Correlation of Donor-specific Anti-endothelial Cells

Antibody Mediated Rejection (AMR) is a major complication of solid organ transplantation. The
main reason for AMR is pre-formed, or de-novo, donor specific antibodies against the donor
HLA antigens. Additional potential targets are antibodies against MIC-A antigens or
antibodies against targets expressed on the donor endothelial cells.

Until recently, no specific means were available to test for the presence of donor-specific
endothelial cell antibodies. The newly introduced XM-One AbSorber® assay allows isolating
precursor endothelial cells from donor peripheral blood, and thus assessing the presence of
donor-specific endothelial cell antibodies.

XM-One AbSorber® is an in-vitro assay that allows for the specific enrichment of precursor
endothelial cells which in turn promotes endothelial cells specific cross match testing.

This assay is currently being used in an on-going Northwestern University (NU) research study
(STU#00029988). The preliminary results of this study indicate that indeed some of the
patients test positive against their respective donors. One potential explanation for this
observation, that was not previously entertained, is that the antibodies causing the positive
cross match response are actually of autoimmune nature. In order to rule-out such a potential
explanation we would like to further test these patients by performing an autologous XM-One
AbSorber® assay in which the recipient sera will be incubated with the patients' own cells
(as opposed to the respective donor cells in the parental study). This information is crucial
for proper analysis of the data obtained in the NU STU#00029988 study.

Initial data from our laboratory indicates that the antigens identified by the XM-One
Absorber® assay differ from the HLA antigens usually identified by routine cross match
assays. Moreover, we were able to document that this is a polymorphic system and therefore
identifying a donor-specific source is critical.

Of the 150 patients already studied under NU research protocol STU#00029988 we found that 19
patients exhibited a positive response in a donor-specific XM-One AbSorber® assay. In this
current research protocol study we want to follow-up on the specimens that exhibited a
positive response in a donor-specific XM-One AbSorber® assay and perform an autologous XM-One
AbSorber® assay to validate the clinical significance of our results.

There has been one multicenter study reported indicating the "XM-One AbSorber® is a quick,
easy to perform on whole blood samples and identifies patients at risk for rejection and
reduced graft function not identified by conventional lymphocyte cross matches" The primary
objective is to complete additional testing for accuracy to determine whether antibodies
directed at donor-specific endothelial cell effect transplant outcome.

The secondary objective is to assess the frequency of autologous antibodies that may be
falsely reported as donor-specific anti-endothelial antibodies in our patient population. The
single center research study we here at Northwestern University have been working on since
May 19, 2010 thus far has resulted in 19 out of 150 specimens tested, have positive results
based on the XM-One AbSorber® assay.

In this prospective study we plan to include all XM-One AbSorber® positive test results from
all recipients of living-donor kidney transplants performed at Northwestern Memorial Hospital
(NMH) since May 19, 2010 initial Institutional Review Board (IRB) approval until 250
transplants are performed. For this research protocol we will be targeting patients to
consent only these individuals who have received a XM-One AbSorber® positive test result.

Each donor / recipient pair are required to send peripheral blood samples to the HLA
laboratory prior to the scheduled transplant in order to perform lymphocyte cross match (to
detect donor specific HLA antibodies; this is (SOC) standard of care). Left over serum and
cells from these tests are being used to isolate an enriched precursor endothelial cell
population and perform the XM-One AbSorber® assay (NU research protocol #STU00029988).

XM-One AbSorber® assay results - both autologous and allogeneic - will be captured and
compared with graft outcome measurements at 3, 6, and 12 months post-transplant. Transplant
outcome will be recorded as creatinine levels at the specific time points, protocol and
for-cause biopsy results within the first year post transplant, diagnosis of acute cellular
or humoral rejection, variation in immunosuppression levels, and any other complications.

Patients that exhibit a positive XM-One AbSorber® allogeneic cross match result will be
requested to donate 4 green top tubes of peripheral blood. Cells obtained from this blood
will be used in an autologous XM-One AbSorber® cross match assay using the original serum
sample used for the allogeneic XM-One AbSorber® cross match assay.

Inclusion Criteria:

1. patients older than 18 years of age

2. patients undergoing living-donor kidney transplant at NMH who have a positive XM-One
AbSorber® positive test result

Exclusion Criteria:

1. patients undergoing deceased donor kidney transplant

2. patients younger than 18 years of age