Quantitative assessment of angiogenesis and osteogenesis after transplantation of bone: Comparison of isograft and allograft bone in mice

We performed a vital microscopic study in mice bearing dorsal skinfold chambers to characterize microvascular perfusion and leukocyte/endothelium interaction and their effects on elongation and mineralization of neonatal isograft and allograft bone. Isograft (C57/BL to C57/BL) and allograft bone (C57/ BL to BALB/C) revascularized simultaneously. However, vascular perfusion and density were lower in allograft bone than in isograft bone. Leukocyte/endothelium interaction was the same in isograft and allograft bones. Revascularization was not detected in allograft bone transplanted to presensitized recipients. Moreover, in preexisting vessels at the trans plantation site, leukocyte/endothelium interaction was altered in allograft bone of presensitized recipients, despite a normal systemic leukocyte count. Femoral growth resulting from thickening of both epiphyses did not differ between experimental groups, however, mineralization occurred in isograft bone only, Isograft bone was histologically intact, allograft bone hypovital and allograft bone in presensitized recipients necrotic 12 days after implantation. Our findings suggest that graft incorporation or rejection is mediated by the microvasculature and that presensi-tizing of recipients accelerates rejection of allograft bone.     

Quantitative assessment of angiogenesis and osteogenesis after transplantation of bone: comparison of isograft and allograft bone in mice

We performed a vital microscopic study in mice bearing dorsal skinfold chambers to characterize microvascular perfusion and leukocyte/endothelium interaction and their effects on elongation and mineralization of neonatal isograft and allograft bone. Isograft (C57/BL to C57/BL) and allograft bone (C57/ BL to BALB/C) revascularized simultaneously. However, vascular perfusion and density were lower in allograft bone than in isograft bone. Leukocyte/endothelium interaction was the same in isograft and allograft bones. Revascularization was not detected in allograft bone transplanted to presensitized recipients. Moreover, in preexisting vessels at the transplantation site, leukocyte/endothelium interaction was altered in allograft bone of presensitized recipients, despite a normal systemic leukocyte count. Femoral growth resulting from thickening of both epiphyses did not differ between experimental groups, however, mineralization occurred in isograft bone only. Isograft bone was histologically intact, allograft bone hypovital and allograft bone in presensitized recipients necrotic 12 days after implantation. Our findings suggest that graft incorporation or rejection is mediated by the microvasculature and that presensitizing of recipients accelerates rejection of allograft bone.     

小鼠异体Sertoli细胞诱导胰岛移植免疫耐受的作用

目的 观察小鼠Sertoli细胞是否能在异体内起到诱导局部免疫耐受、保护共移植异体胰岛的作用.方法 以糖尿病C57小鼠作移植受体,随机分4组,每组6只;以正常BALB/C小鼠为胰岛供体,正常C57小鼠和正常BALB/C小鼠各作为Serloli细胞供体.A组:单纯移植异体胰岛;B组:移植来源于C57小鼠的Sertoli细胞+BALB/C小鼠来源的胰岛;C组:移植均来源于BALB/C小鼠的Sertoli细胞及胰岛;D组:假手术组.监测各组移植受体的血糖尿糖变化,观察移植物的存活时间.结果 A组移植物平均存活时间为(6.50±2.35)d;B组为(55.67±4.84)d;C组为(51.33±5.05)d;D组未观察到血糖正常.B组及C组的移植方式均可逆转糖尿病小鼠的高血糖状态,移植物存活期均较A组有明显延长,其差异有统计学意义(P<0.05);而B组与C组的移植物存活时间差异无统计学意义(P>0.05).结论 同种异体来源的睾丸Sertoli细胞在异体内可起到诱导局部免疫耐受的效果,对共移植同种异体胰岛起到保护作用,其效果与自体睾丸Sertoli细胞相当.     

Cyclosporine mitigates graft coronary artery disease in murine cardiac allografts: description and validation of a novel fully allogeneic model.

BACKGROUND: The effect of cyclosporine (CsA) on the development of graft coronary artery disease (GCAD) is controversial. We developed a novel allogeneic mouse model of heart transplantation and investigated the effect of CsA on acute rejection and GCAD. METHODS: Hearts of FVB mice (H-2(q)) were heterotopically transplanted into 60 C57BL/6 mice (H-2(b)). CsA was administered to recipients at 10, 20 or 30 mg/kg/day for 10 or 30 days after transplantation. Untreated recipients as well as isograft recipients served as controls. Viability of the grafts was assessed daily by palpation. Parenchymal rejection was scored in grafts surviving 30 days in the 30-day treatment groups. GCAD was evaluated by the percentage of luminal narrowing, intima/media ratio and percentage of diseased vessels. Blood CsA and creatinine levels were also evaluated. Results were evaluated statistically. RESULTS: All groups except the untreated control group and the allograft groups treated with 10 or 20 mg for 10 days showed significant graft survival (>/=33% survival for 30 days). An inverse correlation was observed between CsA treatment dose, parenchymal rejection score and degree of GCAD in the 30-day treatment groups. However, graft survival in the 20-mg/kg/day group was significantly better than that in the 30-mg/kg/day group. Serum creatine levels showed no nephrotoxicity. CONCLUSIONS: Relatively high-dose CsA mitigated parenchymal rejection and GCAD of the mouse cardiac allografts. In addition, a valuable mouse model mimicking the clinical course of GCAD was achieved with CsA treatment of 20 mg/kg/day for 30 days.     

Gene transfer for transplantation. Prolongation of allograft survival with transforming growth factor-beta 1.

OBJECTIVE: The authors tested the ability of plasmid gene transfer to express transforming growth factor-beta 1 (TGF-beta 1), prolong allograft survival, and evaluate promoter effects on gene expression. SUMMARY BACKGROUND DATA: Delivery of immunosuppressants directly to allografts using gene transfer and gene therapy approaches may inhibit immune activation while avoiding the systemic toxicity of conventional immunosuppression. Candidate genes include soluble cytokines, which could be expressed at low levels throughout the graft while inducing a local immunosuppressive effect. Transforming growth factor-beta 1 is a soluble cytokine that has pleiotropic immunosuppressive effects. METHODS: Cardiac grafts from syngeneic (CBA/J, H-2k) or allogenic (C57BL/6, H-2b) donors were placed into CBA/J recipients. Purified plasmid DNA-encoding murine TGF-beta 1 or beta-galactosidase (Lac Z) under the control of RSV, SV40, MMTV, or pancreatic elastase promoters was injected into grafts at surgery. The Lac Z expression was determined by histologic examination and TGF-beta 1 expression by graft survival. Cytotoxic T lymphocyte and flow cytometric analyses were performed to evaluate the immunosuppressive effects of TGF-beta 1 in vitro. RESULTS: Plasmid DNA-encoding TGF-beta 1 prolonged survival from 12.6 +/- 1.1 days to 26.3 +/- 2.5 days (p < 0.02, Student's t test). The SV40 promoter was superior to the MMTV promoter in its ability to prolong survival. The effects of the plasmids were specific because Lac Z, antisense TGF-beta 1 inserts, or pancreatic elastase promoter did not prolong allograft survival. Histologic examination demonstrated Lac Z expression at least 14 days post-transplant in myocardial cells. Both RSV and SV40 promoters were effective in this respect, while a control null promoter was not. Toxicity testing showed that gene transfer of TGF-beta 1 did not alter survival or histology of syngeneic grafts. In addition, plasmids and purified TGF-beta 1 protein were not toxic to myoblasts in vitro. Recombinant TGF-beta 1 inhibited cytotoxic T lymphocyte generation and altered T cell surface receptor expression and subset expansion in vitro. CONCLUSION: Gene transfer/therapy with plasmid DNA encoding TGF-beta 1 in vivo achieves immunologic effects that prolong allograft survival. Multiple promoters effectively induce plasmid expression, which is achieved in cardiac myocytes for at least 2 weeks without toxicity or adverse systemic effects. Transforming growth factor-beta 1 inhibits immune responses by different mechanisms, revealed by in vitro analysis of T cell cytolytic function, subset distribution, and receptor display.     

Acceptance of related and unrelated cardiac allografts in neonatally tolerized mice is cardio-specific and transferable by regulatory CD4+ T cells.

BACKGROUND: Non-donor-specific cardiac allograft acceptance is induced in C3H/He (C3H; H-2k) recipients injected as neonates with allogeneic BALB/c (BALB; H-2d) fetal liver cells (FLC). This occurs despite intact reactivity to donor-type and third-party alloantigens in in vitro assays and skin transplants. To investigate a role for regulatory T cells, we performed adoptive transfer studies and specifically assessed CD4+ and CD4- T cells. METHODS: Three cell populations (splenocytes, CD4+, CD4-) derived from neonatally-treated mice with accepted C57BL/6 (B6; H-2b) third-party cardiac grafts were adoptively transferred into sub-lethally-irradiated C3H mice. Reconstituted mice were challenged with B6 cardiac grafts, B6 skin grafts, or unrelated cardiac grafts. Separated cells were assessed in vitro. RESULTS: B6, BALB, and NZW (H-2z) graft acceptance was transferred by unfractionated splenocytes. CD4+ cells transferred B6 graft acceptance (85% survival > 100 days). CD4- cells, unfractionated cells from naive or only irradiated mice, and unfractionated cells from neonatally-treated non-transplanted C3H mice rejected grafts within 35 days. No inoculum induced skin graft acceptance. Co-cultured assays confirmed the suppressive function of CD4+ cells in vitro. CONCLUSIONS: Cardiac allograft acceptance in our model is regulated by CD4+ cells. The regulatory cell population is induced by the cardiac graft itself and mediates in vivo cardiac graft acceptance in a tissue-specific but not donor-strain-specific manner.     

鼠纤维介素在小鼠心脏移植急性排斥反应中的表达及其意义

目的　探讨小鼠同种心脏移植急性排斥反应期间鼠纤维介素 (mfgl2 )在移植心脏组织中的表达及其与组织病理学改变的关系。方法　采用BALB/c小鼠到C5 7BL/ 6小鼠的颈部异位心脏移植作为同种排斥反应模型 ,以抗mgfl2多克隆抗体干预 ,并设同系小鼠心脏移植对照组。采集移植心组织标本作病理学检查 ,以免疫组织化学方法测定mfgl2在移植心脏组织细胞上的表达 ,并对mgfl2的表达进行半定量分析。结果　同系移植对照组移植心脏组织结构正常 ,未见mfgl2表达 ;同种移植组移植心脏组织出现进行性坏死 ,大量单个核细胞浸润 ,并伴有mfgl2的表达 ,且血管内皮细胞表达mfgl2 ;抗mfgl2抗体干预组移植心脏组织损伤较轻 ,移植物的存活时间延长 (P <0 .0 1) ,巨噬细胞、淋巴细胞的浸润和mfgl2表达量也显著减少。结论　mfgl2表达水平与排斥反应所致移植心脏病理损害程度相关 ;抗mfgl2抗体干预能显著减少移植心脏巨噬细胞、淋巴细胞的浸润 ,明显延长移植心脏存活时间。     

CXC趋化因子受体6在小鼠心脏移植排斥反应中的表达及意义

目的 研究CXC趋化因子受体6(CXCR6)在同种异体小鼠心脏移植中的表达及CXC趋化因子配体16(CXCL16)与CXCR6相互作用对移植物存活时间的影响.方法 以野生型Balb/c小鼠(H-2d)为供者(同种移植组),或以野生型C57BL/6小鼠(H-2b)为供者(同系移植组),以野生型C57BL/6小鼠为受者分别行小鼠腹腔异位心脏移植.测定同系和同种移植组小鼠移植心脏CXCR6mRNA的表达,并测定受者脾脏CD8+T淋巴细胞CXCR6的表达.另制作小鼠同种异位心脏移植模型(Balb/c小鼠为供者,C57BL/6小鼠为受者),将其分为实验组和对照组,实验组受者移植当天至发生排斥反应时腹腔注射抗CXCL16抗体,对照组受者同期注射对照抗体.记录两组移植心脏存活时间.进行CD8+T淋巴细胞的细胞毒试验,即用Balb/c小鼠脾细胞免疫C57BL/6小鼠后,获取C57BL/6小鼠脾脏CD8+T淋巴细胞,将Balb/c小鼠脾细胞与C57BL/6小鼠CD8+T淋巴细胞混合培养,分别加入抗CXCL16抗体、小鼠IgG(对照抗体)和抗CD40L抗体.结果 同种移植组移植心脏中CXCR6 mRNA的表达以及脾脏CD8+T淋巴细胞上CXCR6的表达均高于同系移植组和正常对照组.抗CXCL16抗体对CD8+T淋巴细胞的细胞毒活性无影响.与对照组相比较,实验组小鼠移植心脏存活时间并未明显延长.结论 小鼠心脏移植排斥反应中CD8+T淋巴细胞CXCR6的表达上升,阻断CXCL16/CXCR6相互作用并不能延长移植心脏的存活时间.     

Tim-3在小鼠心脏移植受者体内不同部位T淋巴细胞上表达的变化

目的 检测激活的T_H1类淋巴细胞标记分子"T淋巴细胞免疫球蛋白域及粘蛋白域蛋白-3(Tim-3)"在受者体内不同部位T淋巴细胞上表达的变化,探讨其与急性排斥反应的关系.方法 建立小鼠同基因和异基因心脏移植模型(简称:同基因组和异基因组);移植术后第3和第6天,分离和制备两组受者外周血、脾脏、引流淋巴结和移植心内淋巴细胞悬液,采用流式细胞仪检测Tim-3阳性细胞在CD4~+ 和CD8~+ T淋细胞中的比值.结果 两组受者术后外周血和脾脏内Tim-3~+/CD4~+以及Tim-3~+/CD8~+ 的比值比较,差异均无统计学意义(P>O.05).与同基因组比较,异基因组引流淋巴结内Tim-3~+/CD4~+ 比值轻度升高(P<0.05);但异基因组术后第6天与第3天比较,差异无统计学意义(P>0.05).与同基因组比较,移植心内Tim-3~+/CD4~+和TiM-3~+/CD8~+比值均显著升高(P<0.01);异基因组术后第6天与第3天比较.移植心TiM-3~+/CD4~+和Tim-3~+/CD8~+比值也显著升高(P<0.01).结论 小鼠异基因心脏移植受者引流淋巴结和移植心内T淋巴细胞上Tim-3的表达升高与急性排斥反应的进展动态相关.     

Trafficking of donor-derived bone marrow correlates with chimerism and extension of composite allograft survival across MHC barrier

We proposed to evaluate differences between recipient's immune response to vascularized skin and combined vascularized skin/bone allografts, under a 7-day alphabeta-TCR plus cyclosporine (CsA) treatment protocol. Thirty-six transplantations were performed in six groups: group I (isograft control-vascularized skin graft; n=6); group II (isograft control-combined vascularized skin/bone graft; n=6); group III (allograft rejection control group-vascularized skin graft; n=6); group IV (allograft rejection control-combined vascularized skin/bone graft; n=6); group V (allograft treatment-vascularized skin graft; n=6); and group VI (allograft treatment-combined vascularized skin/bone graft; n=6). Isograft transplantations were performed between Lewis rats and allografts were transplanted across the MHC barrier from Brown Norway to Lewis rats. In the allograft treatment group, a combined alphabeta-TCR+CsA protocol was applied for 7 days. All groups were compared clinically, immunologically and histologically. Statistical significance was determined with two-tailed Student's t test. Indefinite graft survival was achieved in the isograft control group (>300 days). Allograft rejection controls rejected within 5 to 9 days posttransplant; chimerism levels were undetectable (<.5%). Allografts under the alphabeta-TCR+CsA protocol had significantly extended survival when skin was combined with bone (61-125 days) compared to vascularized skin allografts (43-61 days). Lymphoid macrochimerism was significantly higher in group VI than group V. Histology confirmed skin and bone viability. Combined vascularized skin/bone allografts had higher and sustained levels of donor-specific chimerism and extended allograft survival.     

The replacement of graft endothelium by recipient-type cells conditions allograft rejection mediated by indirect pathway CD4+ T cells

BACKGROUND: Whereas the participation of alloreactive T cells sensitized by indirect allorecognition in graft rejection is well documented, the nature of recipient antigen presenting cells recognized by indirect pathway CD4+ T cells within the graft has yet to be identified. The purpose of this study was to determine the role played by graft endothelium replacement in the immune recognition of cardiac allografts rejected by indirect pathway CD4+ T cells. METHODS: Transgenic RAG2-/- mice expressing I-Ab-restricted male antigen H-Y-specific TcR were studied for their capacity to reject H-2k male cardiac allografts. Chronic vascular rejection in this model was due to the indirect recognition of H-Y antigen shed from H-2k male allograft and presented by the recipient's own I-Ab APC to transgenic T cells. RESULTS: Immunohistochemical analysis of rejected grafts revealed the presence of numerous microvascular endothelial cells (EC) that expressed recipient's I-Ab MHC class II molecules. This observation suggested that graft endothelium replacement by I-Ab-positive cells of recipient origin could stimulate the rejection of male H-2k graft by I-Ab-restricted H-Y-specific T cells. To investigate further this possibility, hearts from H-2b-into-H-2k irradiation bone marrow (BM) chimera were transplanted in transgenic recipients. A direct correlation was observed between the presence of I-Ab-positive EC within myocardial microvessels and the induction of acute rejection of chimeric H-2k male cardiac allografts transplanted in transgenic recipients. CONCLUSIONS: We conclude that graft endothelium replacement by recipient-type cells is required for the rejection of cardiac allograft mediated by indirect pathway alloreactive CD4+ T cells.     

The replacement of graft endothelium by recipient-type cells conditions allograft rejection mediated by indirect pathway CD4(+) T cells

BACKGROUND: Whereas the participation of alloreactive T cells sensitized by indirect allorecognition in graft rejection is well documented, the nature of recipient antigen presenting cells recognized by indirect pathway CD4(+) T cells within the graft has yet to be identified. The purpose of this study was to determine the role played by graft endothelium replacement in the immune recognition of cardiac allografts rejected by indirect pathway CD4(+) T cells. METHODS: Transgenic RAG2(-/-) mice expressing I-A(b)-restricted male antigen H-Y-specific TcR were studied for their capacity to reject H-2(k) male cardiac allografts. Chronic vascular rejection in this model was due to the indirect recognition of H-Y antigen shed from H-2(k) male allograft and presented by the recipient's own I-A(b) APC to transgenic T cells. RESULTS: Immunohistochemical analysis of rejected grafts revealed the presence of numerous microvascular endothelial cells (EC) that expressed recipient's I-A MHC class II molecules. This observation suggested that graft endothelium replacement by I-A(b)-positive cells of recipient origin could stimulate the rejection of male H-2(k) graft by I-A(b)--restricted H-Y--specific T cells. To investigate further this possibility, hearts from H-2(b)--into--H-2(k) irradiation bone marrow (BM) chimera were transplanted in transgenic recipients. A direct correlation was observed between the presence of I-A(b)-positive EC within myocardial microvessels and the induction of acute rejection of chimeric H-2(k) male cardiac allografts transplanted in transgenic recipients. CONCLUSIONS: We conclude that graft endothelium replacement by recipient-type cells is required for the rejection of cardiac allograft mediated by indirect pathway alloreactive CD4(+) T cells.     

Effects of Each Domain in Recombinant Human Soluble Thrombomodulin on Prolongation of Murine Cardiac Allograft Survival

Thrombomodulin is used to manage disseminated intravascular coagulation. In our murine heart transplantation model, the administration of recombinant human soluble thrombomodulin (rTM) could induce the prolongation of cardiac allograft survival. However, there are limited data on the graft protective effects of each r domain (D1, D2, and D3). In this study, we investigated the effects of each domain of rTM on alloimmune responses in a murine model of cardiac allograft transplantation. Fully vascularized heterotopic hearts from C57BL/6 donors were transplanted into CBA recipients using microsurgical techniques. CBA mice that underwent transplantation of C57BL/6 cardiac allografts were assigned to 4 groups: no treatment and each domain-exposed group. The dosage of each domain was determined based on our previous experiments. Flow cytometry and histologic studies were performed to determine whether Foxp3⁺ regulatory T cells were generated. Untreated and D2-exposed CBA recipients acutely rejected C57BL/6 cardiac allografts within 9 days. Administration of D3 resulted in modest prolongation of allograft survival, and administration of D1 significantly prolonged allograft survival. Histologic studies showed that myocardial damage of allografts from D1- and D3-exposed CBA recipients was controlled compared with that of untreated recipients. In particular, the CD4⁺CD25⁺Foxp3⁺ cell population in the splenocytes of D1-exposed CBA recipients was increased. In conclusion, D1 in rTM could help prolong cardiac allograft survival through regulatory T cell induction and graft protective effects.     

Estradiol enhances murine cardiac allograft rejection under cyclosporin and can be antagonized by the antiestrogen tamoxifen

BACKGROUND: An increased incidence of acute rejection episodes in female heart transplant recipients has been reported in experimental and clinical studies. However, the exact mechanisms of gender-specific differences in alloreactivity are not completely understood. METHODS: C57BL/10 (H-2b) hearts were transplanted into C3H/He (H-2 k) recipients. Four gender combinations were used to test the influence of donor and recipient sex on graft survival. Recipients were treated with CsA, 17beta-estradiol and/or tamoxifen. Additionally mice were ovariectomized prior to transplantation. RESULTS: Treated with CsA, allograft survival in female recipients was 9.16+/-0.41 days as compared with 15.16+/-1.72 days in males. Estradiol administration and oophorectomy had a significant impact on allograft survival in male and female mice under CsA treatment. Tamoxifen combined with CsA significantly prolonged graft survival in female recipients (13.16+/-1.16 days) as compared with CsA treatment alone (9.16+/-0.41 days). CONCLUSION: Female mice show earlier rejection episodes and a shorter graft survival than males. For the first time, tamoxifen has been shown to have a beneficial effect on heart allograft survival in female recipients.     

Characterization and manipulation of T cell immunity to skin grafts expressing a transgenic minor antigen.

BACKGROUND: Minor histocompatibility antigens play a significant role in allograft rejection when donor and recipient are matched at MHC loci. An improved understanding of T cell immunity directed toward a model minor antigen may provide new approaches for preventing graft rejection. METHODS: C57BL/6 (B6) recipient mice were engrafted with skin from B6 beta-galactosidase transgenic (beta-gal tg) donors and the induced T cell immune responses were characterized by cytokine ELISA spot assay. beta-gal-specific immunity was manipulated prior to transplant through preinjection with beta-gal in complete Freund's adjuvant (CFA) or through preinjection with soluble beta-gal i.v. RESULTS: B6 mice rejected beta-gal tg skin by day 25. Rejection was associated with a low frequency of predominantly CD8+, interferon-gamma-producing T cells capable of directly recognizing both beta-gal tg cells and an immunodominant major histocompatibility complex I-restricted peptide derived from the beta-gal protein. Rejection of multiple minor antigen disparate skin and major histocompatibility complex-disparate skin occurred significantly faster, and was associated with a 10- to 30-fold higher frequency of alloreactive T cells, than rejection of beta-gal tg skin. Prepriming of recipients with beta-gal in complete Freund's adjuvant resulted in an increased frequency of beta-gal-specific T cells and accelerated rejection of beta-gal tg skin. Intravenous injection of soluble beta-gal-induced graft tolerance and a lack of detectable beta-gal-specific immunity. CONCLUSIONS: The findings reveal that transgenically expressed beta-gal behaves as a minor transplantation antigen and that manipulation of the beta-gal-specific T cell repertoire can dramatically affect rejection of beta-gal tg skin grafts. The work provides the foundation for mechanistic studies of tolerogenesis to minor antigenic determinants.     

alpha4 integrin in islet allograft rejection.

BACKGROUND: Adhesion molecules are involved in multiple steps of the continuum of allograft rejection. We studied the effects of blockade of the interactions between alpha4 integrin and its ligands, vascular cell adhesion molecule-1 (VCAM-1) and fibronectin, on allograft survival. METHODS: Streptozotocin-induced diabetic CBA (H-2k) mice received islet transplants from BALB/c (H-2d) donors. Recipient mice were treated with antibodies against alpha4 integrin (PS/2), VCAM-1 (MK 2.7), and a peptide corresponding to the binding site of alpha4 integrin on fibronectin (connecting segment 1 peptide, CS1-peptide). Graft function was measured by daily tail vein blood glucose levels, with rejection defined as the return of hyperglycemia. Graft-bearing kidneys were removed for immunohistochemical analysis. RESULTS: Treatment with anti-alpha4 integrin antibody, anti-VCAM-1 antibody, or with CS1-peptide led to long-term survival of islet allografts. Recipients with long-surviving islet grafts did not show tolerance, in that they rejected a second donor-type islet allograft. Although both anti-alpha4 integrin antibody and CS1-peptide completely abolished cellular infiltration of the islet graft 7 days after transplantation, anti-VCAM-1-treated recipients showed a dense peri-islet infiltrate of activated, alpha4 integrin+, cytotoxic T cells. CONCLUSIONS: These data show that alpha4 integrin is critically important to allograft rejection. Anti-VCAM-1 antibody appears to prevent rejection without qualitatively affecting either T cell activation or migration to the graft. Conversely, anti-alpha4 integrin antibody and CS1-peptide may prevent islet allograft rejection by altering either T cell activation or lymphocyte trafficking. Blocking interactions between alpha4 integrin and its ligands may provide novel forms of immunosuppression.