Antithymocyte immunoglobulin in severe aplastic anemia and bone marrow transplantation

A successful desensitization protocol for horse-derived antithymocyte globulin in severe aplastic anemia

BACKGROUND

Horse antithymocyte globulin (h-ATG) (ATGAM(®) ) is the first choice of treatment in very severe patients with aplastic anemia who do not have any HLA matched sibling donor. h-ATG is a heterologous serum that may cause anaphylaxis. Alternative treatment strategies must be planned in case of hypersensitivity. Desensitization must be considered in patients without an alternative treatment of choice. We aimed to present the h-ATG desensitization protocol and consider its effectiveness in patients with aplastic anemia who are hypersensitized with h-ATG and do not have an alternative treatment of choice.

METHODS

Skin prick tests were performed with non-diluted solution in eight very severe patients with aplastic anemia who are followed up in Ege University Children's Hospital. Although skin prick test was found negative in these eight patients, different dilution h-ATG intradermal tests were performed and found positive in all patients. h-ATG desensitization program was started to these hypersensitized patients.

RESULTS

Desensitization program was started to six male and two female very severe patients with aplastic anemia whose ages were between seven and 19 yr (median: 12.9 yr). All of the patients completed the desensitization program. While local reaction was seen in two patients, systemic reaction was seen in one patient and late reaction was seen in one patient during and after desensitization program.

CONCLUSION

A successful desensitization program with h-ATG in children with aplastic anemia is presented. Even though there is not an exposure before to such high allergy potential heterologous serum, skin tests should be performed and desensitization must be started to patients who are hypersensitized to h-ATG. As the expected effectiveness of the treatment is so much, the desensitization protocol can be carried out safely and effectively with trained stuff although allergic reactions can be seen.

Rabbit polyclonal mouse antithymocyte globulin administration alters dendritic cell profile and function in NOD mice to suppress diabetogenic responses

Mouse antithymocyte globulin (mATG) prevents, as well as reverses, type 1 diabetes in NOD mice, through mechanisms involving modulation of the immunoregulatory activities of T lymphocytes. Dendritic cells (DC) play a pivotal role in the generation of T cell responses, including those relevant to the autoreactive T cells enabling type 1 diabetes. As Abs against DC are likely generated during production of mATG, we examined the impact of this preparation on the phenotype and function of DC to elucidate novel mechanisms underlying its beneficial activities. In vivo, mATG treatment transiently induced the trafficking of mature CD8(-) predominant DC into the pancreatic lymph node of NOD mice. Splenic DC from mATG-treated mice also exhibited a more mature phenotype characterized by reduced CD8 expression and increased IL-10 production. The resultant DC possessed a potent capacity to induce Th2 responses when cultured ex vivo with diabetogenic CD4(+) T cells obtained from BDC2.5 TCR transgenic mice. Cotransfer of these Th2-deviated CD4(+) T cells with splenic cells from newly diabetic NOD mice into NOD.RAG(-/-) mice significantly delayed the onset of diabetes. These studies suggest the alteration of DC profile and function by mATG may skew the Th1/Th2 balance in vivo and through such actions, represent an additional novel mechanism by which this agent provides its beneficial activities.

Current status of allogeneic bone marrow transplantation in acquired aplastic anemia

Bone marrow transplantation is an effective therapy for aplastic anemia. Infusion of allogeneic hematopoietic stem cells after high-dose immune suppression restores normal hematopoiesis in most patients and long-term follow-up has confirmed the durability of donor hematopoiesis. However, success of this approach is limited by transplant-related complications, such as graft failure, graft-versus-host disease, and various organ toxicities. Long-term survival rates range from less than 40% to more than 90% in reported series. These rates have improved over the past 20 years due to significant reductions in graft-versus-host disease, interstitial pneumonitis, and early transplant-related mortality. Most long-term survivors have excellent performance status. Late effects such as cataracts, thyroid disorders, joint problems, and therapy-related cancers are observed, especially in patients who received radiation for pretransplant conditioning. Results are best in young patients transplanted with bone marrow from a human leukocyte antigen (HLA)-identical sibling; early transplantation is appropriate in this group. For older patients or those without an HLA-identical related donor, transplants are better reserved for those who fail to respond to immunosuppressive therapy.