Biovetenskaper och näringslära / Biosciences and Nutrition
Abstract
The HLA (Human Leukocyte Antigen) region is the most polymorphic in the
human genome. The extended polymorphism contributes to the ability both
of individuals and populations to combat diversity in the pathogens to
which they are exposed. The region was first discovered through its
influence on transplantation rejection and on antigen-specific immune
responses. Today, we know that HLA molecules are receptors for peptides
derived from self and foreign antigens, which are captured within the
cleft of the HLA molecule and presented to T cells. The interaction
between the T cell receptor (TCR) and the MHCpeptide complex is a first
step in the activation of the T cell. In clinical transplantation HLA
incompatibilities between patient and donor leads to an immune response
directed against the transplanted cells (host versus graft reaction) or
in stem cell transplantation, against the cells of the recipient in
immunodeficient patients (graft versus host reaction, GVHD).
Initially, the HLA antigens were defined using serological typing
techniques. However, human alloantisera are of limited value when
detecting allelic variation located deep within the cleft of the HLA
molecules which is inaccessible to antibodies. Consequently, many
polymorphisms in HLA molecules can be serologically silent or
undetectable by allotypic antisera. During the last few years DNA based
typing techniques have begun to replace the serological techniques in
clinical applications. Initially, the DNA methods were applied to class
11 typing, but more recently they have been used to determine class I
alleles as well. We have developed a polymerase chain reaction-based
technique, using sequence-specific primers (PCR-SSP) for HLA class I and
class 11 typing. In this thesis PCR- SSP typing is described for the DQB
1, DPA 1 and DPB 1 loci.
The recent use of DNA based typing techniques has resulted in many new
HLA alleles being identified. One new allele, DQB 1*0609, which was found
during the development of DQB1-typing by PCR-SSP, is described here.
Finally, we have, retrospectively, studied the correlation between the
grade of HLA matching and the outcome of the transplantation, in patients
receiving stem cells from unrelated donors. We found a high frequency of
severe GVHD and a high mortality rate in patients receiving HLA-B allele
level mismatched stem cells. We also found that patients that received
stem cells from donors mismatched for HLA-C, as well as for the NK cell
KIR ligand motif had a decreased survival and decreased disease- free
survival. Finally, we observed that patients receiving DPA1 mismatched
stem cells had decreased survival and relapse-free survival (RFS), which
indicates that DPA1 polymorphism is immunologically relevant in stem cell
transplantation. These patients also had an increased frequency of
relapses.
In conclusion, genomic HLA class I and II typing adds substantially to
the success of transplantation of hematopoetic stem cells from unrelated
donors. The awareness of HLA class I and II mismatches in a
recipient-donor pair form the basis for the appropriate preand
post-transplantation treatment, which will improve the outcome of the
transplantation