Clyde F. Barker

Immunologically Privileged Sites

Publisher Summary This chapter deals with the immunologically privileged sites. Genetically alien grafts of a wide variety of both normal and malignant tissues have repeatedly been transplanted to anatomically unnatural sites in the body—that is, transplanted heterotopically—for many different though frequently interrelated purposes. The chapter presents a critical account of the status of the known or suspected privileged sites in the body and evaluates their significance from both the immunologic and therapeutic viewpoints. The chapter focuses on following considerations of privileged sites: (1) privileged sites can be created artificially, (2) it is recognized that better understanding of the modus operandi of privileged sites may lead to improvement in the results obtainable with therapeutic allografts, and (3) naturally occurring privileged sites afford important “experiments of nature” pertinent to critical evaluation of the theory of immunologic surveillance against neoplastic disease. Finally, the chapter concludes by highlighting nude mice because their basic congenital athymic status renders them “immunologically privileged” hosts that sustain on an indefinite basis both allografts and xenografts from a wide spectrum of vertebrate donors.

B-Cells Are Required for the Initiation of Insulitis and Sialitis in Nonobese Diabetic Mice

Nonobese diabetic (NOD) mice spontaneously develop an acute onset of hyperglycemia reminiscent of human type I diabetes. The disease is the end result of a mononuclear cell infiltration of pancreatic islets (insulitis), culminating in the selective destruction of islet β-Cells by autoreactive T-cells. NOD mice also exhibit defects in B-cell tolerance as manifested by the presence of autoantibodies against islet cell autoantigens. Based on the potential ability of B-cells to act as antigen presenting cells, we hypothesized that autoreactive B-cells of NOD mice may be necessary for the activation of islet reactive CD4+ T-cells. In the present study, we utilized an anti–μ antibody to induce in vivo depletion of B-cells and found that B-cell depletion completely abrogates the development of insulitis and sialitis in NOD mice. In contrast, control IgG-treated NOD mice developed insulitis and sialitis by 5 weeks of age. Additionally, the discontinuation of anti–μ chain antibody treatment led to the full restoration of the B-cellpool and the reappearance of insulitis and sialitis. Thus, we conclude that B-cells are a requisite cell population for the genesis of the inflammatory lesions of the islets of Langerhans. This finding suggests that autoreactive B-cells may act as the antigen presenting cells necessary for the initial activation of β-cell-reactive CD4+ T-cells implicated in the pathogenesis of autoimmune diabetes.

Elimination of maternally transmitted autoantibodies prevents diabetes in nonobese diabetic mice

The influence of maternally transmitted immunoglobulins on the development of autoimmune diabetes mellitus in genetically susceptible human progeny remains unknown. Given the presence of islet β cell–reactive autoantibodies in prediabetic nonobese diabetic (NOD) mice, we abrogated the maternal transmission of such antibodies in order to assess their influence on the susceptibility of progeny to diabetes. First, we used B cell–deficient NOD mothers to eliminate the transmission of maternal immunoglobulins. In a complementary approach, we used immunoglobulin transgenic NOD mothers to exclude autoreactive specificities from the maternal B-cell repertoire. Finally, we implanted NOD embryos in pseudopregnant mothers of a non-autoimmune strain. The NOD progeny in all three groups were protected from spontaneous diabetes. These findings demonstrate that the maternal transmission of antibodies is a critical environmental parameter influencing the ontogeny of T cell-mediated destruction of islet β cells in NOD mice. It will be important to definitively determine whether the transmission of maternal autoantibodies in humans affects diabetes progression in susceptible offspring.

Effect of Towne Live Virus Vaccine on Cytomegalovirus Disease after Renal Transplant: A Controlled Trial

OBJECTIVE To test the efficacy of vaccination with the Towne live attenuated cytomegalovirus vaccine. DESIGN A double-blind, randomized, placebo-controlled trial in candidates for renal transplantation. The cytomegalovirus serologic status of both recipients and donors were determined, and the recipients were followed for periods of 6 months to 7 years after transplant. SETTING A university transplant center. PATIENTS The analyses were made on 237 patients who were given either vaccine or placebo, received renal transplants, and were followed for at least 6 months. INTERVENTION Subcutaneous inoculation with Towne live attenuated virus or with placebo. MAIN OUTCOME MEASURES The presence of cytomegalovirus infection was defined by virus isolation and antibody tests. If infection occurred, a prearranged scoring system for cytomegalovirus disease was used to objectify disease severity. RESULTS The vaccine was well tolerated, and there were no discernible long-term adverse effects. Recipients who were originally seropositive did not clearly benefit from vaccination. Protective efficacy was analyzed in the group at highest risk for cytomegalovirus disease; recipients who were seronegative at the time of vaccination and who received a kidney from a seropositive donor. Compared with placebo recipients, vaccinated patients in this group had significantly less severe cytomegalovirus disease, with a significant reduction in disease scores (P = 0.03) and 85% decrease in the most severe disease (95% CI, 35% to 96%), although infection rates were similar. Graft survival at 36 months was improved in vaccinated recipients of cadaver kidneys (8 of 16) compared with unvaccinated recipients (4 of 16) (P = 0.04). CONCLUSIONS Previous vaccination of seronegative renal transplant recipients with live cytomegalovirus results in reduction of disease severity mimicking the action of naturally derived immunity.

Insulin independence following isolated islet transplantation and single islet infusions

ObjectiveTo restore islet function in patients whose labile diabetes subjected them to frequent dangerous episodes of hypoglycemic unawareness, and to determine whether multiple transplants are always required to achieve insulin independence. Summary Background DataThe recent report by the Edmonton group documenting restoration of insulin independence by islet transplantation in seven consecutive patients with type 1 diabetes differed from previous worldwide experience of only sporadic success. In the Edmonton patients, the transplanted islet mass critical for success was approximately more than 9,000 IEq/kg of recipient body weight and required two or three separate transplants of islets isolated from two to four cadaveric donors. Whether the success of the Edmonton group can be recapitulated by others, and whether repeated transplants using multiple donors will be a universal requirement for success have not been reported. MethodsThe authors report their treatment with islet transplantation of nine patients whose labile type 1 diabetes was characterized by frequent episodes of dangerous hypoglycemia. ResultsIn each of the seven patients who have completed the treatment protocol (i.e., one or if necessary a second islet transplant), insulin independence has been achieved. In five of the seven patients only a single infusion of islets was required. To date, only one recipient has subsequently lost graft function, after an initially successful transplant. This patient suffered recurrent hyperglycemia 9 months after the transplant. ConclusionsThis report confirms the efficacy of the Edmonton immunosuppressive regimen and indicates that insulin independence can often be achieved by a single transplant of sufficient islet mass.

B lymphocyte–directed immunotherapy promotes long-term islet allograft survival in nonhuman primates

We found that an induction immunotherapy regimen consisting of rabbit anti-thymocyte globulin (Thymoglobulin) and the monoclonal antibody to CD20 rituximab (Rituxan) promoted long-term islet allograft survival in cynomolgus macaques maintained on rapamycin monotherapy. B lymphocyte reconstitution after rituximab-mediated depletion was characterized by a preponderance of immature and transitional cells, whose persistence was associated with long-term islet allograft survival. Development of donor-specific alloantibodies was abrogated only in the setting of continued rapamycin monotherapy.

Popliteal artery aneurysms: Current management and outcome

PURPOSE Thrombosis of popliteal artery aneurysms can produce limb-threatening ischemia. In this setting we have found preoperative thrombolytic therapy to be beneficial. METHODS Thirty-three patients with 54 popliteal artery aneurysms were studied (mean follow-up 62 months). Twenty-one patients (62%) had bilateral popliteal artery aneurysms, and 20 patients (61%) had extrapopliteal arterial aneurysms. Thirty-three (61%) aneurysms had symptoms of compression or ischemia, and 21 (39%) aneurysms had thrombosis. A trend toward thrombosis for larger aneurysms was noted (p < 0.068). RESULTS Forty-five aneurysms were treated with bypass grafting. Five-year graft patency and limb salvage rates were 71% and 90%, respectively. Factors favoring graft patency and limb salvage included presence of two- or three-vessel runoff compared with patients with single- or no-vessel runoff (p < 0.025 graft patency; p < 0.003 limb salvage) and presence of a patent aneurysm (p < 0.005 graft patency and limb salvage). Seven patients diagnosed with thrombosis of their aneurysm and all runoff vessels were treated with preoperative thrombolytic therapy. Complete clearing of thrombus from these arteries was achieved in six of these patients (and from two of these runoff vessels in the remaining patient). These patients had better graft patency (p < 0.005) and limb salvage (p < 0.01) than comparable patients treated with emergency operations. Six amputations were performed in the follow-up interval, none of which were performed in patients having undergone thrombolytic therapy. CONCLUSIONS It is concluded that popliteal aneurysms are managed best by elective repair of patent aneurysms with good runoff. In that difficult situation of the thrombosed popliteal artery aneurysm associated with acute leg ischemia, thrombolytic therapy safely and effectively provides patients with a more favorable alternative than emergency surgery.

Elevated portal vein drug levels of sirolimus and tacrolimus in islet transplant recipients: Local immunosuppression or islet toxicity

The recent success of islet transplantation using the Edmonton protocol involved the use of sirolimus, tacrolimus, and daclizumab for immunosuppression. Islets were infused into the portal circulation after transhepatic access. This protocol provided a unique opportunity to measure sirolimus and tacrolimus levels from the portal vein and compare them to systemic venous levels. A total of 11 portal venous samples with a corresponding peripheral venous sample were obtained from patients undergoing a first or second islet infusion and medication levels were obtained on both types of specimens. The portal-to-systemic drug level ratio ranged from 0.95 to 2.71 for sirolimus and 1.0 to 3.12 for tacrolimus. Given the potential toxicity of these agents to islets, the findings in this study may have implications for designing the next generation of immunosuppressive protocols for islet transplantation.

Peripheral vascular surgery with magnetic resonance angiography as the sole preoperative imaging modality

PURPOSE Magnetic resonance angiography (MRA) is a developing technique that provides arteriograms without the risks associated with iodinated contrast and arterial puncture or the expense of hospitalization. Prior reports have demonstrated the accuracy of peripheral vessel MRA for evaluation of the aorta through pedal vessels. This study sought to determine whether vascular reconstructions could be planned and accomplished on the basis of MRA alone. METHODS Eighty consecutive candidates for bypass with ischemic rest pain or tissue loss were studied with preoperative outpatient MRA of the juxtarenal aorta through the foot. Confirmation of MRA findings was provided by intraoperative intraarterial pressure measurements for proximal vessels and postbypass arteriography for the runoff. Life-table analysis of graft patency and limb salvage was performed. RESULTS Two patients could not tolerate MRA and required contrast arteriography, but all others underwent reconstructive procedures on the basis of MRA alone (11 aortobifemoral, 67 infrainguinal). Intraoperative findings regarding suitability of inflow and outflow vessels confirmed the accuracy of the MRAs in every case. MRA indicated that none of the patients undergoing infrainguinal bypass had significant inflow occlusive disease, and this was confirmed at operation with pressure measurements of inflow vessels that were always within 10 mm Hg (peak systolic) of systemic pressure. The results of intraoperative completion arteriography and preoperative MRAs were identical for all but two patients who had minor discrepancies. All aortobifemoral reconstructions remained patent, and all limbs remained intact. The infrainguinal reconstructions had an 84% limb salvage rate and 78% primary graft patency rate at 21 months. Comparison of charges for patients undergoing preoperative MRA versus contrast angiography showed a cost savings of

Magnetic resonance angiography of peripheral runoff vessels

1288 for each patient treated with preoperative MRA alone. CONCLUSIONS MRA is a noninvasive, cost-effective outpatient imaging technique that, if properly performed and interpreted, is sufficient for planning peripheral bypass procedures. Its use may supplant contrast arteriography in many patients.