Preformed IgG Antibodies Against Major Histocompatibility
Complex Class II Antigens Are Major Risk Factors for
High-grade Cellular Rejection in Recipients of
Heart Transplantation
Silviu Itescu, MD; Thomas C. Tung, MD; Elizabeth M. Burke, BS, RN; Alan Weinberg, MS;
Nader Moazami, MD; John H. Artrip, MD; Nicole Suciu-Foca, PhD; Eric A. Rose, MD;
Mehmet C. Oz, MD; Robert E. Michler, MD
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Background—Preformed anti-HLA antibodies reacting specifically with donor lymphocytes have been associated with
acute vascular rejection and early cardiac allograft failure. However, the effect of preformed anti-HLA antibodies
directed against allogeneic major histocompatibility complex (MHC) class I or II antigens of a donor panel on heart
transplantation outcome has not been extensively studied.
Methods and Results—The study group consisted of 68 patients who received cardiac transplants between 1989 and 1996
and who were at high risk for developing anti-HLA antibodies before transplantation. The effect of preformed antibodies
against allogeneic MHC class I or class II antigens on the development of early high-grade cellular rejection and on
cumulative annual rejection frequency was determined. Both patients with left ventricular assist devices and
retransplantation candidates had a similar increase in the frequency of IgG anti-MHC class II antibodies (IgG anti-II)
compared with control subjects (P,0.0001), whereas the frequency of IgG anti-MHC class I antibodies (IgG anti-I) was
elevated only in patients with left ventricular assist devices. Pretransplantation IgG anti-II predicted early development
of high-grade cellular rejection (P50.006) and higher cumulative annual rejection frequency (P,0.001) in both of these
sensitized patient groups. Among retransplantation recipients, a match between donors 1 and 2 at HLA-A additionally
predicted an earlier time to a high-grade cellular rejection.
Conclusions—These results emphasize the importance of specifically screening heart transplantation candidates for the presence
of IgG antibodies directed against MHC class II molecules and suggest that strategies aimed at their reduction may have an
impact on the onset and frequency of high-grade cellular rejections after transplantation. (Circulation. 1998;98:786-793.)
Key Words: transplantation n risk factors n antibodies
T
he presence of preformed lymphocytotoxic antibodies
reactive against donor lymphocytes in recipient serum,
detected in a routine cross-match, is considered a contraindication to solid organ transplantation because of the high
incidence of humoral allograft rejection, early graft failure,
and poorer patient survival.1–3 These antibodies are primarily
directed against donor major histocompatibility complex
(MHC) class I HLA antigens constitutively expressed by the
allograft endothelium, since nonactivated endothelium does
not express MHC class II HLA antigens. Consequently, the
risk for early graft failure (ie, within the first 24 to 48 hours)
is significantly higher in the presence of a positive cross
match with donor T lymphocytes, which, in the absence of
activation, express only MHC class I antigens, than with
donor B lymphocytes, which strongly express both MHC
class I and II antigens.1 In addition, the real risk for early graft
failure after a positive cross-match appears to reside in the
IgG fraction of donor-specific antibodies.1 An IgM-positive
cross-match can result from the presence of antilymphocytic
autoantibodies, which do not specifically react with donor
HLA allotypes, and their presence may not lead to early graft
failure.1
To identify patients at high risk of having a positive
cross-match with a potential donor, heart transplantation
candidates are prospectively tested for lymphocytotoxic
antibodies against lymphocytes from a donor panel representative of all established HLA specificities, collectively
referred to as measurements of panel-reactive antibodies
(PRA). In addition to predicting an increased likelihood of
donor-reactive anti-HLA antibodies and a consequent risk
of early graft failure related to humoral rejection, several
studies have shown that high levels of pretransplantation
PRA in cardiac allograft recipients are associated with
adverse posttransplantation outcome when compared with
patients with low or negative reactivity.1 High PRA levels
have been associated, in some studies, with increased
Received December 2, 1997; revision received March 11, 1998; accepted April 20, 1998.
From the Department of Surgery, College of Physicians and Surgeons, Columbia University, New York, NY.
Correspondence to Silviu Itescu, MD, Columbia-Presbyterian Medical Center, PH14 –1485, 622 West 168th St, New York, NY 10032.
© 1998 American Heart Association, Inc.
786
Itescu et al
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frequency of acute cellular rejections, decreased long-term
graft survival, and increased mortality rates.4,5 Moreover,
the onset of accelerated coronary artery disease (CAD) in
heart transplantation recipients, the major limitation to
long-term graft survival, has been associated with the
presence of anti-HLA antibodies.6 – 8 Since accelerated
CAD in these patients may be a consequence of cumulative
episodes of high-grade cellular rejections, it is possible
that this association may actually reflect a relation between
anti-HLA antibodies and acute cellular rejection.
In most published series no differentiation has been
made between antibodies reacting with a T-cell and B-cell
panel. Because these lymphoid lineage cells differ with
respect to MHC class II HLA expression, and many centers
only screen for antibodies reactive with T-cell panels,
reports regarding the influence of pretransplantation antiHLA antibodies on posttransplantation outcome may have
significantly underestimated the significance of antibodies
reactive with MHC class II antigens.9 In this study, we
examined the separate effects on posttransplantation clinical outcome of preexisting anti-HLA antibodies with
specificity for either allogeneic MHC class I or class II
antigens. The influence of these antibody types on clinical
outcome was then compared with that predicted by a
standard T-cell PRA. The patients selected for study
consisted of 2 groups considered to be at increased risk for
the development of anti-HLA lymphocytotoxic antibodies:
patients receiving a second cardiac allograft and those on
left ventricular assist device (LVAD) support before transplantation.10 Our results indicate that preformed anti-HLA
IgG antibodies directed against non– donor-specific MHC
class II antigens are a major risk factor for early and more
frequent high-grade cellular rejections after heart transplantation. Moreover, these antibodies were not detected
by a standard T-cell PRA, emphasizing the need to screen
all potential heart transplantation recipients for IgG antibodies reactive with allogeneic B cells.
Methods
Patient Population
Sixty-eight patients at high risk of having elevated levels of
anti-HLA antibodies were studied. These consisted of 2 distinct
patient populations awaiting heart transplantation: 45 primary
allograft recipients supported by LVAD before transplantation
and 23 recipients of a second cardiac allograft. All LVAD
recipients had a TCI device implanted between 1990 and 1996.
The interval of LVAD support ranged from 5 to 541 days, with an
average of 131.46112.3 days. Among the retransplantation population, all patients received their primary allografts between
1983 and 1995 and second grafts between 1989 and 1996. The
time between the first and second transplantations ranged from 9
months to 10.5 years and averaged 5.0762.50 years. The age
distribution was similar among the patients with LVAD
(52.62610.66) and those with retransplantation (48.9169.81).
For the total group of 68 patients, age ranged from 17 to 67 years,
with a mean of 51.37610.46. Both groups had a marked male/
female preponderance (LVAD 37/8, retransplantation 18/5).
Standard triple-therapy immunosuppression (cyclosporine, steroids, and either azathioprine or mycophenolate mofetil) was initiated perioperatively for all patients in both the LVAD and retransplantation groups. Cellular rejection episodes were treated either
August 25, 1998
787
with steroid pulses (oral or intravenous) or cytolytic therapy (OKT3
or ATGAM).
Diagnosis of Cellular and Humoral Rejection
Endomyocardial biopsies (EMB) were performed by the Stanford
Caves technique weekly for the first month after transplantation,
every 10 days for the second month, every 3 weeks for the
subsequent 2 months, then at progressively longer intervals until a
baseline schedule of every 6 months was reached. Four biopsy
fragments were processed for histological analysis, and histological
grades of cellular rejection were assigned by the Billingham criteria.
Humoral rejection was diagnosed by immunofluorescence examination of biopsy specimens demonstrating deposition of complement and immunoglobulin in the absence of mononuclear cell
infiltration. Immunofluorescent studies were performed when clinical parameters were suggestive of humoral rejection.
HLA Typing
Serological typing of HLA-A and HLA-B loci was performed by
standard microcytotoxicity techniques. HLA-DR typing was performed by both serologic analysis and DNA techniques with
sequence-specific oligonucleotide primers and polymerase chain
reaction.
Detection of Anti-HLA Antibodies
Sera were obtained from all patients on the day of transplantation and
screened for the presence of lymphocytotoxic antibodies against
separated T lymphocytes and B lymphocytes obtained from a panel
of 70 individuals representative of all HLA class I and class II
antigens found in the North American population. Sera were
screened for complement-mediated lytic activity in the presence or
absence of dithiothreitol (DTT). Total T-cell PRA was considered
positive if serum, in the absence of DTE, reacted against .10% of
the T-cell reference panel.
Determination of Anti-HLA Antibody Specificity
for MHC Class I or Class II Antigens
Working definitions for IgG antibodies against HLA class I
molecules (IgG anti-I) or class II molecules (IgG anti-II) were
established in our laboratory using, as reference, sera from 28
heart transplantation recipients with PRA values .10% and with
anti-HLA class I and class II specificities defined by standard tail
analysis. Because MHC class I antigens are constitutively expressed by both T cells and B cells, IgG antibodies against HLA
class I molecules (IgG anti-I) were considered present in our
analysis when the DTT-treated serum reacted with .10% of both
the T-cell reference panel and the B-cell panel. This working
definition for IgG anti-I correlated in 100% (20/20) of cases with
the presence in patient sera of antibodies with defined HLA class
I specificities.
To concomitantly identify and discriminate IgG antibodies
against HLA class II molecules (IgG anti-II) in the presence of
IgG anti-I, we established an algorithm that used the ratio of
serum reactivity to B cells versus T cells because MHC class II
antigens are constitutively expressed by B cells but not T cells. To
confirm this working definition using sera with defined IgG
anti-HLA class II specificities, a logistic regression analysis was
performed by a maximum likelihood procedure using Biological
Management Database Program statistical software to calculate
the IgG anti-II predictive value for the ratios of B-cell serum
reactivity/T-cell serum reactivity of 1.25, 1.50, 1.75, 2.00, and
3.00. Maximal sensitivity (91%) for identifying sera with reactivity against defined HLA class II antigens was obtained with a
ratio of B-cell/T-cell serum reactivity of 2.00 (model coefficient
23.481, SE 1.19, P50.0002). Therefore, IgG antibodies against
both MHC class I and class II molecules were considered present
if DTE-treated serum reacted against .10% of both the T- and
B-cell reference panels, and the B-cell reactivity exceeded the
T-cell reactivity by at least 2-fold. IgG anti-II were also considered present if the DTT-treated serum reacted against .10% of
788
Anti-HLA Class II IgG Antibodies and Cellular Rejection
TABLE 1. Increased Frequency of Anti-HLA Antibodies in LVAD Recipients and
Retransplantation Candidates Compared With Control Subjects
Control Subjects
NYHA Class IV
(n566), n (%)
LVAD Recipients
(n545), n (%)
T-cell PRA
9 (13)
23 (64)*
11.6
5 (22)
IgG anti-I
2 (3)
19 (43)*
25.6
1 (6)
IgG anti-II
2 (3)
14 (33)*
15.5
5 (29)*
Odds Ratio
Retransplantation
Candidates
(n523), n (%)
Odds Ratio
14.0
Statistical analyses were performed by construction of 232 contingency tables, with odds ratios and P values
calculated by x2 analysis. IgG anti-I and IgG anti-II were concomitantly present in 7 LVAD retransplantation patients.
*P,0.0001.
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the B-cell but not the T-cell reference panel. Testing the validity
of this approach with the use of sera analyzed by tail analysis
confirmed that 100% of the samples that reacted only with B cells
(n511) contained antibodies with anti-HLA class II specificities.
Overall, the use of these combined criteria for identifying IgG
anti-II (ie, reactivity only with B cells or at least 2-fold higher
reactivity with B cells than T cells) correctly identified patients
with MHC class II serum reactivity with 94% sensitivity and 88%
specificity.
Study Design and Statistical Analysis
The frequency of serum reactivity for IgG anti-I, IgG anti-II, or total
T-cell PRA was compared between New York Heart Association
class IV control subjects awaiting heart transplantation (n566) and
either LVAD recipients (n545) or retransplantation candidates
(n523). For each variable tested, a 232 table was constructed to
compare the frequencies in the study population with the frequencies
in control subjects with heart failure. Odds ratios were calculated by
dividing the product of A3D by the product of B3C, where A and
B are individuals in each group positive for the variable tested, and
C and D are individuals in the groups negative for the variable. x2
analysis was used to determine the P value. Group differences for
continuous variables, for example, waiting time to transplantation,
were analyzed by Student’s t test.
The influence of various potential immunologic risk factors on the
time to the first high-grade (3A/3B) cellular rejection after transplantation was determined by Kaplan-Meier actuarial analysis, with P
values calculated by log rank statistics.11
The Cox proportional hazards regression model was used for the
multivariate analysis of time to first high-grade rejection.12 This is a
multiple regression analysis for examining time-dependent outcomes
and their potential associated risk factors by modeling a linearized
function of a set of p covariates. The model may be written as
l(t)5l0(t)e(b1x11b2x21. . .bpsp)
where l0(t) is the baseline hazard when all the x variables (covariates) equal 0. The effect of a particular risk factor is equal to ebI for
each unit of xi.
The interpretation of a risk factor allowed into the model with a
value of P,0.05 is that it is an independent risk factor associated
with the event, over and above other potential risk factors included
in the equation. The risk ratio is the ratio of the estimated hazard for
those with the characteristic variable in question to the estimated
hazard for those without, controlling for other variables (or covariates). Any possible grouping effects (ie, LVAD recipients versus
retransplantation recipients) were corrected by stratification in the
Cox model. The variables analyzed included the presence or absence
of each antibody type before transplantation (total T-cell PRA, IgG
anti-I, IgG anti-II, IgM anti-I, IgM anti-II); donor and recipient age,
sex, and race; donor-recipient matching at the HLA-A, B, and DR
loci; and ischemic time.
Because nonfatal morbid events such as cellular rejections can
occur repeatedly in the same patient, cumulative high-grade (3A/3B)
rejections were modeled by the method of Wei et al13 by taking into
account the correlation of repeated episodes within each patient. This
method computes robust variance estimates that allow for the
dependence among multiple event times.
For all statistical analyses, data were analyzed with the SAS
System software.
Results
Anti-HLA Antibodies in Sensitized Individuals
As shown in Table 1, compared with NYHA class IV control
subjects awaiting heart transplantation, the frequencies of
anti-MHC class I IgG antibodies and total T-cell PRA were
increased only among LVAD recipients In contrast, the
frequency of anti-MHC class II IgG antibodies was significantly higher in both LVAD recipients and retransplantation
candidates than in NYHA class IV heart failure control
subjects (33% and 29% versus 3%, respectively, P,0.0001).
We next sought to determine whether the production of
either IgG anti-I or anti-II was influenced by perioperative
transfusion of blood products. Among the LVAD recipients
who developed anti-HLA antibodies as defined by a positive
T-cell PRA, 90% had received perioperative blood products,
with a mean of 16 U of red blood cell transfusions (range 0
to 88) and 12 U of platelets (range 0 to 36). By Kaplan-Meier
univariate analysis, at the median duration of LVAD implantation of 4 months, 8% of patients who received ,6 platelet
units developed IgG anti-I antibodies compared with 63%
who received .6 U (P50.002). In contrast, perioperative red
blood cell transfusions did not influence the production of
IgG anti-I in these analyses. The development of IgG anti-II
was not influenced by either the number of perioperative red
blood cell or platelet transfusions.
Presence of IgG Anti-MHC Class I Antibodies
Increases Waiting Time to Heart Transplantation
At our institution a positive prospective donor-specific crossmatch is considered a contraindication to heart transplantation, and none of the patients in this study were given
transplantation across a positive cross-match. Therefore, individuals whose sera are repeatedly positive in cross-match
reactions have longer waiting times until a cross-match
negative donor is found. Because prospective cross-matches
are only performed with unseparated donor lymphocytes,
which are predominantly T cells expressing MHC class I
antigens, we investigated the effects of IgG anti-I on waiting
time to heart transplantation. As expected, LVAD recipients
with IgG anti-I had a significantly longer waiting time than
those without these antibodies (175 vs 90 days, P50.009).
Similarly, LVAD recipients with a total T-cell PRA also had
Itescu et al
August 25, 1998
789
Figure 1. Recipients of a second cardiac allograft (n545) and patients supported by LVADs before their first
transplantation (n523) have similar
times to a first high-grade posttransplantation cellular rejection.
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a longer waiting time than those without these antibodies
(190 vs 87 days, P50.015). The presence of IgG anti-II did
not affect the waiting time to transplantation (LVAD 139 vs
114 days, P50.50) as these antibodies were not identified
when donor-specific cross-matching was performed on unseparated peripheral blood mononuclear cells.
Presence of IgG Anti-MHC Class II Antibodies at
Time of Transplantation Predicts Shorter
Duration to First High-grade Cellular Rejection
for LVAD and Retransplantation Recipients
As shown in Figure 1, the time intervals between transplantation and the first high-grade cellular rejection were similar
for both LVAD recipients and retransplantation recipients,
with one quarter of both populations rejecting by 80 days. For
this reason, the influence of each antibody type on this
outcome was examined not just in each group separately but
on the combined group of all patients at high risk.
As shown in Figure 2, IgG anti-II detected at the time of
transplantation was highly predictive of early high-grade
cellular rejection in the posttransplantation period for the
combined group of patients receiving a second graft or
previously receiving LVAD support. This observation held
when each group was studied separately (data not shown).
The median time for a high-grade rejection was 70 days for
patients positive for IgG anti-II. In contrast, the actuarial
freedom from rejection never fell ,50% in .1700 days of
follow-up for patients without IgG anti-II (odds ratio524.3,
P50.006). As shown in Figure 3, the presence of IgG anti-I
was also a moderate risk factor for a high-grade rejection;
however, this did not reach statistical significance (P50.08).
Finally, the presence of a positive total T-cell PRA at the time
of transplantation was not at all predictive of early high-grade
rejection (Figure 4). Additionally, neither the presence of
IgM anti-I nor IgM anti-II at the time of transplantation
influenced the time to a high-grade cellular rejection (P50.94
and P50.79, respectively).
Presence of IgG Anti-MHC Class II Antibodies Is
a Major Risk Factor for Posttransplantation
Cellular Rejections
By Cox proportional hazard modeling for multivariate analysis, the only risk factors identified to predict an early
high-grade cellular rejection were the presence of pretransplantation IgG anti-II (P50.018) and, to a lesser extent, IgG
anti-I (P50.086) (see Table 2). These observations held for
both LVAD and retransplantation recipients. None of the
other variables tested in this analysis were predictive of
Figure 2. Among a combined group of
patients at high risk for sensitization
(n568), pretransplantation IgG against
MHC class II molecules (IgG anti-II)
predicts an earlier time to a first highgrade cellular rejection.
790
Anti-HLA Class II IgG Antibodies and Cellular Rejection
Figure 3. Among a combined group of
patients at high risk for sensitization
(n568), pretransplantation IgG against
MHC class I molecules (IgG anti-I) is a
weaker predictor for a first high-grade
cellular rejection than IgG anti-II.
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rejection in this group of sensitized individuals, including
T-cell PRA; matching at the HLA-DR, -B, or -A loci;
ischemic time; or donor age.
Presence of Pretransplantation IgG Anti-MHC
Class II Antibodies Is Associated With Higher
Cumulative Annual Rejection Frequencies
As shown in Table 3, those patients with IgG anti-II detected
at the time of transplantation had higher cumulative annual
rejection frequencies than those without these antibodies
(0.846 vs 0.169 high-grade rejections per patient year of
follow-up). Among the demographic and immunologic variables examined, including the other antibody types, only
pretransplantation IgG anti-II was predictive of a higher
cumulative annual rejection frequency (P,0.001). Neither
the presence of IgG anti-I nor total T-cell PRA significantly
influenced the cumulative annual rejection frequencies.
Matching Between First and Second Donor at
HLA-A Locus Predicts Early High-grade Cellular
Rejection for Recipients of Second
Cardiac Allograft
As shown in Figure 5, among retransplantation recipients,
those who received a second allograft that shared one or more
HLA-A locus antigens with the first donor had a significantly
shorter time to a first high-grade cellular rejection. This
difference was most notable in the first posttransplantation
month, in which 67% of retransplantation recipients of a
donor 1– donor 2 HLA-A match had a high-grade cellular
rejection compared with only 5% of those not receiving a
heart from a second donor matched at HLA-A with the first
donor (P50.0026, odds ratio 30.0). This risk factor was
independent of any anti-HLA IgG antibody effect, since only
1 of 6 patients with donor 1– donor 2 HLA-A match had IgG
anti-II pretransplantation. Matching of the first and second
donors at the HLA-B and DR loci did not influence the
duration to early rejections among the retransplantation
recipients.
Discussion
In this study, we investigated the effects of anti-HLA antibodies present in 2 populations of sensitized individuals
awaiting heart transplantation. IgG antibodies against non–
donor-specific MHC class II molecules were detected at
increased frequency among both LVAD recipients and retransplantation candidates. The presence of IgG antibodies
against MHC class II molecules detected in recipient serum at
the time of transplantation was found to be a major risk factor
both for the development of early high-grade cellular rejections and for significantly increased cumulative annual rejection frequencies. These observations were independently
Figure 4. Positive total T-cell PRA
before transplantation has no effect on
time to a first high-grade cellular
rejection.
Itescu et al
TABLE 2. Multivariate Analysis of Risk Factors for First
High-grade Cellular Rejection After Transplantation
Coefficient6SE
P
Risk Ratio
95% Confidence
Interval
IgG anti-II
1.03560.4393
0.0184
2.816
(1.19, 6.66)
IgG anti-I
0.90860.5295
0.0863
2.480
(0.88, 7.00)
Variable
By multivariate analysis, with Cox proportional hazards model, pretransplantation IgG anti-II, and to a lesser extent IgG anti-I, is predictive of earlier first
high-grade cellular rejection after heart transplantation in highly sensitized
individuals (n568).
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confirmed in both populations of sensitized individuals.
Neither anti-MHC class I IgG antibodies nor lymphocytotoxic antibodies detected in a conventional PRA assay were
found to be predictive of earlier cellular rejections or increased cumulative annual rejection frequencies. Because
both anti-HLA antibodies and early cellular rejections have
been associated with accelerated graft vasculopathy in heart
transplantation,6 – 8,14,15 these results emphasize the importance
of specifically screening heart transplantation candidates for
the presence of IgG antibodies against MHC class II molecules and suggest that strategies aimed at their reduction may
have an impact on the long-term outcome of cardiac allograft
recipients.
Although previous studies have identified adverse effects
of anti-HLA IgG antibodies on early posttransplantation graft
rejection and survival, especially in instances of a positive
donor-specific cross-match with unseparated donor mononuclear cells,1–3 in none of these studies was a distinction made
between antibodies directed against MHC class I versus class
II antigens. Acute vascular rejection and early graft failure are
primarily caused by preformed antibodies against MHC class
I molecules, as MHC class II antigens are not expressed
constitutively on graft vascular endothelium. Because 80% to
90% of unseparated lymphocytes are T cells, which constitutively express MHC class I but not class II molecules, a
prospective cross-match with the use of unseparated donor
mononuclear cells will identify the presence in recipient sera
of IgG antibodies against donor MHC class I antigens but will
fail to identify antibodies against donor MHC class II
antigens. Because of the potential risk of acute vascular
rejection, a positive donor-specific T-cell cross-match is
generally considered a contraindication for heart transplantation at our institution. In this study, the presence of IgG
antibodies against a panel of MHC class I antigens was found
TABLE 3. Influence of Pretransplantation Anti-HLA Antibodies
in Sensitized Patients (n568) on Cumulative Annual Rejection
Frequencies of Subsequent Heart Transplantation
Cumulative Annual Rejection Frequency
(No. of 3A or 3B Rejections/yr)
Positive
Negative
P
IgG anti-II
0.846
0.169
,0.001
IgG anti-I
0.611
0.291
0.09
T-cell PRA
0.468
0.328
0.88
Cumulative high-grade (3A/3B) rejections were modeled by the method of
Wei, Lin, and Weissfeld.13
August 25, 1998
791
to correlate with a prolonged waiting time to heart transplantation because of repeated instances of positive cross-matches
with potential donors.
The mechanism by which the presence of pretransplantation IgG antibodies against HLA class II antigens relates
to the posttransplantation development of earlier and more
frequent high-grade cellular rejections remains conjectural
at present. Recent cumulative evidence has emerged that
the indirect pathway of CD4 T-cell activation plays a
major role in acute and chronic cardiac allograft rejection
caused by reactivity against donor alloantigenic HLA
peptides processed by host antigen-presenting cells such as
macrophages, dendritic cells, and B cells. In previous
studies, we have shown that acute cellular rejection of
cardiac allografts is accompanied by the appearance both
in the circulation and in the allograft of recipient T cells,
which react with donor HLA-DR peptides presented by
self–antigen-presenting cells.16 Primary rejections appear
to be invariably accompanied by indirect recognition of a
dominant HLA-DR allopeptide,16,17 whereas recurrent rejections appear to be accompanied by intermolecular
spreading and T-cell recognition of multiple donor
HLA-DR alloantigenic determinants.17 Similar patterns of
progressive intramolecular and intermolecular HLA-DR
epitope spreading can be detected in heart transplantation
recipients developing accelerated transplantation-related
CAD.18 This diversification of the immune response has
been postulated to be driven by sensitized B cells that bind
soluble HLA-DR molecules by using specific surface Ig
receptors, endocytose these molecules, and subsequently
present multiple HLA-DR allopeptides to CD4 T cells.19 –21
Therefore, the relation between recurrent high-grade cellular rejections and preexisting IgG anti-MHC class II
antibodies documented in this study may be secondary to
the presence in allosensitized patients of circulating presensitized memory B cells capable of reacting with
HLA-DR molecules and presenting cryptic epitopes to
helper CD4 T cells. The presence of alloreactive B cells in
sensitized candidates may reflect either exposure to alloantigens after administration of blood products, pregnancy,
or prior transplantation or induction of a broad state of
B-cell hyperreactivity caused by an abnormal cytokine
milieu in LVAD recipients.22
In our study, an additional risk factor for early highgrade cellular rejection of the second allograft in retransplantation recipients was a match at the HLA-A MHC class
I locus between the first and second donors. Because this
study was relatively small, the association between donor
1– donor 2 HLA-A locus match and cellular rejection
needs further confirmation. However, the fact that only 1
of 6 patients with a donor 1– donor 2 match also had IgG
anti-II indicates that for retransplantation recipients,
matching between donors at the HLA-A locus and preformed IgG anti-II may be independent risk factors for
high-grade cellular rejection.
Because the presence of IgG anti-MHC class I or II
antibodies in sensitized patients leads to a prolonged
waiting time for transplantation, early posttransplantation
humoral rejection, and earlier and more frequent posttrans-
792
Anti-HLA Class II IgG Antibodies and Cellular Rejection
Figure 5. For retransplantation recipients, matching between the first and
second donors at the HLA-A locus
predisposes to earlier onset of highgrade cellular rejection after
transplantation.
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plantation cellular rejections, strategies to reduce the
levels of these antibodies before transplantation are needed
for this rapidly enlarging pool of patients awaiting heart
transplantation. Prior experience with sensitized patients
has focused on immunosuppressive therapies initiated after
transplantation, including plasmapheresis3 and photophoresis,23 to avoid the negative consequences of these
pretransplantation antibodies. We emphasize the need to
carefully screen all patients at risk for sensitization before
transplantation and to identify the presence, isotype, and
specificity of anti-HLA antibodies that portend heightened
risk for adverse posttransplantation outcomes. Moreover,
our results show that whereas a T-cell PRA may be useful
for identifying individuals at risk of having a positive
donor-specific cross-match and, potentially, of vascular
allograft rejection, it has no predictive value for subsequent cellular rejection. We therefore advocate that all
patients before transplantation should be specifically
screened for the presence of antibodies against both MHC
class I and class II antigens and that immunosuppressive
strategies be instituted. These strategies will need to be
tailored to the antibody specificity detected in any given
patient and the clinical complication it portends. Such
strategies might include the use of intravenous immunoglobulin,24 plasmapheresis,25 or Protein A column immunoadsorption26 to deplete circulating antibody levels or
B-cell immunosuppression with agents such as cyclophosphamide to interrupt pathways of B-cell alloantigenic
presentation.25 In view of the increasing use of LVAD
support and the growing numbers of patients awaiting
retransplantation, high priority should be given to evaluation of therapeutic protocols aimed at reducing anti-HLA
antibodies before heart transplantation.
References
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Downloaded from http://circ.ahajournals.org/ by guest on June 17, 2017
Preformed IgG Antibodies Against Major Histocompatibility Complex Class II Antigens
Are Major Risk Factors for High-grade Cellular Rejection in Recipients of Heart
Transplantation
Silviu Itescu, Thomas C. Tung, Elizabeth M. Burke, Alan Weinberg, Nader Moazami, John H.
Artrip, Nicole Suciu-Foca, Eric A. Rose, Mehmet C. Oz and Robert E. Michler
Downloaded from http://circ.ahajournals.org/ by guest on June 17, 2017
Circulation. 1998;98:786-793
doi: 10.1161/01.CIR.98.8.786
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