Enhancing alloreactivity does not restore GVHD induction but augments skin graft rejection by CD4⁺ effector memory T cells

Cellular Strategies for Separating GvHD from GvL in Haploidentical Transplantation

GvHD still remains, despite the continuous improvement of transplantation platforms, a fearful complication of transplantation from allogeneic donors. Being able to separate GvHD from GvL represents the greatest challenge in the allogeneic transplant setting. This may be possible through continuous improvement of cell therapy techniques. In this review, current cell therapies are taken into consideration, which are based on the use of TCR alpha/beta depletion, CD45RA depletion, T regulatory cell enrichment, NK-cell-based immunotherapies, and suicide gene therapies in order to prevent GvHD and maximally amplify the GvL effect in the setting of haploidentical transplantation.

The Adaptation Model of Immunity: Signal IV Matters Most in Determining the Functional Outcomes of Immune Responses

Current research in immunology and immunotherapy is fully influenced by the self-nonself model of immunity. This theoretical model suggests that alloreactivity results in graft rejection, whereas tolerance toward self-antigens expressed by malignant cells facilitates cancer development. Similarly, breakage of immunological tolerance toward self-antigens results in autoimmune diseases. Accordingly, immune suppression is recommended for the management of autoimmune diseases, allergy, and organ transplantation, whereas immune inducers are used for the treatment of cancers. Although the danger model, the discontinuity model, and the adaptation model are proposed for a better understanding of the immune system, the self-nonself model continues to dominate the field. Nevertheless, a cure for these human diseases remains elusive. This essay discusses current theoretical models of immunity, as well as their impacts and limitations, and expands on the adaptation model of immunity to galvanize a new direction for the treatment of autoimmune diseases, organ transplantation, and cancer.

Naive T-Cell Depletion to Prevent Chronic Graft-Versus-Host Disease

PURPOSE

Graft-versus-host disease (GVHD) causes morbidity and mortality following allogeneic hematopoietic cell transplantation. Naive T cells (TN) cause severe GVHD in murine models. We evaluated chronic GVHD (cGVHD) and other outcomes in three phase II clinical trials of TN-depletion of peripheral blood stem-cell (PBSC) grafts.

METHODS

One hundred thirty-eight patients with acute leukemia received TN-depleted PBSC from HLA-matched related or unrelated donors following conditioning with high- or intermediate-dose total-body irradiation and chemotherapy. GVHD prophylaxis was with tacrolimus, with or without methotrexate or mycophenolate mofetil. Subjects received CD34-selected PBSC and a defined dose of memory T cells depleted of TN. Median follow-up was 4 years. The primary outcome of the analysis of cumulative data from the three trials was cGVHD.

RESULTS

cGVHD was very infrequent and mild (3-year cumulative incidence total, 7% [95% CI, 2 to 11]; moderate, 1% [95% CI, 0 to 2]; severe, 0%). Grade III and IV acute GVHD (aGVHD) occurred in 4% (95% CI, 1 to 8) and 0%, respectively. The cumulative incidence of grade II aGVHD, which was mostly stage 1 upper gastrointestinal GVHD, was 71% (95% CI, 64 to 79). Recipients of matched related donor and matched unrelated donor grafts had similar rates of grade III aGVHD (5% [95% CI, 0 to 9] and 4% [95% CI, 0 to 9]) and cGVHD (7% [95% CI, 2 to 13] and 6% [95% CI, 0 to 12]). Overall survival, cGVHD-free, relapse-free survival, relapse, and nonrelapse mortality were, respectively, 77% (95% CI, 71 to 85), 68% (95% CI, 61 to 76), 23% (95% CI, 16 to 30), and 8% (95% CI, 3 to 13) at 3 years.

CONCLUSION

Depletion of TN from PBSC allografts results in very low incidences of severe acute and any cGVHD, without apparent excess risks of relapse or nonrelapse mortality, distinguishing this novel graft engineering strategy from other hematopoietic cell transplantation approaches.

The Yin and Yang dualistic features of autophagy in thermal burn wound healing

Burn healing should be regarded as a dynamic process consisting of two main, interrelated phases: (a) the inflammatory phase when neutrophils and monocytes infiltrate the injury site, through localized vasodilation and fluid extravasation, and (b) the proliferative-remodeling phase, which represents a key event in wound healing. In the skin, both canonical autophagy (induced by starvation, oxidative stress, and environmental aggressions) and non-canonical or selective autophagy have evolved to play a discrete, but, essential, “housekeeping” role, for homeostasis, immune tolerance, and survival. Experimental data supporting the pro-survival roles of autophagy, highlighting its Yang, luminous and positive feature of this complex but insufficient explored molecular pathway, have been reported. Autophagic cell death describes an “excessive” degradation of important cellular components that are necessary for normal cell function. This deadly molecular mechanism brings to light the darker, concealed, Yin feature of autophagy. Autophagy seems to perform dual, conflicting roles in the angiogenesis context, revealing once again, its Yin–Yang features. Autophagy with its Yin–Yang features remains the shadow player, able to decide quietly whether the cell survives or dies.

Repurposing a novel anti-cancer RXR agonist to attenuate murine acute GVHD and maintain graft-versus-leukemia responses

The nuclear receptor (NR) subclass, retinoid X receptors (RXRs), exert immunomodulatory functions that control inflammation and metabolism via homodimers and heterodimers, with several other NRs, including retinoic acid receptors. IRX4204 is a novel, highly specific RXR agonist in clinical trials that potently and selectively activates RXR homodimers, but not heterodimers. In this study, in vivo IRX4204 compared favorably with FK506 in abrogating acute graft-versus-host disease (GVHD), which was associated with inhibiting allogeneic donor T-cell proliferation, reducing T-helper 1 differentiation, and promoting regulatory T-cell (Treg) generation. Recipient IRX4204 treatment reduced intestinal injury and decreased IFN-γ and TNF-α serum levels. Transcriptional analysis of donor T cells isolated from intestines of GVHD mice treated with IRX4204 revealed significant decreases in transcripts regulating proinflammatory pathways. In vitro, inducible Treg differentiation from naive CD4+ T cells was enhanced by IRX4204. In vivo, IRX4204 increased the conversion of donor Foxp3- T cells into peripheral Foxp3+ Tregs in GVHD mice. Using Foxp3 lineage-tracer mice in which both the origin and current FoxP3 expression of Tregs can be tracked, we demonstrated that IRX4204 supports Treg stability. Despite favoring Tregs and reducing Th1 differentiation, IRX4204-treated recipients maintained graft-versus-leukemia responses against both leukemia and lymphoma cells. Notably, IRX4204 reduced in vitro human T-cell proliferation and enhanced Treg generation in mixed lymphocyte reaction cultures. Collectively, these beneficial effects indicate that targeting RXRs with IRX4204 could be a novel approach to preventing acute GVHD in the clinic.

More Than Skin Deep: Autophagy Is Vital for Skin Barrier Function

The skin is a highly organized first line of defense that stretches up to 1.8 m² and is home to more than a million commensal bacteria. The microenvironment of skin is driven by factors such as pH, temperature, moisture, sebum level, oxidative stress, diet, resident immune cells, and infectious exposure. The skin has a high turnover of cells as it continually bares itself to environmental stresses. Notwithstanding these limitations, it has devised strategies to adapt as a nutrient-scarce site. To perform its protective function efficiently, it relies on mechanisms to continuously remove dead cells without alarming the immune system, actively purging the dying/senescent cells by immunotolerant efferocytosis. Both canonical (starvation-induced, reactive oxygen species, stress, and environmental insults) and non-canonical (selective) autophagy in the skin have evolved to perform astute due-diligence and housekeeping in a quiescent fashion for survival, cellular functioning, homeostasis, and immune tolerance. The autophagic “homeostatic rheostat” works tirelessly to uphold the delicate balance in immunoregulation and tolerance. If this equilibrium is upset, the immune system can wreak havoc and initiate pathogenesis. Out of all the organs, the skin remains under-studied in the context of autophagy. Here, we touch upon some of the salient features of autophagy active in the skin.

Memory T cells: A helpful guard for allogeneic hematopoietic stem cell transplantation without causing graft-versus-host disease

Graft-versus-host disease (GVHD) is a major complication of allogeneic hematopoietic stem cell transplantation (AHSCT) and the major cause of nonrelapse morbidity and mortality of AHSCT. In AHSCT, donor T cells facilitate hematopoietic stem cell (HSC) engraftment, contribute to anti-infection immunity, and mediate graft-versus-leukemia (GVL) responses. However, activated alloreactive T cells also attack recipient cells in vital organs, leading to GVHD. Different T-cell subsets, including naïve T (T_N) cells, memory T (T_M) cells, and regulatory T (T_reg) cells mediate different forms of GVHD and GVL; T_N cells mediate severe GVHD, whereas T_M cells do not cause GVHD, but preserve T-cell function including GVL. In addition, metabolic reprogramming controls T-cell differentiation and activation in these disease states. This minireview focuses on the role and the related mechanisms of T_M cells in AHSCT, and the potential manipulation of T cells in AHSCT.

Outcomes of acute leukemia patients transplanted with naive T cell-depleted stem cell grafts

BACKGROUND

Graft-versus-host disease (GVHD) is a major cause of morbidity and mortality following allogeneic hematopoietic stem cell transplantation (HCT). In mice, naive T cells (TN) cause more severe GVHD than memory T cells (TM). We hypothesized that selective depletion of TN from human allogeneic peripheral blood stem cell (PBSC) grafts would reduce GVHD and provide sufficient numbers of hematopoietic stem cells and TM to permit hematopoietic engraftment and the transfer of pathogen-specific T cells from donor to recipient, respectively.

METHODS

In a single-arm clinical trial, we transplanted 35 patients with high-risk leukemia with TN-depleted PBSC grafts following conditioning with total body irradiation, thiotepa, and fludarabine. GVHD prophylactic management was with tacrolimus immunosuppression alone. Subjects received CD34-selected PBSCs and a defined dose of TM purged of CD45RA+ TN. Primary and secondary objectives included engraftment, acute and chronic GVHD, and immune reconstitution.

RESULTS

All recipients of TN-depleted PBSCs engrafted. The incidence of acute GVHD was not reduced; however, GVHD in these patients was universally corticosteroid responsive. Chronic GVHD was remarkably infrequent (9%; median follow-up 932 days) compared with historical rates of approximately 50% with T cell-replete grafts. TM in the graft resulted in rapid T cell recovery and transfer of protective virus-specific immunity. Excessive rates of infection or relapse did not occur and overall survival was 78% at 2 years.

CONCLUSION

Depletion of TN from stem cell allografts reduces the incidence of chronic GVHD, while preserving the transfer of functional T cell memory.

TRIAL REGISTRATION

ClinicalTrials.gov (NCT 00914940).

Blockade of Syk ameliorates the development of murine sclerodermatous chronic graft-versus-host disease

BACKGROUND

Murine sclerodermatous chronic graft-versus-host disease (Scl-cGVHD) is a model for human Scl-cGVHD and systemic sclerosis (SSc). Syk is expressed in most of hematopoietic cells, fibroblasts, and endothelial cells. Syk is a protein tyrosine kinase that has an important role in transmitting signals from a variety of cell surface receptors.

OBJECTIVE

This study aims to investigate the effect of R788 (fostamatinib sodium), an oral prodrug that is rapidly converted to a potent inhibitor of Syk, R406, on Scl-cGVHD.

METHODS

R788 was orally administered twice a day to allogeneic recipients from day 14 to day 42 after bone marrow transplantation (BMT). In vitro, proliferation of GVHD-derived CD4(+) T cells and CD11b(+) cells was analyzed by R406.

RESULTS

Allogeneic BMT increased Syk phosphorylation in T, B, and CD11b(+) cells. The administration of R788 attenuated severity and fibrosis of Scl-cGVHD. The elevated expressions of CXCR4 on T cells, B cells, and CD11b(+) cells were significantly down-regulated by R788 treatment. R788 reduced memory CD4(+) T cells (CD44(hi)CD62L(-)CD4(+)). R406 inhibited proliferation of GVHD CD4(+) T cells and CD11b(+) cells in vitro. In addition, R788 treatment, inhibited proliferation of CD11b(+) cells in Scl-cGVHD mice. R788 treatment also reduced skin mRNA expressions of MCP-1, MIP-1α, IFN-γ, IL-13, IL-17A, and TGF-β1, but not influenced RANTES, CXCL12, and TFN-α.

CONCLUSION

Blockade of Syk suppressed migration factor of immune cells and antigen-specific memory CD4(+) T cells and proliferation and activation of GVHD CD4(+) T cells and CD11b(+) cells. The current studies suggested that Syk inhibitor is a potential candidate for use in treating patients with Scl-cGVHD and SSc.

Allospecific CD4(+) effector memory T cells do not induce graft-versus-host disease in mice

We studied whether allospecific CD4(+) effector memory T cells (T(EM)) could induce graft-versus-host disease (GVHD) using a novel GVHD model induced solely by CD4(+) T cell receptor transgenic TEa cells. Allospecific T(EM) generated in a lymphopenic host bore a typical memory phenotype. Moreover, these cells were able to elicit a faster and more effective proliferative response on challenge with alloantigen in vitro and to mediate "second-set" skin graft rejection in vivo. However, these allospecific T(EM) were unable to induce GVHD. Allospecific T(EM) recipients became tolerant to alloantigen as a result of clonal deletion. Even though allospecific T(EM) were able to respond to alloantigen initially, the expansion of these cells and inflammatory cytokine production during GVHD were dramatically decreased. The inability of allospecific T(EM) to sustain the alloresponse may be a result of enhanced activation-induced cell death. These observations provide insight into how allospecific CD4(+) T(EM) respond to alloantigen during GVHD and underscore the fundamental differences in alloresponses mediated by allospecific T(EM) in graft rejection and GVHD settings.

Nephro and neurotoxicity of calcineurin inhibitors and mechanisms of rejections: A review on tacrolimus and cyclosporin in organ transplantation

CONTEXT

In the meadow of medical sciences substituting a diseased organ with a healthy one from another individual, dead or alive, to allow a human to stay alive could be consider as the most string event. In this article we review the history of transplantation, mechanisms of rejection, nephro-neurotoxicity of tacrolimus and cyclosporin in organ transplantations.

EVIDENCE ACQUISITIONS

Directory of Open Access Journals (DOAJ), Google Scholar, Pubmed (NLM), LISTA (EBSCO) and Web of Science have been searched.

RESULTS

The first reference to the concept of organ transplantation and replacement for therapeutic purposes appears to be to Hua-To (136 to 208 A.D), who replaced diseased organs with healthy ones in patients under analgesia induced with a mixture of Indian hemp. In 1936, the first human renal transplant performed by Voronoy in Russia. The first liver transplant in humans was performed on March 1, 1963 by Starzl in Denver, USA. Medawar was the first to assert that rejection was an immunological response, with the inflammatory reaction due to lymphocyte infiltration. Consequently, rational immunosuppressive therapies could inhibit deleterious T-cell responses in an antigen specific manner.

CONCLUSIONS

Searching related to the history of organ transplantation from mythic to modern times suggests that, to prevent graft rejection, minimize nephro and neuro toxicity monitoring of immunosupressive concentrations could provide an invaluable and essential aid in adjusting dosage to ensure adequate immunosuppression.

Memory lapses in graft-versus-host disease

"Faster, better, more" is the conventional benchmark used to define responses of memory T cells when compared with their naïve counterparts. In this issue of the European Journal of Immunology, Mark and Warren Shlomchik and colleagues [Eur. J. Immunol. 2011. 41: 2782-2792] make the intriguing observation that murine memory CD4(+) T-cell populations enriched for alloreactive precursors are fully capable of rejecting allogeneic skin grafts but yet are incapable of inducing significant graft-versus-host disease. These observations add to the emerging concept that memory CD4(+) T-cell development is more nuanced and complex than predicted by conventional models. In particular, the data suggest that it may be just as important to consider what naïve or effector cells have "lost" in their transition to memory.

A repertoire-independent and cell-intrinsic defect in murine GVHD induction by effector memory T cells

Effector memory T cells (T(EM)) do not cause graft-versus-host disease (GVHD), though why this is has not been elucidated. To compare the fates of alloreactive naive (T(N)) or memory (T(M)) T cells, we developed a model of GVHD in which donor T cells express a transgene-encoded TCR specific for an antigenic peptide that is ubiquitously expressed in the recipient. Small numbers of naive TCR transgenic (Tg) T cells induced a robust syndrome of GVHD in transplanted recipients. We then used an established method to convert TCR Tg cells to T(M) and tested these for GVHD induction. This allowed us to control for the potentially different frequencies of alloreactive T cells among T(N) and T(M), and to track fates of alloreactive T cells after transplantation. T(EM) caused minimal, transient GVHD whereas central memory T cells (T(CM)) caused potent GVHD. Surprisingly, T(EM) were not inert: they, engrafted, homed to target tissues, and proliferated extensively, but they produced less IFN-γ and their expansion in target tissues was limited at later time points, and local proliferation was reduced. Thus, cell-intrinsic properties independent of repertoire explain the impairment of T(EM), which can initiate but cannot sustain expansion and tissue damage.