Thota, R. | Search bioRxiv

bioRxiv2025

Submicron-Sampling of Living Cells by Macrophages

SUMMARY PARAGRAPHAn effective immune system must sample and appreciate healthy-self identity to prevent autoimmunity and to contrast to pathogenic insults1-3. Self-proteins are presented to T cells in the thymus during immune cell development2,3, and must be presented throughout the body to both maintain regulatory T cell populations4-6 and provide a tonic signal to maintain conventional T cells over time7-9. The ready observations of continuous apoptosis in some organs together with the ingestion of that material by myeloid populations has led to a conventional understanding of ongoing cell-death as a major source of self-antigens10, complemented in some situations by uptake of free-floating cell-derived vesicles. Here, we used a series of companion imaging and vesicular labeling technologies to reveal an alternate process undertaken by macrophages that results in non-destructive and direct sampling of living cells. The process requires cell-cell contact, does not require caspase activation, and takes place via a trogocytosis-like stretching of the target cell into the macrophage, leading to the generation of submicron-sized vesicles containing cytoplasm. Using a high-dimensional flow-based method for labeling vesicles ingested under this versus other conditions, we find that live-sampled material is distinctly processed, is poorly subject to fusion with lysosomes, and produces ensuing differential effects on the presentation of those to CD4 versus CD8 T cells. Disrupting this trafficking by redirecting antigen to the lysosome significantly reduced the associated macrophage-mediated priming of CD8 T cells. This demonstrates an important and substantial sampling of living cells by the immune system, with clear consequences for maintaining the border of immunity.

immunology↗

bioRxiv2025

The spontaneous neoantigen-specific CD4+ T cell response to a growing tumor is functionally and phenotypically diverse.

CD4+ T cells play critical roles in the positive and negative regulation of cellular immunity through the many functional subsets they comprise. The progressive growth of immunogenic tumors which nonetheless generate mutation-specific T cells suggests that effective immune control may be avoided or suppressed at the level of the neoantigen-specific CD4+ T cell response. We used a tetramer specific for a validated neoantigen, CTLCH129>Q/I-Ek, to characterize the ontogeny of natural CD4+ T cell responses to an aggressive and poorly immunogenic Major Histocompatibility Complex Class II (MHCII)-deficient tumor, SCC VII, during progressive growth or following therapeutic peptide vaccination. We find that the natural CD4+ T cell response to a growing tumor is phenotypically and functionally diverse, with distinct subsets including type 1 helper (Th1), T follicular helper (Tfh)-like, and regulatory T cell (Treg) lineages appearing as early as 9 days after tumor implantation. Therapeutic vaccination using the CLTCH129>Q peptide in adjuvant plus -PD-1 sharply reduces the frequency of CLTCH129>Q-specific Treg frequency in both tumor and tumor-draining lymph node (tdLN). Single cell transcriptomic analysis of CLTC-specific CD4+ T cells recapitulated and extended the diversity of the response, with TCRs of varying affinity found within each functional subset. The TCR affinity differences did not strictly correlate with function, however, as even the lowest affinity TCRs isolated from Treg can mediate therapeutic efficacy against established tumors in the setting of adoptive cellular therapy (ACT). These findings offer unprecedented insight into the functional diversity of a natural neoantigen-specific CD4+ T cell response and show how immunotherapeutic intervention influences the phenotype, magnitude, and efficacy of the anti-tumor immune response. What is already known on this topicLittle is known about the ontogeny, architecture, development of the CD4+ NeoAg-specific repertoire induced by progressively-growing tumor. This study was performed to address this topic and contribute new information to aid in its understanding What this study addsThis study reveals that the NeoAg-specific CD4+ T cell response to a growing tumor is phenotypically and functionally diverse, featuring a range of functional T cells subsets including TH1, TFH, and Treg expressing a range of functional TCR avidities, and demonstrates how an immunotherapeutic NeoAg vaccine can alter their relative composition within the tumor and tumor-draining lymph node. How this study might affect research, practice or policyThis study offers new insights into the diversity of NeoAg-specific CD4+ T cells and their response to a tumor in the presence or absence of immunotherapeutic intervention. This information could lead to new approaches to immune monitoring in the clinical setting of checkpoint blockade immunotherapy and cancer vaccines. Furthermore, we show that Treg can be a potent source of TCRs that can mediate therapeutic benefit in the setting of adoptive cell therapy (ACT).

immunology↗