No abstract

Background The mechanisms contributing to clinical immune tolerance remain incompletely understood. This study provides evidence for specific immune mechanisms that are associated with a model of operationally defined clinical tolerance. Objective Our overall objective was to study laboratory changes associated with clinical immune tolerance in antigen-induced T cells, basophils, and antibodies in subjects undergoing oral immunotherapy (OIT) for peanut allergy. Methods In a phase 1, single site study, we studied participants (n=23) undergoing peanut OIT and compared them to age-matched allergic controls (n=20) undergoing standard of care (abstaining from peanut) for 24 months. Participants were operationally defined as clinically immune tolerant (IT) if they had no detectable allergic reactions to a peanut oral food challenge after 3 months of therapy withdrawal (IT, n=7) while those that had an allergic reaction were categorized as non-tolerant (NT, n=13). Results Antibody and basophil activation measurements did not statistically differentiate between NT vs. IT. However, T-cell function and demethylation of FOXP3 CpG sites in antigen-induced Treg were significantly different between IT vs. NT participants. When IT participants were withdrawn from peanut therapy for an additional 3 months (total of 6 months); only 3 participants remained "immune tolerant" and 4 participants regained sensitivity along with increased methylation of FOXP3 CpG sites in antigen-induced Treg. Conclusion In summary, modifications at the DNA level of antigen-induced T-cell subsets may be predictive of a state of operationally-defined clinical "immune tolerance" during peanut OIT.

SUMMARY Assays that can characterize MSC immune potency need to be identified for use in advanced clinical trials. MSCs possess a number of putative regenerative and immunomodulatory properties, and an assay matrix approach may best capture involved effector pathways. We have tested two assay systems to measure the potency of MSCs derived from human subjects: MSC secretome analysis and a quantitative RNA-based array for genes specific to immunomodulatory and homing properties of MSCs. Secretome analysis identified a unique cytokine signature that is upregulated by MSCs or downregulated in responder PBMCs and correlated with T cell suppression. Use of interferon-γ as a surrogate for the action of activated PBMCs on MSCs served as an alternative for the use of human PBMCs as responder cells in a potency assay. Our approach and results define and simplify the multifunctional or matrix responses of MSCs and may serve as a platform for robust potency analysis.

We have previously demonstrated that cryopreservation and thawing lead to altered MSC functionalities. Here, we further analyzed MSC's fitness post freeze-thaw. We have observed that thawed MSC can suppress T-cell proliferation when separated from them by transwell membrane and the effect is lost in a MSC:T-cell coculture system. Unlike actively growing MSCs, thawed MSCs were lysed upon coculture with activated autologous PBMCs and the lysing effect was further enhanced with allogeneic PBMCs. The use of DMSO-free cryoprotectants or substitution of HSA with human platelet lysate in freezing media and use of autophagy or caspase inhibitors did not prevent thaw defects. We tested the hypothesis that IFNγ pre-licensing before cryobanking can enhance MSC fitness post thaw. Post thawing, IFNγ licensed MSCs inhibit T cell proliferation as well as fresh MSCs and this effect can be blocked by 1-methyl Tryptophan, an IDO inhibitor. In addition, IFNγ prelicensed thawed MSCs inhibit the degranulation of cytotoxic T cells while IFNγ unlicensed thawed MSCs failed to do so. However, IFNγ prelicensed thawed MSCs do not deploy lung tropism in vivo following intravenous injection as well as fresh MSCs suggesting that IFNγ prelicensing does not fully rescue thaw-induced lung homing defect. We identified reversible and irreversible cryoinjury mechanisms that result in susceptibility to host T-cell cytolysis and affect MSC's cell survival and tissue distribution. The susceptibility of MSC to negative effects of cryopreservation and the potential to mitigate the effects with IFNγ prelicensing may inform strategies to enhance the therapeutic efficacy of MSC in clinical use.

SummaryMesenchymal stromal cells have shown clinical promise; however, variations in treatment responses are an ongoing concern. We previously demonstrated that MSCs are functionally stunned after thawing. Here, we investigated whether this cryopreservation/thawing defect also impacts the postinfusion biodistribution properties of MSCs. Under both static and physiologic flow, compared with live MSCs in active culture, MSCs thawed from cryopreservation bound poorly to fibronectin (40% reduction) and human endothelial cells (80% reduction), respectively. This reduction correlated with a reduced cytoskeletal F-actin content in post-thaw MSCs (60% reduction). In vivo, live human MSCs could be detected in murine lung tissues for up to 24 hr, whereas thawed MSCs were undetectable. Similarly, live MSCs whose actin cytoskeleton was chemically disrupted were undetectable at 24 hr postinfusion. Our data suggest that post-thaw cryopreserved MSCs are distinct from live MSCs. This distinction could significantly affect the utility of MSCs as a cellular therapeutic.