In vitro assays of allosensitization

A cell-engineered system to assess tumor cell sensitivity to CD8+ T cell-mediated cytotoxicity

In vitro assays that evaluate CD8+ T cell-mediated cytotoxicity are important to aid in the development of novel therapeutic approaches to enhance anti-tumor immune responses. Here, we describe a novel cytotoxicity co-culture assay that circumvents the problem of highly variable allogeneic responses and obviates the constraints of HLA-restriction between effector and target cells. We show that this assay can be easily applied to a panel of tumor cell lines to provide additional insights into intrinsic drivers of sensitivity/resistance to T cell-mediated killing, and to evaluate the impact of targeted therapies on both tumor and T cell compartments.

Human immune-cell response towards diverse xenogeneic and allogeneic decellularized biomaterials

BACKGROUND

Immunological knowledge on processed biological implants and mesh-prostheses is still mainly based on animal models, lacking information on the species-specific human immune response. We hypothesized that in contrast to human tissue even decellularized xenogenic specimens would lead to significant and tissue source dependent human immune reactions.

METHODS

Specimens from processed allogenic and xenogenic pulmonary arteries, pericardium or dermis, were co-cultured with human peripheral blood mononuclear cells (PBMNC). Proliferative responses were measured in tritiated thymidine incorporation assays (n = 10). Stimulation indices (SI), calculated as counts-per-minute of co-cultured PBMNC divided by the cpm of basic cell proliferation, were compared.

RESULTS

Compared to native porcine pulmonary artery tissue decellularization significantly reduced human PBMNC proliferation (mean SI: 48.7 vs. 18.0, p < 0.01), which was still higher compared to the human equivalent (SI: 0.7 vs. 1.7). Also the processed human dermal implant did not elicit immune response (SI: 1.5), whereas the decellularized and cross-linked porcine dermis lead to a significant human cell-proliferation (SI: 8.4, p < 0.01). Interestingly, both the processed human (SI: 15.2) and bovine pericardial patches (SI: 15.1) led to higher immune cell proliferation.

CONCLUSION

Even decellularized or cross-linked xenogenic cardiovascular and reconstructive biomaterials elicit increased human immune responses not seen in the majority of allogenic specimens tested.

Norm- and hypo-fractionated radiotherapy is capable of activating human dendritic cells

Despite the transient immunosuppressive properties of local radiotherapy (RT), this classical treatment modality of solid tumors is capable of inducing immunostimulatory forms of tumor-cell death. The resulting 'immunotoxicity' in the tumor, but not in healthy tissues, may finally lead to immune-mediated destruction of the tumor. However, little is known about the best irradiation scheme in this setting. This study examines the immunological effects of differently irradiated human colorectal tumor cells on human monocyte-derived dendritic cells (DC). Human SW480 tumor cells were irradiated with a norm-fractionation scheme (5 × 2 Gy), a hypo-fractionated protocol (3 × 5 Gy), and with a high single irradiation dose (radiosurgery; 1 × 15 Gy). Subsequently, human immature DC (iDC) were co-incubated with supernatants (SN) of these differently treated tumor cells. Afterwards, DC were analyzed regarding the expression of maturation markers, the release of cytokines, and the potential to stimulate CD4(+) T-cells. The co-incubation of iDC with SN of tumor cells exposed to norm- or hypo-fractionated RT resulted in a significantly increased secretion of the immune activating cytokines IL-12p70, IL-8, IL-6, and TNFα, compared to iDC co-incubated with SN of tumor cells that received a high single irradiation dose or were not irradiated. In addition, DC-maturation markers CD80, CD83, and CD25 were also exclusively elevated after co-incubation with the SN of fractionated irradiated tumor cells. Furthermore, the SN of tumor cells that were irradiated with norm- or hypo-fractionated RT triggered iDC to stimulate CD4(+) T-cells not only in an allogenic, but also in an antigen-specific manner like mature DC. Collectively, these results demonstrate that norm- and hypo-fractionated RT induces a fast human colorectal tumor-cell death with immunogenic potential that can trigger DC maturation and activation in vitro. Such findings may contribute to the improvement of irradiation protocols for the most beneficial induction of anti-tumor immunity.

Use of SNARF-1 to measure murine T cell proliferation in vitro and its application in a novel regulatory T cell suppression assay

The green fluorescent dye carboxyfluorescein diacetate succinimidyl ester (CFSE) has been used to track the proliferation of T cells in vitro. Such assays often incorporate more than one population of cells, but the paucity of alternative, spectrally distinct dyes suitable for measuring proliferation has hampered the simultaneous tracking of multiple cell populations; furthermore, CFSE is not compatible with green fluorescent protein (GFP), used to identify T cells in various transgenic mice. We have therefore validated the use of the far red dye seminaphthorhodafluor-1 (SNARF)-1 - originally developed to measure intracellular pH - to track murine T cell proliferation in vitro, demonstrating its ability to distinguish multiple cycles of proliferation over three days in a similar fashion to CFSE. The small changes in fluorescence emission attributed to intracellular alkalinisation of proliferating T cells have minimal impact on the ability of SNARF-1 to track cell division and this dye induces minimal cell death at the concentration used in this application. On the basis of these results, we have developed a novel in vitro murine T cell suppression assay, in which the proliferation of both conventional T cells (Tcons) stained with SNARF-1 and regulatory T cells (Tregs) stained with CFSE can be measured simultaneously. We have also demonstrated that SNARF-1 may be used to stain Tcons in assays of suppression involving 'designer' Tregs, generated by the transduction of CD4(+) T cells with constructs encoding the Foxp3(gfp) fusion protein.

Management of the sensitized adult heart transplant candidate

Heart transplant recipients sensitized to human leukocyte antigens comprise a challenging subgroup of patients. Sensitization has been associated with a variety of effects that determine short-term and long-term outcomes. These include a higher rate of acute rejection and graft loss, and a heightened risk for developing cardiac allograft vasculopathy. Because of improvements in both tissue typing and immunomodulatory therapies coupled with the growing population receiving mechanical circulatory support/LVAD, the percent of sensitized patients listed for heart transplantation has increased, inflicting a greater burden to the already scarce donor pool. Despite these potentially adverse developments, pre-transplant immunologic management has resulted in decreased waiting times and outcomes that were not possible over 10 yr ago. The following review will focus on the contemporary management of the sensitized heart transplant candidate and highlight therapies that have allowed the successful transplantation of this growing and challenging patient population, including several approaches in development.

Immunosuppression in the sensitized heart transplant recipient

PURPOSE OF REVIEW

The proportion of heart transplant candidates who are allosensitized has increased over time. Advances in tissue typing and immunosuppression have improved the rate of successful transplant in this challenging population. Recently published data regarding contemporary approaches to desensitization prior to and immunosuppression following transplant are summarized.

RECENT FINDINGS

Continued progress in measurement and characterization of antibodies and strategies to abrogate antibody production both prior to and following heart transplant have been encouraging. Updates on the role of non-human leukocyte antigen antibodies and the impact of mechanical circulatory support on allosensitization are provided. Data on current desensitization strategies, including the increasing use of monoclonal antibodies, are provided and the potential role of complement inhibitors will be reviewed. Increasing experience with potent novel agents is likely to provide the opportunity to improve transplant outcomes for highly sensitized patients.

SUMMARY

Although allosensitized heart transplant candidates remain a management challenge, excellent outcomes can be achieved with contemporary approaches. Advances in the understanding of B-cell biology are anticipated to further broaden options and improve outcomes.

Mechanisms of tolerance to parental parathyroid tissue when combined with human allogeneic thymus transplantation

BACKGROUND

The induction of tolerance toward third-party solid organ grafts with allogeneic thymus tissue transplantation has not been previously demonstrated in human subjects.

OBJECTIVE

Infants with complete DiGeorge anomaly (having neither thymus nor parathyroid function) were studied for conditions and mechanisms required for the development of tolerance to third-party solid organ tissues.

METHODS

Four infants who met the criteria received parental parathyroid with allogeneic thymus transplantation and were studied.

RESULTS

Two of 3 survivors showed function of both grafts but subsequently lost parathyroid function. They demonstrated alloreactivity against the parathyroid donor in mixed lymphocyte cultures. For these 2 recipients, parathyroid donor HLA class II alleles were mismatched with the recipient and thymus. MHC class II tetramers confirmed the presence of recipient CD4(+) T cells with specificity toward a mismatched parathyroid donor class II allele. The third survivor has persistent graft function and lacks alloreactivity toward the parathyroid donor. All parathyroid donor class II alleles were shared with either the recipient or the thymus graft, with minor differences between the parathyroid (HLA-DRB1∗1104) and thymus (HLA-DRB1∗1101). Tetramer analyses detected recipient T cells specific for the parathyroid HLA-DRB1∗1104 allele. Alloreactivity toward the parathyroid donor was restored with low doses of IL-2.

CONCLUSION

Tolerance toward parathyroid grafts in combined parental parathyroid and allogeneic thymus transplantation requires matching of thymus tissue to parathyroid HLA class II alleles to promote negative selection and suppression of recipient T cells that have alloreactivity toward the parathyroid grafts. This matching strategy may be applied toward tolerance induction in future combined thymus and solid organ transplantation efforts.

The immunological monitoring of kidney and liver transplants in adult and pediatric recipients

Over the last half century, kidney and liver transplantation have been recognized as the treatment of choice for adult and children with end-stage renal or liver failure. Infants present a relative naïve immune system, but they are capable of mounting both cellular and humoral immune responses to the foreign antigens presented by the allograft. Immune monitoring is a way of measuring functional and molecular correlates of immune reactivity which may provide clinically useful information for identifying patients who have an increase risk of acute rejection prior to clinical symptoms or develop transplant tolerance. However, although numerous assays have been shown to predict rejection, to date no assays have been demonstrated to detect or predict transplantation tolerance. This is a summary of the published literature on promising antigen-specific and non-antigen-specific assays used for immunological monitoring in solid organ transplantation. This work also attempts to review their applicability to pediatric transplantation, specifically, pediatric kidney and liver recipients.