Multipotent mesenchymal stromal cells (MSC) have been widely explored for cell-based therapy of immune-mediated, inflammatory, and degenerative diseases, due to their immunosuppressive, immunomodulatory, and regenerative potentials. Preclinical studies and clinical trials have demonstrated promising therapeutic results although these have been somewhat limited. Aspects such as low in vivo MSC survival in inhospitable disease microenvironments, requirements for ex vivo cell overexpansion prior to infusions, intrinsic differences between MSC and different sources and donors, variability of culturing protocols, and potency assays to evaluate MSC products have been described as limitations in the field. In recent years, priming approaches to empower MSC have been investigated, thereby generating cellular products with improved potential for different clinical applications. Herein, we review the current priming approaches that aim to increase MSC therapeutic efficacy. Priming with cytokines and growth factors, hypoxia, pharmacological drugs, biomaterials, and different culture conditions, as well as other diverse molecules, are revised from current and future perspectives.

Type 1 diabetes mellitus (DM) results from a cell-mediated autoimmune attack against pancreatic beta cells.¹ The course of autodestruction is subclinical until the amount of beta-cell mass is insufficient to maintain glucose homeostasis. Thus, at the time of clinical diagnosis, approximately 60% to 80% of the beta-cell mass has been destroyed.²

Accumulated clinical experience indicates that there is an inverse association between beta-cell function and chronic complications of type 1 diabetes mellitus (DM)—the higher the C-peptide levels (an indirect measure of viable beta-cell function), the lower the incidence of microvascular complications of type 1 DM.¹ Since the establishment of the autoimmune etiology of type 1 DM in the late 1970s, many clinical trials analyzing the effects of different types of immune interventions demonstrated that beta-cell preservation is an achievable target in different degrees.^2,3

Autologous hematopoietic SCT (AHSCT) has been investigated in the past as a therapeutic alternative for multiple sclerosis (MS). Despite advances in clinical management, knowledge about mechanisms involved with clinical remission post transplantation is still limited. Abnormal microRNA and gene expression patterns were described in MS and have been suggested as disease biomarkers and potential therapeutic targets. Here we assessed T- and B-cell reconstitution, microRNAs and immunoregulatory gene expression after AHSCT. Early immune reconstitution was mainly driven by peripheral homeostatic proliferation. AHSCT increased CD4⁺CD25^hiFoxP3⁺ regulatory T-cell counts and expression of CTLA-4 and GITR (glucocorticoid-induced TNFR) on CD4⁺CD25^hi T cells. We found transient increase in exhausted PD-1⁺ T cells and of suppressive CD8⁺CD28⁻CD57⁺ T cells. At baseline, CD4⁺ and CD8⁺ T cells from MS patients presented upregulated miR-16, miR-155 and miR-142-3p and downregulated FOXP3, FOXO1, PDCD1 and IRF2BP2. After transplantation, the expression of FOXP3, FOXO1, PDCD1 and IRF2BP2 increased, reaching control levels at 2 years. Expression of miR-16, miR-155 and miR-142-3p decreased towards normal levels at 6 months post therapy, remaining downregulated until the end of follow-up. These data strongly suggest that AHSCT normalizes microRNA and gene expression, thereby improving the immunoregulatory network. These mechanisms may be important for disease control in the early periods after AHSCT.

Key Points: Clinical response of SSc patients after AHSCT is associated with thymic and bone marrow rebounds. Responder patients showed higher Treg and Breg counts and lower pre-/post-AHSCT TCR repertoire overlap than nonresponder patients.

Autologous hematopoietic stem cell transplantation (AHSCT) increases C-peptide levels and induces insulin-independence in patients with type 1 diabetes. This study aimed to investigate how clinical outcomes may associate with the immunological status, especially concerning the balance between immunoregulation and autoreactivity. Twenty-one type 1 diabetes patients were monitored after AHSCT, and assessed every six months for duration of insulin independence, C-peptide levels, frequencies of islet-specific autoreactive CD8+ T-cells, regulatory lymphocyte subsets, thymic function and T-cell repertoire diversity. In median follow-up of 78 (range 15-106) months, all patients became insulin-independent, resuming insulin after median of 43 (range 6-100) months. Patients were retrospectively divided into short- or prolonged-remission-groups, according to duration of insulin independence. For the entire follow-up, CD3+CD4+ T-cell numbers remained lower than baseline in both groups, whereas CD3+CD8+ T-cell levels did not change, resulting in a CD4/CD8 ratio inversion. Memory CD8+ T-cells comprehended most of T-cells detected on long-term follow-up of patients after AHSCT. B-cells reconstituted to baseline levels at 2-3 months post-AHSCT in both patient groups. In the prolonged-remission-group, baseline islet-specific T-cell autoreactivity persisted after transplantation, but regulatory T-cell counts increased. Patients with lower frequencies of autoreactive islet-specific T-cells remained insulin-free longer and presented greater C-peptide levels than those with lower frequencies of these cells. Therefore, immune monitoring identified a subgroup of patients with superior clinical outcome of AHSCT. Our study shows that improved immunoregulation may balance autoreactivity endorsing better metabolic outcomes in patients with lower frequencies of islet-specific T-cells. Development of new strategies of AHSCT is necessary to increase frequency and function of T and B regulatory cells and decrease efficiently autoreactive islet-specific T and B memory cells in type 1 diabetes patients undergoing transplantation.