000, incorporates various pro-tolerogenic interventions in both the donor to the recipient, with the aim of facilitating graft acceptance and improving outcome. This review seeks to provide an overview of the current understanding of tolerance in ITx and outline recent advances in this domain.

Cell therapy in transplantation: A comprehensive review of the current applications of cell therapy in transplant patients with the focus on Tregs, CAR Tregs, and Mesenchymal stem cells

Organ transplantation is a practical treatment for patients with end-stage organ failure. Despite the advances in short-term graft survival, long-term graft survival remains the main challenge considering the increased mortality and morbidity associated with chronic rejection and the toxicity of immunosuppressive drugs. Since a novel therapeutic strategy to induce allograft tolerance seems urgent, focusing on developing novel and safe approaches to prolong graft survival is one of the main goals of transplant investigators. Researchers in the field of organ transplantation are interested in suppressing or optimizing the immune responses by focusing on immune cells including mesenchymal stem cells (MSCs), polyclonal regulatory Tcells (Tregs), and antigen-specific Tregs engineered with chimeric antigen receptors (CAR Tregs). We review the mechanistic pathways, phenotypic and functional characteristics of these cells, and their promising application in organ transplantation.

IL-35 and IL-18 Serum Levels in Children With Acute Lymphoblastic Leukemia: The Relationship With Prognostic Factors

Acute lymphoblastic leukemia (ALL) is the most common type of cancer among children. In this study, we investigated the serum levels of interleukin (IL)-35 and IL-18 in children with ALL to compare with healthy subjects and find their relationship with prognostic factors and response to therapy. IL-35 and IL-18 serum concentrations in 40 children diagnosed with ALL and 35 age-matched and sex-matched healthy children were measured using ELISA. The association between cytokine levels and patients' clinical and laboratory data were determined. A significant difference was found in IL-35 serum levels between the patients (3.6±1.5 ng/mL) and controls (2.5±1.8 ng/mL) (P=0.007). No significant difference in IL-18 serum levels between these groups was observed. A positive correlation between IL-35 and IL-18 levels was detected (P=0.001). The authors found that patients with lower platelet count had higher IL-35 concentration (P=0.003). By considering a cut-off value of 6.21 ng/mL (mean±2SD of controls) for IL-35, it was found that white blood cell (WBC) count was higher in patients with IL-35 >6.21 ng/mL (P=0.016), and the majority of these patients had T-ALL (P=0.01). Although the mean overall survival in patients with IL-35 >6.21 ng/mL was shorter (937±381 d) than in those with IL-35 ≤6.21 ng/mL (1567±103 d), but the result was not significant (P=0.1, log-rank test). The IL-18 level was associated with a lower hemoglobin level (P=0.027). These data suggested a role for IL-35 in ALL development. The significant relation of IL-35 to white blood cells and platelet counts may imply a possible influence of IL-35 on ALL prognosis.

Correlation Between Stem and Progenitor Cells Number and Immune Response in Patients After Allogeneic Kidney Transplant

Background

Stem and progenitor cells are of great interest in all medical procedures involving tissue regeneration. There is a consensus that the use of stem cells after solid organ transplantation may play a role in tissue repair and in immunosuppression. The aim of this study was to determine possible relations between stem cell count and the immune response in a group of patients after kidney transplantation.

Material/Methods

The study was conducted on a group of 100 patients who underwent kidney transplantation. The following phenotypic markers of the studied cell subpopulations were adopted: T_reg cells (CD3⁺CD4⁺CD25^high), circulating hematopoietic cells (CD34⁺CD133⁺CD45⁺CD38⁻), and non-hematopoietic cells (Lin⁻CXCR4⁺CD133⁻CD45⁻). Cell subpopulations were assessed using LSRII flow cytometer (BD Biosciences, San Jose, CA, USA).

Results

Positive correlation was observed between non-hematopoietic stem cells percentage and recipient’s platelets count (P=0.04). Moreover, a higher percentage of non-hematopoietic cells was accompanied by lower numbers of B lymphocytes (P=0.03) and T_reg cells (P=0.02).

Conclusions

Our study revealed significant associations between the intensity of ongoing immune response processes and tissue damage, and the release of stem and progenitor cells into circulation. These findings suggest their role in the stimulation of protective processes in terms of graft regeneration.

Adipose-derived cellular therapies in solid organ and vascularized-composite allotransplantation

PURPOSE OF REVIEW

Controlling acute allograft rejection following vascularized composite allotransplantation requires strict adherence to courses of systemic immunosuppression. Discovering new methods to modulate the alloreactive immune response is essential for widespread application of vascularized composite allotransplantation. Here, we discuss how adipose-derived cellular therapies represent novel treatment options for immune modulation and tolerance induction in vascularized composite allotransplantation.

RECENT FINDINGS

Adipose-derived mesenchymal stromal cells are cultured from autologous or allogeneic adipose tissue and possess immunomodulatory qualities capable of prolonging allograft survival in animal models of vascularized composite allotransplantation. Similar immunosuppressive and immunomodulatory effects have been observed with noncultured adipose stromal-vascular-fraction-derived therapies, albeit publication of in-vivo stromal vascular fraction cell modulation in transplantation models is lacking. However, both stromal vascular fraction and adipose derived mesenchymal stem cell therapies have the potential to effectively modulate acute allograft rejection via recruitment and induction of regulatory immune cells.

SUMMARY

To date, most reports focus on adipose derived mesenchymal stem cells for immune modulation in transplantation despite their phenotypic plasticity and reliance upon culture expansion. Along with the capacity for immune modulation, the supplemental wound healing and vasculogenic properties of stromal vascular fraction, which are not shared by adipose derived mesenchymal stem cells, hint at the profound therapeutic impact stromal vascular fraction-derived treatments could have on controlling acute allograft rejection and tolerance induction in vascularized composite allotransplantation. Ongoing projects in the next few years will help design the best applications of these well tolerated and effective treatments that should reduce the risk/benefit ratio and allow more patients access to vascularized composite allotransplantation therapy.