cPRA Increases With DQA,DPA, and DPB Unacceptable Antigens in the Canadian cPRA Calculator

A calculated panel reactive antibody (cPRA) estimates the percentage of donors with unacceptable antigens (UA) for a recipient. cPRA may be underestimated in transplant candidates with UA to DQA, DPA, and DPB if these are not included in the calculation program. To serve the National Canadian Transplant Programs, a cPRA calculator was developed with complete molecular typing for all donors at HLA‐A, B, C, DRB1, DRB3/4/5, DQA1, DQB1, DPA1, and DPB1, all resolved to serologic equivalents. The prevalence of UA at DQA, DPA and DPB was evaluated in a sensitized regional population. The impact of adding these additional UA to cPRA was calculated alone and in combination, and compared to the baseline cPRA for UA at A, B, C, DR, DR51/52/53, and DQ. Of 740 sensitized transplant candidates, 18% of total and 32% with cPRA≥95% had DQA UA. Twenty‐seven percent of total and 54% with cPRA≥95% had DPB UA. Of 280/740 subjects with these UA, 36/280 (13%) had cPRA increase of >20% when they were included, 7% increased cPRA to ≥80% and 6% to ≥95%. Inclusion of DQA, DPA, and DPB UA in Canadian cPRA calculations improves the accuracy of cPRA where these are relevant in allocation.     

Donor‐specific chimeric antigen receptor Tregs limit rejection in naive but not sensitized allograft recipients

Cell therapy with autologous donor‐specific regulatory T cells (Tregs) is a promising strategy to minimize immunosuppression in transplant recipients. Chimeric antigen receptor (CAR) technology has recently been used successfully to generate donor‐specific Tregs and overcome the limitations of enrichment protocols based on repetitive stimulations with alloantigens. However, the ability of CAR‐Treg therapy to control alloreactivity in immunocompetent recipients is unknown. We first analyzed the effect of donor‐specific CAR Tregs on alloreactivity in naive, immunocompetent mice receiving skin allografts. Tregs expressing an irrelevant or anti‐HLA‐A2‐specific CAR were administered to Bl/6 mice at the time of transplanting an HLA‐A2⁺ Bl/6 skin graft. Donor‐specific CAR‐Tregs, but not irrelevant‐CAR Tregs, significantly delayed skin rejection and diminished donor‐specific antibodies (DSAs) and frequencies of DSA‐secreting B cells. Donor‐specific CAR‐Treg–treated mice also had a weaker recall DSA response, but normal responses to an irrelevant antigen, demonstrating antigen‐specific suppression. When donor‐specific CAR Tregs were tested in HLA‐A2‐sensitized mice, they were unable to delay allograft rejection or diminish DSAs. The finding that donor‐specific CAR‐Tregs restrain de novo but not memory alloreactivity has important implications for their use as an adoptive cell therapy in transplantation.     

Regulatory T cells for tolerance

Regulatory T cells (Tregs) are critical mediators of immune homeostasis and hold significant promise in the quest for transplantation tolerance. Progress has now reached a critical threshold as techniques for production of clinical therapies are optimised and Phase I/II clinical trials are in full swing. Initial safety and efficacy data are being reported, with trials assessing a number of different strategies for the introduction of Treg therapy. It is now more crucial than ever to elucidate further the function and behaviour of Tregs in vivo and ensure safe delivery. This review will discuss the current state of the art and future directions in Treg therapy.     

On the elusive TCR specificity of thymic regulatory T cells

Therapies using thymus‐derived regulatory T cells (Tregs) are promising strategies for preventing autoimmunity or graft rejection. The efficacy of these approaches is, however, contingent on a better understanding of Treg mode of action, especially about factors controlling their activation in vivo. Although key parameters of Treg suppression have been identified, little information is available on Treg activation in vivo via the TCR. In light of recent studies using TCR transgenic mouse models as well as unpublished data, we discuss evidence in support of the view that Treg TCR specificities are not necessarily highly diverse, that the accessibility of Treg selective antigens control Treg development, and that peptides derived from MHC class II (MHC‐II) could be prevailing antigens involved in Treg selection. This novel perspective provides insights on Treg development as well as a conceptual basis to a significant contribution of MHC‐II derived peptides in the shaping of the Treg TCR repertoire.     

T cell antigenicity and immunogenicity of allogeneic exosomes

Extracellular vesicles, including exosomes, are regularly released by allogeneic cells after transplantation. Recipient antigen-presenting cells (APCs) capture these vesicles and subsequently display donor MHC molecules on their surface. Recent evidence suggests that activation of alloreactive T cells by the so-called cross-dressed APCs plays an important role in initiating the alloresponse associated with allograft rejection. On the other hand, whether allogeneic exosomes can bind to T cells on their own and activate them remains unclear. In this study, we showed that allogeneic exosomes can bind to T cells but do not stimulate them in vitro unless they are cultured with APCs. On the other hand, allogeneic exosomes activate T cells in vivo and sensitize mice to alloantigens but only when delivered in an inflammatory environment.     

Egr-1 in vascular smooth muscle cell proliferation in response to allo-antigen

BACKGROUND: Early growth response factor-1 (Egr-1) plays an important role in regulating multiple factors involved in the progression of vascular lesions. This study examined our hypothesis that Egr-1 plays a critical role in the early stage of chronic cardiac allograft rejection and in the proliferation of the smooth muscle cell response to alloantigen. MATERIALS AND METHODS: Antisense Egr-1 oligodeoxynucleotide (ODN) was ex vivo gene transfected into the donor hearts from DBA/2 mice, followed by heterotopic allografting into B10.D2 recipients. The allografts were harvested on day 30. Egr-1 and its target molecules, such as platelet-derived growth factor (PDGF)-A, basic fibroblastic growth factor (bFGF), vascular cell adhesion molecule (VCAM)-1, transforming growth factor (TGF)-beta and nonmuscle myosin heavy chain B (SMemb), were identified immunohistochemically, and the percentage of the lumen occluded by the intima was calculated. For the cell proliferation assay, sensitized T cells were harvested from B10.D2 recipients as stimulator and then added to the SMCs, which were harvested from DBA/2 mouse aorta. Cellular proliferation was measured and Egr-1 and its target gene expression were examined by real-time RT-PCR. RESULTS: Egr-1 and its target genes were expressed in the thickened intima from untreated recipients. Egr-1 antisense ODN inhibited not only Egr-1 expression but also its target genes and significantly suppressed intimal thickening of coronary arteries. Egr-1 antisense ODN also significantly inhibited cell proliferation and expressions of Egr-1 and Egr-1 target genes in a mixed cell culture model. CONCLUSION: We conclude that Egr-1 plays an important role in the formation of the cardiac allograft vasculopathy responding to alloantigens.     

GP IIb三种基因多态性之间的关系及GP IIbT13959G在血小板输注耐受中的作用

目的:研究血小板膜糖蛋白Ⅱb(GPIIb)三种基因多态性之间的关系及GPIIbT13959G在血小板输注耐受中的作用。方法:聚合酶链反应-单链构型多态性分析检测110例正常人GPIIb基因第26和30外显子(Exon26,Exon30)及21内含子(Intron21)基因多态性,进行基因序列分析,研究这些基因多态性是否存在连锁关系;应用Fok1酶切法对147例血液病人人类血小板抗原-3(humanplateletantigen-3,HPA-3)基因进行分型,并与110例正常人进行比较;将接受单采血小板输注的44例血液病人随机分为HPA-3同型输注组和对照组,血小板输注3次以后检测血小板抗体。结果:正常人GPIIb存在基因多态性,表现分别为gDNA13959位点T→G,16977位点C→T,11996～12004位点9个碱基缺失,且三者具有同步性。Fox1酶切分析结果表明,正常人和血液病人的HPA-3a基因频率分别为83.6%(92/110)和81.9%(119/147),HPA-3b基因频率分别为16.4%(18/110)和19.1%(28/147),两者之间差异无统计学意义(P>0.05)。血液病人接受单采血小板输注后,HPA-3同型输注组血小板抗体阴性,而对照组有2例存在血小板抗体,其中1例为HPA-3a抗体。结论:(1)GPIIb基因存在gDNA13959位点T→G,16977位点C→T,11996～12004位点9个碱基缺失,这3个位点的多态性可能存在完全连锁关系;(2)血液病人与正常人的HPA-3基因频率相同;(3)HPA-3系统可能是我国人群产生血小板输注耐受的原因之一。     

Analysis of platelet membrane glycoprotein polymorphisms in Glanzmann thrombasthenia showed the French gypsy mutation in the αIIb gene to be strongly linked to the HPA-1b polymorphism in β3

Summary.  We have tested the DNA of a large series of Glanzmann thrombasthenia patients for polymorphisms in platelet membrane glycoproteins. To our surprise, we noted a high prevalence of the HPA-1b allele of β3, the minority allele in a normal population. This proved to be due to the presence of nine patients homozygous for the so-called French gypsy mutation (IVS15[ + 1]G→A) in αIIb. Seven of these patients were homozygous for the HPA-1b alloantigen and the other two heterozygous HPA-1a/1b. As the αIIb and β3 genes are both on chromosome 17, it is highly probable that the French gypsy mutation first arose on a chromosome encoding HPA-1b. For other adhesion receptors, no major differences were seen in the distribution of the A1, A2 and A3 alleles in the α2 gene, or in the Kozak or HPA-2 polymorphisms of GPIbα, suggesting that none of these alleles result in increased survival in Glanzmann thrombasthenia.     

Comparative study of regulatory T cells expanded ex vivo from cord blood and adult peripheral blood

In this study, we expanded regulatory T cells (Tregs) ex vivo from CD4(+) CD25(+) T cells from cord blood (CB) and CD4(+) CD25(+) CD127(-) T cells from adult peripheral blood (APB) and compared the suppressive functions of the newly generated Tregs. The Tregs from CB and APB were expanded either in two cycles with a polyclonal stimulus or in two cycles with an alloantigen stimulus in the first cycle and a polyclonal stimulus in the second cycle. Cell yield after Treg expansion with polyclonal stimulation was greater than that of Tregs expanded with combined alloantigen and polyclonal stimulation. The expanded Tregs expressed high levels of Foxp3, CD39 and cytotoxic T-lymphocyte antigen-4 and low levels of CD127, interleukin-2 and interferon-γ. After two cycles of expansion, the CB Tregs maintained expression of the GARP gene and showed greater suppressive function than APB Tregs. The CB Tregs that were expanded with two cycles of polyclonal stimulation suppressed not only the polyclonal antigen-driven responder T (T(resp)) cell proliferation but also the HLA mismatched dendritic cell-driven T(resp) cell proliferation. When CB and APB Tregs were expanded with a primary alloantigen stimulus followed by a secondary polyclonal stimulus, the Tregs showed a potent, antigen-specific suppressive capacity. The Tregs expanded with two cycles of polyclonal stimulation from both CB and APB alleviated acute graft-versus-host disease symptoms and prolonged survival in a murine model of graft-versus-host disease. In conclusion, CB Tregs expanded with two cycles of polyclonal stimulation had a stronger immunosuppressive function than APB Tregs. It is feasible to obtain human functional alloantigen-specific Tregs expanded ex vivo from CB and APB in large numbers.