Pathologic features of response to neoadjuvant anti-PD-1 in resected non-small-cell lung carcinoma: a proposal for quantitative immune-related pathologic response criteria (irPRC).

Background: Neoadjuvant anti-PD-1 may improve outcomes for patients with resectable NSCLC and provides a critical window for examining pathologic features associated with response. Resections showing major pathologic response to neoadjuvant therapy, defined as ≤10% residual viable tumor (RVT), may predict improved long-term patient outcome. However, %RVT calculations were developed in the context of chemotherapy (%cRVT). An immune-related %RVT (%irRVT) has yet to be developed. Patients and methods: The first trial of neoadjuvant anti-PD-1 (nivolumab, NCT02259621) was just reported. We analyzed hematoxylin and eosin-stained slides from the post-treatment resection specimens of the 20 patients with non-small-cell lung carcinoma who underwent definitive surgery. Pretreatment tumor biopsies and preresection radiographic 'tumor' measurements were also assessed. Results: We found that the regression bed (the area of immune-mediated tumor clearance) accounts for the previously noted discrepancy between CT imaging and pathologic assessment of residual tumor. The regression bed is characterized by (i) immune activation-dense tumor infiltrating lymphocytes with macrophages and tertiary lymphoid structures; (ii) massive tumor cell death-cholesterol clefts; and (iii) tissue repair-neovascularization and proliferative fibrosis (each feature enriched in major pathologic responders versus nonresponders, P < 0.05). This distinct constellation of histologic findings was not identified in any pretreatment specimens. Histopathologic features of the regression bed were used to develop 'Immune-Related Pathologic Response Criteria' (irPRC), and these criteria were shown to be reproducible amongst pathologists. Specifically, %irRVT had improved interobserver consistency compared with %cRVT [median per-case %RVT variability 5% (0%-29%) versus 10% (0%-58%), P = 0.007] and a twofold decrease in median standard deviation across pathologists within a sample (4.6 versus 2.2, P = 0.002). Conclusions: irPRC may be used to standardize pathologic assessment of immunotherapeutic efficacy. Long-term follow-up is needed to determine irPRC reliability as a surrogate for recurrence-free and overall survival.

DOCK2 interacts with FLT3 and modulates the survival of FLT3-expressing leukemia cells.

The FMS-like tyrosine kinase-3 (FLT3) gene is the most commonly mutated gene in acute myeloid leukemia (AML), and patients carrying internal tandem duplication (ITD) mutations have a poor prognosis. Long-term inhibition of FLT3 activity in these patients has been elusive. To provide a more complete understanding of FLT3 biology, a mass spectroscopy-based screen was performed to search for FLT3-interacting proteins. The screen identified dedicator of cytokinesis 2 (DOCK2), which is a guanine nucleotide exchange factor for Rho GTPases, and its expression is limited to hematolymphoid cells. We show that DOCK2 is expressed in leukemia cell lines and primary AML samples, and DOCK2 co-immunoprecipitates with wild-type FLT3 and FLT3/ITD. Knockdown (KD) of DOCK2 by shRNA selectively reduced cell proliferation and colony formation in leukemia cell lines with increased FLT3 activity, and greatly sensitized these cells to cytarabine treatment, alone and in combination with FLT3 tyrosine kinase inhibitors. DOCK2 KD in an FLT3/ITD-positive leukemia cell line also significantly prolonged survival in a mouse xenograft model. These findings suggest that DOCK2 is a potential therapeutic target for novel AML treatments, as this protein regulates the survival of leukemia cells with elevated FLT3 activity and sensitizes FLT3/ITD leukemic cells to conventional antileukemic agents.