Quantitative estimation of permeability surface-area product in astroglial brain tumors using perfusion CT and correlation with histopathologic grade

BACKGROUND AND PURPOSE

Glioma angiogenesis and its different hemodynamic features, which can be evaluated by using perfusion CT (PCT) imaging of the brain, have been correlated with the grade and the aggressiveness of gliomas. Our hypothesis was that quantitative estimation of permeability surface area product (PS), cerebral blood volume (CBV), cerebral blood flow (CBF), and mean transit time (MTT) in astroglial brain tumors by using PCT will correlate with glioma grade. High-grade gliomas will show higher PS and CBV as compared with low-grade gliomas.

MATERIALS AND METHODS

PCT was performed in 32 patients with previously untreated astroglial tumors (24 high-grade gliomas and 8 low-grade gliomas) by using a total acquisition time of 170 seconds. World Health Organization (WHO) glioma grades were compared with PCT parameter absolute values by using Student or nonparametric Wilcoxon 2-sample tests. Receiver operating characteristic (ROC) analyses were also done for each of the parameters.

RESULTS

The differences in PS, CBV, and CBF between the low- and high-grade tumor groups were statistically significant, with the low-grade group showing lower mean values than the high-grade group. ROC analyses showed that both CBV (C-statistic 0.930) and PS (C-statistic 0.927) were very similar to each other in differentiating low- and high-grade gliomas and had higher predictability compared with CBF and MTT. Within the high-grade group, differentiation of WHO grade III and IV gliomas was also possible by using PCT parameters, and PS showed the highest C-statistic value (0.926) for the ROC analyses in this regard.

CONCLUSIONS

Both PS and CBV showed strong association with glioma grading, high-grade gliomas showing higher PS and CBV as compared with low-grade gliomas. Perfusion parameters, especially PS, can also be used to differentiate WHO grade III from grade IV in the high-grade tumor group.

Prevalence of HBV and HCV in blood donors in Kanpur during the period 1997 through 2005

Viral hepatitis transmitted by parenteral route is emerging as a far more dreaded public health challenge than any other illness. We have collected the data of HBV and HCV seropositivity in replacement and voluntary donors in our Blood Bank during the period January 1997 to December 2005. The results were as follows: Total number of cases studied in 1997 to 2005 - 115073 HbsAg positive cases - 1976 (1.7172%) Anti HCV positive cases - 463 (0.4024%) The overall picture is showing a more or less stable prevalence rate of hepatitis cases among blood donors, who were apparently healthy.

Early effector T cells producing significant IFN-gamma develop into memory

Currently, transition of T cells from effector to memory is believed to occur as a consequence of exposure to residual suboptimal Ag found in lymphoid tissues at the waning end of the effector phase and microbial clearance. This led to the interpretation that memory arises from slightly activated late effectors producing reduced amounts of IFN-gamma. In this study, we show that CD4 T cells from the early stage of the effector phase in which both the Ag and activation are optimal also transit to memory. Moreover, early effector T cells that have undergone four divisions expressed significant IL-7R, produced IFN-gamma, and yielded rapid and robust memory responses. Cells that divided three times that had marginal IL-7R expression and no IFN-gamma raised base level homeostatic memory, whereas those that have undergone only two divisions and produced IFN-gamma yielded conditioned memory despite low IL-7R expression. Thus, highly activated early effectors generated under short exposure to optimal Ag in vivo develop into memory, and such transition is dependent on a significant production of the cell's signature cytokine, IFN-gamma.

In trans T cell tolerance diminishes autoantibody responses and exacerbates experimental allergic encephalomyelitis

A number of Ag-specific approaches have been developed that ameliorate experimental allergic encephalomyelitis (EAE), an animal model for the human autoimmune disease multiple sclerosis. Translation to humans, however, remains a consideration, justifying the search for more insight into the mechanism underlying restoration of self-tolerance. Ig-proteolipid protein (PLP) 1 and Ig-myelin oligodendrocyte glycoprotein (MOG) are Ig chimeras carrying the encephalitogenic PLP 139-151 and MOG 35-55 amino acid sequence, respectively. Ig-PLP1 ameliorates EAE in SJL/J (H-2(s)) mice while Ig-MOG modulates the disease in C57BL/6 (H-2(b)) animals. In this study, we asked whether the chimeras would suppress EAE in F(1) mice expressing both parental MHC alleles and representing a polymorphism with more relevance to human circumstances. The results show that Ig-MOG modulates both PLP1 and MOG peptide-induced EAE in the F(1) mice, whereas Ig-PLP1 counters PLP1 EAE but exacerbates MOG-induced disease. This in trans aggravation of MOG EAE by Ig-PLP1 operates through induction of PLP1-specific T cells producing IL-5 that sustained inhibition of MOG-specific Abs leading to exacerbation of EAE. Thus, in trans T cell tolerance, which should be operative in polymorphic systems, can aggravate rather than ameliorate autoimmunity. This phenomenon possibly takes place through interference with protective humoral immunity.

Innocuous IFNgamma induced by adjuvant-free antigen restores normoglycemia in NOD mice through inhibition of IL-17 production

The role of Th17 cells in type I diabetes (TID) remains largely unknown. Glutamic acid decarboxylase (GAD) sequence 206–220 (designated GAD2) represents a late-stage epitope, but GAD2-specific T cell receptor transgenic T cells producing interferon γ (IFNγ) protect against passive TID. Because IFNγ is known to inhibit Th17 cells, effective presentation of GAD2 peptide under noninflammatory conditions may protect against TID at advanced disease stages. To test this premise, GAD2 was genetically incorporated into an immunoglobulin (Ig) molecule to magnify tolerance, and the resulting Ig-GAD2 was tested against TID at different stages of the disease. The findings indicated that Ig-GAD2 could not prevent TID at the preinsulitis phase, but delayed TID at the insulitis stage. More importantly, Ig-GAD2 sustained both clearance of pancreatic cell infiltration and β-cell division and restored normoglycemia when given to hyperglycemic mice at the prediabetic stage. This was dependent on the induction of splenic IFNγ that inhibited interleukin (IL)-17 production. In fact, neutralization of IFNγ led to a significant increase in the frequency of Th17 cells, and the treatment became nonprotective. Thus, IFNγ induced by an adjuvant free antigen, contrary to its usual inflammatory function, restores normoglycemia, most likely by localized bystander suppression of pathogenic IL-17–producing cells.

Outcome of sixty four cases of ethylene dibromide ingestion treated in tertiary care hospital

BACKGROUND AND AIMS

In view of high incidence and mortality due to ethylene dibromide poisoning, a prospective study was planned to assess demographic, toxicological, clinical profile and outcome.

MATERIAL AND METHODS

Prospectively collected data of sixty four patients with ethylene dibromide poisoning were reviewed. All the patients were from Gwalior and neighbouring districts.

RESULTS

Majority were males in the age group 21-30 years. Out of sixty-four cases 26 patients (40.6%) survived and 38 patients (59.4%) expired. Nausea vomiting and pain abdomen were most common symptoms at presentation. Diarrhoea, drowsiness, palpitations and oliguria were other features. Pulse rate was normal (< 100) in 22 (84.6%) survived patients whereas it was > 100 in 24 (63.1%) of expired patients at the time of admission (p value = 0.0004199). Half ampoule (1.5ml.) of ethylene dibromide was sufficient as fatal dose. Mortality was 20% and 46.15% with half and one ampoule respectively. Best outcome was when the patient presented to the hospital within six hours. Death occurred anywhere between twelve hours and five days. Gastrointestinal toxicity was predominant at presentation. Nausea, vomiting and abdominal pain was present in all the patients. Nephrotoxicity 32 (50%), hepatotoxicity 28 (43.8%), cardiotoxicity 28 (43.8%), central nervous system 8 (12.5%) toxicity and hypoglycemia 24 (37.5%) were also observed.

CONCLUSION

Ethylene dibromide is highly toxic. Patients who consumed half to one ampoule usually survived with supportive care provided they presented to the hospital within six hours. Pulse rate more than 100 at presentation was a poor prognostic factor. Patients with normal pulse and blood pressure at admission had better prognosis.

Role of perfusion CT in glioma grading and comparison with conventional MR imaging features

BACKGROUND AND PURPOSE

Perfusion imaging using CT can provide additional information about tumor vascularity and angiogenesis for characterizing gliomas. The purpose of our study was to demonstrate the usefulness of various perfusion CT (PCT) parameters in assessing the grade of treatment-naïve gliomas and also to compare it with conventional MR imaging features.

MATERIALS AND METHODS

PCT was performed in 19 patients with glioma (14 high-grade gliomas and 5 low-grade gliomas). Normalized ratios of the PCT parameters (normalized cerebral blood volume [nCBV], normalized cerebral blood flow [nCBF], normalized mean transit time [nMTT]) were used for final analysis. Conventional MR imaging features of these tumors were assessed separately and compared with PCT parameters. Low- and high-grade gliomas were compared by using the nonparametric Wilcoxon 2-sample tests.

RESULTS

Mean nCBV in the high- and low-grade gliomas was 3.06 +/- 1.35 and 1.44 +/- 0.42, respectively, with a statistically significant difference between the 2 groups (P = .005). Mean nCBF for the high- and low-grade gliomas was 3.03 +/- 2.16 and 1.16 +/- 0.36, respectively, with a statistically significant difference between the 2 groups (P = .045). Cut points of >1.92 for nCBV (85.7% sensitivity and 100% specificity), >1.48 for nCBF (71.4% sensitivity and 100% specificity), and <1.94 for nMTT (92.9% sensitivity and 40% specificity) were found to identify the high-grade gliomas. nCBV was the single best parameter; however, using either nCBV of >1.92 or nCBF of >1.48 improved the sensitivity and specificity to 92.9% and 100%, respectively. The sensitivity and specificity for diagnosing a high-grade glioma with conventional MR imaging were 85.7% and 60%, respectively.

CONCLUSIONS

PCT can be used for preoperative grading of gliomas and can provide valuable complementary information about tumor hemodynamics, not available with conventional imaging techniques. nCBV was the single best parameter correlating with glioma grades, though using nCBF when nCBV was <1.92 improved the sensitivity. An nCBV threshold of >1.92 was found to identify the high-grade gliomas.

Acute bone crises in sickle cell disease: the T1 fat-saturated sequence in differentiation of acute bone infarcts from acute osteomyelitis

AIM

To prove the hypothesis that acute bone infarcts in sickle cell disease are caused by sequestration of red blood cells (RBCs) in bone marrow, and to evaluate the unenhanced T1 fat-saturated (fs) sequence in the differentiation of acute bone infarction from acute osteomyelitis in patients with sickle-cell disease.

MATERIALS AND METHODS

Two studies were undertaken: an experimental study using in-vitro packed red blood cells and normal volunteers, and a retrospective clinical study of 86 magnetic resonance imaging (MRI) studies. For the experimental study containers of packed RBCs were placed between the knees of four healthy volunteers with a saline bag under the containers as an additional control, and were scanned with the pre-contrast T1-fs sequence. Signal intensity (SI) ratios were obtained for packed RBCs:skeletal muscle and packed RBCs:saline. For the clinical study, the SIs of normal bone marrow, packed RBCs, bone and/or soft-tissue lesions, and normal skeletal muscle of 74 patients (86 MRI studies) were measured using unenhanced, T1 fat-saturated MRI. The ratios of the above SIs to normal skeletal muscle were calculated and subjected to statistical analysis.

RESULTS

Fifty-one of 86 MRI studies were included in the final analysis. The ratios of SIs for normal bone marrow, packed red cells, bone infarction, acute osteomyelitis, and soft-tissue lesions associated with bone infarct, compared with normal skeletal muscle were (mean+/-SD) 0.9+/-0.2, 2.1+/-0.7, 1.7+/-0.5, 1.0+/-0.3, and 2.2+/-0.7, respectively. The difference in the ratio of SIs of bone infarcts and osteomyelitis was significant (p=0.003). The final diagnoses were bone infarction (n=50), acute osteomyelitis (n=1), and co-existent bone infarction and osteomyelitis (n=2). Seven patients who had suspected osteomyelitis underwent image-guided aspiration.

CONCLUSION

Acute bone infarcts in sickle cell disease are caused by sequestration of red blood cells in the bone marrow. The unenhanced, T1-fat-saturated sequence alone is diagnostic for acute bone infarcts. Contrast enhancement aids in the diagnosis of acute osteomyelitis. MRI can thus help in early diagnosis, specific treatment, and preventing empirical antibiotic therapy.

Phase I/II study of neoadjuvant bevacizumab with radiation therapy and 5-fluorouracil in patients with rectal cancer: initial results

4041

Background: A phase I/II study of neoadjuvant bevacizumab with 5-fluorouracil and radiation therapy in patients with locally advanced rectal cancer was undertaken to determine whether inhibition of VEGF is safe and has clinical benefits by enhancing chemo- radiation therapy. Methods: 22 patients with endoscopic ultrasound or surface coil MRI staged T3/T4 non-metastatic rectal cancer were enrolled from 2001–2006. All patients completed 4 cycles of neoadjuvant therapy including: 1) bevacizumab infusion (5 or 10 mg/kg) on day 1 of each cycle; 2) peripheral venous infusion 5-FU (225 mg/m2/24 hours) administration each treatment week of cycles 2 - 4; 3) external beam irradiation delivery (50.4 Gy in 28 fractions over 5.5 weeks); and 4) surgery 7 to 9 weeks after completion of all neoadjuvant therapy. Correlative studies were undertaken before and during the trial. We collected serial tumor biopsies, PET-FDG scans, and analyzed blood and urine for potential biomarkers. Results: Mean pre-therapy tumor size was 4.7 cm (2–9 cm). Post-treatment surgical specimens usually had well-demarcated shallow ulcerations with a mean diameter of 2.4 cm (0.7–6 cm). In response to the neoadjuvant regimen, all patients had significantly (p<0.01) decreased FDG-uptake by PET. Histologic examination showed no residual primary cancer in 5 patients (ypT0). Of 17 patients with residual disease, microscopic disease usually occurred as malignant glands embedded in fibrosis (ypT1 in 3 patients, ypT2 in 4 patients, ypT3 in 10 patients). Downstaging was seen in 12/22 tumors. 8 patients had microscopic nodal metastases. Bevacizumab alone and combined treatment were both associated with increased plasma VEGF and PlGF levels in 18/18 patients (P<0.01 at all 4 timepoints compared to baseline). Viable CECs were decreased by VEGF blockade at day 3 (P<0.01 compared to baseline), and peak CEC levels during treatment was correlated with histologic tumor response (2.77 [1.18–3.18] for T3 patients, n=9 versus 1.14 [0.82–1.53] for T0-T2 patients, n=12; p=0.05). Conclusions: Addition of bevacizumab at a dose of 5 mg/kg to standard chemo-radiation is safe in patients with locally advanced rectal cancer. Bevacizumab is active and the combined regimen yields promising results.

[Table: see text]

Single fraction radiosurgery of epidural spinal cord compression: Tumor control and neurologic outcome

2041

Purpose: Spine radiosurgery improves the pain and quality of life in spine metastasis. Phase II study was performed to determine the clinical efficacy of radiosurgery for malignant epidural spinal cord compression. Method: Total 67 patients with 93 lesions of epidural spinal cord compression at the solitary spine level were accrued. All patients had pathology-proven malignancy and had epidural tumor seen on MRI or CT scan. For radiosurgery, grossly visible tumor including the involved spine was treated with single fraction radiosurgery dose of 14–20 Gy. Spinal cord dose constraint was 10 Gy to 10% partial volume of the cord. Followup included neurological exam and imaging studies every 2 months. Endpoints were radiographic tumor control and neurological outcome. Median followup time was 8 months (2–30 months). Results: Objective radiographic tumor response was seen in 82% of patients. At 2 months, complete response was in seen 27%, partial response in 30%, and minimal response in 23%, Epidural tumor progressed in 6% at or the adjacent spine level. Thecal sac patency (= decompression effect) seen on T2-weighted MR image was improved in 82% of the lesions. There was average 68% volumetric reduction of tumor at the level of most severe cord compression. This tumor reduction opened the thecal sac patency to average 75% following radiosurgery, compared to 45% before radisourgery (p<0.05). Majority of patients with neurological deficit prior to radiosurgery were ambulatory with an improved neurological function or remained clinically stable. There was one case of likely long-term radiation-induced myelopathy 13 months after radiosurgery. Conclusion: Single fraction radiosurgery achieves significant tumor response and decompressive effect of spinal cord compression. Even minimal tumor response relieves the spinal cord compression and potential neurologic improvement. Spine radiosurgery can be a viable treatment option for spinal cord compression.

No significant financial relationships to disclose.

A phase II trial of AZD2171 (cediranib), an oral pan-VEGF receptor tyrosine kinase inhibitor, in patients with recurrent glioblastoma

2001

Background: AZD2171 (cediranib) is a potent, oral pan-VEGF receptor tyrosine kinase inhibitor with a half-life of 20 hours compatible with once-daily dosing. A primary target of AZD2171, VEGFR2, is expressed on glioblastoma endothelium. We have demonstrated normalization of tumor vessels in recurrent glioblastoma patients treated with daily doses of AZD2171. Normalization has rapid onset, is reversible and is associated with alleviation of brain edema [Cancer Cell 2007; 11: 83]. Methods: In this phase II study of 30 recurrent glioblastoma subjects the primary endpoint was the proportion of patients alive and progression-free at 6 months (APF6). Secondary endpoints include radiographic response proportion; progression-free survival; overall survival and toxicity. At this time we are presenting radiographic response data and toxicity on the first 16 consecutive patients and APF6, PFS and OS on all 30 patients. Complete information will be available on all 30 patients at the time of presentation. Results: Twenty-eight patients have experienced disease progression and two patients remain in follow-up without progression. The primary and secondary endpoints are tabulated below: Only one of the first 16 patients was removed from the study due to toxicity (fatigue). Dose limiting toxicities of hypertension, fatigue and diarrhea were observed in 9/16 patients. There were no intracerebral hemorrhages. AZD2171 alleviated brain edema, a major cause of morbidity in glioblastoma patients, and had a steroid-sparing effect in the first 16 patients enrolled. Blood biomarkers were serially assessed and elevated levels of bFGF, SDF1a and viable circulating endothelial cells correlated with disease progression. Conclusions: AZD2171 has activity in patients with recurrent glioblastoma. Combination studies of AZD2171 with radiation and chemotherapy are planned.

[Table: see text]

[Table: see text]

Distinct subsets of dendritic cells drive tolerance in two models of CD4 T cell mediated autoimmunity (129.14)

Dendritic cells (DCs) are professional antigen presenting cells that are capable of presenting both self and foreign antigens to T cells thereby inducing either tolerance or immunity respectively. What is still not clear is whether T cell tolerance requires a specific subset or any population of DCs can drive tolerance. To address this question different subsets of DCs were tested for suppression of autoimmunity in two major animal models- type I diabetes (T1D) and experimental allergic encephalomyelitis (EAE).

There are 3 major subsets of DCs in spleen- CD8α+, CD8α−CD4+ and CD8α−CD4−. In this study we investigated the ability of these subsets to induce tolerance in TID and EAE. Indeed the CD8α−CD4− DC subset mediated protection against diabetes in non-obese diabetic (NOD) mice. In fact, mice had reduced destructive infiltration within the islets and the antigen-specific lymphocytes showed reduced proliferation and an increase in IFNγ and IL-10 response. Surprisingly, in EAE it is the CD8α−CD4+ DC subset that supported protection against the disease. The lymphocytes from treated mice displayed more of a Th1 biased response. Both the protective subsets were mature and expressed significant levels of class II MHC and costimulatory molecules. However, the subsets trafficked differently to spleen and draining lymph nodes. Thus, distinct DC subsets drive tolerance in the two models of autoimmunity despite the fact that both diseases are mediated by CD4+ T cells.

Research supported by grants DK65748 and NS37406 from NIH.

Visualizing mechanisms of peripheral tolerance against autoreactive T cells (129.35)

Where and how T cell tolerance happens remains largely undefined. Here, we used an established in vivo model and investigated the site and the mechanisms that govern APC-mediated inactivation of autoreactive T cells.

Fcγ receptor-deficient (FcγR−/−) mice were induced for experimental allergic encephalomyelitis (EAE), with a myelin oligodendrocyte glycoprotein (MOG) 35-55 peptide and when the disease became apparent the mice were given FcγR+/+ APCs and treated with Ig-MOG, a tolerogenic Ig expressing MOG peptide. Under this regimen the mice were able to reverse their EAE only when given FcγR+/+ APCs that can present Ig-MOG and carry out T cell tolerance. This system was then used to visualize encounter of the APCs with the pathogenic T cells. The results indicate that tolerance occurs in a time dependent fashion when both the T cells and APCs have accumulated in sufficient number at the encounter site but unlike immunity, can take place in the non-draining lymph nodes. Two-Photon microscopy analysis revealed that tolerized T cells exhibit organ-specific changes in motility, pattern of migration and trafficking which could be related to functional matters as tolerance manifest the form of Th2 deviation in the lymph node and anergy in the spleen.

Research supported by grant NS37406 from NIH.

A developmental maturation of a dendritic cell subset controls the Th2 bias of neonatal immunity through IL-12 production and downregulation of IL-13Rα1 (95.2)

Neonates are susceptible to microbial infections and allergic reactions due to lack of Th1 immunity and skewing of Th2 response. Analysis of primary response in neonates showed that Th1 and Th2 cells develop upon priming with antigen on the day of birth. However, Th1 cells display up-regulated expression of IL-13Rα1 that was found to associate with IL-4Rα and provide a receptor that can be used by both IL-4 and IL-13. Upon rechallenge with antigen, IL-4 produced by Th2 cells utilizes IL-13Rα1/ IL-4Rα receptor to drive apoptosis of Th1 cells hence bias of neonatal immunity towards Th2. Here, we demonstrate that up-regulation of IL-13Rα1 is due to inability of neonatal antigen presenting cells to produce IL-12. In fact, supply of exogenous IL-12 during priming with antigen minimizes IL-13Rα1 expression, leading to inhibition of apoptosis and restoration of Th1 secondary immunity. Interestingly, lack of IL-12 is due to delayed maturation of CD8α+CD4− subset of dendritic cells. However, by day 6 after birth CD8α+CD4− DCs accumulate and produce significant amounts of IL-12 that diminishes IL-13Rα1 expression, leading to inhibition of Th1 apoptosis and restoration of an adult-like Th1 immunity. Thus, developmental maturation of DC subsets is responsible for bias of neonatal immunity towards Th2 providing susceptibility to microbial infections and allergic reactions.

Research supported by grant R01 AI 48541 from NIH.

MHC polymorphism translates T cell tolerance into B cell autoimmunity. (131.29)

Experimental allergic encephalomyelitis (EAE) is a mouse model for human multiple sclerosis (MS). While effective treatments of EAE have been developed, adapting these for use in human MS has proven difficult and therefore investigations into this model continue. Here, we examine the effects of MHC polymorphism on the control of tolerance. Our previous studies have shown that treatment of EAE with immunoglobulins (Ig) containing proteolipid protein (PLP) or myelin oligodendrocyte glycoprotein (MOG) epitopes reverses ongoing disease in both SJL/J and C57Bl/6 mice. We used F1(SJL/J x Bl/6) mice to test Ig-PLP and Ig-MOG for reversal of compatible as well as “in trans” EAE wherein disease induced by MOG epitope is treated with Ig-PLP and EAE induced by PLP epitope is treated with Ig-MOG. The findings indicated that EAE induced in F1 mice by PLP is successfully treated with Ig-PLP or Ig-MOG. However, an asymmetrical effect was observed for the treatment of MOG EAE whereby Ig-MOG reverses MOG EAE while Ig-PLP exacerbated MOG induced EAE. The mechanism underlying disease exacerbation correlated with a cytokine-induced Ig class switch among anti-MOG antibodies during treatment with Ig-PLP.

Research supported by grant NS37406 from NIH.

Treg Development and Suppression of Experimental Allergic Encephalomyelitis (129.28)

Many autoimmune disorders have been linked to a lack in T regulatory cells. As such, an understanding of how these cells develop and mature is critical. While thymic T cell selection has been described, this process remains largely undefined for Tregs. Since only the DM20 form of proteolipid protein (PLP) is expressed in the thymus during fetal and neonatal life, thymic selection against PLP139-151 which is missing in DM20 is not operative during those periods. PLP139-151 (designated PLP1) as well as PLP1 derived altered peptide with degenerate affinity to PLP1-specific T cells were expressed on immunoglobulin (Ig) and the resulting chimeras were used to cross the maternal placenta, deliver the peptides from mother to fetus, and restore peptide selection during the fetal and neonatal period. This model was then used to determine whether Tregs are subject to thymic selection and to gauge the affinity required for such selection. The findings indicate that selection of functional Tregs requires high affinity. Indeed, Ig chimeras harboring high avidity peptides facilitated development of Tregs that conferred protection against experimental allergic encephalomyelitis (EAE) while chimeras incorporating low affinity peptide did not drive selection of Tregs and the animals remained susceptible to EAE.