Adoptive cell transfer of T-cell receptor-engineered lymphocytes: lessons from recent modeling

Regulatory T Cells: Serious Contenders in the Promise for Immunological Tolerance in Transplantation

Regulatory T cells (Tregs) play an important role in immunoregulation and have been shown in animal models to promote transplantation tolerance and curb autoimmunity following their adoptive transfer. The safety and potential therapeutic efficacy of these cells has already been reported in Phase I trials of bone-marrow transplantation and type I diabetes, the success of which has motivated the broadened application of these cells in solid-organ transplantation. Despite major advances in the clinical translation of these cells, there are still key questions to be addressed to ensure that Tregs attest their reputation as ideal candidates for tolerance induction. In this review, we will discuss the unique traits of Tregs that have attracted such fame in the arena of tolerance induction. We will outline the protocols used for their ex vivo expansion and discuss the future directions of Treg cell therapy. In this regard, we will review the concept of Treg heterogeneity, the desire to isolate and expand a functionally superior Treg population and report on the effect of differing culture conditions. The relevance of Treg migratory capacity will also be discussed together with methods of in vivo visualization of the infused cells. Moreover, we will highlight key advances in the identification and expansion of antigen-specific Tregs and discuss their significance for cell therapy application. We will also summarize the clinical parameters that are of importance, alongside cell manufacture, from the choice of immunosuppression regimens to the number of injections in order to direct the success of future efficacy trials of Treg cell therapy. Years of research in the field of tolerance have seen an accumulation of knowledge and expertise in the field of Treg biology. This perpetual progression has been the driving force behind the many successes to date and has put us now within touching distance of our ultimate success, immunological tolerance.

T regulatory cell therapy in transplantation: stability, localization and functional specialization

PURPOSE OF REVIEW

There is great hope that cellular therapy with regulatory T cells (Tregs) will be an effective way to induce alloantigen specific tolerance, ultimately allowing for reduction or elimination of nonspecific immunosuppression. In the past, considerable effort was focused on defining the optimal ways to isolate and expand Tregs from peripheral or cord blood. Now that expansion of therapeutically relevant numbers of Tregs is feasible, we need to consider what is going to happen to the cells when they are transferred in vivo.

RECENT FINDINGS

For optimal function, Tregs must be able to traffic to the correct location(s) and, despite the presence of immunosuppressive therapy, live long enough to transfer their regulatory function to recipient T cells. Within the Treg pool, there are also functionally specialized subsets, identified by chemokine receptor expression and/or cytokine production, which control their trafficking and relative ability to suppress different types of T helper cells, respectively. Recent findings imply that the plasticity of appropriately obtained populations of Tregs may not be of as great concern as previously suggested. Experimental data have also provided evidence as to how one might design adjunctive treatment that best supports the viability and function of Tregs after transfer.

SUMMARY

Knowledge of how Tregs work in transplantation comes from studies that do not recapitulate how these cells will be used in humans. There is a need to develop better preclinical models to study how the in-vivo function of human Tregs can be optimized to ensure they can meet the challenge of inducing transplantation tolerance.

In vivo SPECT reporter gene imaging of regulatory T cells

Regulatory T cells (Tregs) were identified several years ago and are key in controlling autoimmune diseases and limiting immune responses to foreign antigens, including alloantigens. In vivo imaging techniques including intravital microscopy as well as whole body imaging using bioluminescence probes have contributed to the understanding of in vivo Treg function, their mechanisms of action and target cells. Imaging of the human sodium/iodide symporter via Single Photon Emission Computed Tomography (SPECT) has been used to image various cell types in vivo. It has several advantages over the aforementioned imaging techniques including high sensitivity, it allows non-invasive whole body studies of viable cell migration and localisation of cells over time and lastly it may offer the possibility to be translated to the clinic. This study addresses whether SPECT/CT imaging can be used to visualise the migratory pattern of Tregs in vivo. Treg lines derived from CD4⁺CD25⁺FoxP3⁺ cells were retrovirally transduced with a construct encoding for the human Sodium Iodide Symporter (NIS) and the fluorescent protein mCherry and stimulated with autologous DCs. NIS expressing self-specific Tregs were specifically radiolabelled in vitro with Technetium-99m pertechnetate (^99mTcO₄⁻) and exposure of these cells to radioactivity did not affect cell viability, phenotype or function. In addition adoptively transferred Treg-NIS cells were imaged in vivo in C57BL/6 (BL/6) mice by SPECT/CT using ^99mTcO₄⁻. After 24 hours NIS expressing Tregs were observed in the spleen and their localisation was further confirmed by organ biodistribution studies and flow cytometry analysis. The data presented here suggests that SPECT/CT imaging can be utilised in preclinical imaging studies of adoptively transferred Tregs without affecting Treg function and viability thereby allowing longitudinal studies within disease models.