Enhanced detection of antigen-specific T cells by a multiplexed AIM assay

Abstract

Broadly applicable methods to identify and characterize antigen-specific CD4⁺ and CD8⁺ T cells are key to immunology research, including studies of vaccine responses and immunity to infectious diseases. We developed a multiplexed activation-induced marker (AIM) assay that presents several advantages compared to single pairs of AIMs. The simultaneous measurement of four AIMs (CD69, 4-1BB, OX40, and CD40L) creates six AIM pairs that define CD4⁺ T cell populations with partial and variable overlap. When combined in an AND/OR Boolean gating strategy for analysis, this approach enhances CD4⁺ T cell detection compared to any single AIM pair, while CD8⁺ T cells are dominated by CD69/4-1BB co-expression. Supervised and unsupervised clustering analyses show differential expression of the AIMs in defined T helper lineages and that multiplexing mitigates phenotypic biases. Paired and unpaired comparisons of responses to infections (HIV and cytomegalovirus [CMV]) and vaccination (severe acute respiratory syndrome coronavirus 2 [SARS-CoV-2]) validate the robustness and versatility of the method.

Keywords: 4-1BB (CD137); Antigen-specific CD4(+) T cells; CD40L (CD154); CD69; CP: Immunology; OX40 (CD134); activation-induced marker (AIM) assay; antigen-specific CD8(+) T cells; flow cytometry; infection-induced T cell responses; vaccine-induced T cell responses.