Alloantibodies against MHC Class I: A Novel Mechanism of Neonatal Pancytopenia Linked to Vaccination

Abstract

Fetal/neonatal alloimmune thrombocytopenia is a frequent disease in humans where alloantibodies against platelet Ags lead to platelet destruction and hemorrhage. Although a role in the disease for Abs against MHC has been suspected, this has not been formally demonstrated. Since 2007, a hemorrhagic syndrome due to thrombocytopenia and designated as bovine neonatal pancytopenia (BNP) has been recognized in calves in several European countries. An inactivated antiviral vaccine is strongly suspected to be involved in this syndrome because of its highly frequent use in the dams of affected calves. In this study, we show that BNP is an alloimmune disease, as we reproduced the signs by transferring serum Abs from vaccinated BNP dams into healthy neonatal calves. Ab specificity was strongly associated with the presence of allogeneic MHC class I Abs in the dams. MHC class I staining was also observed on Madin–Darby bovine kidney cells, a cell line related to the one used to produce the vaccine Ag. Our report emphatically demonstrates that alloimmunization against MHC class I is associated with a substantial risk of developing cytopenia-associated syndromes in neonates when a cell line of the same species is used to produce an inactivated vaccine injected into the mother.

The risks of using allogeneic cell lines for vaccine production: the example of Bovine Neonatal Pancytopenia

“…To manufacture this vaccine, BVD virus is cultured in Madin-Darby bovine kidney (MDBK) cells [30] and, following purification, combined with a novel proprietary adjuvant (Procison-A TM ; a micro-fluidized oil-in-water adjuvant composed of Quil-A, Cholesterol, mineral oil [31]). High levels of residual bovine proteins have been detected in Pregsure© [8,9,32] and alloantibodies from BNP cows have been shown to recognize MDBK cells [8,9,12,19]. Furthermore, experimental immunization of calves with Pregsure© confirmed that vaccination induces alloantibodies that bind MDBK cells and leukocytes [10,19].…”

“…Furthermore, serum and colostrum from BNP cows were shown to contain alloantibodies that bind to peripheral blood leukocytes, platelets and bone marrow cells [9,11,12,[18][19][20][21], and intravenous infusion of these antibodies was sufficient to induce the disease [9]. The bovine epitheliochorial placenta presents a complete barrier to the transfer of immunoglobulins from the cow to the fetus, and thus the calf is completely dependent on ingestion of colostrum for maternal immunoglobulin transfer [22], explaining why BNP only occurs postpartum.…”

“…It is now clear that BNP is caused by vaccine-induced maternal alloantibodies which are transferred from mother to calf via the colostrum (first milk rich in maternal antibodies). These alloantibodies, which are specific for major histocompatibility complex class I (MHC I) molecules, are generated in response to residual cell-line material found within a specific vaccine containing a novel adjuvant formulation [8][9][10][11][12]. BNP therefore highlights important issues regarding the safety of using allogeneic cell lines for vaccine production.…”

“…By using sera from BNP cows to immunoprecipitate antigens from the surface of MDBK cells [8] and peripheral blood leukocytes [9], MHC I molecules were identified as a target of BNP alloantibodies. Using transfected cell lines, sera from BNP cows were also shown to bind specifically to the MHC I alleles present on MDBK cells and to induce complement-mediated cytotoxicity [11].…”

“…Even allowing for underreporting of cases, it became clear that factors other than Pregsure© vaccination alone must therefore determine whether BNP develops in the calf. Following identification of MHC I as the antigenic target in BNP, it was hypothesized that epitope differences between the MHC I alleles expressed by MDBK cells and a given cow would determine the induction of alloantibodies and, conversely, that epitope similarities between MDBK cells and a given calf would determine its propensity to develop the disease [8,9]. Subsequently this was supported by the finding that Pregsure© vaccinated cows generate a unique profile of MHC I-specific alloantibodies, presumably reflecting the degree of alloantigen mismatch between their MHC I alleles and those of the vaccine cell line [11,12].…”