Fields of scholarship#

In the last five decades a multitude of studies has shown that the polymorphism of the HLA system plays an important role in the mutual Fetal ­ Maternal tolerance during pregnancy, the prognosis of blood component therapy and organ and haemopoietic stem cell transplantation and the susceptibility for or resistance against a great number of infectious and immuno-pathogenic diseases. Van Rood played a key role in the unravelling of the HLA polymorphism and the application of this information to the study of all three fields mentioned above.

I The discovery of HLA and its polymorphism#

In the late fifties several workers had shown that antibodies against leukocyte alloantigen could be induced by blood transfusion, but, because they were multi-specific and soon lost their specificity, they proved difficult to work with and typing for these antigens was not possible.The first major contribution by van Rood was his observation (Nature 1958) that pregnancy could induce leukocyte antibodies as well. The pregnancy induced leukocyte antibodies were of course less polyclonal than blood transfusion induced antibodies and for reasons which are still not well understood can be detected in women many decades after the last pregnancy.

His second important contribution was the development of a methodology and its application to identify useful typing reagents for the HLA antigens. In brief, the sera from a large number of women who had formed leukocyte alloantibodies during pregnancy were tested against the leucocytes obtained from 100 unrelated donors. A computer-assisted cluster analysis at a time, that computers were still a rarity, identified two clusters of sera with high internal consistency i.e. they reacted or did not react with the leucocytes of approximately the same donors. The deter­minants so recognized were of contrasting specificity and could be shown to be coded for by allelomorphic genes (Thesis (cum laude) 1962, J.Clin. Invest 1963). They are now known as HLA-Bw4 and -Bw6.

The importance of this discovery did not lie only in the fact that it was a first description of diallelic antigens in the HLA system but above all in providing a systematic approach by which the complexity of the HLA system could be unravelled. Using this approach Van Rood and collaborators described 9 HLA antigens and a diallelic system not linked to HLA (the group Five system).

Together with Balner, Van Rood developed a protocol by which it could be demonstrated that these leukocyte antigens were in fact transplanta­tion antigens. At the same time but independently Dausset and Van Rood suggested that the majority of these antigens might belong to one system; Dausset on the basis of association data, Van Rood on family data. An intensive international cooperation made it possible to unravel the complexity of the HLA system further.

Next Amos, Bain, Eijsvoogel, Yunis and notably Bach discovered that the HLA system contained a separate locus, HLA-D, that coded for determinants which were able to induce blast formation in allogeneic T lymphocytes and can be studied in the mixed culture Lymphocyte (MLC) test originally described by Bach et al. and Bain et al.

In 1973 Van Rood and his collaborators described a serological method to identify antibodies which recognised these HLA-D determinants. Many of these genes predispose for HLA associated diseases.

II Translational research#

During the studies on the genetic complexity of the HLA system a consci­entious effort was made to implement the information so obtained in the clini­c, as can be exemplified as follows:

1. The first HLA matched platelet transfusions in the treatment of aplastic anaemia were given in Leiden, in 1964.

2. After demonstrating in a retrospective study that HLA matching could improve kidney graft survival, van Rood. proposed and actually started the first international organ-exchange organization: Eurotransplant. There after similar organisations have been started all over the world. The activities in Euro­transplant have not only led to improved patient care but provided also new possibilities for (clinical) research. These included under more a possible explanation for the pre-transplant blood­ transfusion effect., which is dependent on a sharing of a HLA class II antigen between blood transfusion donor and recipient.

3. The first successful bone marrow transplant to treat a boy suffering from Severe Combined Immune Deficiency in Europe with the help of the bone marrow of an HLA identical sibling donor was done in Leiden at the same time that similar transplants were done in the USA. There after patients were also treated for malignancies such as acute and chronic leukaemia’s. However many of the patients in need of a stem cell donor do not have an HLA identical sibling . Van Rood proposed already in 1972 (Transpl. Proc. VI no. 4: 411, 1974) to start a registry, called Europdonor, of HLA typed blood transfusion donors, who were willing to donate stem cell to an unrelated and anonymous patient. In 2009 there are almost 13 million of such donors listed in 100 different registries and cord blood banks on all five continents, which can be found in "Bone Marrow Donors Worldwide", another initiative of van Rood

4. HLA and disease#

The Leiden group was the first to present significant evidence that an epidemic first of typhoid fever and next of yellow fever, which decimated a colony of Dutch immigrants in Surinam, shifted the frequency of HLA Class II determinants in the survivors and their descendants. A classical example of Darwinian selection.

A concerted effort has also been made to study the genetic factors involved in the occurrence of major endemic diseases. A model for such studies was leprosy. About 12 million people are suffering from this disease in which failure of cellular immunity plays a major role. Systematic studies from the Leiden group have brought forward the following important points:

a. the genetic predisposition for the diseases is probably not governed by the HLA system but by a locus or loci outside the HLA system.

b. The HLA system does play a role however in determining in patients who have been infected whether they get the lepromatous or the tuberculoid form of the disease. The tuberculoid form of the disease is far more frequent in patients who are carrying the DR3 antigen.

This has led to an ongoing effort to develop vaccines for this debilitating disease.

III Fetal ­Maternal Tolerance#

After the observation in 1958 that pregnancy per se could induce the formation of HLA antibodies in about 30% of pregnant women, van Rood noted in 1988 that patients on the waiting list for a renal transplant, who were highly immunised due to previous blood transfusions, a rejected kidney etc. had nevertheless not formed antibodies against antigens known to be in linkage disequilibrium such as HLA-A1 - -B8, -A3 - -B7 etc. He wondered, probably inspired by previous observations by Ray Owen, whether this was due to tolerance to the Non Inherited Maternal Antigens to which the patient has been exposed during pregnancy and breast feeding. This turned out to be the case (Claas et al, Science 1988). This observation has practical consequences in renal transplantation and CB stem cell transplantation, but also for the predisposition for and protection against rheumatoid arthritis**

5. A follow-up of this study has shown that non-inherited maternal antigens might induce a form of (partial) tolerance of the child towards the mother. This has possibly important consequences for organ and bone marrow trans­plantation and the pathogenesis of auto-immune diseases.