T cell-mediated immunity targeting polyomavirus BK

Transplant recipients are treated with immunosuppressive agents to prevent
rejection of the allograft, a process mediated by the host*s immune system. The
ensuing impairment of the different compartments of the immune system, among
which most prominently the T cell compartment then leads to inadequate defence
against invading microorganisms among which viruses.

Polyomavirus BK (BKV) is a double-stranded DNA virus that resides in a latent
state in the urogenital tract in 70-90% of the general population and is not
associated with disease in immunocompetent individuals. However, in
immunocompromised patients, especially in transplant recipients and to a lesser
degree also in HIV patients, BKV currently is a prominent troublemaker. In
renal transplant recipients it is the leading cause of graft failure, causing
nephritis in up to 7% of cases. In haematopoietic stem cell recipients, BKV
causes severe haemorrhagic cystitis in up to 30% of patients, a clinical entity
leading to significantly prolonged hospitalisation and increased mortality.
Apart from the clinical aspects, also a significant amount of resources is
currently being directed towards the monitoring of BKV replication in urine and
blood in order to pre-emptively identify patients at risk of nephropathy or
haemorrhagic cystitis.

Currently, the only mode of therapy with established efficacy is tapering of
immunosuppressive agents so that the host*s immune system can mount a response
against the virus. However, in transplant recipients this is a double-edged
sword since the reconstituted immune responses not only target BKV, but also
the allograft, therewith causing rejection. As such, it is of paramount
importance that new modes of therapy targeting BKV are identified.

T cells, and more specifically CD8+ T cells, play an important role in the
protection against viral infections, and have been shown to be important in
keeping BKV infection at bay in transplant recipients. Currently, little is
known about the T cell responses directed against BKV in healthy or
immunocompromised patients. As such, in-depth knowledge of the qualitative and
quantitative aspects of the T cell response targeting BKV, will aid in the
search for new future modes of therapy such as for example vaccination or the
infusion of ex-vivo generated BKV-specific T cells as been done previously in
the case of Epstein-Barr virus (EBV) and cytomegalovirus (CMV) associated
disease.

Clarifying the qualitative and quantitative aspects of the T cell response
targeting and controlling polyomavirus BKV.

The study will involve one group of study subjects comprising 400 renal
transplant recipients with or without BKV reactivation. The clinical management
of these renal transplant recipients included is not to be influenced on any
level by this study.

Blood samples will be obtained at several specific time points, in order for us
to be able to identify changes in T cell numbers and phenotype in the context
of the course of the disease. Sampling moments comprise: once
pre-transplantation, and then consecutively at 3, 6, 9 and 12 months in the
first year after transplantation. After the first year, the sampling frequency
will be reduced to once every two years. If the patient shows BKV reactivation,
the sampling frequency will be increased to once every month during the first
year after transplantation and once every 3 months after the first year
post-transplantation.
Blood samples will comprise 45 ml blood for the isolation of peripheral blood
mononuclear cells (among which lymphocytes), 4.5 ml for serum measurements, 4.5
for plasma measurements and 4.5 for virologic measurements.
As such, patients will not have to come to the hospital more often than would
be required of them normally. Also, patients do not have to undergo more
peripheral venous punctions than that they would otherwise.

In order to identify BKV reactivation, real-time quantitative polymerase chain
reaction (rt-QPCR) is used on plasma samples in all patients to measure the
viral load. During the pre-transplantation work-up, and after having given
written informed consent, the patient will be included, and will subsequently
undergo the sampling protocol as described above.

For the identification of numbers of T cells, we will utilise fluorescent
antibodies targeting a variety of different cell markers measured by
flowcytometry. To identify MHCI and MHCII-restricted BKV-specific T cell
responses, we will respectively utilize fluorescent HLAI-BKV-peptide tetramers
and BKV-antigen pulsed APCs. Further phenotypic analysis will occur through the
use of fluorescent antibodies and flowcytometry. Functionality of BKV-specific
T cells will be assessed by measurement of the various cytokines, chemokines
and effector molecules. Lastly, new T cell epitopes will be identified using an
epitope discovery assay.

Using these laboratory techniques, we will be able to compare T cell numbers,
phenotypes and T cell epitopes over the different time points, therewith
revealing what kind of T cells, T cell functions and T cell epitopes are
important in controlling BKV infection.

At the same time points, urine samples will be collected and frozen. At a later
time point they will be analysed for the presence of pro-and anti-inflammatory
cytokines and chemokines.

Patients will be burdened with the donation of extra blood samples and urine
samples in addition to the samples needed for clinical practice. The sampling
moments for patients will be done once pre-transplantation, followed by
respectively 3, 6, 9 and 12 months during the first year post-transplantation.
Thereafter, sampling moments are reduced to a 2 yearly basis. The sampling
comprises 58.5 ml per sampling moment, including 45 ml for the isolation of
peripheral blood mononuclear cells (among which lymphocytes) plus 4.5 ml for
plasma measurements, 4.5 ml for serum measurements and 4.5 for virologic
measurements. When the virologic measurements reveal viral (re)activation,
sampling moments will be increased to a monthly basis in the first year
post-transplantation and to a 3 monthly basis in the period after the first
year post-transplantation, up until viral clearance. On the same time points,
urine samples will also be obtained. As such, patients will not have to come
to the hospital more often than would be required of them normally. Also,
patients do not have to undergo more peripheral venous punctions than that they
would otherwise. The individual patient will not directly benefit from these
extra samples taken. We regard the risk and the burden to be minimal.