Ig heavy chain CDR3 size diversities are similar after conventional peripheral blood and ex vivo expanded hematopoietic cell transplants

Human IgG repertoire of malaria antigen-immunized human immune system (HIS) mice

Humanized mouse models present an important tool for preclinical evaluation of new vaccines and therapeutics. Here we show the human variable repertoire of antibody sequences cloned from a previously described human immune system (HIS) mouse model that possesses functional human CD4+ T cells and B cells, namely HIS-CD4/B mice. We sequenced variable IgG genes from single memory B-cell and plasma-cell sorted from splenocytes or whole blood lymphocytes of HIS-CD4/B mice that were vaccinated with a human plasmodial antigen, a recombinant Plasmodium falciparum circumsporozoite protein (rPfCSP). We demonstrate that rPfCSP immunization triggers a diverse B-cell IgG repertoire composed of various human VH family genes and distinct V(D)J recombinations that constitute diverse CDR3 sequences similar to humans, although low hypermutated sequences were generated. These results demonstrate the substantial genetic diversity of responding human B cells of HIS-CD4/B mice and their capacity to mount human IgG class-switched antibody response upon vaccination.

Reconstitution of the Ig Heavy Chain CDR3 Repertoire after Allogeneic Haematopoietic Stem Cell Transplantation with Myeloablative or Reduced-Intensity Conditioning Regimens

The objective of this study was to investigate B-lymphocyte reconstitution in patients undergoing allogeneic haematopoietic stem cell transplantation (HSCT) after myeloablative conditioning (MAC) or reduced-intensity conditioning (RIC) regimens. B-lymphocyte reconstitution was studied by monitoring the CDR3 repertoire with spectratyping. We demonstrate a delay in the recovery of the B-lymphocyte repertoire, measured by variation in size distribution of the immunoglobulin H CDR3 in patients conditioned with RIC compared to MAC. We found no general explanation for this finding, but when clinical data for each patient were studied in detail, we could identify a cause for the oligoclonality of the B-lymphocyte repertoire after HSCT with RIC for each of the patients. Older patients and donors, low cell dose at transplantation, relapse, graft-versus-host disease (GVHD) and its treatment as well as cytomegalovirus infection and its treatment are all possible causes for the restriction of the B-lymphocyte repertoire observed in this study. Taken together, reconstitution of the B-lymphocyte repertoire after HSCT is a process dependent on multiple factors and differs between patients. The conditioning regimen may be of importance, but data from this study suggest that individual factors and the various complications occurring after HSCT are more likely to determine the development of the B-lymphocyte repertoire.

Human fetal, cord blood, and adult lymphocyte progenitors have similar potential for generating B cells with a diverse immunoglobulin repertoire

Several characteristics of the immunoglobulin (Ig) repertoire in fetuses and adults set them apart from each other. Functionally, this translates into differences in the affinity and effectiveness of the humoral immune response between adults and the very young. At least 2 possibilities could explain these differences: (1) fetal and adult lymphocyte progenitors differ significantly in their potential to form a diverse repertoire, and (2) factors extrinsic to the immunoglobulin locus are more influential to the character of the repertoire. To address this we used nonobese diabetic-severe combined immunodeficient-β2 microglobulin knockout (NOD/SCID/β2m-/-) mice reconstituted with human B-cell progenitors to compare the immunoglobulin repertoire potential of human fetal, cord blood, and adult sources. We found nearly identical VH and JH gene segment use and only modest differences in the third complementarity determining region of the immunoglobulin heavy chain (HCDR3). We conclude that the repertoire potential is remarkably similar regardless of the age of the individual from which progenitors are derived. Age-related differences in the immunoglobulin repertoire and variance of B-cell responses to immunization appear to arise from selection rather than from changes in recombination of the immunoglobulin locus itself. From the standpoint of the Ig repertoire, an immune system reconstituted from fetal or neonatal stem cells would likely be as diverse as one generated from adult bone marrow.