 Immune Cell Abundance Identifier, M.O.C.L.A.I., is a novel gene set signature-based method for accurately estimating the abundance of 24 immune cell types, including 18 T cell subsets from gene expression data. This method was evaluated using both sequencing data and publicly available expression data, demonstrating its superior performance compared to other methods. Furthermore, M.O.C.L.A.I. was applied to immunotherapy data sets to build a model for predicting the immunotherapy response with high accuracy. This article was authored by Yerou Miao, Jiang Zheng, Qian Lei, and others.