ALAIN01—Alemtuzumab in Autoimmune Inflammatory Neurodegeneration

Mechanisms of Action and Neuroprotective Potential

Tobias Ruck; Ali Maisam Afzali; Karl-Friedrich Lukat; Maria Eveslage; Catharina C. Gross; Steffen Pfeuffer; Stefan Bittner; Luisa Klotz; Nico Melzer; Heinz Wiendl; Sven G. Meuth

Disclosures

BMC Neurol. 2016;16(34) 

In This Article

Discussion

Approved for the treatment of active RRMS alemtuzumab has demonstrated a favourable risk-benefit profile under the precautions of an intensive surveillance program. Alemtuzumab leads to a sustained reprogramming of the immune system lasting for at least several years and is associated with considerable adverse events, which necessitate the early recognition for therapy in time. For the best possible risk-benefit ratio deeper insights into the MOA are clearly needed to identify markers for treatment response and adverse event risk.

So far, the mechanism by which alemtuzumab exerts its therapeutic effects in MS is not fully elucidated. Initial clinical trials demonstrated efficiency of alemtuzumab rather in RRMS then SPMS pointing towards effects directed against acute inflammatory processes predominantly driven by adaptive immunity in contrast to neurodegenerative processes partially driven by innate immunity.[40] This is thought to be related to the limited expression of CD52 on innate immune cells leading to resistance to alemtuzumab mediated depletion. A study of Buggins and colleagues (2002) observed a loss of CD52 in tissue-resident human innate immune cells during maturation or differentiation.[41] The relatively unaffected innate immune system as well as the limited immune cell depletion in primary and secondary lymphoid tissues (as observed in humanized CD52 mice[4]) are believed to explain the low incidence of severe or opportunistic infections despite the long-lasting lymphopenia.

Besides quantitative effects, especially the qualitative effects of alemtuzumab reprogramming the immune system might underlie its long-lasting effects. CD4+CD25highCD127low regulatory T cells have been demonstrated to be relatively increased in the CD4+ T cell compartment, although absolute numbers remain low hampering further investigations.[7,8] Significantly increased levels of the immunoregulatory cytokines TGFβ-1 and IL-10 were observed. Furthermore, Th2 cells dominate the CD4+ T cell pool, while pro-inflammatory Th 1 and Th 17 cells are reduced in association with a reduction in IFN-γ, IL-12, IL-17, IL-21, IL-23 and IL-27 serum levels.[42] Jones and colleagues detected an increased expression of the inhibitory receptors PD-1 and LAG-3 on CD4+ T cells.[7] Our study intends to confirm and understand the underlying mechanisms of these findings as well as to expand them. Therefore a detailed immune phenotyping of different immune cell subsets and their properties is planned for the peripheral blood as well as the CSF. There has been no investigation of the CSF compartment so far under alemtuzumab treatment; however this promises deeper insight into the immune processes in the CNS.

The functional properties of T cells will be extensively investigated post alemtuzumab treatment including proliferation, cytokine production as well as immune regulatory and cytotoxic propensity. The spatial and functional changes observed over time will help to understand the reprogramming effects of alemtuzumab. The expression profiles of activating or inhibitory molecules on T cells will be assessed to gain insights into the fundamental alterations in immunological networks. The clonal expansion of autoreactive T cells is believed to be critically involved in the local immune reactions in MS.[43] A restoration of T cell diversity might therefore have beneficial effects to MS disease activity and will be assessed by spectratyping over study time.

Another focus of our study is on the migrational capacity of T cells after alemtuzumab treatment. It is assumed for MS that autoimmune T cells migrate into the CNS after they have been activated in the periphery.[44–46] A study of Havari and colleagues has recently shown that anti-murine CD52 treatment had no effect on the migratory ability of immune cells.[47] However, since results from animal experiments cannot be easily transferred these findings have to be further evaluated in humans. Moreover, CD52 has been shown to play a role in transendothelial migration of T cells through human umbilical vein endothelial cell monolayers.[48]

More uncertainty surrounds the neuroprotective potential of alemtuzumab compared to anti-inflammatory effects. A post hoc subgroup analysis of the CAMMS223 trial demonstrated a significant improvement in EDSS scores even in patients without pre-treatment clinical disease activity (EDSS improvement by 0.31 points, P < 0.005) indicating potential neuroprotective effects of alemtuzumab.[15] In vitro experiments with peripheral blood mononuclear cells of alemtuzumab treated patients produced increased amounts of neurotrophins and were able to prolong survival of murine neurons and oligodendrocytes.[15] However, immune cells producing neurotrophins have not been detected in the CNS of alemtuzumab treated patients so far. Moreover, the short half-lives and the inability to pass the blood-brain-barrier (BBB) of neurotrophins argue against an effect of peripherally detected neurotrophic factors in the CNS.[49] Combining longitudinal clinical (SAD, SRD), MRI (brain atrophy, structural integrity) and experimental (neurotrophins and markers for neurodegeneration in the CSF, impact on neuronal networks in vitro) our study intends to evaluate potential neuroprotective properties of alemtuzumab.

A "two-hit model" of lymphopenia-associated autoimmunity is currently the prevailing hypothesis explaining the occurrence of secondary autoimmunity post alemtuzumab treatment.[50] The "first hit" is supposed to be triggered by the lymphopenia enabling self-antigen responsive T cells to proliferate after escaping depletion.[51,52] Apart from genetic or environmental factors, increased IL-21 levels are proposed as potential "second hit" by increasing T cell cycling consequently enhancing the stochastic probability of self-antigen encounter.[53] Moreover, IL-21 is associated with the induction of Th 17 cells,[54] B cell differentiation, antibody production[55] and inhibition of Treg function[56,57] potentially promoting secondary autoimmune disorders. Therefore, IL-21 has been suggested as a potential biomarker for the risk of secondary autoimmunity by Jones and colleagues,[53] however verification in a large prospective cohort is still missing.[58] Moreover, the original ELISA kit used in the study by Jones and colleagues is not commercially available anymore and currently purchasable options have shown reduced predictive value[58] potentially limiting the conclusions drawn from the IL-21 ELISA in our study. However, with the combination of an in-depth phenotyping and a detailed surveillance of secondary autoimmune responses our study might be able to identify new risk markers.

Besides risk markers, it is a big unmet need to identify reliable markers for treatment response to allow for better therapy guidance. A differential lymphocyte reconstitution, which has been proposed as a potential marker, was not confirmed in subsequent studies.[6,59] The aforementioned analysis of T cell diversity might provide a new opportunity in this matter since a recent report demonstrated differences in the rate and quality of TCR diversity restoration.[7]

We are fully aware that the defined number of patients limits the possibility of definite conclusions; however this is not the focus of our study. Our study is meant as a "nested discovery cohort" for questions related to measuring immune reprogramming, potential neuroprotective mechanisms as well as lymphopenia-associated secondary autoimmunity. The results will pave the way for further investigations with larger cohorts evaluating and validating our findings.

Trial Status

Recruitment on-going.

Comments

3090D553-9492-4563-8681-AD288FA52ACE

processing....