INTRODUCTION
Although many people consider CD4, Th17 cells as central effectors in
autoimmunity, response to therapy has indicated that B-cell-depleting
drugs exhibit high-efficacy in autoimmune and neuroimmunological
diseases [1-3]. As such, not only are CD20-depleting agents approved
for B-cell-related cancers, but they are increasingly being used on- and
off-label in autoimmune diseases [1,4]. Ocrelizumab has recently
been licensed for the treatment of multiple sclerosis (MS) and
antibodies including ofatumumab and ublituximab are in development for
MS [5-7]. In addition, rituximab, which is approved for rheumatoid
arthritis (RA) and pemphigus vulgaris, is frequently used off-label in
MS, neuromyelitis optica spectrum disorders (NMOSD), and a variety of
other autoimmunities [1, 3, 5, 8]. Such off-label use provides
valuable insights into the biology of CD20-depleting therapy [3]. As
such, cells within the memory B-cell subsets appear to be important
targets for disease control and their depletion and slow-repopulation
may, in part, account for the long-term, disease control seen from
short-term treatment cycles with alemtuzumab, cladribine, ocrelizumab
and rituximab [2, 3, 9, 10]. As such, using rituximab to deplete
repopulating memory B-cell when they reach pre-defined levels can
maintain clinical remission, whilst reducing the frequency of infusions
in: RA, NMO, MS and other conditions [3, 11-13]. Translating this
knowledge may help improve the benefit: risk balance of ocrelizumab
[9]. This is currently, highly relevant as repeated 6-monthly CD20
depletion is associated with IgM and then IgA and IgG
hypogammaglobulinaemia in some individuals and also a small, but
increased risk of severe infections [14-16].
Immunological issues of COVID-19. The severe acute respiratory
syndrome coronavirus 2 (SARS-CoV-2), causing coronavirus disease 2019
(COVID-19) has killed hundreds of thousands of humans in a global
pandemic [17]. Severe COVID-19 is often associated with lymphopaenia
[18], initially causing great concern over the use of
immunosuppressive agents. In some cases, this led to the cessation or
delay of treatment of autoimmunity 19, 20]. However, it is
increasingly evident that lymphopaenia is a consequence rather than a
cause of infection [20, 21]. Whilst the immune system eliminates
SARS-CoV-2 in most individuals (Figure 1), viral escape, immune
exhaustion and elevated cytokine release can lead to hyper-activation of
the innate immune response, vascular damage and hyper-coagulation
(Figure 1), which can lead to significant morbidity, acute respiratory
distress, multi-organ failure and, in some cases, death [17,18 22].
Whilst immunotherapy may have some value in treating severe COVID-19
[23], the development of a SARS-CoV-2 vaccine is considered to be
important for protecting the uninfected [24]. A vaccination
programme should help create herd-immunity against the COVID-19 virus
[25]. Therefore, not only is it relevant to determine how disease
modifying treatments (DMT) influence susceptibility to infection and
length of the carrier state, it is also important to consider how DMT
may influence immunity to reinfection and potential vaccine responses
[20].
Surprisingly, there is limited, published data concerning the influence
of ocrelizumab on immune subsets, vaccine responses, durability of
response and the safety of extending infusion intervals. This prompted
us to report data available within the public domain that addressed some
of these safety concerns [9]. These data indicate that delaying
ocrelizumab [9] and rituximab [10, 26] re-infusion should be
associated with minor risk of MS reactivation, based on B-cell subset
depletion and re-population kinetics [9].
CD20-B-cell depleting agents do not markedly expose people to
life-threatening COVID-19. Based on previous understanding of the
immune response to SARS-CoV and SARS-CoV-2, animal studies of the
elimination of coronaviruses, informative COVID-19 case reports and
preliminary reports of COVID-19 pathology [20, 27-29], the biology
of MS, MS-treatments, and COVID-19 suggested that halting treatment may
cause more harm than good, through ineffective disease control [20,
30]. This suggested that a more pragmatic approach, supported by
others in the field of MS and other conditions may be of value [9, 31,
32]. It appears that the innate immune response, and perhaps later
anti-viral CD8 T-cell responses, could eliminate the SARS-CoV2, before
significant antibody responses had developed [20, 28, 33] (Figure
1). This suggested that most MS treatments that largely exhibit limited
persistent effects on the innate immune and CD8 T-cell responses, would
have limited influence on COVID-19. As such, SARS-CoV-2 is eliminated by
the majority of people with MS and other autoimmunities on
immunotherapies, without significant consequences [34-52] (Table 1).
Anti-viral antibodies, notably those targeting the receptor binding
domain of the viral-spike protein clearly neutralize the virus
[53,54] and can contribute to the elimination of the primary
SARS-CoV-2 infection in humans [55,56]. However, B-cells do not
appear to be an absolute requirement for recovery. This is shown by the
recovery of people genetically lacking B-cells, such as with X-linked
hypogammaglobulinemia [57, 58] and is reinforced by the finding that
the vast majority of people treated with CD20 B-cell depleting agents in
MS recover from COVID-19 [36-52](Table 1). Furthermore, B-cell
depletion is unlikely to influence, or be significantly influenced by,
the vascular pathology and hyper-coagulopathy that are major
pathological features in COVID-19 that contribute to the acute
respiratory distress syndrome, cardiovascular, cerebrovascular and other
non-pulmonary morbidities [9, 20, 22, 59, 60] (Figure 1).
Importantly, it provides another rationale why immunosuppressive
treatments in MS and other autoimmunities [44, 61, 62] have not
noticeably influenced COVID-19 susceptibility and prognosis. As such,
people with MS appear to respond to SARS-CoV-2 in a similar way to the
general population, where severe disease is notably influenced by age
and comorbidities, such as diabetes and obesity [18, 43, 44, 62].
Whilst this information is further consolidated by biology and the
clinical evidence (Table 1), it may focus attention away from issues of
being infected with SARS-CoV-2 [20], to methods of avoiding
SARS-CoV-2 infection in uninfected individuals discussed below.
Ocrelizumab is the only DMT that is licenced across the spectrum of
primary-progressive and relapsing MS [5]. In comparison to other
high efficacy DMT used in MS, it has limited monitoring requirements,
fewer restrictions on usage compared to cladribine and alemtuzumab and
off-label alternatives are widely used and pharmacovigilance reports
have been released [8, 40, 63]. Therefore, it is perhaps not
surprising that there is currently more information about the influence
of CD20-depletion and COVID-19 disease outcome than for other
high-efficacy DMT in MS [49,44] (Table 1). This is consistent with,
albeit limited, information in people with rheumatic diseases [62,
64] indicating that people generally recover, whilst the few reported
deaths may be linked to co-morbidities [44]. The suggestion that
rituximab treatment may increase risk of infection should be considered
in the context of possible sampling biases, though could be supported by
data reported in social media from Sweden [40, 52] (Table 1). It is
evident that both rituximab and ocrelizumab cause IgM
hypogammaglobulinaemia in some people within a few treatment cycles and
this and IgA and IgG hypogammaglobulinaemia increases with repeated
infusions, potentially contributing to infection [9, 14-16]. A
delayed IgM response to SARS-CoV-2, which usually appears a few days
after symptom onset, may contribute to disease severity [65, 66].
With time, CD20-depletion is also associated with reduced IgA responses
[15] and likewise early IgA responses may also be important for
efficient clearance of SARS-CoV-2 [15, 67, 68]. However, as yet
there is no compelling evidence that CD20-depletion increases severity
of COVID-19 compared to the general population [40, 41], although in
people with genetically dysfunctional B-cells, this has been suggested
[58]. In addition, hypogammaglobulinemia may inhibit SARS-CoV-2
cross-reactive, protective-antibodies generated from immunity from
previous coronavirus infection, which has been shown at the T and B-cell
level [69, 70], and seen previously with SARS and common
cold-causing coronaviruses [71]. In contrast, it has been questioned
whether benefit may be imparted [37, 43], since B-cell depletion
could lead to limited antibody-mediated enhancement of macrophage
activity and complement-mediated damage and antibody levels have been
associated with severe COVID-19 [67, 72, 73]. Although some people
seroconvert and generate an anti-SARS-CoV-2 response, this is expected
to be, and sometimes is, blunted or absent due to the inhibition of
antibody responses by anti-CD20 B-cell depletion [39, 50]. The
antibody titre required for protection against SARS-CoV-2 and the
quality and the neutralizing potential of the antibody response after
CD20-depletion are currently unknown [39, 50]. However, even in
non-immunosuppressed, notably asymptomatic cases that produce low titre
antibody responses, many people do not produce a marked or long-lasting
neutralizing antibody response [74-76]. Perhaps, benefit may be
achieved by vaccination to boost immunity.
Infection of SARS-CoV-2 infection induces immunity. Although
there is much hope for the impact of vaccination on generating immunity
to SARS-CoV-2, there is no guarantee of protection or
prolonged-protection [24, 76]. Repeated infection is observed with
other endemic human coronaviruses that cause common colds suggesting
that recurrent reinfections may also occur with SARS-CoV-2 [77].
This strongly supports the contribution of macrophages in viral control
and the limited and transient induction of adaptive immunity [77].
Possible re-infection with SARS-Cov-2 has also been suggested by the
finding of positive, polymerase chain reaction (PCR) detected SARS-CoV-2
nucleic acid, swabs after a number of negative swabs [78]. However,
it is clear that this may be due to non-infective viral particles or
artefacts created by sampling location and the testing systems used. As
such PCR-positive swabs can be found in faeces long after loss of
nasopharyngeal positive PCR findings indicating that the virus may
persist for some time and that the PCR test detects fragments of the
viral nucleic acid and not necessarily infective virus [79, 80].
Importantly, contact tracing of hundreds of people with positive tests
after previous negative tests and hospital discharge, failed to detect
any evidence of the production of infective virus and subsequent viral
spread to contacts [80]. Importantly, animal model studies show that
immunity to SARS-COV-2 develops after primary infection that can rapidly
eliminate the virus on re-exposure (28, 29, 81]. This can be
stimulated via vaccination in animals and in humans, to generate
neutralizing antibodies [82, 83]. In most cases, but not always,
neutralizing antibodies persist for a number of months [75,76] and
following SARS coronavirus infection, SARS-CoV-specific antibodies were
detectable for a year or two before they disappeared [84], probably
due to lack of antigenic-stimulation following elimination of the virus.
However, as new responses will be generated from CD20+ naïve B-cells,
these responses would be anticipated to be blunted by B-cell depleting
agents.
CD20 antibodies inhibit vaccine responses . It has been shown
that rituximab depletes naïve B-cells in the blood, lymphoid tissue and
to some extent the bone marrow and can also disrupt germinal centre
formation in secondary lymphoid tissues (3, 85, 86]. Though the
influence of ocrelizumab on B-cell subsets and vaccine responses have
not been published, trial (NCT02545868) data has been reported in
meetings and adopted in the Summary of Product Characteristics produced
as part of the regulatory label [63, 87]. Importantly, the data has
been deposited on a trial registration site (www.clinicaltrials.gov)
allowing data extraction, as shown here (Figure 2). It is evident that
there is a lower frequency of seroconversion and reduced titre to:
23-valent pneumococcal polysaccharide vaccine (23-PPV) (Figure 2A,B)
with or without a booster vaccine (Figure 2C), keyhole limpet
haemocyanin (KLH) neoantigen (Figure 2D), tetanus toxoid vaccine (Figure
2E,F) and seasonal influenza vaccines (Figure 2G-I). The percentage of
people with MS who gave a positive response (Titre ≥ 0.2IU/mL or 4 fold
increase in titre is baseline levels ≥ 0.1IU) to tetanus vaccine 8 weeks
after vaccination was 23.9% in the ocrelizumab group compared to 54.5%
in the control group (no DMT except interferon-beta). The geometric mean
anti-tetanus toxoid specific antibody titres at 8 weeks were 3.74 and
9.81 IU/ml, respectively. Although these vaccine booster responses to
tetanus toxoid were clearly blunted (Figure 2C), the titres were
generally above protective levels (0.16IU/mL) [88], even at
baseline. The percentage of people with MS on ocrelizumab with
seroprotective titres against five influenza strains ranged from
20.0−60.0% and 16.7−43.8% pre-vaccination and at 4 weeks
post-vaccination from 55.6−80.0% in people treated with ocrelizumab and
75.0−97.0% in the control group, respectively (Figure 2G). However,
haemaggulination inhibition titres were reduced (Figure 2H). Likewise,
whilst there was a positive response to ≥ 5 serotypes in polyvalent
pneumococcal vaccine (23-PPV) at 4 weeks after vaccination (71.6% in
the ocrelizumab group and 100% in the control group), the frequency of
seroconversion and antibody titres were however, markedly reduced
(Figure 2A). Furthermore, a booster of the 13-PPV vaccine administered 4
weeks later did not markedly enhance the response to 12 serotypes in
common with 23-PPV (Figure 2C), further indicating the blunting of the
vaccine responses. This was also seen using KLH (Figure 2D). It is
likely that this would be reduced further following repeated infusion of
ocrelizumab, as hypogammaglobulinaemia, notably of within IgM production
develops and increases whilst IgG hypogammaglobulinaemia develops over a
longer time frame (9, 15].
The relatively poor vaccine response in people treated with ocrelizumab
was predictable and consistent with that seen following vaccination in
people treated with rituximab, suggesting that this is an issue for all
classes of anti-CD20 antibodies used in the treatment of cancer and
autoimmune diseases. There was a reduced titre and seroconversion rate
(37.5% vs 75.0% healthy controls) of people with NMOSD following
vaccination against influenza (H1N1) virus 3-5 week after treatment with
rituximab [89]. Furthermore, vaccine responses toStreptococcus pneumoniae and influenza were still impaired in
people with idiopathic thrombocytopenia and RA six months after
treatment [90, 91]. This conclusion was also supported by studies in
RA following treatment with rituximab, with a more markedly blunted
seroconversion and titre when vaccinated during periods of peripheral
B-cell depletion with influenza [92], hepatitis B vaccines [93],
PPV-23, KLH [90] and a greater, but still blunted vaccine response
6-10 months after infusion [92]. However, despite a relative lack of
memory B-cells, CD19-repopulated individuals could mount a robust recall
response, as shown in people with pemphigus vulgaris [94]. This
suggests that it is possible to create a time-window to vaccinate an
individual due to the differential kinetics of repopulation with
pathogenic memory B-cells and naïve B-cells that will allow immunity to
new infections [3, 95, 96]. In addition, ocrelizumab does not appear
to impair pre-existing humoral immunity [97]. This suggests that
people with MS who receive the SARS-CoV-2 vaccine if and when it becomes
available will be able to start treatment with ocrelizumab without
risking vaccine-acquired immunity. However, the effect of
ocrelizumab-induced hypogammaglobulinaemia on the levels of protection
from prior immunisations is unknown and warrants further investigation.
Repopulation kinetics of ocrelizumab . If COVID-19-related
vaccine responses become a key concern among people with MS, or other
autoimmune diseases, choosing treatment options, the selection of
B-cell-depleting agents that allow quick repopulation of B-cells may be
relevant for optimum vaccine-readiness. Continuous B-cell depletion with
ocrelizumab and rituximab will clearly limit naïve B-cell repopulation,
however memory B-cell depletion persists for a significant time after
depletion with rituximab and alemtuzumab, consistent with the
slow-repopulation of this subset [95, 96, 98, 99]. This suggests a
possibility for extended interval dosing or dosing interruption to allow
immature B-cells to recover to facilitate vaccination, whilst
maintaining low levels of pathogenic memory B-cells. Data suggests that
this is feasible, at least with rituximab [94]. The timing required
for this to occur for ocrelizumab is likely to be substantially longer.
Repletion with rituximab occurs within about 6 months of treatment and
is completed within 12 months due to repopulation of the immature/mature
(naïve) B-cell pool [26, 95]. Monthly subcutaneous treatment with
ofatumumab takes a median of 49 weeks (Range 14-102 weeks) for CD19
B-cell repletion after six 60 mg cycles of treatment and immature
(CD19+,CD38+, CD10+) cells repopulate quickly [100]. This may have
some merits for ofatumumab if the rapid repopulation of B-cells can be
confirmed with more prolonged usage, once ofatumumab is licenced to
treat MS. Repopulation of B-cells subsets following ocrelizumab has not
been reported previously, but we report here, the influence of
ocrelizumab on B-cell subsets from the phase II open label extension
study (Figure 3A&B) [101]. It was found that CD4 and CD8 T-cell
numbers were relatively unaffected (Figure 3A&B), even during active
treatment (Figure 3B). CD19 B-cells subsets, including memory (CD19+,
CD27+, CD38low) B-cells are completely depleted during
active treatment (Figure 3B). Even following cessation of treatment
CD19+ B-cells remain low for 6-12 months after the last infusion (Figure
3A). It is evident, however, that the memory B-cell pool remained
depleted for much longer, at least 18 months (Figure 3A & B) and
probably even longer in many individuals [101]. This is consistent
with the durability of relapse inhibition and adds further support that
cells within this subset are important in MS disease pathogenesis [2,
9]. However, there appeared to be some recovery of the naïve (CD19+,
CD21, IgD+, IgM+) B-cell pool during this time (Figure 3A), suggesting
potential to generate new antibody responses, which may be crucial to
mount an immune response during infections and vaccinations. As found
with rituximab, naïve/mature B-cell repopulation will coincide with CD19
repopulation [26, 95] and would take a median 62-72 weeks after
three (95% confidence interval 59.7-73.0 weeks, n=51) or four cycles
(95% confidence interval 59.1-85.4. Range 27-175 weeks, n=51),
respectively [101]. Such levels would require monitoring as there is
marked variability in repopulation kinetics between individuals, and is
in part a product of the ocrelizumab fixed-dosing schedule, as it is
clear that the intensity of B-cell depletion and repopulation speed
relates to the body mass index of the individual [102, 103]. This
suggests that dose-adjustment for weight may have some benefit, as
currently used in the treatment of people with MS with oral cladribine
[104]. Cladribine can be considered to be a chemical-CD19 depleting
agent that markedly depletes memory B-cells, whilst generally
maintaining T-cells within the lower limit of normal. The compound is
rapidly eliminated allowing CD19, naïve B-cells to recover within a
median of 30 weeks after treatment [104-106]. Alemtuzumab is
administered at a low dose (36-60mg) per cycle, compared to ocrelizumab
(600mg) and rituximab (500-1000mg), and has a relatively short half-life
compared to ocrelizumab [107]. Alemtuzumab markedly depletes T-cells
and memory B-cells, but naïve B-cells rapidly repopulate [96, 99]
and vaccine-related antibody responses can be induced within 6 months of
infusion [108]. This further supports the concept of a “window for
vaccination” for CD20-depleting antibodies.
However, whilst B-cell responses to a variety of different vaccines are
clearly inhibited by CD20-depletion, despite some inhibition of CD20
T-cells [95, 109], at least inactivated herpes zoster vaccine can
induce T-cells responses [110]. This may be relevant if the CD8
T-cell response is a vital part of the coronavirus specific immunity, as
reported for SARS-CoV [27, 111]. This feature may reduce concern
about the limited antibody responses that may be generated following
administration of a SARS-CoV-2 vaccine. Although adenoviral vaccines
have shown some value in generating neutralizing antibodies and
cytopathic T-cells in early human studies [83], live and attenuated
viruses are contraindicated in immunosuppressed people [63]. It
remains to be seen if SARS-CoV-2 DNA-RNA vaccines [24], will be
useful in people taking immunosuppressive agents. However, it is
important that people with autoimmunity continue to be offered the
benefit that high–efficacy immunotherapy can provide. With time,
further knowledge will emerge that may help guide treatment selection
within the COVID-19 and post-COVID-19 era.
Funding : This received study received no funding.
Acknowledgements. The authors thank Roche and
clinicaltrialsdata.request.com for providing access to the clinical
trial data.
Declarations: DB, MM, KS and GG have received compensation for
either consultancies and presentations and advisory board activities
from Genentech/Roche. However, Roche/Genentech were not involved in the
decision to write and submit this manuscript. SA, CAKK, GP, ASK and SR
have nothing to disclose. DB has received compensation for activities
related to Canbex therapeutics, InMune Biol, Lundbeck, Japan tobacco,
Merck, Novartis. MM has received speaking honoraria from Sanofi-Genzyme.
KS has received compensation for activities related to Biogen, Eisai,
Elan, Fiveprime, Lipomed, Merck, Novartis, Sanofi-Genzyme and Teva. GG
has received compensation for activities from AbbVie, Actelion, Atara
Bio, Bayer-Schering Healthcare, Biogen, Celgene, GW Pharma, GSK,
Ironwood, Japanese Tobacco, Merck, Merck-Serono, Mertz, Novartis,
Pfizer, Sanofi-Genzyme, Synthon, Takeda , Teva, UCB Pharma and Vertex
Pharmaceuticals.