OBJECTIVES/GOALS: Few preclinical models exist to study how tumors transition from prolonged stable disease ('equilibrium') to progressive disease ('escape'). We characterized a new murine tumor model the exhibits such behavior, and sought to identify and validate the role of unique tumor-infiltrating immune cell subsets in this process. METHODS/STUDY POPULATION: We evaluated growth of NPK-C1 (originally LM7304; received from Dr. Cory Abate-Shen at Columbia University), a cell line developed from spontaneous prostate cancer lung metastases in NPK mice (Nkx3.1CreERT2/+Ptenflox/floxKrasLSL-G12D/+R26R-LSL-YFP/+), in immune competent (C57BL/6) and immune deficient mice (J/Nu). We determined the role of CD4 and CD8 T cells in regulating the 'equilibrium to escape’ growth dynamics of NPK-C1 via in vivo cell depletions at key inflection points of tumor growth. To deeply profile the immune contexture of NPK-C1 at these inflection points, we developed a 28-color immunophenotyping panel for use on a Cytek Aurora spectral flow cytometer. We performed dimensionality reduction and clustering analyses on these data using tSNE and FlowSOM algorithms within FlowJo (v10.6). RESULTS/ANTICIPATED RESULTS: We found that activated CD4 effector T cells are enriched in regressing NPK-C1 tumors, highlighting a role for CD4 T cells in antitumor immunity. CD8 T cells are also important for NPK-C1 control; specifically central memory-like cytotoxic CD8 T cells. Depletion of either CD4 or CD8 T cells during the equilibrium phase of NPK-C1 growth confirmed the role of these cells in antagonizing NPK-C1 escape. Tregs as a whole were counterintuitively enriched in regressing tumors, however high dimensional analysis reveals their significant phenotypic diversity, with a number of Treg subpopulations enriched in progressing tumors. In the myeloid compartment, we found that iNOS+ DC-like cells are enriched in regressing tumors, while CD103+ DCs are associated with late stage tumor progression. DISCUSSION/SIGNIFICANCE: In total, these analyses of the NPK-C1 model provide novel insights into the roles of lymphoid and myeloid populations throughout key phases of tumor/immune co-evolution, and highlight a role for multi-dimensional flow cytometry-based analyses to more deeply understand immune cell dynamics in the tumor microenvironment.