A double-blind, randomized-withdrawal, placebo-controlled study to evaluate the efficacy and safety of human plasma-derived C1-esterase inhibitor as add-on to standard of care for the treatment of refractory antibody mediated rejection in adult renal transplant recipients

See protocol P26-29:

1.1 Background
Antibody-mediated rejection (AMR) is associated with poor long-term allograft
and patient survival [Takemoto et al, 2004; Dalla Vecchia et al, 1997; Emonds
et al, 2000; Fine et al, 1979; Stegall et al, 2011; Montgomery et al, 2011b].
Antibody-mediated rejection is mediated primarily by donor-specific antibody
(DSA) directed against the human leukocyte antigen (HLA) class I and/or class
II molecules present on the vascular endothelium and tubules of the
transplanted kidney [Miller et al, 2004; Montgomery et al, 2011a; Pascual et
al, 2008; Stegall et al, 2012; Gulleroglu et al, 2013]. This antibody-antigen
interaction activates the classical complement pathway, resulting in direct
cellular damage and initiation of an inflammatory response which results in
further damage to the allograft [Burns et al, 2008; Grafals and Akalin, 2009;
Stegall et al, 2011; Stegall et al, 2012]. Left unchecked, the endothelial
damage caused by complement activation can result in allograft thrombosis,
tissue necrosis, and endothelial cell detachment from the basement membrane,
which are all characteristic histological features of AMR [Nguyen and Butani,
2013]. This early injury is later complicated by the proliferation of
myofibroblasts leading to progressive scarring of the kidney graft [Gulleroglu
et al, 2013]. This process eventually leads to transplant glomerulopathy, as
evidenced by double contouring of the glomerular basement membrane. These
irreversible anatomical lesions, including intimal thickening of the
peritubular capillaries (PTCs), permanently compromise allograft function
[Colvin, 2007; Cornell et al, 2008; Kittleson and Kobashigawa, 2012; Nankivell
and Alexander, 2010; Crespo et al, 2001; Loupy et al, 2017; Stites et al,
2015].

Clinically, patients with AMR may have fever, fatigue, irritability, pain over
the allograft site, and rapid onset of renal dysfunction (decrease in urine
output and estimated glomerular filtration rate [eGFR]). Several risk factors
have been associated with the occurrence of acute AMR; the patients at greatest
risk are sensitized (DSA+) to their donors after exposure to human HLA proteins
through a prior transplant, blood transfusion, and/or pregnancy [Stegall et al,
2011; Lefaucheur et al, 2010; Eurotransplant, 2013]. Patients may also develop
AMR post-transplant via (de novo) production of DSA in response to the
allograft HLA proteins. Renal failure patients with DSA are generally excluded
from receiving a transplant; therefore, AMR is a rare (5 to 7%), but serious
and morbid complication of kidney transplantation.

There are no approved therapies for AMR; however, intravenous immunoglobulin
(IVIg) therapy with plasmapheresis can successfully treat 50 to 75% of cases on
the short term [Montgomery et al, 2016]. If ongoing AMR is inadequately
treated, or is refractory to treatment, transplant glomerulopathy occurs.
Concurrently, there is a progressive decline in renal function [Djamali et al,
2014] manifested by decline in glomerular filtration rate (GFR) until the
allograft is lost and dialysis and/or re-transplantation is necessary.

Since DSA activates the classical complement pathway which results in
inflammation and eventual TG, complement inhibition should prevent the damage
which is associated with early graft loss. A recently completed pilot study of
a human plasma derived C1-esterase inhibitor product for the treatment of AMR
suggests that C1-esterase inhibitor, as an adjunct to IVIg and plasmapheresis,
may protect the allograft [Montgomery et al, 2016]. Another study of complement
inhibition showed that long-term suppressive therapy with a C1 esterase
inhibitor product could be used to rescue patients with AMR refractory to IVIg
and plasmapheresis [Viglietti et al, 2016a]. This protocol seeks to study
complement inhibition by C1-esterase inhibitor in a placebo-controlled manner
as a treatment for refractory AMR in renal transplant recipients.

1.2 Background Information on C1-esterase inhibitor

1.2.1 Overview
C1-esterase inhibitor belongs to the family of serine protease inhibitors. It
has important inhibiting potential on several of the major cascade systems of
the human body, including the coagulation, complement, and contact cascades, as
well as the fibrinolytic system. In the complement cascade system C1-esterase
inhibitor inactivates its substrates by covalently binding to the active sites
preventing the actions of C1r (subcomponent of complement component C1), C1s
(activated form of complement component C1), and manose-associated serine
proteases.
C1-esterase inhibitor is a soluble, single chain glycoprotein containing 478
amino acid residues organized into three beta sheets and eight or nine alpha
helices. The heavily glycosylated molecule has an apparent molecular weight of
105 kD, of which the carbohydrate chains comprise 26% to 35%.

CSL Behring*s C1-esterase inhibitor product (*C1-esterase Inhibitor, Human [500
IU/mL]*, abbreviated as *C1-INH*) is human plasma-derived, and available at a
concentration of 500 IU/mL after reconstitution. A detailed description of the
chemistry, pharmacology, efficacy, and safety of C1-INH is provided in the
Investigator*s Brochure [C1-INH (500 IU/mL) Investigator*s Brochure, 2017].

1.2.2 Nonclinical Evaluation
Nonclinical studies of C1-esterase inhibitor products have demonstrated an
acceptable safety profile and pharmacokinetic (PK) properties.
In nonclinical studies with the currently marketed C1-esterase inhibitor
product Berinert (CSL Behring), C1-esterase inhibitor was well tolerated and no
toxicity was observed in single-dose intravenous (IV) toxicity studies in rats
and mice at doses up to 6000 IU/kg, and in a repeated-dose IV toxicity study in
rats at a dose of 200 IU/kg for 14 days [C1-INH (500 IU/mL) Investigator*s
Brochure, 2017].
Local tolerance studies in rabbits were conducted with Berinert, investigating
IV and subcutaneous (SC) routes of administration [C1-INH (500 IU/mL)
Investigator*s Brochure, 2017]. No treatment-related local reactions were
observed at IV Berinert injection sites; erythema and edema were observed at SC
Berinert injection sites with a slightly higher incidence and/or intensity when
compared to control sites. Overall, a single IV, intra-arterial, SC, or
intramuscular injection of Berinert was locally well-tolerated in rabbits.
To investigate the thrombogenic potential of C1-esterase inhibitor products
(Berinert and C1-INH), thrombogenicity studies based on the established Wessler
rabbit model of venous stasis-induced thrombosis were conducted [C1-INH (500
IU/mL) Investigator*s Brochure, 2017]. Potential pro-thrombotic effects of
C1-esterase inhibitor were studied following IV administration, as this route
of administration leads to higher peak plasma levels, which are considered most
relevant for potential pro-thrombotic effects. Following single IV
administration of doses up to 800 IU/kg to rabbits, no thrombus formation could
be observed.

1.2.3 Clinical Experience with C1-INH in Transplant
C1-esterase inhibitor products have been studied in kidney transplant patients
for the treatment of acute AMR, prevention of AMR, and for the treatment of
refractory AMR. Case reports and small clinical trials have been conducted,
which suggest efficacy of C1-esterase inhibitor for the treatment of AMR in
kidney transplant patients.

C1-esterase inhibitor has been evaluated for the prevention of AMR in
HLA-sensitized kidney transplant recipients. A phase 1/2, exploratory,
randomized, placebo-controlled, single center trial using Berinert was
conducted in 20 desensitized (prior to transplant) subjects for the prevention
of AMR following renal allograft transplantation [Vo et al, 2015]. Subjects
received either 20 IU/kg Berinert or placebo intra-operatively (intravenously),
then twice weekly for 7 doses. No subjects developed AMR in the Berinert group;
1 (10%) developed AMR in the placebo group at 1 month following treatment. At 6
months, 2 (20%) subjects developed AMR in the Berinert group; 3 (30%) developed
AMR in the placebo group. Berinert was generally well tolerated in this
population, with no study drug related serious adverse events (SAEs).

Another C1-INH product (Cinryze; Shire Viropharma Incorporated) was evaluated
as treatment in subjects with AMR. A phase 2b, multicenter, double-blind,
randomized, placebo-controlled pilot study was conducted to evaluate the use of
Cinryze as add-on therapy to standard of care (ie, IVIg/plasmapheresis) in 18
subjects with acute AMR [Montgomery et al, 2016]. Subjects received IV Cinryze
(n = 9) or placebo (n = 9); treatment was 5000 U (approximately 60 U/kg) IV on
Day 1 then 2500 U (approximately 30 U/kg) IV every other day (6 doses) for 2
weeks for a total of 20,000 units. Both groups showed similar improvements in
histopathology parameters on biopsies (Banff Classification) obtained one week
after cessation of study drug (Day 20). Seven of 9 (78%) subjects receiving
Cinryze and 6 of 9 (67%) receiving placebo had resolution of their AMR; the
most prominent feature of the improvement on biopsy was seen as a decrease in
C4d staining. Cinryze-treated subjects achieved supra-physiologic C1-esterase
inhibitor levels of a median 1.73-fold above normal, and Cinryze was considered
to be generally well tolerated without any serious safety concerns.

A prospective, historically matched controlled single-arm pilot study was
conducted to evaluate the efficacy and safety of Berinert added to high-dose
IVIg for the treatment of refractory AMR (nonresponsive to standard of care) in
6 subjects [Viglietti et al, 2016a]. Subjects received 20 IU/kg Berinert
intravenously on Days 1, 2, and 3 and then twice weekly and 2 grams/kg IVIg
(Privigen; CSL Behring) every month for 6 months. All Berinert-treated subjects
showed an improvement in eGFR after 6 months of treatment. At Month 6, study
subjects with positive C4d staining in peritubular capillaries decreased from
83% (5/6) at baseline to 17% (1/6) with treatment, and anti-HLA DSA C1q binding
decreased from 100% (6/6) to 17% (1/6). No death or allograft loss was observed
in patients treated with Berinert. One SAE (gastrointestinal bleeding) occurred
in 1 subject, which was considered not related to the study drug. One subject
experienced an adverse event (AE) of an episode of deep vein thrombosis of a
lower limb 5 months after inclusion in the study, which led to discontinuation
of Berinert. The episode was subsequently determined to be caused by local
venous compression due to a popliteal cyst, and was considered not related to
study drug.

The primary objective of the study is to evaluate the efficacy of C1-INH in the
treatment of refractory AMR in renal allograft recipients.

The secondary objectives of the study are:

1. To further evaluate the efficacy of C1-INH in the treatment of refractory
AMR in renal allograft recipients.
2. To evaluate the safety of C1-INH in the treatment of refractory AMR in renal
allograft recipients.
3. To evaluate the pharmacokinetics of C1-INH during the treatment of
refractory AMR in renal allograft recipients.

This is a double-blind, randomized-withdrawal, placebo-controlled study
consisting of 2 treatment periods, a post-treatment Follow-up Period, and
Retreatment Period(s) (if needed).

Eligible subjects will enter into the 13-week, open-label Treatment Period 1,
during which all subjects will receive C1-INH. Subjects who respond to
treatment with C1 INH by Week 12 as assessed by pre-defined responder criteria
will be randomized into Treatment Period 2 of the study; those subjects who do
not respond to treatment will enter a 45-month Non-responder Follow-up Period.
Subjects who are responders will be randomized to receive either C1-INH or
placebo during Treatment Period 2.

See protocol P31-32:

1.4 Potential Risks and Benefits
Consistent safety of Berinert administered intravenously for the on-demand,
acute treatment of HAE attacks has been observed in over 30 years of use, with
949,282,930 IU sold worldwide for the period from 1985 and 04 August 2016.
Post-marketing surveillance has shown that Berinert is safe and well tolerated
when used at the recommended dosage for the treatment of acute HAE attacks. No
case reports concerning proven Hepatitis A Virus, Hepatitis B Virus, Hepatitis
C Virus (HCV), or Human Immunodeficiency Virus 1 or 2 infections resulting
from the use of Berinert have been received.

In addition, routine use of C1-INH (500 IU/mL) for prophylaxis against HAE
attacks has been studied in 2 phase 3 clinical trials in subjects with HAE. As
of 17 May 2016, 91 subjects were treated with 40 IU/kg C1-INH, 98 subjects were
treated with 60 IU/kg C1-INH, and 1 subject was treated with 80 IU/kg. In
total, 148 subjects received at least 1 dose of * 40 IU/kg C1-INH (combined
treatments), with 85 of these subjects having a cumulative duration of exposure
to C1-INH of * 1 year. The mean cumulative exposure to C1-INH over the course
of both phase 3 studies combined was similar for both the 40 IU/kg and 60 IU/kg
doses (39.3 weeks for 40 IU/kg; 40.3 weeks for 60 IU/kg); the single subject
who was treated with 80 IU/kg received that dose for 7.1 weeks. For all
subjects who received treatment with SC C1-INH twice weekly, there was no
dose-dependent safety concern.

Risks associated with C1-esterase inhibitor products include
hypersensitivity/anaphylactic-type reactions, thromboembolic events (TEEs), and
potential virus transmission:
* Hypersensitivity/Anaphylactic-type Reactions: Hypersensitivity and
anaphylactic-type reactions have been reported rarely with the use of
C1-esterase inhibitor products in patients with HAE. Hypersensitivity or
anaphylactic reactions in this study population are expected to be rare because
the subjects have normal, physiologic C1-esterase inhibitor, as opposed to in
the HAE population. Nonetheless, anaphylaxis will be specifically monitored
during this study.
* Thromboembolic Events: Thromboembolic events have been occasionally reported
following the use of C1-esterase inhibitor products, in particular in patients
receiving off-label high doses of up to 500 IU/kg IV in the context of cardiac
surgery and extracorporeal circulation. At the doses to be used in this
clinical study (60 IU/kg IV; 60 IU/kg SC), a causal relationship between TEEs
and the use of C1-esterase inhibitor has not been established. Nonetheless,
TEEs will be specifically monitored during this study.
* Potential Virus Transmission: C1-INH contains human plasma-derived C1
esterase inhibitor and, therefore, has the potential for virus transmission to
recipients. However, Berinert and C1-INH has a high margin of virus safety with
the risk of virus transmission minimized by donor selection and screening
criteria, and by reducing enveloped and non-enveloped viruses using
pasteurization, nanofiltration methods, and chromatography [De Serres et al,
2003]. Each subject will provide a retention sample before and after treatment
with the investigational product for potential future serology assessments.

Additional information on C1-INH can be found in the C1-INH investigator*s
brochure [C1-INH (500 IU/mL) Investigator*s Brochure, 2017].

Without treatment, up to 90% of study subjects with refractory AMR would
otherwise go on to lose their kidney graft and have associated mortality risk
[Viglietti et al, 2016b]. Given the low probability of potential risks and the
implementation of study procedures that will closely monitor the safety of
study subjects, the associated benefit/risk assessment is acceptable for
subjects who participate in the study.