During the SARS-CoV-2 pandemic, novel and traditional vaccine strategies have been deployed globally. We investigated whether antibodies stimulated by mRNA vaccination (BNT162b2), including 3 rd dose boosting, differ from those generated by infection or adenoviral (ChAdOx1-S and Gam-COVID-Vac) or inactivated viral (BBIBP-CorV) vaccines. We analyzed human lymph nodes after infection or mRNA vaccination for correlates of serological differences. Antibody breadth against viral variants is less after infection compared to all vaccines evaluated, but improves over several months. Viral variant infection elicits variant-specific antibodies, but prior mRNA vaccination imprints serological responses toward Wuhan-Hu-1 rather than variant antigens. In contrast to disrupted germinal centers (GCs) in lymph nodes during infection, mRNA vaccination stimulates robust GCs containing vaccine mRNA and spike antigen up to 8 weeks post-vaccination in some cases. SARS-CoV-2 antibody specificity, breadth and maturation are affected by imprinting from exposure history, and distinct histological and antigenic contexts in infection compared to vaccination.

The relationship of SARS-CoV-2 pulmonary infection and severity of disease is not fully understood. Here we show analysis of autopsy specimens from 24 patients who succumbed to SARS-CoV-2 infection using a combination of different RNA and protein analytical platforms to characterize inter-patient and intra-patient heterogeneity of pulmonary virus infection. There is a spectrum of high and low virus cases associated with duration of disease. High viral cases have high activation of interferon pathway genes and a predominant M1-like macrophage infiltrate. Low viral cases are more heterogeneous likely reflecting inherent patient differences in the evolution of host response, but there is consistent indication of pulmonary epithelial cell recovery based on napsin A immunohistochemistry and RNA expression of surfactant and mucin genes. Using a digital spatial profiling platform, we find the virus corresponds to distinct spatial expression of interferon response genes demonstrating the intra-pulmonary heterogeneity of SARS-CoV-2 infection.

We generated mice in which a functional RAG2:GFP fusion gene is knocked in to the endogenous RAG2 locus. In bone marrow and thymus, RAG2:GFP expression occurs in appropriate stages of developing B and T cells as well as in immature bone marrow IgM+ B cells. RAG2:GFP also is expressed in IgD+ B cells following cross-linking of IgM on immature IgM+ IgD+ B cells generated in vitro. RAG2:GFP expression is undetectable in most immature splenic B cells; however, in young RAG2:GFP mice, there are substantial numbers of splenic RAG2:GFP+ cells that mostly resemble pre-B cells. The latter population decreases in size with age but reappears following immunization of older RAG2:GFP mice. We discuss the implications of these findings for current models of receptor assembly and diversification.

We generated mice harboring germline mutations in which the enhancer element located 9 kb 3' of the immunoglobulin kappa light chain gene (3'E kappa) was replaced either by a single loxP site (3'E kappa delta) or by a neomycin resistance gene (3'E kappa N). Mice homozygous for the 3'E(kappa delta) mutation had substantially reduced numbers of kappa-expressing B cells and increased numbers of lambda-expressing B cells accompanied by decreased kappa versus lambda gene rearrangement. In these mutant mice, kappa expression was reduced in resting B cells, but was normal in activated B cells. The homozygous 3'E(kappa)N mutation resulted in a similar but more pronounced phenotype. Both mutations acted in cis. These studies show that the 3'E(kappa) is critical for establishing the normal kappa/lambda ratio, but is not absolutely essential for kappa gene rearrangement or, surprisingly, for normal kappa expression in activated B cells. These studies also imply the existence of additional regulatory elements that have overlapping function with the 3'E(kappa) element.

T cell receptor (TCR) beta chain allelic exclusion occurs at the thymocyte CD4- 8- (double-negative, or DN) to CD4+ 8+ (double-positive, or DP) transition, concurrently with differentiation and cellular expansion, and is imposed by a negative feedback loop in which a product of the first rearranged TCRbeta allele arrests further recombination in the TCRbeta locus. All of the major events associated with the development of DP cells can be induced by the introduction of TCRbeta or activated Lck transgenes. Here, we present evidence that the signaling pathways that promote thymocyte differentiation and expansion of RAG-deficient DN cells but not those that suppress rearrangements of endogenous TCRbeta genes in normal DN cells are engaged by activated Ras. We propose that TCRbeta allelic exclusion is mediated by effector pathways downstream of Lck but independent of Ras.

During lymphocyte development, V(D)J recombination is highly regulated in the contexts of lineage specificity, developmental-stage specificity, and allelic exclusion (4, 5). In addition, developing lymphocytes use strategies that require productive V(D)J rearrangements for continued developmental progression (4, 5). For example, Ig heavy chain (IgH) variable-region genes are assembled in progenitor (pro) B cells via an ordered process in which D H -to-J H rearrangement occurs on both alleles before V H -to-DJ H rearrangement. Productive V H -to-DJ H rearrangements produce cell-surface expression of IgH chains that signal expansion and differentiation of pro-B cells to the pre-B cell stage. This expression of IgH chains also signals the cessation of further V H -to-DJ H rearrangement via feedback regulation. Pro-B cells that first assemble nonproductive V H -to-DJ H rearrangements proceed to rearrange their second allele.Both RAG1 and RAG2 are required for V(D)J recombination, because RAG1-or RAG2-deficient mice exhibit a complete block in lymphocyte development at the progenitor stage (6, 7). In addition, RAG1 and RAG2 together are sufficient to initiate V(D)J recombination in vitro (8). Nearly all in vitro studies of RAG function have used the minimal regions of RAG1 (amino acids 384-1,008 of 1,040) and RAG2 (amino acids 1-383 of 527) required for activity, because full-length RAG1 and RAG2 are largely insoluble. However, the activities of these mutant ''core'' proteins differ from those of the full-length RAGs when assayed with extrachromosomal substrates in transfected cells. In this context, the mutant core RAG proteins support V(D)J recombination with reduced efficiency and with different levels and types of recombination products (9-15).Although not required for the biochemistry of V(D)J recombination, the noncore regions of RAG1 and RAG2 are conserved throughout evolution. For example, sequence conservation across the entire RAG2 protein from pufferfish to humans is Ϸ60%, with conservation of the noncore C-terminal region slightly higher than the core domain (16). Therefore, the noncore regions of RAG1 and RAG2 may serve important accessory and͞or regulatory functions in chromosomal V(D)J recombination. Consistent with this notion, studies of Abelson murine leukemia virus-transformed pre-B cells have suggested that the noncore regions of RAG1 are important for IgH locus D H -to-J H rearrangement (17), whereas the C terminus of RAG2 is more important for V H -to-DJ H rearrangement than for D H -to-J H rearrangement (18). The C terminus of RAG2 is predicted to fold into a plant homeodomain (PHD) (19,20), a motif found in a number of chromatin-associated proteins including some that have chromatin-modifying activities (21-24).To investigate potential in vivo function of the RAG2 noncore region in chromosomal V(D)J recombination and normal lymphocyte development, we have generated and characterized mice containing specific replacement of the full-length endogenous RAG2 gene with a gene encoding the mouse core...

We have used gene-targeted mutation to assess the role of the T cell receptor delta (TCR delta) enhancer (E delta) in alphabeta and gammadelta T cell development. Mice lacking E delta exhibited no defects in alphabeta T cell development but had a severe reduction in thymic and peripheral gammadelta T cells and decreased VDJ delta rearrangements. Simultaneous deletion of both E delta and the TCR alpha enhancer (E alpha) demonstrated that residual TCR delta rearrangements were not driven by E alpha, implicating additional elements in TCR delta locus accessibility. Surprisingly, while deletion of E delta severely impaired germline TCR delta expression in double-negative thymocytes, absence of E delta did not affect expression of mature delta transcripts in gammadelta T cells. We conclude that E delta has an important role in TCR delta locus regulation at early, but not late, stages of gammadelta T cell development.

RAG1 and RAG2 are the lymphocyte-specific components of the V(D)J recombinase. In vitro analyses of RAG function have relied on soluble, highly truncated “core” RAG proteins. To identify potential functions for noncore regions and assess functionality of core RAG1 in vivo, we generated core RAG1 knockin (RAG1c/c) mice. Significant B and T cell numbers are generated in RAG1c/c mice, showing that core RAG1, despite missing ∼40% of the RAG1 sequence, retains significant in vivo function. However, lymphocyte development and the overall level of V(D)J recombination are impaired at the progenitor stage in RAG1c/c mice. Correspondingly, there are reduced numbers of peripheral RAG1c/c B and T lymphocytes. Whereas normal B lymphocytes undergo rearrangement of both JH loci, substantial levels of germline JH loci persist in mature B cells of RAG1c/c mice, demonstrating that DJH rearrangement on both IgH alleles is not required for developmental progression to the stage of VH to DJH recombination. Whereas VH to DJH rearrangements occur, albeit at reduced levels, on the nonselected alleles of RAG1c/c B cells that have undergone D to JH rearrangements, we do not detect VH to DH rearrangements in RAG1c/c B cells that retain germline JH alleles. We discuss the potential implications of these findings for noncore RAG1 functions and for the ordered assembly of VH, DH, and JH segments.