Allotype Reagents Distinguish Donor and Recipient Antibodies after Hematopoietic Transplantation.
Authors: Boiko Julie R. , Sahaf Bita , Miklos David B. 
Published: October 2019

Abstract
Allogeneic immune responses provide beneficial graft-versus-leukemia (GVL) and detrimental graft-versus-host disease (GVHD). To characterize allogeneic B cells and their antibodies in relation to GVHD and GVL, antigen specific assays are required to distinguish donor and recipient antibodies. Inherited polymorphisms in heavy chain constant regions of immunoglobulin can be recognized by allotype specific monoclonal antibodies. We hypothesize that B cell reconstitution differs after myeloablative and nonmyeloablative (NMA) HCT with clinical implications. To test this, we developed allotype ELISAs to quantify donor and recipient antibody responses for specific infectious and allogeneic antigens. Human sera were screened by ELISA coating monoclonal antibodies specific for human allotypes (IgG1m(f), m(z), m(a), IgG2m(n), and IgG3m(g1)) at titers providing shared dynamic ranges. Pre-transplant sera from 48 patients and their donors were serially diluted, and allotype-specific immunoglobulin was detected by alkaline phosphatase-conjugated polyclonal anti-human IgG. Allotype-null sera clearly segregated from wild-type sera with 10-fold absorbency differences. Each null phenotype was confirmed by total IgG and isotype-specific quantification. Overall, IgG1m(f) was null in 8 of 96 sera (null allele frequency 29%), and IgG2m(n) was null in 23 of 96 (null allele frequency 48%). Six patients were null for both, and overall 17 of 48 donor/recipient transplant pairs were informative for either allotype. Nulls for the remaining three allotypes were infrequently recognized limiting their clinical utility. Additionally, we measured monoclonal IgG1 purified from 5 multiple myeloma patients identifying three null alleles, one wild-type, and a single intermediate polymorphism. Labeled conjugation of the wild-type monoclonal IgG1 enables competitive inhibition analysis of null allotype improving null allotype sensitivity for engraftment less than 5%.
Sera were collected monthly from all HCT patients informative for allotype antibody. Three NMA HCT patients who underwent total lymphoid irradiation and anti-thymoglobulin (TLI/ATG) conditioning have donors that are null for IgG2m(n) and are being prospectively assessed for recipient antibody loss. Their recipient allotype-specific IgG persists at pretransplant recipient levels in all three patients measured six months after NMA HCT, and the lead patient expresses 100% pretransplant recipient allotype antibody ten months after HCT. Conversely, a single NMA patient null for IgG2m(n) with a wild-type donor has no detectable IgG2m(n) donor antibodies four months after HCT despite having 100% donor peripheral B cell engraftment measured 30 days after NMA HCT. In contrast, an informative patient undergoing myeloablative HCT developed 25% IgG2m(n) donor specific antibodies 3 months post-transplant, and 50% at 7 months. Others have reported donor allotype specific antibody achieves full engraftment by 6 months after myeloablative HCT (Van Tol et al. Blood 1996). Our ongoing preliminary studies suggest NMA HCT patients experience delayed donor antibody onset and prolonged recipient antibodies as compared to patients undergoing myeloablative HCT. In order to confirm this, we are measuring antigen-specific donor allotype antibody reconstitution for infectious antigens (EBV and tetanus) and allogeneic H-Y antigens.