Direct interactions between tumor and immune cells mediate the antitumor effect of all modern cancer immunotherapeutic agents. Simultaneously, tumor cells have evolved mechanisms of evasion, including the downregulation of HLA-I, potentially disrupting the mechanism of action employed by many immune checkpoint inhibitors. And yet, the in situ interplay between these cells within the tumor immune microenvironment (TIME) remains elusive. Recent advances in histologic multiplex bioimaging platforms have enabled in-depth molecular characterization of single cells within spatially preserved and clinically archived tumor tissues. Herein, we applied multiplex immunofluorescence to excisional lymph node biopsies from 14 patients with metastatic melanoma who experienced clear objective responses to immunotherapy (7 complete response; 7 progressive disease) to determine distinguishing features of the TIME in the pretreatment setting. Distinct regions of the TIME were evaluated using 35 proteins probing tumor, immune, and vasculature components across 323 fields of view. Single-cell compositional analysis confirmed established prognostic immune cell types including increased prevalence of cytotoxic T cells within the tumor core fields of view of responders. Integrating single-cell quantification with the spatial arrangement of cellular neighborhoods surrounding tumor cells revealed novel, spatial immune signatures capable of stratifying TIME based on clinical response. Our analysis revealed dynamic cellular composition of the tumor-centric cellular neighborhood (TCCN) based on anatomic subregion, functional expression of HLA-I by the index tumor cell and ultimately clinical response to immunotherapy. Overall, this study provides an analytic framework to resolve the cellular complexity of the TIME, increasingly relevant to the outcomes of modern cancer immunotherapy.
Significance:
Findings from this work propose a novel approach to resolving clinical heterogeneity of the TIME by objectively quantifying the cellular interactions occurring in metastatic melanoma lymph node tissue utilizing multiplex immunofluorescence. This study provides an analytic and biologically derived unit of measure, the TCCN which is customizable for studying critical paracrine interactions within spatially preserved tissue of various cancers and across the spectrum of multiplex imaging modalities.
Human cytomegalovirus (HCMV) induces long-lasting T-cell immune responses that control but do not clear infection. Typical responses involve private T-cell clones, expressing T-cell antigen receptors (TCRs) unique to a person, and public T-cell clones with identical TCRs active in different people. Here, we report the development of a pretherapeutic immunostimulation modality against HCMV for human T cells, CD3 copotentiation, and the clonal analysis of its effects in recall assays at single-cell resolution. CD3 copotentiation of human T cells required identification of an intrinsically inert anti-CD3 Fab fragment that conditionally augmented signaling only when TCR was coengaged with antigen. When applied in recall assays, CD3 copotentiation enhanced the expansion of both public and private T-cell clones responding to autologous HLA-A2(+) antigen-presenting cells and immunodominant NLVPMVATV (NLV) peptide from HCMV pp65 protein. Interestingly, public vs private TCR expression was associated with distinct clonal expansion signatures in response to recall stimulus. This implied that besides possible differences in their generation and selection in an immune response, public and private T cells may respond differently to pharmacoimmunomodulation. Furthermore, a third clonal expansion profile was observed upon CD3 copotentiation of T-cell clones from HLA-A2(−) donors and 1 HLA-A2(+) presumed-uninfected donor, where NLV was of low intrinsic potency. We conclude that human T-cell copotentiation can increase the expansion of different classes of T-cell clones responding to recall antigens of different strengths, and this may be exploitable for therapeutic development against chronic, persistent infections such as HCMV.
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