after more than 10 years of clinical use of hsct for severe and refractory aid , animal studies suggested that this approach could be beneficial for human type 1 diabetes mellitus ( t1 dm ) . in addition , further support for this approach was derived from clinical studies in which the effectiveness of immunosuppression for early - onset t1 dm and the beneficial effects of hsct in diabetic patients with hematological disorders were observed . specifically , beneficial effects of hsct in various aids , and in experimental models of t1 dm , together with low / moderate doses of immunosuppressive drugs in human t1 dm , were documented , whereas hsct in individuals with long - standing t1 dm was ineffective , and transfer of t1 dm from donor to recipient in allogeneic hsct was noted . on the basis of the evidence discussed above , hsct for early - onset t1 dm was proposed in review articles in 2001 ( ref . 17 ) and 2002 ( ref . 18 ) , and a clinical protocol , designed by investigators at northwestern university in chicago , usa ( richard burt ) and the university of so paulo in ribeiro preto , brazil ( jlio voltarelli and others ) was approved by local and national institutional review boards , permitting the initiation of this study in 2003 in brazil . since 2003 , our research group in brazil has been conducting an original study of non - myeloablative ahsct in patients with newly diagnosed t1 dm . the objective of the treatment is to stop autoimmune destruction of -cells with high - dose immunosuppressive drugs ( cyclophosphamide and rabbit antithymocyte globulin ) , and to  reset ' the deleterious immunological system with one that is reconstituted by an ahsct . the rationale for this therapy is to both preserve residual -cell mass and to facilitate endogenous mechanisms of -cell regeneration . hematopoietic stem cells probably do not have the capacity to differentiate into large numbers of  cells ; therefore , these cells are used solely to regenerate a new immune system that lacks autoreactive memory cells against pancreatic antigens ( see below ) . however , it has been suggested that ahsct may shift the balance from a destructive immune response to immune tolerance through clonal exhaustion , regulatory cells , cytokine alterations , and changes in t- or b - cell repertoires . the procedure of ahsct consists of several steps from patient selection through long - term follow - up . most patients interested in the study were excluded for not fulfilling enrollment criteria , especially the required short time period ( 6 weeks ) between the first diagnosis of t1 dm and therapy , positivity for anti - glutamic acid decarboxylase antibodies , or a lack of a complete understanding of and compliance with the study protocol . patients enrolled in the study underwent hsc mobilization from the bone marrow , using granulocyte colony - stimulating factor ( 10  mcg / day ) and cyclophosphamide ( 2  g / m ) . mobilized hsc were collected by leukapheresis , cryopreserved , thawed , and infused unmanipulated ( minimum of 2.0  million / kg ) after preconditioning with cyclophosphamide ( 200  mg / kg ) and rabbit antithymocyte globulin ( 4.5  mg / kg ) . apart from the diabetic status , all the treated patients were in good health before transplantation , which explains in part the low frequency and severity of adverse effects ( see below ) . this outcome is also explained by the rapid engraftment of neutrophils ( mean of 9 days ) and platelets ( mean of 10 days ) . his insulin requirements increased progressively up to 12 months following transplantation , when he abandoned follow - up and when his insulin dose was 250% above baseline . his hemoglobin a1c level was 11.1% at 12 months and his c - peptide concentration did not increase . a possible cause for this poor clinical response may have been his very low -cell reserve , predicted by the previous diagnosis of diabetic ketoacidosis , and further impaired by the apoptotic effect of glucocorticoids used to prevent rabbit antithymocyte globulin reactions . considering these possibilities , we decided not to use glucocorticoids in the conditioning regimen in the following patients and did not include those with previous diabetic ketoacidosis . in july 2009 , after a mean follow - up of 36.1 months ( range 12 to 65 months ) , all but two of the subsequent 22 patients became independent of exogenous insulin , most of them shortly after being placed on high - dose immunosuppression and occasionally even before sc infusion . nine patients remained insulin - independent following its discontinuation for a mean period of 40 months ( range from 23 to 59 months ; figure 1 ) . eleven out of 20 patients had to resume insulin injections after varying periods of insulin independence , ranging from 6 to 47 months . ten of the subjects required 3050% of their baseline insulin doses after , and patient no . two patients ( nos . 2 and 4 ) became transiently insulin independent for 47 months and 43 months , respectively . after 4 and 2 months of resuming insulin injections at daily doses of 0.25  iu / kg and 0.20  iu / kg , respectively , we opted to treat these individuals with sitagliptin at 100  mg / day orally . 4 ) , and both remained independent of exogenous insulin for 12 months and 13 months , respectively , ( figure 2 ) . sitagliptin is a dipeptidyl peptidase-4 inhibitor , a member of a novel class of oral antihyperglycemic agents . this medication enhances meal - stimulated active glucagon - like peptide 1 and glucose - dependent insulinotropic polypeptide levels , improves measures of -cell function , suppresses glucagon levels produced by -cells , and increases -cell mass in rodent models . it also inhibits t - cell aggression against -cells . the 21st patient presented with previous ketoacidosis , and the 20th patient received steroids ( 300  mg hydrocortisone ) along with stem cell infusion to prevent reactions to rabbit antithymocyte globulin . there was a statistically significant reduction of mean hemoglobin a1c levels after transplantation , and all insulin - independent patients achieved a1c levels of < 7% ( upper limit of good glucose control ) during follow - up . -cell function was analyzed by measuring the area under the curve of serum c - peptide levels during the mixed - meal tolerance test . during the follow - up period , both group of patients , continuously and transiently insulin independent , showed a significant elevation of c - peptide levels of more than two times of the mean area under the curve . in face of the good metabolic results that were obtained , the adverse effects appeared acceptable . with respect to acute complications , most patients had febrile neutropenia , nausea , vomiting , and alopecia due to the immunosuppressive agents used in the mobilization and conditioning phases of the protocol . bilateral pneumonia of unidentified etiology , requiring supplementary oxygen , responded completely to broad - spectrum antibiotics in patient nos . 2 and 22 . these were the only severe acute complications of the transplantation procedure . during long - term follow - up , 2 presented with graves ' disease at 3.5 years post - transplantation , and patient no . 3 developed autoimmune hypothyroidism and transient renal dysfunction due to rhabdomyolysis , a complication that was successfully treated with levothyroxine . these late - onset endocrine abnormalities presented by these three patients may have been caused by the transplant procedure itself or may have been part of an autoimmune polyendocrine syndrome that is frequently associated with t1 dm . of the 16 enrolled men , 13 had sperm examinations done before treatment : 11/13 had abnormal sperm morphology and abnormal motility scores , and 2/13 had low sperm - cell counts ( one patient presented with bilateral cryptorchidism ) . during the follow - up , two male patients had children after transplantation ( one of them did not have spermograms before and after transplantation ) . we are currently performing exhaustive studies of immunoreconstitution ( phenotypic and functional ) in the transplanted patients in order to unravel the mechanisms by which ahsct produces clinical benefits in type 1 diabetic patients . compared with pretransplant profiles , preliminary results show that after transplantation there is an increase in the number of regulatory cd4cd25foxp3 t cells and th2 cytokine - producing cells . in addition , we detected after ahsct , profound qualitative and quantitative changes in t - cell receptor repertoire , as well as alterations in the expression of pro- and anti - apoptotic genes ( malmegrim , personal communication ) . anti - glutamic acid decarboxylase autoantibodies decreased in most patients but did not correlate with clinical response . further preliminary data from our ongoing immune reconstitution studies resemble those observed in other aids after ahsct . these results support the suggested hypothesis that a new and more tolerant immune system is generated after this treatment , explaining the reduction of autoimmune destruction of insulin - producing cells and clinical improvement ( mechanism no . other possible mechanisms by which hsct may operate in aid are the specific actions of high - dose immunosuppression ( mechanism no . 1 , table 2 ) and/or tissue repair mediated by transdifferentiation and engraftment of administered bone marrow stem cells ( mechanism no . however , in the presence of anti - glutamic acid decarboxylase autoantibodies and without specific immunological reactivity tests to -cell antigens , we can not be sure that our treatment blocks autoimmune attack to endocrine pancreas more efficiently and for longer time than other immunosuppressive interventions , particularly anti - t - cell therapies . our clinical trial was approved by the national institutional review board and it was registered at http://clinicaltrials.gov under number nct00315133 . our preliminary study of ahsct in a subset of non - ketoacidotic newly diagnosed t1 dm patients yielded a number of unexpected positive results : 20/21 patients were able to stop insulin use after initiation of high - dose immunosuppression , and nine patients maintained this status after a mean follow - up of 40 months ( maximum of 59 months ) . ten patients relapsed after stopping insulin use , and one patient who received steroids during conditioning never became insulin independent . in this group , two patients regained insulin independence after treatment with sitagliptin , which was associated with an increase in c - peptide levels . longer follow - up and controlled studies are needed to evaluate the full potential of this novel therapy of early t1 dm . the underlying mechanism of action of the various components of the ahsct ( cyclophosphamide , atg , and stem cells ) can not be studied by direct methods in humans ; however , our current immune reconstitution studies and similar studies in other aids suggest that the immune system is reset toward a tolerant phenotype , as evidenced by increased regulatory t - cell numbers and by the regeneration of a different and more diverse t - cell receptor repertoire . we hypothesize that the combination of high - dose immunosuppression and hsc infusions function synergistically to downregulate autoreactive t cells , to renew the immune system , and to improve the immune regulatory networks . although our approach provides the proof of principle that high - dose immunosuppression coupled with autologous hsc boosting can revert early - onset t1 dm in humans , it will hardly solve the overall problem of the disease . first , only a small subset of patients with early - onset t1 dm were successfully treated with ahsct , whereas millions of patients with long - standing t1 dm will likely need another type of stem cell to regenerate pancreatic -cells and other damaged tissues . second , ahsct is an expensive , cumbersome , and complex procedure performed in specialized bone marrow transplantation facilities , and has the potential of causing life - threatening short- and long - term complications . in the future , more simple approaches such as pharmacological , biological , or cellular immunoregulatory interventions may accomplish the same therapeutic goal in millions of type 1 diabetic patients . besides hsc , other types of stem cells , such as embryonic , mesenchymal , or those from umbilical cord blood , may be promising candidates to fulfill this role ( reviewed in ref ahsct and islet / pancreas transplantation remain currently the only treatment options to durably reverse the disease in humans . however , the utility of ahsct will have to be tested in other groups of patients ( with previous ketoacidosis , with longer duration of the disease , and in young children ) . the potential of incretin enhancers , such as sitagliptin , to restore insulin independence , as observed in two of our patients who relapsed after hsct , illustrates the possible role of combination therapies ( stem cells plus immunosuppression plus regenerative compounds ) in the future treatment of t1 dm . type 2 diabetes mellitus ( dm2 ) is associated with insulin resistance and secretory dysfunction of the  cells . there are now experimental , epidemiological , and clinical evidences , suggesting the involvement of immune system and inflammatory mediators in both pathogenic mechanisms of dm2 . although the initiating events of -cells lesion are different in dm1 and dm2 , the final pathway of pancreatic -cell death have similarities in dm1 and dm2 , suggesting the potential of immunological and regenerative interventions in dm2 as well . cellular therapy with stem cells for glycemic control has been tested in experimental models for some years , and various sources of stem cells to replace pancreatic -cells are now under investigation . however , there are only few studies of such approaches reported in humans . reported improvements in glycemic control and c - peptide levels and reduction in insulin requirements in patients with dm2 submitted to combined therapy of intrapancreatic autologous stem cell infusion and hyperbaric oxygen therapy . reported the same benefits in patients with dm2 after intra - arterial infusion of autologous bone marrow - derived stem cells . although there are many obstacles to be overcome before regenerative therapy becomes a real option to treat dm2 , in the future it may become an important strategy to attain metabolic control and in prevention of chronic complications . our preliminary study of ahsct in a subset of non - ketoacidotic newly diagnosed t1 dm patients yielded a number of unexpected positive results : 20/21 patients were able to stop insulin use after initiation of high - dose immunosuppression , and nine patients maintained this status after a mean follow - up of 40 months ( maximum of 59 months ) . ten patients relapsed after stopping insulin use , and one patient who received steroids during conditioning never became insulin independent . in this group , two patients regained insulin independence after treatment with sitagliptin , which was associated with an increase in c - peptide levels . longer follow - up and controlled studies are needed to evaluate the full potential of this novel therapy of early t1 dm . the underlying mechanism of action of the various components of the ahsct ( cyclophosphamide , atg , and stem cells ) can not be studied by direct methods in humans ; however , our current immune reconstitution studies and similar studies in other aids suggest that the immune system is reset toward a tolerant phenotype , as evidenced by increased regulatory t - cell numbers and by the regeneration of a different and more diverse t - cell receptor repertoire . we hypothesize that the combination of high - dose immunosuppression and hsc infusions function synergistically to downregulate autoreactive t cells , to renew the immune system , and to improve the immune regulatory networks . although our approach provides the proof of principle that high - dose immunosuppression coupled with autologous hsc boosting can revert early - onset t1 dm in humans , it will hardly solve the overall problem of the disease . first , only a small subset of patients with early - onset t1 dm were successfully treated with ahsct , whereas millions of patients with long - standing t1 dm will likely need another type of stem cell to regenerate pancreatic -cells and other damaged tissues . second , ahsct is an expensive , cumbersome , and complex procedure performed in specialized bone marrow transplantation facilities , and has the potential of causing life - threatening short- and long - term complications . in the future , more simple approaches such as pharmacological , biological , or cellular immunoregulatory interventions may accomplish the same therapeutic goal in millions of type 1 diabetic patients . besides hsc , other types of stem cells , such as embryonic , mesenchymal , or those from umbilical cord blood , may be promising candidates to fulfill this role ( reviewed in ref ahsct and islet / pancreas transplantation remain currently the only treatment options to durably reverse the disease in humans . however , the utility of ahsct will have to be tested in other groups of patients ( with previous ketoacidosis , with longer duration of the disease , and in young children ) . the potential of incretin enhancers , such as sitagliptin , to restore insulin independence , as observed in two of our patients who relapsed after hsct , illustrates the possible role of combination therapies ( stem cells plus immunosuppression plus regenerative compounds ) in the future treatment of t1 dm . type 2 diabetes mellitus ( dm2 ) is associated with insulin resistance and secretory dysfunction of the  cells . there are now experimental , epidemiological , and clinical evidences , suggesting the involvement of immune system and inflammatory mediators in both pathogenic mechanisms of dm2 . although the initiating events of -cells lesion are different in dm1 and dm2 , the final pathway of pancreatic -cell death have similarities in dm1 and dm2 , suggesting the potential of immunological and regenerative interventions in dm2 as well . cellular therapy with stem cells for glycemic control has been tested in experimental models for some years , and various sources of stem cells to replace pancreatic -cells are now under investigation . however , there are only few studies of such approaches reported in humans . reported improvements in glycemic control and c - peptide levels and reduction in insulin requirements in patients with dm2 submitted to combined therapy of intrapancreatic autologous stem cell infusion and hyperbaric oxygen therapy . reported the same benefits in patients with dm2 after intra - arterial infusion of autologous bone marrow - derived stem cells . although there are many obstacles to be overcome before regenerative therapy becomes a real option to treat dm2 , in the future it may become an important strategy to attain metabolic control and in prevention of chronic complications .
in this review , we present ( 1 ) a brief discussion of hematopoietic stem cell transplantation ( hsct ) for severe and refractory autoimmune diseases ( aids ) from its beginning in 1996 through recently initiated prospective randomized clinical trials ; ( 2 ) an update ( up to july 2009 ) of clinical and laboratory outcomes of 23 patients with newly diagnosed type 1 diabetes mellitus ( t1 dm ) , who underwent autologous hsct at the bone marrow transplantation unit of the ribeiro preto medical school , university of so paulo , brazil ; ( 3 ) a discussion of possible mechanisms of action of hsct in aids , including preliminary laboratory data obtained from our patients ; and ( 4 ) a discussion of future perspectives of stem cell therapy for t1 dm and type 2 dm , including the use of stem cell sources other than adult bone marrow and the combination of cell therapy with regenerative compounds .