PROJECT SUMMARY. Lung adenocarcinomas (LUAD) driven by oncogenic receptor tyrosine kinases (RTKs), including mutant EGFR and ALK, ROS1 and RET fusion proteins represent ~25% of LUAD and exhibit impressive responses to precision targeted tyrosine kinase inhibitors (TKIs). However, significant heterogeneity in response to TKI therapy exists between patients as manifested by variation in depth of response (DepOR), characterized as “residual disease” burden, as well as the duration of the therapeutic response (i.e., time to progression (TTP) or progression-free survival (PFS)). A deep cellular and molecular understanding of the variation in TKI responsiveness among oncogene-driven LUAD subsets is predicted to inform novel pathways that may be manipulated for therapeutic gain in these cancers. Inhibitors of the PD1/PD-L1-axis are now integral to lung cancer treatment, but are ineffective in subsets of LUAD driven by oncogenic RTKs, even when PD-L1 positive. Based on their lack of response to immunotherapies and lower mutation burden, it is tempting to consider host immunity as irrelevant to RTK-driven LUAD subsets and the therapeutic actions of TKIs. However, our published and preliminary findings and an emerging literature demonstrate that host immune cells are significant contributors to the therapeutic benefit of precision oncology agents. We reported that EGFR-targeted TKIs induce an interferon gamma (IFN) transcriptional response program as well as increased T cell signatures, both of which positively associate with longer TTP in EGFR-mutant LUAD patients. Moreover, studies with pretreatment biopsies from ALK+ lung tumors reveal an association of myeloid cell-neutrophil content and shortened PFS. Finally, using novel murine orthotopic models of EGFR and ALK+ LUAD, we demonstrate that the durability of TKI therapeutic responses requires adaptive immunity. The precise role of adaptive and innate immune cells in oncogene-targeted drug action represents a significant knowledge gap. The proposed studies will use pretreatment and on-treatment lung cancer patient specimens and innovative orthotopic immunocompetent models driven by oncogenic EGFR, ALK and RET to explore how TKIs alter the immune microenvironment to regulate therapeutic response. Findings from syngeneic immunocompetent C57BL/6 hosts reveal pronounced and durable tumor shrinkage responses to TKIs, but reduced DepOR and rapid progression on continuous treatment when propagated in immune-deficient mice, revealing a critical role for adaptive immunity. Our proposed studies will address two major knowledge gaps: 1) How does the composition of the tumor microenvironment (TME), both before and on-treatment, influence the DepOR and TTP? 2) What are the specific chemokine pathways and immune cell types that positively and negatively contribute to therapeutic responsiveness? We hypothesize that the observed TKI responses in RTK-driven lung tumors represent integration of direct TKI growth inhibit...