Pre-T cell receptor Self-MHC Sampling Restricts Thymocyte Dedifferentiation
- PMID: 36410718[PubMed].
Programming T lymphocytes to distinguish self from non-self is a vital, multi-step process arising in the thymus. Signalling through the pre-T cell receptor (preTCR), a CD3-associated heterodimer comprising an invariant pTα chain and a clone-specific β chain, constitutes a critical early checkpoint in thymocyte development within the αβ T-cell lineage. PreTCRs arrayed on double negative (DN) thymocytes, like αβ TCRs appearing on double positive (DP) thymocytes, ligate peptides bound to MHC molecules (pMHC) on thymic stroma but via a different molecular docking strategy. Here we show the consequences of those distinctive interactions for thymocyte progression, using synchronized fetal thymic progenitor cultures differing in the presence or absence of pMHC on support stroma, determining single cell transcriptomes at key thymocyte developmental transitions. Although MHC negative stroma fosters αβ T lymphocyte differentiation, the absence of pMHC-preTCR interplay leads to deviant thymocyte transcriptional programming associated with dedifferentiation. Highly proliferative DN and DP subsets with antecedent characteristics of T cell lymphoblastic and myeloid malignancies emerge. Compensatory upregulation of diverse MHC class Ib proteins in B2m/H2-Ab1 MHC knockout mice partially safeguards in vivo thymocyte progression although, with ageing, disseminated DP thymic tumours may develop. Thus, beyond fostering β chain repertoire broadening for subsequent αβ TCR utilization, preTCR-pMHC interaction limits cellular plasticity to facilitate normal thymocyte differentiation and proliferation that, if absent, introduces developmental vulnerabilities.