Effects of Immunosuppressive Therapy on Cell Mediated Immunity in Idiopathic Acquired Aplastic Anaemia

Aplastic Anaemia is a clonal haematological disorder characterised by bone marrow hypoplasia and pancytopenia, in the absence of any abnormal cells or increased reticulin. Idiopathic acquired aplastic anaemia accounts for more than 50% cases where immune mediated pathophysiology had been proposed. Altered counts and ratio of CD4+ and CD8+ T cells result in increased apoptosis of haematopoietic stem cells, resulting in bone marrow hypoplasia. Aplastic anaemia is a clonal disorder with clonal evolution to other haematological disorders i.e. hypoplastic myelodysplastic syndrome, Paroxysmal nocturnal haemoglobinuria (PNH) and acute leukemia. Previous studies had reported that >50% cases of aplastic anaemia are transformed into PNH during the course of disease.

Haemopoietic stem cells transplant is the treatment of choice however, this option is either unavailable or un-affordable for majority of people in developing countries including Pakistan. Standard immunosuppressive therapy (IST) includes anti-Thymocyte Globulin (ATG), is also an expensive option and needs extensive monitoring therefore, not a very favourable option for most of the patients. Other immunosuppressive drugs particularly calcineurin inhibitors like Cyclosporine and Tacrolimus, had shown promising results. These drugs act by decreasing the raised counts of CD4+ and CD8+ T cells. Almost all the patients diagnosed with idiopathic acquired aplastic anaemia in Pakistan are treated on these drugs either alone or in combination with other drugs. No study has been conducted so far to evaluate the effects of different immunosuppressive drugs on T cells at different stages and length of treatment. This study was planned to evaluate the effectiveness of these drugs in restoring the immunological imbalance in idiopathic aplastic anaemia.

The counts and ratios of CD4+ and CD8+ T cells were performed on blood samples of 60 patients, using FACSCount system (BD Biosciences). Our study population included patients of Pakistani and Afghan nationalities, both genders and of paediatric and adults age. PNH screening was done by Hams test however, none of the patient was positive. Patients on active treatment were categorized into different groups on the basis of drugs they were receiving i.e. Cyclosporine only, Cyclosporine with Oxymetholone and Tacrolimus groups. Patients who were newly diagnosed and treatment naive at the time of inclusion, were also included along with a group of patients who had completed their treatment and were in remission (either complete or partial).

Findings of our study showed that the disease was more prevalent in males of paediatric and young adult age. CD4+ T cell counts and CD4/CD8 ratios were prominently decreased in paediatric group receiving IST however, no significant difference was noted in counts or ratios in adult patients. CD8+ T cell counts did not show any remarkable reduction with treatment in adult patients but slightly decreased counts were noted in paediatric group. All the patients in different treatment groups showed an overall reduction of CD4+, CD8+ T cell counts and ratios as compared to treatment naive cases. This difference was more pronounced in patients receiving Cyclosporine with Oxymetholone and Tacrolimus. Cyclosporine levels were done and found to be consistent with the dose and treatment status but the therapeutic levels of Tacrolimus were never achieved however, significant improvement was observed even in sub-therapeutic levels. Off-treatment cases had their CD4+, CD8+ T cell counts and ratios within the lower normal range of CD4+, CD8+ T cell counts and CD4/CD8 ratio, suggestive of an alteration in T cell biology with IST, maintaining these counts within normal range for an indefinite period.

Length of treatment has a great impact on the outcome of disease as well as relapse prevention however not studied in detail in aplastic patients treated on immunosuppressive drugs. Results of our study suggests that treatment for more than 6 months followed by slow tapering is more effective in normalizing the counts and ratios of CD4+ and CD8+ T cells. Our study was the first of its kind to evaluate the effects of different immunosuppressive drugs on CD4+ and CD8+ T cell counts and CD4/CD8 ratio, in our population. Further studies are needed to understand the underlying mechanisms responsible for this immunological imbalance as well as response to different treatment options available.