individuals with type 1 diabetes who contacted the national institutes of health ( nih ) recruitment office were asked to complete a questionnaire . at the nih clinical center , 47 patients were selected for testing and 20 were enrolled ( table 1 ; fig . inclusion criteria were 1 ) age 1860 years , 2 ) c - peptide 0.3 ng / ml ( 0.1 nmol / l ) at baseline or after arginine stimulation , 3 ) positive antibodies ( gad65 , ica-512 ) and/or a typical history of type 1 diabetes , 4 ) duration of disease 5 years , and 5 ) bmi 2030 kg / m . exclusion criteria were gastroparesis , diabetic nephropathy , insulin requirement 0.8 units  kg  day , and hypoglycemia unawareness . to determine reference values , we performed mixed - meal testing in three healthy individuals ( all female , mean age 33.3  11.1 years , bmi 21.7  1.8 kg / m ) . this study ( nct00064714 ) was approved by the institutional review board of the national institute of diabetes and digestive and kidney diseases . clinical and immunological characteristics of the 20 enrolled patients at screening patients 116 were randomized to one of four study arms and patients 114 completed the trial . of the patients , 16 of 20 had high - susceptibility hla haplotypes ; 1 had a mixed and 1 a protective haplotype ( indicated in bold print ) . * homozygosity is highly likely but could only be proven by family studies , which were not available ; hla type could not be differentiated with certainty ( 0301 vs. 0328 ) ; underlined numbers indicate that the haplotype belongs to one of five most susceptible subtypes ( 25 ) . study design ( a ) and timeline for testing procedures ( b ) : 20 patients entered the optimization period , 16 were randomized , and 14 completed the entire trial . b : a , arginine stimulation test ; m , mixed - meal test ; t , t - cell proliferation test . the study followed a prospective randomized open - label crossover design ( fig . 1 ) . it consisted of an optimization period of 24 months during which the nih study team improved the patients ' glucose control . patients then entered the run - in period , a 4-month period during which no major changes in diabetes management were made . at screening and during the run - in period , patients underwent a total of four arginine stimulation tests and two mixed - meal tests to determine baseline c - peptide secretion ( fig . thereafter , subjects were randomized to one of four treatment arms ( insulin only , insulin plus exenatide , insulin plus exenatide plus daclizumab , or insulin plus daclizumab ) . after 6 months ( period a ) , patients treated with exenatide discontinued its administration , whereas patients not previously treated with exenatide initiated it . the treatment assignment regarding daclizumab remained unchanged during this second 6-month interval ( period b ) . in both periods a and b , three arginine stimulation tests and one mixed - meal test were performed . finally , enrollees entered a 3-month extension period , in which they continued the assigned treatment of period b. special attention was paid to prevent or treat vitamin d deficiency , hyperlipidemia , and hypertension . exenatide ( byetta ; amylin , san diego , ca ) was administered subcutaneously via a noncommercial pen that allowed dose adjustments in 2.5-g increments . dose and frequency were gradually increased from 2.5 g twice daily to 10 g four times daily . at the onset of exenatide therapy , insulin bolus doses were reduced by 50% , whereas basal insulin ( for insulin pump users ) and long - acting insulin doses ( for multiple  daily injection users ) remained unchanged . daclizumab ( zenapax ; roche , nutley , nj ) was infused intravenously at 2 mg / kg over 30 min once monthly . arginine and mixed - meal tests were performed after an overnight fast . with pretest blood glucose levels of 150 mg / dl ( 8.3 nmol / l ) , baseline blood samples were obtained at 10 and 0 min before intravenous infusion of 5 g arginine ( 10% solution ) . samples were collected from the contralateral cephalic vein at 2 , 3 , 4 , 5 , 7 , 9 , and 10 min and immediately placed on ice until centrifuged at 2,000 rpm for 10 min at 4c . blood samples were obtained at 10 , 0 , 15 , 30 , 45 , 60 , 90 , 120 , 150 , 180 , and 240 min . at time point 0 min , patients consumed boost high protein ( 7 ml / kg body wt , maximally 400 ml ) in 10 min . c - peptide was determined with a solid - phase , two - site immunochemiluminescent assay ( esoterix , lower limit of detection 0.05 ng / ml [ 0.02 nmol / l ] ) . cross - reactivity with insulin was < 0.01% at 100 and 200 u / ml human insulin . glucagon was measured using a double - antibody radioimmunoassay ( esoterix , lower limit of detection 10 pg / ml ) . acetaminophen was determined by a particle - enhanced turbidimetric inhibition immunoassay with the analytical range 10300 g / ml ( lowest detectable dose 2.5 g / ml ) . total glp-1 was measured with a radioimmunoassay ( millipore , lower limit of detection 3.0 pmol / l ) . 1b ) in two different laboratories ( m. dosch , toronto , canada ; and b. brooks - worrell and j. palmer , seattle , wa ) ( 12 ) . at both sites , t - cell proliferation in response to diabetes - related antigens was determined by direct h - thymidine incorporation . samples were labeled as positive for autoimmunity if the t - cells proliferated to 3 ( toronto ) or 4 ( seattle ) of the test antigens compared with responses against unspecific control antigens . the toronto laboratory used a panel of 12 predefined diabetes - related peptide or protein antigens and included exogenous interleukin-2 in the assay medium . the seattle laboratory used mixtures of antigen eluted from gel - fractionated human islet cell proteins with 18 size fractions separated by sds polyacrylamide gel . hla haplotypes were determined using sequence - specific primers at the department of transfusion medicine at the nih clinical center . sample size calculations were based on data from 1 ) nih patients having undergone islet transplantation with no c - peptide before transplantation but measurable c - peptide after transplantation and 2 ) data on the variability of individual patient values in periods similar to the run - in period of this study . sample size estimates were designed to detect a 50% increase of c - peptide levels on exenatide treatment , resulting in a sample size estimate of 12 patients . primary outcome measures were based on basal ( 10 and 0 min ) and stimulated ( single highest value during test procedure ) c - peptide levels . these were measured monthly before and during arginine stimulation during the last 3 months of each treatment period ( fig . c - peptide values were averaged across these three time points . because 50% of patients also received daclizumab , two - way analyses of variance ( anovas ) were run to assess daclizumab treatment and its possible interaction with exenatide : daclizumab usage was a second factor and the period - sequence by daclizumab interaction term was included . because the p values for the interaction term were highly nonsignificant ( basal p = 0.74 ; stimulated p = 0.81 ) , as were the p values for the overall effect of daclizumab ( basal p = 0.87 ; stimulated p = 0.84 ) , the daclizumab and no - daclizumab groups were combined in the main analyses of exenatide . to eliminate confounding due to a possible period effect ( e.g. , due to prolonged intensive insulin treatment ) , the test based on the two - sample t approach was used ( 13 ) . two - sided p values 0.05 were considered significant and results were presented as means  sd if not indicated otherwise . it consisted of an optimization period of 24 months during which the nih study team improved the patients ' glucose control . patients then entered the run - in period , a 4-month period during which no major changes in diabetes management were made . at screening and during the run - in period , patients underwent a total of four arginine stimulation tests and two mixed - meal tests to determine baseline c - peptide secretion ( fig . thereafter , subjects were randomized to one of four treatment arms ( insulin only , insulin plus exenatide , insulin plus exenatide plus daclizumab , or insulin plus daclizumab ) . after 6 months ( period a ) , patients treated with exenatide discontinued its administration , whereas patients not previously treated with exenatide initiated it . the treatment assignment regarding daclizumab remained unchanged during this second 6-month interval ( period b ) . in both periods a and b , three arginine stimulation tests and one mixed - meal test were performed . finally , enrollees entered a 3-month extension period , in which they continued the assigned treatment of period b. special attention was paid to prevent or treat vitamin d deficiency , hyperlipidemia , and hypertension . exenatide ( byetta ; amylin , san diego , ca ) was administered subcutaneously via a noncommercial pen that allowed dose adjustments in 2.5-g increments . dose and frequency were gradually increased from 2.5 g twice daily to 10 g four times daily . at the onset of exenatide therapy , insulin bolus doses were reduced by 50% , whereas basal insulin ( for insulin pump users ) and long - acting insulin doses ( for multiple  daily injection users ) remained unchanged . daclizumab ( zenapax ; roche , nutley , nj ) was infused intravenously at 2 mg / kg over 30 min once monthly . arginine and mixed - meal tests were performed after an overnight fast . with pretest blood glucose levels of 150 mg / dl ( 8.3 nmol / l ) , baseline blood samples were obtained at 10 and 0 min before intravenous infusion of 5 g arginine ( 10% solution ) . samples were collected from the contralateral cephalic vein at 2 , 3 , 4 , 5 , 7 , 9 , and 10 min and immediately placed on ice until centrifuged at 2,000 rpm for 10 min at 4c . blood samples were obtained at 10 , 0 , 15 , 30 , 45 , 60 , 90 , 120 , 150 , 180 , and 240 min . at time point 0 min , patients consumed boost high protein ( 7 ml / kg body wt , maximally 400 ml ) in 10 min . c - peptide was determined with a solid - phase , two - site immunochemiluminescent assay ( esoterix , lower limit of detection 0.05 ng / ml [ 0.02 cross - reactivity with insulin was < 0.01% at 100 and 200 u / ml human insulin . glucagon was measured using a double - antibody radioimmunoassay ( esoterix , lower limit of detection 10 pg / ml ) . acetaminophen was determined by a particle - enhanced turbidimetric inhibition immunoassay with the analytical range 10300 g / ml ( lowest detectable dose 2.5 g / ml ) . total glp-1 was measured with a radioimmunoassay ( millipore , lower limit of detection 3.0 pmol / l ) . 1b ) in two different laboratories ( m. dosch , toronto , canada ; and b. brooks - worrell and j. palmer , seattle , wa ) ( 12 ) . at both sites , t - cell proliferation in response to diabetes - related antigens was determined by direct h - thymidine incorporation . samples were labeled as positive for autoimmunity if the t - cells proliferated to 3 ( toronto ) or 4 ( seattle ) of the test antigens compared with responses against unspecific control antigens . the toronto laboratory used a panel of 12 predefined diabetes - related peptide or protein antigens and included exogenous interleukin-2 in the assay medium . the seattle laboratory used mixtures of antigen eluted from gel - fractionated human islet cell proteins with 18 size fractions separated by sds polyacrylamide gel . hla haplotypes were determined using sequence - specific primers at the department of transfusion medicine at the nih clinical center . sample size calculations were based on data from 1 ) nih patients having undergone islet transplantation with no c - peptide before transplantation but measurable c - peptide after transplantation and 2 ) data on the variability of individual patient values in periods similar to the run - in period of this study . sample size estimates were designed to detect a 50% increase of c - peptide levels on exenatide treatment , resulting in a sample size estimate of 12 patients . primary outcome measures were based on basal ( 10 and 0 min ) and stimulated ( single highest value during test procedure ) c - peptide levels . these were measured monthly before and during arginine stimulation during the last 3 months of each treatment period ( fig . c - peptide values were averaged across these three time points . because 50% of patients also received daclizumab , two - way analyses of variance ( anovas ) were run to assess daclizumab treatment and its possible interaction with exenatide : daclizumab usage was a second factor and the period - sequence by daclizumab interaction term was included . because the p values for the interaction term were highly nonsignificant ( basal p = 0.74 ; stimulated p = 0.81 ) , as were the p values for the overall effect of daclizumab ( basal p = 0.87 ; stimulated p = 0.84 ) , the daclizumab and no - daclizumab groups were combined in the main analyses of exenatide . to eliminate confounding due to a possible period effect ( e.g. , due to prolonged intensive insulin treatment ) , the test based on the two - sample t approach was used ( 13 ) . two - sided p values 0.05 were considered significant and results were presented as means  sd if not indicated otherwise . patient characteristics are shown in table 1 . the 9 male and 11 female caucasian patients ( mean age 39.5  11.1 years ) had type 1 diabetes duration of 21.3  10.7 years . at screening , a1c was 7.3  1.1% ( range 5.610.2% ) . patients used multiple daily injections ( mdi , n = 7 ) or continuous subcutaneous insulin infusions ( insulin pump , n = 13 ) . four patients were antibody negative but had a typical history of type 1 diabetes with childhood onset and/or positive family history and high - risk hla haplotypes ( table 1 ) . only patients 10 and 18 had mixed or entirely protective hla haplotypes , which may explain their presentation at an older age . of 47 subjects who underwent detailed screening procedures , 40 completed both arginine stimulation and mixed - meal tests : 55% had measurable c - peptide in both tests , 12.5% only after arginine stimulation , and 17.5% only in the mixed - meal test . thus , 85% had detectable c - peptide 0.05 ng / ml ( 0.02 nmol / l ) in two common stimulation tests . once intensified glucose management began ( but before introduction of exenatide and daclizumab ) , 4 patients ( patients 1720 ) discontinued their participation due to fear of hypoglycemia or psychosocial problems . in the remaining 14 patients , a1c decreased from 7.2  0.9% at screening to 6.5  0.7% at the end of the run - in period ( p = 0.0003 ) . the pharmacological ( arginine ) and physiological ( mixed - meal ) stimulation of c - peptide was reduced by intensified insulin treatment ( fig . 2a ) during the run - in period . all patients secreted less c - peptide compared to their screening results ( p < 0.0001 for basal and stimulated c - peptide ) , and 11 patients ( 69% ) had no detectable c - peptide in their first arginine stimulation test in this study period . results of c - peptide responses to arginine stimulation ( a and b ) and changes of insulin doses and weight according to treatment assignment ( c ) . c - peptide results are shown at screening ( basal versus stimulated c - peptide , p < 0.0001 ) and during run - in period ( tests were conducted in months 2 , 3 , and 4 of run - in period [ basal versus stimulated c - peptide , p = 0.0078 ] ) ( a ) after 6 months of exenatide therapy versus not having received exenatide ( irrespective of assignment to daclizumab ) ( b ) with reference to mean results of run - in period . data are means  sem . to convert c - peptide from conventional ( ng / ml ) to si units ( nmol / l ) , multiply by factor 0.333 . c - peptide secretion was insignificantly higher during exenatide treatment , and the addition of daclizumab did not change this outcome ( fig . mean basal c - peptide levels were 0.029 ng / ml ( 0.01 nmol / l ) higher on exenatide versus off exenatide ( 95% ci 0.058 to 0.115 ng / ml , p = 0.48 ) , and stimulated c - peptide levels were 0.024 ng / ml ( 0.008 nmol / l ) higher on exenatide ( 95% ci 0.090 to 0.138 ng / ml , p = 0.66 ) . further , there was no difference when analyzing c - peptide secretion depending on the study period when exenatide was administered . all but one patient ( patient 13 ) lost weight during the 6-month period on exenatide ( 74.2  12.6 vs. 78.4  12.1 kg on vs. off exenatide , respectively ; p = 0.0003 ) . the observed weight loss ranged between 1.1 and 8.8 kg ( mean 4.1  2.9 kg ) . glucose control did not change as reflected by similar a1c values ( 6.51  0.56 vs. 6.64  0.64% on vs. off exenatide , respectively ; p = 0.39 ) , but insulin requirements were reduced ( total daily dose 0.48  0.11 vs. 0.55  0.13 units  kg  day on vs. off exenatide , respectively ; p = 0.0062 ) . this reduction was caused by 30% lower preprandial insulin doses ( short - acting insulin doses 0.18  0.05 vs. 0.25  0.09 units  kg  day on vs. off exenatide , respectively ; p = 0.0056 ) . irrespective of exenatide treatment , episodes of hypoglycemia ( defined as glucose values < 55 mg / dl [ 3.0 nmol / l ] ) were rare ( 1.21  1.72 vs. 0.93  1.21 episodes per week on vs. off exenatide , respectively ; p = 0.45 ) . fasting glucagon levels remained unchanged whether patients received exenatide or not and were indistinguishable from those of normal control subjects . in contrast to results from patients with type 2 diabetes , meal - stimulated glucagon levels were not suppressed by exenatide , with neither area under the curve nor peak levels being different according to treatment status . exenatide administered before a mixed meal delayed gastric emptying ( a ; p = 0.041 ) and glucose absorption ( b ; p = 0.052 ) , did not change glucagon levels ( c ; p = 0.414 ) , and suppressed glp-1 ( d ; p = 0.024 ) . p values reflect differences of areas under the curve comparing patients ' results on and off exenatide ; data are means  sem . to convert glucose from conventional ( mg / dl ) to si units ( nmol / l ) , multiply by factor 0.0555 . the toronto laboratory returned complete results for all 44 samples shipped to the laboratory , whereas the seattle laboratory returned complete results for 28 of 44 samples due to problems with sample viability or high or low background proliferation ( table 1 ) . all subjects tested positive for diabetes - related t - cell autoreactivity in one or both of the assays used at one or more time points . using the toronto assay , 13 of 16 subjects were consistently positive , whereas only 1 subject was consistently negative , and that subject tested positive by the seattle assay . the seattle assay was more variable , but the majority ( 16 of 28 ) of tests was concordant with the toronto result . of 47 subjects who underwent detailed screening procedures , 40 completed both arginine stimulation and mixed - meal tests : 55% had measurable c - peptide in both tests , 12.5% only after arginine stimulation , and 17.5% only in the mixed - meal test . thus , 85% had detectable c - peptide 0.05 ng / ml ( 0.02 nmol / l ) in two common stimulation tests . once intensified glucose management began ( but before introduction of exenatide and daclizumab ) , 4 patients ( patients 1720 ) discontinued their participation due to fear of hypoglycemia or psychosocial problems . in the remaining 14 patients , a1c decreased from 7.2  0.9% at screening to 6.5  0.7% at the end of the run - in period ( p = 0.0003 ) . the pharmacological ( arginine ) and physiological ( mixed - meal ) stimulation of c - peptide was reduced by intensified insulin treatment ( fig . 2a ) during the run - in period . all patients secreted less c - peptide compared to their screening results ( p < 0.0001 for basal and stimulated c - peptide ) , and 11 patients ( 69% ) had no detectable c - peptide in their first arginine stimulation test in this study period . results of c - peptide responses to arginine stimulation ( a and b ) and changes of insulin doses and weight according to treatment assignment ( c ) . c - peptide results are shown at screening ( basal versus stimulated c - peptide , p < 0.0001 ) and during run - in period ( tests were conducted in months 2 , 3 , and 4 of run - in period [ basal versus stimulated c - peptide , p = 0.0078 ] ) ( a ) after 6 months of exenatide therapy versus not having received exenatide ( irrespective of assignment to daclizumab ) ( b ) with reference to mean results of run - in period . data are means  sem . to convert c - peptide from conventional ( ng / ml ) to si units ( nmol / l ) , multiply by factor 0.333 . c - peptide secretion was insignificantly higher during exenatide treatment , and the addition of daclizumab did not change this outcome ( fig . mean basal c - peptide levels were 0.029 ng / ml ( 0.01 nmol / l ) higher on exenatide versus off exenatide ( 95% ci 0.058 to 0.115 ng / ml , p = 0.48 ) , and stimulated c - peptide levels were 0.024 ng / ml ( 0.008 nmol / l ) higher on exenatide ( 95% ci 0.090 to 0.138 ng / ml , p = 0.66 ) . further , there was no difference when analyzing c - peptide secretion depending on the study period when exenatide was administered . all but one patient ( patient 13 ) lost weight during the 6-month period on exenatide ( 74.2  12.6 vs. 78.4  12.1 kg on vs. off exenatide , respectively ; p = 0.0003 ) . the observed weight loss ranged between 1.1 and 8.8 kg ( mean 4.1  2.9 kg ) . glucose control did not change as reflected by similar a1c values ( 6.51  0.56 vs. 6.64  0.64% on vs. off exenatide , respectively ; p = 0.39 ) , but insulin requirements were reduced ( total daily dose 0.48  0.11 vs. 0.55  0.13 units  kg  day on vs. off exenatide , respectively ; p = 0.0062 ) . this reduction was caused by 30% lower preprandial insulin doses ( short - acting insulin doses 0.18  0.05 vs. 0.25  0.09 units  kg  day on vs. off exenatide , respectively ; p = 0.0056 ) . irrespective of exenatide treatment , episodes of hypoglycemia ( defined as glucose values < 55 mg / dl [ 3.0 nmol / l ] ) were rare ( 1.21  1.72 vs. 0.93  1.21 episodes per week on vs. off exenatide , respectively ; p = 0.45 ) . 3b ) . fasting glucagon levels remained unchanged whether patients received exenatide or not and were indistinguishable from those of normal control subjects . in contrast to results from patients with type 2 diabetes , meal - stimulated glucagon levels were not suppressed by exenatide , with neither area under the curve nor peak levels being different according to treatment status . exenatide administered before a mixed meal delayed gastric emptying ( a ; p = 0.041 ) and glucose absorption ( b ; p = 0.052 ) , did not change glucagon levels ( c ; p = 0.414 ) , and suppressed glp-1 ( d ; p = 0.024 ) . p values reflect differences of areas under the curve comparing patients ' results on and off exenatide ; data are means  sem . to convert glucose from conventional ( mg / dl ) to si units ( nmol / l ) , multiply by factor 0.0555 . the toronto laboratory returned complete results for all 44 samples shipped to the laboratory , whereas the seattle laboratory returned complete results for 28 of 44 samples due to problems with sample viability or high or low background proliferation ( table 1 ) . all subjects tested positive for diabetes - related t - cell autoreactivity in one or both of the assays used at one or more time points . using the toronto assay , 13 of 16 subjects were consistently positive , whereas only 1 subject was consistently negative , and that subject tested positive by the seattle assay . the seattle assay was more variable , but the majority ( 16 of 28 ) of tests was concordant with the toronto result . this clinical trial was based on the observation that some endogenous insulin secretion may persist in long - standing type 1 diabetes ( 14 ) and on the assumption that such function might recover ( 15 ) . our data and results from other investigators support the notion that residual -cells either avoid autoimmune - mediated cell death and/or that new -cells are generated throughout life ( 16 ) . we were able to document that the surviving -cells not only contribute a minimal amount of insulin but respond to various stimuli with prompt insulin release . several studies suggest that -cell survival is mostly limited by the ever - vigilant autoimmunity ( 17 ) . our results confirmed diabetes - associated t - cell reactivity in almost all subjects even after up to 3 decades of disease duration . few studies of t - cell autoimmunity have been performed in long - standing diabetes , and in particular there are no blinded controlled studies distinguishing people with diabetes from control subjects . it has been shown that pancreatic - draining lymph nodes harbor many insulin - reactive t - cells in subjects with long - standing type 1 diabetes compared with healthy control subjects ( 18 ) . because the t - cell assays in our study were performed at the end of the run - in period , the excellent glucose control may have induced -cell quiescence , protecting -cells from immune killing and thereby promoting autoreactive t - cells to traffic out of the pancreatic - draining lymph nodes and into the bloodstream . although our present results do not support the original hypothesis that near - normal glycemia , in combination with exenatide and daclizumab , can induce clinically relevant -cell recovery , it can not be ruled out that other interventions might . indeed , plausible explanations exist for our negative findings , including minimal residual -cell mass associated with advanced patient age and prolonged duration of disease as well as insufficient immunosuppression ( 19,20 ) . another factor might have been excellent glucose control because animal studies suggest hyperglycemia may be necessary to promote -cell proliferation ( 21 ) . furthermore , recent studies have questioned exenatide 's ability to promote -cell proliferation ( 22,23 ) . although our results are based on data from 14 patients taking exenatide for 69 months , it is important to note that this crossover study has the equivalent power to a parallel group study with 56 patients ( 28 patients in each group , intervention and control ) . thus , the sample size is small but comparable to other relevant studies in the field . furthermore , looking at only the possible positive effect of exenatide , our data allow us to claim at a 97.5% level of confidence that the treatment caused 0.115 ng / ml improvement in basal c - peptide secretion , which we did not regard as clinically relevant . at the same time , important knowledge about the natural history of -cell function was gained . we found that the majority of patients with long - standing type 1 diabetes had surviving -cells , which promptly responded to standard physiologic and pharmacologic stimuli . this finding highlights the importance of standardizing pretest conditions such as ambient blood glucose and exogenous insulin dosing when evaluating -cell function . of special clinical interest is the exenatide - induced weight loss and reduction in insulin requirements without increased frequency of hypoglycemia . in contrast to the expected suppression of inappropriately elevated glucagon levels ( 24 ) , we did not see reduced hyperglucagonemia with exenatide . we speculate that this is due to the long - standing abnormal intra - islet cross talk between - and -cells . in conclusion , residual -cells may play an important role as a potential source of new -cells in future trials , especially in younger patients and at an earlier stage of the disease . more combination therapies that include immunomodulators with agents that improve -cell function and growth are needed to expand residual -cell mass to a degree that individuals with type 1 diabetes may eventually become insulin independent .
objectivein patients with long - standing type 1 diabetes , we investigated whether improved -cell function can be achieved by combining intensive insulin therapy with agents that may 1 ) promote -cell growth and/or limit -cell apoptosis and 2 ) weaken the anti-cell autoimmunity.research design and methodsfor this study , 20 individuals ( mean age 39.5  11.1 years ) with long - standing type 1 diabetes ( 21.3  10.7 years ) were enrolled in this prospective open - label crossover trial . after achieving optimal blood glucose control , 16 subjects were randomized to exenatide with or without daclizumab . 
 endogenous insulin production was determined by repeatedly measuring serum c-peptide.resultsin 85% of individuals with long - standing type 1 diabetes who were screened for participation in this trial , c - peptide levels 0.05 ng / ml ( 0.02 
 nmol / l ) were found . 
 residual -cells responded to physiological ( mixed - meal ) and pharmacological ( arginine ) stimuli . during exenatide treatment , patients lost 4.1  2.9 kg body wt and insulin requirements declined significantly ( total daily dose on exenatide 0.48  0.11 vs. 0.55  0.13 units  kg1  day1 without exenatide ; p = 0.0062 ) . 
 no signs of further activation of the underlying autoimmune disease were observed . 
 exenatide delayed gastric emptying , suppressed endogenous incretin levels , but did not increase c - peptide secretion.conclusionsin long - standing type 1 diabetes , which remains an active autoimmune disease even decades after its onset , surviving -cells secrete insulin in a physiologically regulated manner . 
 however , the combination of intensified insulin therapy , exenatide , and daclizumab did not induce improved function of these remaining -cells .