Herein, we present an interesting case of a MS patient who, 2 months following Alemtuzumab treatment, displayed neutropenia with essentially no B cells and very low levels of CD4 T cells; there was a predominance of CD8 T and NK cells, while LGL cells predominated in the blood smear examination. The exact mechanism of early neutropenia associated with Alemtuzumab treatment is a challenging issue. In our case of neutropenia, direct toxic effects of Alemtuzumab on neutrophils are unlikely. Consumption of complement constituents was not noted in the peripheral blood tests. The concept of autoimmune neutropenia, previously described in Alemtuzumab-treated MS patients (very rare), would seem an unlikely causative factor in our case, because such a manifestation would require a longer time interval from Alemtuzumab treatment [
7]. Adverse events of Alemtuzumab treatment include infusion-related actions, infections, and secondary autoimmune disorders [
8]. Neutropenia may also occur due to secondary autoimmunity after alemtuzumab [
9]. The risk of developing secondary autoimmunity is greatest in the first 5 years of follow-up (mean time to development was 995 days following first treatment [
9]. So, neutropenia is typically delayed and occurs after immune reconstitution [
9]. The most intriguing feature of the present case concerns the expansion of the LGL cell population in the peripheral blood of this Alemtuzumab-treated MS patient. Immunophenotypic analysis showed that LGL cells are likely to be primarily NK and, to a lesser extent, CD8 T cells. Under healthy conditions, LGLs make up 5% to 15% of peripheral blood. LGL are characterized by elevated cytoplasmic:nuclear ratio and plenty azurophilic granules [
10]. Initially, LGL were categorized in the lineage of natural killer (NK) cells. Nevertheless, it is now well-known that LGL comprise both cytotoxic T lymphocytes (CTL, CD3+) and NK cells (CD3−), both of which belong to the lymphoid lineage and act as principal mediators of cell-mediated cytotoxicity [
10]. Polyclonal expansions of LGL have been observed in healthy elderly and are usually transient, after viral infections such as Epstein–Barr virus and cytomegalovirus, or associated with neoplasms and autoimmune disorders [
11].
We suggest that LGL play an active role in the development of neutropenia in our case. Highly suggestive of the operation of an immune-mediated mechanism for the Alemtuzumab-induced neutropenia is the responsiveness to corticosteroids. A short therapeutic protocol with low doses of prezolon led to a constant rise in neutrophil levels and to the normalization of white blood counts. This effect of corticosteroids was accompanied by a reduction in the levels of LGL in the peripheral blood and this effect was stable for at least of 1 month of close monitoring of our patient. Importantly, we performed immunophenotypic analysis of peripheral blood 1 month after the resolution of neutropenia. The percentage of NK cells remained increased, whereas the percentage of CD3 + CD8+ showed a significant reduction compared to their levels upon neutropenia development (Additional file
1: Table S1). This observation suggests that prednisolone treatment did not affect the survival of NK cells, but led to lympholysis of CD3 + CD8+ T cells and favored in overall the reconstitution of neutrophil numbers. This in turn suggests that such CD3 + CD8+ T cells were the main mediators of the neutropenic effect.
Our finding of neutropenia post-Alemtuzumab therapy in a setting of significant cytotoxic T cell-LGL proliferation is highly reminiscent of the potential role of the expanded LGL population in peripheral blood in the pathogenesis of Rituximab-induced neutropenia [
12]. Late-onset neutropenia (LON) after rituximab was mainly reported in lymphoma-patients and occurred from 1 month up to 1 year after drug initiation. LGL phenotype has been shown to be associated with neutropenia through various mechanisms such as FAS\FAS ligand mediated neutrophil apoptosis, Fas\Fas ligand independent cytokine\chemokine-related myelosuppression and secretion of inflammatory mediators. Other proposed mechanisms include the presence of antineutrophil antibodies and the role of genetic polymorphisms in the immunoglobulin G (IgG) receptor FCγ RIIIA [
13,
14]. An important recent study revealed that 6-months after alemtuzumab treatment CD56bright NK cells were expanded, albeit without alteration in their cytolytic function [
15]. Of note, increased numbers of NK cells have also been observed in Hashimoto thyroiditis, which is considered to be a common autoimmune manifestation following alemtuzumab therapy. The exact mechanisms of autoimmunity following alemtuzumab therapy are not fully understood and immune reconstitution changes in cell repertoire could account for immune reactions against self. In this process, the role of CD56bright NK cells as well as cytotoxic CD8 T cells warrants further investigation.
In our patient, neutropenia was observed in a setting of normal hemoglobin level and platelet count (Additional file
1: Table S1), thus making the possibility of toxic (chemotherapy-related) or other (e.g. viral) underlying factors being responsible for our observations very remote. To our knowledge this if the first study to show the association of Alemtuzumab with LGL proliferation and neutropenia development. The exact triggering mechanism of LGL expansion is elusive until now. The present case indicates that clinicians should be aware of this particular side effect of Alemtuzumab, strongly implying the need of a close laboratory evaluation of patients after drug administration. Taken together, the results reported here challenge the currently published notion that severe Alemtuzumab-related neutropenia in the setting of MS should be treated with G-SCF. Considering the published data of the detrimental effect of G-SCF in MS disease evolution, we suggest prednisolone as an alternative therapeutic option. Therefore, we suggest complete blood count analysis every 15 days during the first 3 months following drug initiation and search for LGL cell expansion if neutropenia evolves. Moreover, we suggest early therapeutic intervention for Alemtuzumab-induced Grade-III neutropenia with low-dose corticosteroids.