Natural killer cell activity in multiple sclerosis patients treated with recombinant interferon-alpha 2

The Role of Interferon-α in Neurodegenerative Diseases: A Systematic Review

BACKGROUND

Neurodegenerative diseases (NDs) impose significant financial and healthcare burden on populations all over the world. The prevalence and incidence of NDs have been observed to increase dramatically with age. Hence, the number of reported cases is projected to increase in the future, as life spans continues to rise. Despite this, there is limited effective treatment against most NDs. Interferons (IFNs), a family of cytokines, have been suggested as a promising therapeutic target for NDs, particularly IFN-α, which governs various pathological pathways in different NDs.

OBJECTIVE

This systematic review aimed to critically appraise the currently available literature on the pathological role of IFN-α in neurodegeneration/NDs.

METHODS

Three databases, Scopus, PubMed, and Ovid Medline, were utilized for the literature search.

RESULTS

A total of 77 journal articles were selected for critical evaluation, based on the inclusion and exclusion criteria. The studies selected and elucidated in this current systematic review have showed that IFN-α may play a deleterious role in neurodegenerative diseases through its strong association with the inflammatory processes resulting in mainly neurocognitive impairments. IFN-α may be displaying its neurotoxic function via various mechanisms such as abnormal calcium mineralization, activation of STAT1-dependent mechanisms, and increased quinolinic acid production.

CONCLUSION

The exact role IFN-α in these neurodegenerative diseases have yet to be determine due to a lack in more recent evidence, thereby creating a variability in the role of IFN-α. Future investigations should thus be conducted, so that the role played by IFN-α in neurodegenerative diseases could be delineated.

Natural Killer Cells in Multiple Sclerosis: Entering the Stage

Studies investigating the immunopathology of multiple sclerosis (MS) have largely focused on adaptive T and B lymphocytes. However, in recent years there has been an increased interest in the contribution of innate immune cells, amongst which the natural killer (NK) cells. Apart from their canonical role of controlling viral infections, cell stress and malignancies, NK cells are increasingly being recognized for their modulating effect on the adaptive immune system, both in health and autoimmune disease. From different lines of research there is now evidence that NK cells contribute to MS immunopathology. In this review, we provide an overview of studies that have investigated the role of NK cells in the pathogenesis of MS by use of the experimental autoimmune encephalomyelitis (EAE) animal model, MS genetics or through ex vivo and in vitro work into the immunology of MS patients. With the advent of modern hypothesis-free technologies such as single-cell transcriptomics, we are exposing an unexpected NK cell heterogeneity, increasingly blurring the boundaries between adaptive and innate immunity. We conclude that unravelling this heterogeneity, as well as the mechanistic link between innate and adaptive immune cell functions will lay the foundation for the use of NK cells as prognostic tools and therapeutic targets in MS and a myriad of other currently uncurable autoimmune disorders.

CX3CR1-dependent recruitment of mature NK cells into the central nervous system contributes to control autoimmune neuroinflammation

Fractalkine receptor (CX3CR1)-deficient mice develop very severe experimental autoimmune encephalomyelitis (EAE), associated with impaired NK cell recruitment into the CNS. Yet, the precise implications of NK cells in autoimmune neuroinflammation remain elusive. Here, we investigated the pattern of NK cell mobilization and the contribution of CX3CR1 to NK cell dynamics in the EAE. We show that in both wild-type and CX3CR1-deficient EAE mice, NK cells are mobilized from the periphery and accumulate in the inflamed CNS. However, in CX3CR1-deficient mice, the infiltrated NK cells displayed an immature phenotype contrasting with the mature infiltrates in WT mice. This shift in the immature/mature CNS ratio contributes to EAE exacerbation in CX3CR1-deficient mice, since transfer of mature WT NK cells prior to immunization exerted a protective effect and normalized the CNS NK cell ratio. Moreover, mature CD11b(+) NK cells show higher degranulation in the presence of autoreactive 2D2 transgenic CD4(+) T cells and kill these autoreactive cells more efficiently than the immature CD11b(-) fraction. Together, these data suggest a protective role of mature NK cells in EAE, possibly through direct modulation of T cells inside the CNS, and demonstrate that mature and immature NK cells are recruited into the CNS by distinct chemotactic signals.

Mitoxantrone induces natural killer cell maturation in patients with secondary progressive multiple sclerosis

Mitoxantrone is one of the few drugs approved for the treatment of progressive multiple sclerosis (MS). However, the prolonged use of this potent immunosuppressive agent is limited by the appearance of severe side effects. Apart from its general cytotoxic effect, the mode of action of mitoxantrone on the immune system is poorly understood. Thus, to develop safe therapeutic approaches for patients with progressive MS, it is essential to elucidate how mitoxantrone exerts it benefits. Accordingly, we initiated a prospective single-arm open-label study with 19 secondary progressive MS patients. We investigated long-term effects of mitoxantrone on patient peripheral immune subsets using flow cytometry. While we corroborate that mitoxantrone persistently suppresses B cells in vivo, we show for the first time that treatment led to an enrichment of neutrophils and immunomodulatory CD8^low T cells. Moreover, sustained mitoxantrone applications promoted not only persistent NK cell enrichment but also NK cell maturation. Importantly, this mitoxantrone-induced NK cell maturation was seen only in patients that showed a clinical response to treatment. Our data emphasize the complex immunomodulatory role of mitoxantrone, which may account for its benefit in MS. In particular, these results highlight the contribution of NK cells to mitoxantrone efficacy in progressive MS.

The role of natural killer cells in curbing neuroinflammation

Natural killer (NK) cells are evolutionarily early lymphocytes that lack antigen-specific receptors and, hence, are considered to be part of the innate immune system. The majority of research on NK cells has focused on their ability to lyse "target cells", generally identified by low or absent MHC Class I expression, such as tumor cells and virus infected cells. However, an alternative role of these leukocytes as regulators of adaptive (and potentially destructive) immune responses, in particular organ-specific autoimmune diseases, has been increasingly recognized. Here we discuss the growing body of evidence that NK cells limit damage in autoimmune demyelinating disease by inhibiting autoreactive T cell responses without harming resident neurons or glia.

Frequency of blood CX3CR1-positive natural killer cells correlates with disease activity in multiple sclerosis patients

Multiple sclerosis (MS) is an autoimmune disease of the central nervous system (CNS) characterized by enormous variability in its clinical presentation and course, and for which clear diagnostic parameters are lacking. Here we performed an RNA screen in peripheral mononuclear cells from relapsing-remitting (RR) and primary progressive (PP) MS patients compared with healthy donors (HD) that indicated, among other findings, a role for the chemokine receptor CX3CR1 as a diagnostic marker. Gene expression and flow cytometric analyses demonstrated a significantly lower expression of CX3CR1 in MS patients compared with healthy individuals. The subpopulation of cells responsible for causing this reduced expression of CX3CR1 consisted exclusively of natural killer (NK) cells. Importantly, we found a correlation between disease activity and frequency of CX3CR1-positive NK cells in RRMS patients. These findings emphasize the role of NK cells in the development and course of MS and provide evidence for CX3CR1 expression as a marker for MS patients and disease activity.

Clinical relapses of multiple sclerosis are associated with 'novel' valleys in natural killer cell functional activity

Natural killer (NK) cells are implicated in the pathogenesis of multiple sclerosis (MS). Nine relapsing-remitting MS (RRMS) patients along with age, sex, and NK responder status matched controls were studied serially. Although the average NK cell functional activity (FA) was not significantly different between both groups, four clinical relapses in RRMS patients were associated with the development of 'novel' valleys in FA. These valleys are of greater depth and duration than cyclical valleys observed in both RRMS and controls, precede the onset of clinical attacks, and are observed in RRMS but not controls. In both RRMS and controls, cyclical peaks and valleys in FA are determined by the number of CD33+, CD3-CD56+, and to a lesser extent CD3+CD56+ cells capable of binding targets and inducing cell-mediated cytotoxicity (CMC). In contrast, 'novel' valleys in FA result from a reduction in the ability of CD3-CD56+ bound to targets to induce CMC. The results suggest that RRMS patients are at greater risk for clinical relapses during 'novel' valleys in FA. Furthermore, these valleys are the result of cells with a NK cell phenotype being unable to deliver a 'lethal' hit to targets.

A role for natural killer cells in the immunopathogenesis of multiple sclerosis

Seventeen relapsing-remitting (R/R) multiple sclerosis (MS) patients and age/sex matched controls were studied every 6 weeks for 2 years. Disease activity, determined both clinically and by serial MRI, was correlated with natural killer (NK) cell functional activity (FA) and phenotype. Mean NK cell FA is significantly lower in MS patients, compared to controls (P < 0.001), while variability around the means is significantly greater (P < 0.01). The spectrum of mean NK cell FA, observed in the patient cohort, along with cyclical nature of the FA and phenotype over time, observed in both patients and controls, may begin to explain the discrepant results reported in previous studies. In R/R MS, there is a significant correlation between reductions (valleys) in NK cell FA and the development of active lesions on MRI, new (P < 0.001) or enlarging (P = 0.05). More importantly, a significant number of active lesions, new (P = 0.01) and enlarging (P = 0.02), are preceded by a reduction in NK cell FA. The correlation between the onset of clinical attacks and valleys of NK cell FA is also significant (P = 0.002). When taken together, the results suggest that reductions (valleys) in NK cell FA represent periods of susceptibility for the development of active lesions on MRI and clinical attacks. A significant positive correlation is also identified between mean NK cell FA for each R/R MS patient and total number of active MRI lesions developed by that patient over the 2 years (P = 0.001). The results would suggest that R/R MS patients with a higher mean NK cell FA are at greater risk for the development of active lesions. These results support the proposal that NK cells may play a role in the immunopathogenesis of R/R MS.

Pharmacodynamics of recombinant IFN-beta during long-term treatment of malignant melanoma

The pharmacodynamics and biologic activities of recombinant human interferon-beta (rHuIFN-beta) derived from chinese hamster ovary (CHO) cells were examined during long-term therapy in 7 melanoma patients. The CHO-derived rHuIFN-beta was given s.c. in a dose of 3 x 10(6) U three times per week for 24 weeks. Serum levels of IFN could not be detected before and 48 h after the s.c. injections. 2'-5'-Oligoadenylate synthetase (2-5 OAS), beta 2-microglobulin, and neopterin levels increased significantly 48 h after application, with a maximum after 96 h. Subsequently, the values decreased and remained only slightly elevated during the long-term therapy. Natural killer (NK) cell activity increased in the first 96 h significantly and fell below pretreatment values after 4 weeks. The decrease of biologic response could not be attributed to the occurrence of anti-IFN-beta antibodies because only 2 of the 7 patients developed neutralizing antibodies after 16 and 24 weeks of treatment, respectively. This trial confirms the biologic potency of CHO-derived rHuIFN-beta. However, the selected parameters demonstrate that immunostimulation is only possible over a short treatment period.

Circulating natural killer cells but not cytotoxic T lymphocytes are reduced in patients with active relapsing multiple sclerosis and little clinical disability as compared to controls

Triple antibody flow cytometry was used to compare the populations of CD56+ effector cells in the peripheral circulation of 29 patients with relapsing multiple sclerosis (MS) and little disability who were exacerbation-free for over 2 months and 29 healthy control subjects. Populations were characterized by two panels of antibodies (CD8, CD16, CD56 and CD3, CD8, CD56), as well as by size or granularity. In the MS patients, mature natural killer (NK) cells (CD3-CD8-CD56+) of small size and low granularity were significantly reduced compared to normals (P(0.0003). The quantities of other effector cells (cytotoxic T lymphocytes, large granular lymphocytes and monocytes) were not different in MS patients compared to the control subjects. Also, we identified a previously unrecognized population of CD56+ monocytes (CD3-CD14+CD56+) in both the normal control subjects and the MS patients which would have been misclassified as NK cells using one or two antibody cytometry employed in previous studies.

Cytolysis of oligodendrocytes is mediated by killer (K) cells but not by natural killer (NK) cells

The cytotoxic activity of killer (K) cells against enriched cultures of bovine oligodendrocytes (BOL) was investigated in multiple sclerosis (MS) and controls. Human K cells mediated cytotoxicity to primary cultures of BOL in the presence of anti-BOL antiserum in all study groups, while BOL were resistant to human natural killer (NK) cells. Cytotoxic activity was significantly reduced in MS when compared to age-matched normal controls but not when compared to other neurologic disease (OND) patients. K cell-mediated lysis of BOL could also be induced with anti-galactocerebroside antibody but not with other antibodies including those specific for OL antigens (myelin basic protein, proteolipid apoprotein, and 2',3'-cyclic nucleotide 3'-phosphodiesterase). Enrichment of the effector population indicated that antibody-dependent cell-mediated cytotoxicity (ADCC) to BOL was mediated by large granular lymphocytes, and the effector population was further characterized by flow cytometry. The effector cells mediating ADCC could be inhibited by protein A of Staphylococcus aureus, and by K562 cells in cold competition assay. These observations indicate that oligodendrocytes are resistant to NK cells but are susceptible to cytolysis mediated by K cells. This may represent a potentially important immune mechanism in the pathogenesis of MS.

Natural killer cells and autoimmunity

In various autoimmune diseases it appears that NK activity is impaired, and that this phenomenon is significant in disease development. Impairment of NK activity may be the result of two different mechanisms. In systemic autoimmune diseases, in which various target organs are involved (nonorgan-specific), the peripheral blood NK level is generally lower than normal. This most likely allows the expression of autoimmune phenomena such as B cell hyperactivity and polyclonal antibody production, as is seen in SLE, due to a defect in the termination of the immune response. In autoimmune diseases with more localized, organ-specific lesions one can detect increased NK activity at the target organ itself. In these instances, the cytotoxic characteristic of the NK cell is more prominent. This theory explains why both increased and decreased NK activity may be observed in autoimmune diseases. In some disorders in which decreased NK activity was suspected of being crucial, immunomodulators, known to increase NK activity, were administered. Yet it is still difficult to separate the NK activity from the effect of the remaining immune system.

Immunosuppressive effects of recombinant interferon-alpha during long-term treatment of cancer patients

Interferons (IFN) are known to modulate immune responses in an either stimulatory or inhibitory manner. Most of the knowledge about immunomodulatory activities of IFN comes from investigations of IFN effects on cells in vitro. This study examines the influence which long-term treatment with recombinant interferon-alpha 2 exerts on immune functions in cancer patients. Serial in vitro immune function studies of peripheral blood mononuclear cells were done to determine parameters of B-cell and T-cell functions as well as natural killer (NK)-cell activity. The authors detected profound suppression of in vitro immunoglobulin synthesis and lymphocyte proliferation as well as depression of NK-cell activity during IFN treatment. All suppressed immune functions normalized on discontinuation of IFN therapy. The authors conclude from these observations that, apart from their beneficial effects, IFN produce substantial immunosuppression.

Natural killer (NK) cells in chronic progressive multiple sclerosis patients treated with lymphoblastoid interferon

Natural killer (NK) cell functional activity, as defined by the lysis of 51Cr-labelled K-562 cells, and number, defined phenotypically by anti-Leu-11, are significantly decreased in chronic progressive multiple sclerosis (MS) when compared to normal controls. When age- and sex-matched populations are compared, NK cell functional activity is again significantly reduced in MS compared to controls but not when compared to a control group of other medical disease (OMD). The MS group could be differentiated from the OMD group, however, when results of NK cell functional activity are combined with NK cell phenotype. With the administration of lymphoblastoid interferon daily for 6 months, NK cell activity increased significantly at 48 h and at 1 week. By 1 month, activity decreased to a level slightly above placebo treatment values. The results likely reflect interferon's enhancement of mature NK cell activity combined with a variable effect on recruitment of pre-NK cells.

The placebo effect during a double blind trial of recombinant alpha 2 interferon in multiple sclerosis patients: immunological and clinical findings

A double-blind, placebo controlled trial of recombinant alpha 2 interferon in relapsing/remitting multiple sclerosis patients was performed to assess the clinical and immunological responses to treatment. This study demonstrated that natural killer (NK) cell activity, known to be enhanced by interferon (IFN) treatment, increased during the first week of treatment in both the IFN and placebo treatment groups. After the first week of treatment NK cell activity returned to baseline levels in both groups, and subsequently declined in the IFN treatment group. Patients in both groups improved clinically, as evidenced by a reduction in the exacerbation rate. Furthermore, a similar incidence of adverse reactions to treatment were reported by both groups. The mechanism underlying the response to placebo is not known. However, it is unlikely that the long term clinical improvement (one year) in either group is related to the transient increase in NK cell activity.

Modulation of immune functions by long-term treatment with recombinant interferon-alpha 2 in a patient with hairy-cell leukemia

Serial in vitro immune function studies of peripheral blood mononuclear cells (PBMC) were carried out during the long-term treatment with recombinant interferon-alpha 2 (IFN-alpha 2) in a patient with hairy-cell leukemia (HCL). Parameters of B- and T-cell functions as well as NK-cell activity were determined. Treatment with IFN-alpha 2 is associated with temporary and long-term depression of some immune functions, but can also normalize immune responses: in vitro-induced immunoglobulin synthesis, which was normal at diagnosis, was inhibited during the first weeks of IFN therapy but subsequently rose to normal levels. Lymphocyte proliferative responses to mitogens and antigens that were markedly reduced pretherapeutically were further depressed by IFN treatment but, with the exception of pokeweed mitogen (PWM)-induced responses, normalized completely by the 15th to 17th week of treatment. Cocultivation of PBMC with monocytes from normal individuals enhanced depressed lymphocyte proliferative responses. NK-cell activity, which was low at diagnosis, did not rise to the normal range during IFN treatment, but rapidly normalized when IFN therapy was stopped. A discussion is presented on the implications of the alteration of immune functions by treatment with IFN.

The effects of long-term administration of recombinant alpha-2 interferon on lymphocyte subsets, proliferation, and suppressor cell function in multiple sclerosis

The immunological effects of long-term treatment with recombinant alpha-2 interferon (rIFN-alpha 2) were investigated in multiple sclerosis (MS) patients treated with 2 X 10(6) units of IFN or a placebo three times per week for one year. A mild lymphopenia was observed in IFN patients who also showed a decrease in the absolute number of total T cells in the blood (OKT3 binding cells); however, the percentage of cells reacting with OKT3, OKT4, and OKT8 antibodies did not change significantly during the study. The percentage of cells reacting with the Leu-7 antibody, which recognizes NK cells, was unchanged. During MS exacerbations, placebo patients showed a tendency for decreased levels of OKT3 and OKT8 cells. In contrast, IFN patients did not demonstrate a decrease in either OKT3 or OKT8 cells during disease attacks. Concanavalin A (ConA)-induced suppressor cell activity was depressed in both IFN and placebo-treated patients during attacks. Lymphoproliferative responses to phytohemagglutinin, pokeweed mitogen, and ConA were unchanged. These studies demonstrate that long-term treatment with rIFN-alpha 2 induces a generalized T-cell lymphopenia, but at this dose does not significantly affect the profiles of T-cell subsets and suppressor cell function in MS patients.