Biology subjects

Castro, T. B.

Publications and source records attributed to Castro, T. B..

4 recordsLinked to original sources

bioRxiv2025

Replaying germinal center evolution on a quantified affinity landscape

Darwinian evolution of immunoglobulin genes within germinal centers (GCs) underlies the progressive increase in antibody affinity following antigen exposure. Whereas the cellular mechanics of how competition between B cells produces increases in affinity are well established, the evolutionary dynamics of this process are less clear. We developed an experimental evolution model where we "replay" over one hundred monoclonal GC reactions, assigning affinities to each cell using deep mutational scanning. Our data reveal how GCs achieve predictable outcomes by means of noisy but persistent selection on an affinity landscape whose exploration is heavily constrained by somatic hypermutation biases. We infer a fitness landscape that quantitatively recapitulates the affinity maturation trajectory of our clone and find that apparent features of GC selection such as permissiveness to low-affinity lineages and rapid plateauing of affinity are likely artifacts of survivorship biases that distort our view of how B cell affinity progresses over time.

immunology↗

bioRxiv2022

Identification of dendritic cell-T cell interactions driving immune responses to food

The intestinal immune system must concomitantly tolerate food and commensals and protect against pathogens. Dendritic cells (DCs) orchestrate these immune responses by presenting luminal antigens and inducing functional differentiation of CD4+ T cells into regulatory (pTreg) or pro-inflammatory (Th) subsets. However, the exact nature of the DCs inducing tolerance or inflammation to dietary antigens has been difficult to define. Using an intestine-adapted Labeling Immune Partnerships by SorTagging Intercellular Contacts (LIPSTIC) combined with single-cell transcriptomics, we characterized DCs presenting dietary antigens in the context of tolerance or infection. At steady-state, migratory cDC1 and cDC2 DCs, but not resident DCs, were found to present dietary antigen to cognate CD4+ T cells. Whereas cDC2s promoted T cell activation, only cDC1s induced their differentiation into pTregs. Infection with the helminth Strongyloides venezuelensis abrogated cDC1 presentation of dietary antigens, preventing pTreg and oral tolerance induction. In contrast, Heligmosomoides polygyrus infection only partially affected cDC1s, allowing oral tolerance to be maintained. An expanded population of cDC2s that induced type-2 immunity during both helminth infections did not present dietary antigens, demonstrating that compartmentalized presentation of luminal antigens can prevent food-specific Th2 responses during inflammatory conditions. Our data uncover novel cellular mechanisms by which tolerance to food is induced and can be disrupted during infections.

immunology↗

bioRxiv2022

Proximity-dependent labeling identifies dendritic cells that prime the antitumor CD4+ T cell response

Dendritic cells (DCs) are uniquely capable of transporting tumoral antigens to tumor-draining lymph nodes (tdLNs), and also interact with effector T cells within the tumor microenvironment (TME) itself, mediating both natural antitumor immunity and the response to checkpoint blockade immunotherapy. Using LIPSTIC (Labeling Immune Partnerships by SorTagging Intercellular Contacts)-based single-cell transcriptomics, we identify individual DCs capable of presenting antigen to CD4+ T cells in the tdLN as well as inside the tumor microenvironment (TME). Our findings reveal that DCs with similar hyperactivated transcriptional phenotypes interact with helper T cells both within tumors and in the tdLN, and that checkpoint blockade drugs enhance these interactions. These findings show that a relatively small fraction of DCs is responsible for most of the antigen presentation within the tdLN and TME to both CD4+ and CD8+ tumor-specific T cells and that classical checkpoint blockade enhances CD40-driven DC activation at both sites.

immunology↗

bioRxiv2020

Cyclin D3 drives inertial cell cycling in dark zone germinal center B cells

During affinity maturation, germinal center (GC) B cells alternate between proliferation and so-matic hypermutation in the dark zone (DZ) and affinity-dependent selection in the light zone (LZ). This anatomical segregation imposes that the vigorous proliferation that allows clonal expansion of positively-selected GC B cells takes place ostensibly in the absence of the signals that triggered selection in the LZ, as if by "inertia." We find that such inertial cycles specifically require the cell cycle regulator cyclin D3. Cyclin D3 dose-dependently controls the extent to which B cells proliferate in the DZ and is essential for effective clonal expansion of GC B cells in response to strong T follicular helper (Tfh) cell help. Introduction into the Ccnd3 gene of a Burkitt lymphoma-associated gain-of-function mutation (T283A) leads to larger GCs with increased DZ proliferation and, in older mice, to clonal B cell lymphoproliferation, suggesting that the DZ inertial cell cycle program can be coopted by B cells undergoing malignant transformation.

immunology↗