Elimination of alloantibodies by immunoablative high-dose cyclophosphamide

Desensitization for solid organ and hematopoietic stem cell transplantation

Desensitization protocols are being used worldwide to enable kidney transplantation across immunologic barriers, i.e. antibody to donor HLA or ABO antigens, which were once thought to be absolute contraindications to transplantation. Desensitization protocols are also being applied to permit transplantation of HLA mismatched hematopoietic stem cells to patients with antibody to donor HLA, to enhance the opportunity for transplantation of non-renal organs, and to treat antibody-mediated rejection. Although desensitization for organ transplantation carries an increased risk of antibody-mediated rejection, ultimately these transplants extend and enhance the quality of life for solid organ recipients, and desensitization that permits transplantation of hematopoietic stem cells is life saving for patients with limited donor options. Complex patient factors and variability in treatment protocols have made it difficult to identify, precisely, the mechanisms underlying the downregulation of donor-specific antibodies. The mechanisms underlying desensitization may differ among the various protocols in use, although there are likely to be some common features. However, it is likely that desensitization achieves a sort of immune detente by first reducing the immunologic barrier and then by creating an environment in which an autoregulatory process restricts the immune response to the allograft.

Pulse cyclophosphamide therapy in refractory warm autoimmune hemolytic anemia: a new perspective

Treatment of steroid refractory autoimmune hemolytic anemia (AIHA) is challenging especially with no evidence based consensus guide lines and limited resources. The aim of this study was to evaluate the efficacy of pulse cyclophosphamide therapy in patients with severe refractory warm AIHA. The prospective study was designed to evaluate the efficacy of pulse cyclophosphamide-1 g/month for four consecutive months-in 17 patients (10 males and 7 females) with severe refractory warm AIHA [13 primary AIHA and 4 (females) secondary to SLE], all studied patients failed to respond to high dose of steroid therapy ± azathioprine ± intravenous immunoglobulin ± oral cyclophosphamide. Mean hemoglobin level, reticulocytic count and direct antiglobulin test were assessed before and after cyclophosphamide treatment every month. After the 4th cycle of cyclophosphamide (82 %, 14 patients) achieved partial response while the remaining (17 %, 3 patients) showed no response, while after 6 months follow up 47 % (8 patients) show complete response, while 53 % (9 patients) showed partial response. The mean hemoglobin levels were significantly increased after the 1st, 2nd, 3rd and 4th months of pulse cyclophosphamide therapy when compared to before treatment (P < 0.01, P < 0.001, P < 0.001 and P < 0.001) respectively, and the mean reticulocyte (%) were significantly decreased after the 2nd, 3rd and 4th months (P < 0.05, P < 0.01 and P < 0.001) respectively. We conclude that pulse cyclophosphamide therapy is well tolerated and induces good response in patients with severe refractory warm AIHA.

Partially mismatched transplantation and human leukocyte antigen donor-specific antibodies

The presence of donor human leukocyte antigen (HLA)-specific antibodies (DSA) increases engraftment failure risk in partially HLA-mismatched, or HLA-haploidentical, allogeneic marrow (alloBMT) transplantation. As pre-existing sensitization to HLA antigens is not well characterized among candidates for HLA-haploidentical alloBMT, we retrospectively evaluated both the incidence and relative strength of DSA in this patient population. Based on correlations of solid-phase antibody assays on the Luminex (Luminex, Austin, TX) platform with actual crossmatch tests, DSA were characterized as weak for results that were consistent with negative flow cytometric crossmatch results or as moderate-to-strong for results consistent with positive flow cytometric or cytotoxicity crossmatches. We evaluated 296 alloBMT candidates; 111 (37.5%) were female. DSA were detected in 43 (14.5%) candidates, mostly among female candidates (42.9% female versus 12.5% male). Moderate-to-strong DSA strength was more frequently encountered when directed against haploidentical donors as compared with mismatched unrelated donors. DSA were most commonly detected in female patients directed against their children. Because the presence of DSA has been considered prohibitive for HLA-mismatched alloBMT, we additionally report a desensitization methodology used to reduce DSA to negative or weak levels, ie, levels well below those detectable in a flow cytometric crossmatch. Nine patients without other available donors underwent desensitization. Eight who reduced their DSA to negative or weak levels proceeded to alloBMT and achieved full donor engraftment. These data support routine DSA evaluation in all patients considered for mismatched alloBMT; however, for patients with no other viable options, desensitization to weak or negative DSA levels may afford the opportunity for successful transplantation.

High-dose cyclophosphamide for autoimmunity and alloimmunity

High-dose cyclophosphamide (high-CY) is a potent immunosuppressive regimen that is increasingly used to mitigate both autoimmune and alloimmune conditions. Differential expression of aldehyde dehydrogenase between hematopoietic stem cells and lymphocytes accounts for the differential sensitivity of these cells to high-CY and explains why this regimen is immunosuppressive but not myeloablative. This article describes the clinical translation of high-CY for the treatment of autoimmune and alloimmune conditions.

Autoimmune enteropathy in children and adults

Autoimmune enteropathy is a rare disorder characterized by severe and protracted diarrhea, weight loss from malabsorption and immune-mediated damage to the intestinal mucosa, generally occurring in infants and young children, although some cases of adult onset have been reported in the literature. Pathogenetic mechanisms involve immunological disorders, in which the presence of antienterocyte autoantibodies, although detected since first description, seems now to be secondary. As occurs frequently in autoimmunity, subjects with autoimmune enteropathy may be affected by other autoimmune disorders, sometimes leading to particular forms, i.e. the IPEX syndrome and the APECED syndrome. The prognosis of autoimmune enteropathy patients depends on the severity of digestive symptoms (including fecal output), on the severity and extension of histological lesions along the gastrointestinal apparatus, and on the presence of extra-intestinal involvement. Management of autoimmune enteropathy patients is based on nutritional support and adequate hydration to ensure optimal growth and development, together with immunosuppressive therapy. Recently, biological agents have been introduced, with apparent beneficial effects.

Intensive immunosuppression with high dose cyclophosphamide but without stem cell rescue for severe autoimmunity: advantages and disadvantages

Hematopoietic stem cell transplantation (HSCT) for the treatment of severe autoimmune disorders continues to show great promise. The morbidity and mortality of the approach is relatively low and clinical benefit has been demonstrated in many, but not all patients. Furthermore, relapse following HSCT is not uncommon. Most centers now prefer nonmyeloablative conditioning regimens using high dose cyclophosphamide prior to SCT; however, emerging data show that high dose cylophosphamide can be administered safely without the need for HSCT. Eliminating the use of HSCT after high dose cyclophosphamide shortens the duration of the procedure by several weeks, markedly reduces the cost of the procedure and eliminates the potential of reinfusing autoreactive lymphoctes with the autograft.

Reduced intensity HLA-haploidentical BMT with post transplantation cyclophosphamide in nonmalignant hematologic diseases

Allogeneic blood or marrow transplantation (BMT) is potentially curative for a variety of life-threatening nonmalignant hematologic diseases such as paroxysmal nocturnal hemoglobinuria (PNH) and hemoglobinopathies. The application of BMT to treat these disorders is limited by the lack of suitable donors and often end-organ damage from the underlying disease. We treated three patients with thrombotic PNH, one of whom also had sickle cell disease, with a nonmyeloablative, HLA-haploidentical BMT with post-transplant CY. Rapid engraftment without GVHD occurred in two of the patients, including the patient with sickle cell disease. Both patients are disease free with full donor chimerism and require no immunosuppressive therapy, with follow-up of 1 and 4 years, respectively. Nonmyeloablative, HLA-haploidentical BMT with post-transplant CY is a promising approach for patients with life-threatening nonmalignant hematologic disease who lack an HLA-matched sibling donor.

Humoral immunity is the dominant barrier for allogeneic bone marrow engraftment in sensitized recipients

We evaluated the relative contribution of the humoral and cellular arms of the immune response to bone marrow cells transplanted into sensitized recipients. We report here for the first time that humoral immunity contributes predominantly to allosensitization. Although the major role for nonmyeloablative conditioning is to control alloreactive host T cells in nonsensitized recipients, strikingly, none of the strategies directed primarily at T-cell alloreactivity enhanced engraftment in sensitized mice. In evaluating the mechanism behind this barrier, we found that humoral immunity plays a critical role in the rejection of allogeneic marrow in sensitized recipients. Adoptive transfer of as little as 25 microL serum from sensitized mice abrogated engraftment in secondary naive recipients. With the use of microMT mice as recipients, we found that T-cell-mediated immunity plays a secondary but still significant role in allorejection. Targeting of T cells in sensitized B-cell-deficient microMT mice enhanced alloengraftment. Moreover, both T- and B-cell tolerance were achieved in sensitized recipients when allochimerism was established, as evidenced by the acceptance of second donor skin grafts and loss of circulating donor-specific Abs. These findings have important implications for the management of sensitized transplant recipients and for xenotransplantation in which B-cell reactivity is a predominant barrier.

Management of Patients With Preformed Reactive Antibodies Who Are Awaiting Cardiac Transplantation

Patients with elevated levels of preformed reactive antibodies to HLA antigens have higher rates of organ rejection than do patients without such antibodies. Consequently, before proceeding with transplantation, many medical centers do prospective cross-matching, that is, mix lymphocytes from the organ donor with sera from the prospective organ recipient, to determine whether a higher rejection rate or an immediate episode of rejection will occur. The problem has been compounded by the increased frequency of preformed reactive antibodies in patients with ventricular assist devices who are awaiting cardiac transplantation. Performing a prospective cross-match can be time-consuming and often is impossible because of the unstable condition of the organ donor or travel logistics, leading to increased costs for transplantation and longer waiting times for recipients. A variety of treatments are used in cardiac transplantation programs in attempts to reduce the concentration of preformed reactive antibodies. Each of these treatments has accompanying complications and considerations for the transplant team. Each treatment must also be assessed for therapeutic response. Options for managing patients with preformed antibodies and a case report are presented.

Allosensitization in heart transplantation: implications and management strategies

The detection of anti-human leukocyte antigen (HLA) donor-specific antibodies has been associated with a variety of clinical syndromes that determine short-term and long-term outcomes of cardiac transplant recipients, including an increased incidence of early and more severe allograft rejection and cardiac allograft vasculopathy. Recent surveys indicate marked heterogeneity in clinical protocols for detection and management of sensitization in heart transplantation. The commonly performed complement-dependent cytotoxicity assay is insensitive compared with newer methods such as flow cytometry for antibody screening. The imperative exists to create strategies that can decrease the level of sensitization and increase the likelihood for a negative crossmatch. In this effort, several strategies have been suggested, including administration of intravenous immunoglobulin, apheresis, and combination therapies using potent immunosuppression, particularly with cyclophosphamide. The future of managing allosensitization may be in induction of a chimeric state to allow graft tolerance.

High-dose cyclophosphamide for refractory autoimmune hemolytic anemia

High-dose cyclophosphamide, without stem cell rescue, has been used successfully to treat aplastic anemia and other autoimmune disorders. To determine the safety and efficacy of high-dose cyclophosphamide among patients with severe refractory autoimmune hemolytic anemia, we treated 9 patients with cyclophosphamide (50 mg. kg(-1). d(-1) for 4 days) who had failed a median of 3 (range, 1-7) other treatments. The median hemoglobin before treatment was 6.7 g/dL (range, 5-10 g/dL). The median time to reach an absolute neutrophil count of 500/microL or greater was 16 days (range, 12-18 days). Six patients achieved complete remission (normal untransfused hemoglobin for age and sex), and none have relapsed after a median follow-up of 15 months (range, 4-29 months). Three patients achieved and continue in partial remission (hemoglobin at least 10 g/dL without transfusion support). High-dose cyclophosphamide was well tolerated and induced durable remissions in patients with severe refractory autoimmune hemolytic anemia.

Anti-idiotypic antibodies from highly sensitized patients stimulate B cells to produce anti-HLA antibodies

BACKGROUND

Sustained allosensitization increases waiting time for transplantation and increases the risk of rejection. The purpose of this study is to examine the effect of anti-idiotypic antibodies on B-cell responses and to define their role in alloantibody production.

METHODS

The Immunoglobulin G (IgG) fraction, or the sera of 19 highly sensitized (HS) patients was absorbed to remove anticlass I antibody and was incubated with B cells. The culture supernatant was assayed for antihistocompatibility leukocyte antigen (HLA) antibody and tested for reactivity against a panel of normal lymphocytes. Similar studies were performed in 5 of the 19 patients who had a fall in alloantibody levels.

RESULTS

The IgG (HS) fraction induced anti-HLA antibody from normal and autologous B cells in all 19 HS patients studied. The reactivity to HLA antigens in the culture supernatant was similar to the sera for each patient studied. The in vitro generated anti-HLA antibody bound to the IgG fraction used to stimulate the B cells. The in vitro production of anti-HLA antibodies was absent in the serum of all five patients who became nonsensitized.

CONCLUSIONS

All patients who have high levels of alloantibody have anti-idiotypic antibodies in their sera that stimulate B cells to produce anti-HLA class I antibody similar in reactivity to that of their own sera. In the patients who have nondetectable alloantibodies in their sera, the stimulating anti-idiotypes are not measurable. Anti-idiotypic antibodies may act as a vaccine and cause sustained levels of alloantibody production.

High-dose cyclophosphamide for aplastic anemia and autoimmunity

High-dose cyclophosphamide was developed as a conditioning regimen for allogeneic bone marrow transplantation. Later, it was discovered that high-dose cyclophosphamide spares early hematopoietic stem cells because of their relatively high levels of the enzyme aldehyde dehydrogenase; thus, high-dose cyclophosphamide is a potent immunosuppressive agent, but nonmyeloablative. Recent reports demonstrate that high-dose cyclophosphamide without bone marrow transplantation induces durable treatment-free remissions in severe aplastic anemia and a variety of other autoimmune disorders; however, there is lingering concern about the safety of this approach.

Multilineage glycosylphosphatidylinositol anchor-deficient haematopoiesis in untreated aplastic anaemia

Aplastic anaemia and paroxysmal nocturnal haemoglobinuria (PNH) are closely related disorders. In PNH, haematopoietic stem cells that harbour PIGA mutations give rise to blood elements that are unable to synthesize glycosylphosphatidylinositol (GPI) anchors. Because the GPI anchor is the receptor for the channel-forming protein aerolysin, PNH cells do not bind the toxin and are unaffected by concentrations that lyse normal cells. Exploiting these biological differences, we have developed two novel aerolysin-based assays to detect small populations of PNH cells. CD59 populations as small as 0.004% of total red cells could be detected when cells were pretreated with aerolysin to enrich the PNH population. All PNH patients displayed CD59-deficient erythrocytes, but no myelodysplastic syndrome (MDS) patient or control had detectable PNH cells before or after enrichment in aerolysin. Only one aplastic anaemia patient had detectable PNH red cells before exposure to aerolysin. However, 14 (61%) had detectable PNH cells after enrichment in aerolysin. The inactive fluorescent proaerolysin variant (FLAER) that binds the GPI anchors of a number of proteins on normal cells was used to detect a global GPI anchor deficit on granulocytes. Flow cytometry with FLAER showed that 12 out of 18 (67%) aplastic anaemia patients had FLAER-negative granulocytes, but none of the MDS patients or normal control subjects had GPI anchor-deficient cells. These studies demonstrate that aerolysin-based assays can reveal previously undetectable multilineage PNH cells in patients with untreated aplastic anaemia. Thus, clonality appears to be an early feature of aplastic anaemia.