The characterization of T cells that reside in kidney transplants

It is becoming increasingly apparent that memory T cells of the peripheral
circulation are phenotypically and functionally distinct from memory T cells
that reside in specific organ systems such as the central nervous system, the
skin, the gut and the lungs. Upon priming of naïve T cells with their cognate
antigens, as presented by specialized dendritic cells (DCs), T-cells undergo
tissue-specific programming that allows them to home to, and reside in the
organ system where they are most needed. There, these cells provide a first
line of defence against microorganisms that have a propensity for invading that
specific organ system.
For example, T cells that have been instructed by specialized DCs present in
the Peyer*s patches and the mesenteric lymph nodes in the intestine, start
expressing several localizing molecules such as CCR9 and α4β7 integrin by which
they home and bind to their ligands, CCL25 and MadCAM-1 that are exclusively
expressed by endothelial cells and epithelial cells also located in the
intestine, thereby transforming them into *gut-homing T cells*. Recently, our
group showed that there are specialized CD8+ T cells that reside in the lung.
These cells expressed the αE inetgrin CD103 which mediates binding to lung
epithelium. Interestingly, this subset of T cells is not present in the
peripheral circulation and is specific only for the respiratory influenza
virus,but not for the systemic viruses Epstein-Barr virus (EBV) and
Cytomegalovirus. As such, these cells seem to provide a localized first line of
response to respiratory viruses.
Taken together, we now hypothesize that there are also T cells with a unique
phenotype that confer a localized protection against renotrope viruses in the
kidney. For example, polyomavirus BK (BKV) is strongly renotrope and latently
infects 70 to 90 percent of the population. Normally it does not cause any
known disease in immunocompetent individuals. However, in immunocompromised
patients, such as renal transplant recipients, BKV frequently (re)activates and
may cause BKV-associated nephropathy (BKVN). Currently, with no other
therapeutic strategy available other than tapering the immunosuppressive
regimen, BKVN is a major cause of graft loss in renal transplantation.
Moreover, tapering of the immunosuppressive regimen, in order for the patient*s
immune system to mount an antiviral response, is a double-edged sword since it
will also lead to more rejection of the allograft. Therefore, more specific
treatments targeting BKV are direly needed to improve the outcome of kidney
transplantation. Given the strong association between BKV-associated disease
and immunodeficiency, and conversely, the lack of BKV-associated disease in
immunocompetent individuals, the normal, mostly T cell-mediated immune
response, seems to be of particular value in keeping BKV at bay. As such,
knowledge about the T cell response may lead to new therapeutic insights where
BKV is specifically targeted rather than also compromising the allograft by the
tapering of immunosuppressive medication. Examples of highly specific
therapeutic strategies that have used such knowledge and that are currently
already applied in transplantation medicine, are vaccination and the adoptive
transfer of EBV- and CMV-specific T cells.
In kidney transplant recipients, kidney-resident T cells could also be
of importance in allograft rejection due to so called heterologous immunity. It
is known that virus-specific T cells can cross-react with human leukocyte
antigen (HLA)-antigenic peptide complexes. Such cross-reactive T cells would be
harmless in a healthy individual where they confer protection against their
cognate antigen, but might respond to a *foreign* allograft in the context of
transplantation, as such mediating allograft rejection. Viral (re)activation is
not uncommon in renal transplant patients due to the immunosuppressive
medication, pre-existing antiviral and cross-reactive T cells will expand owing
to the antigenic pressure. Indeed, both acute and chronic allograft rejection
has been associated with several viral infections, amongst which importantly
CMV. The significance of cross-reactive T cells as a negative influence on
graft survival was further established in several mouse models. In
pathogen-free mice, tolerance to the allograft was readily induced by treatment
with monoclonal antibodies that block T cell co-stimulation, such as
anti-CD154. However, this effect was abrogated by inducing viral infections.
Also, mice that were previously infected with multiple viruses proved to be
refractory to tolerance, whilst uninfected mice or mice infected with only a
single virus, were still susceptible to tolerance induction.
Given the above, it is important to gain knowledge about T cells
present the kidney. The technology to extract these T cells from small tissue
samples is available in our research group and we have extentive experience
with the analyses of the phenotype and function of virus and allo-specific T
cells. Therefore, we ask permission to obtain additional tissue samples during
renal allograft biopsies in kindey transplant recipients that occur on standard
clinical indications or for research purposes.

The characterization of T cells that reside in kidney transplants.
The characterization of the T cell-mediated antiviral responses in kidneys
The role of kidney-resident T cells in acute and chronic allograft rejection

If transplant recipients undergo a kidney biopsy after transplantation because
of standard clinical evaluation, they will be asked to donate one extra tissue
sample. In addition, transplant recipients will be asked to donate 57 ml of
peripheral venous blood and an urine sample on the same day. In this way, T
cells residing in the kidney can be compared to peripherally circulating T
cells from the same individual. If biopsy moments coincide with a
blood-withdrawal in context of the Allegro study (CCMO registration number
NL32205.042.10) or BK virus study (CCMO registration number NL39356.018.12), no
extra blood sample will be obtained. Peripheral blood mononuclear cells (PBMCs)
will be isolated and stored in liquid nitrogen until further use. Function ,
phenotype and specificity of peripheral and renal T cells will be analyzed by
flow cytometry as described in the research protocol.

A kidney biopsy bears the risk of the formation of a hematoma in the biopted
kidney. We regard this additional risk on the formation of hematoma due to the
extra biopsy to be small.