Aplastic Anemia in the Context of Hemolytic Paroxysmal Nocturnal Hemoglobinuria: Feasibility of Antibody-Based Intensive Immunosuppression during Eculizumab Treatment

Paroxysmal nocturnal hemoglobinuria (PNH) may present as hemolytic (classical PNH) or aplastic (AA/PNH syndrome) PNH. While classical PNH patients requires anti-complement treatment (eculizumab), the treatment of AA/PNH patients should target their bone marrow failure (BMF) by immunosuppression (IST), or even bone marrow transplantation (BMT). However, in a few patients clinically meaningful AA and hemolysis may be concomitant, eventually justifying both IST and eculizumab. To date there is no standard treatment for this rare condition. Here we investigated the prevalence of this condition based on a large cohort of PNH patients seen at our reference centers at St. Louis Hospital (Paris) and Federico II University (Naples), looking for patients who have received "intensive IST" in combination with eculizumab. Amongst a total of 145 PNH patients seen between 2007 and 2016, we have identified 6 patients who have received intensive IST during eculizumab treatment ; thus, roughly the prevalence of severe BMF associated with hemolysis is around 5%. All the 6 patients have been initially classified as AA/PNH syndrome at time of eculizumab starting, but did not require specific treatment before; they were all on eculizumab treatment at the standard dose of 900 mg fortnightly, with adequate control of intravascular hemolysis. Five of the patients fulfilled the criteria of severe AA, the latter had very severe isolated neutropenia, and was diagnosed with an immune-mediated agranulocytosis. Since no patient had a HLA-matched related donor for BMT, all the patients received intensive IST according to different institutional regimens; eculizumab was not discontinued to minimize the risk of rebound intravascular hemolysis and thrombotic complications. Three patients (2 AA and 1 agranulocytosis) received standard IST with horse-antithymocyte globulin (h-ATG, 40 mg/kg for 4 consecutive days) combined cyclosporine A (CsA). The 3 other AA patients received alemtuzumab (3-10-30-30 mg subcutaneously in 4 consecutive days) and CsA within the prospective trial NCT00895739; one of these patients a few months later also received a second IST course with rabbit-ATG (3.5 mg/kg for 5 consecutive days) and CsA. All the patients completed the scheduled treatment without any side effect, including infusion-related reactions. Lymphocyte depletion was observed in all patients irrespective of sustained therapeutic complement blockade, with lymphocyte count dropping <100/μL in all cases and lasting for several days (or even months in the case of alemtuzumab). All patients remained on eculizumab treatment, even if one AA patient required an increase of the dose up to 1200 mg because of pharmacokinetic breakthrough; in 2 patients 50% hemolytic complement (CH50) was systematically monitored during the treatment course, without showing any significant change from status at pre-IST treatment. All the patients were available for response assessment at 6 months; globally, 3 out of 6 showed a hematological response. The agranulocytosis patient achieved a partial response (PR) requiring G-CSF chronic treatment. Among the 5 AA patients, we observed 2 CR (1 with h-ATG and 1 with alemtuzumab) and 1 PR (after alemtuzumab); this latter was converted into a CR after a second IST course with r-ATG. One of the CR relapsed at 3 years showing clonal evolution toward a myelodysplastic syndrome, and finally died. All the other patients are alive, keeping their hematological response; of the 3 non-responders, 1 was rescued with an unrelated transplantation, and 2 remain on eculizumab treatment (one has developed thromboembolic complications).

This is the first systematic description of the management of severe BMF in PNH patients on anti-complement treatment; we first observed that this rare challenging condition may pertain to about 5% of PNH patients. Then we demonstrated that intensive IST, based on either polyclonal or monoclonal anti-lymphocyte antibodies can be safely delivered even in concomitance of eculizumab. Pharmacological lymphocyte depletion was achieved irrespective of terminal complement inhibition. Clinical efficacy was in the expected range as in broader AA populations, with an overall reponse rate of 50%. Based on these data, intensive IST delivered on top of eculizumab should be considered in PNH patients who develop severe AA during eculizumab treatment lacking a low-risk bone marrow transplant procedure.